Considering a plurality of time constants ^ for obtaining spectroscopic information Technical Field The invention relates to a spectrometer device for obtaining spectroscopic information on at least one object, and to a method of obtaining spectroscopic information on at least one object. The invention further relates to a computer program, a computer-readable storage medium and to a non-transient computer-readable medium. Such devices and methods can, in general, be used for investigating or monitoring purposes, in particular, in the infrared (IR) spectral region, especially in the near-infrared (NIR) spectral region, and in the visible (VIS) spectral region, e.g. in a spectral region allowing to mimic a human's ability of color sight. However, further applica- tions are feasible. Background art Spectrometer devices are known to be efficient tools for obtaining information on the spectral properties of an object, when emitting, irradiating, reflecting and/or absorbing light. Spectrome- ter devices, thus, may assist in analyzing samples or other tasks in which information on the spectral properties of an object is of interest. Usually, in spectrometer devices, spectral information is obtained via one or more detectors and one or more wavelength-selective optical elements, such as one or more dispersive optical ele- ments, filters such as bandpass filters, prisms, gratings, interferometers, or the like. The detec- tors may comprise any type of light-sensitive element, such as one or more single or multiple pixel detectors, line detectors or array detectors having one- or two-dimensional arrays of pix- els. Further, spectrometer devices may comprise one or more light sources. Thus, in spectros- copy, typically, tunable light sources, e.g. lasers, and/or broad-band emitting light sources are used, such as halogen-gas filled light bulbs and/or hot filaments. However, additionally or alter- natively, other light sources, such as light emitting diodes have also been proposed for the visi- ble spectral region. As an example, US 2010/208261 A1 describes a device for determining at least one optical property of a sample. The device comprises a tunable excitation light source for applying excita- tion light to the sample. The device furthermore comprises a detector for detecting detection light emerging from the sample. The excitation light source comprises a light-emitting diode ar- ray, which is configured at least partly as a monolithic light-emitting diode array. The monolithic light-emitting diode array comprises at least three light-emitting diodes each having a different emission spectrum. US 8,164,050 B2 describes a multi-channel source assembly for downhole spectroscopy that has individual sources that generate optical signals across a spectral range of wavelengths. A combining assembly optically combines the generated signals into a combined signal and a routing assembly that splits the combined signal into a reference channel and a measurement
channel. Control circuitry electrically coupled to the sources modulates each of the sources at unique or independent frequencies during operation. Further, US 7,061,618 B2 describes integrated spectroscopy systems, wherein in some exam- ples, integrated tunable detectors, using one or multiple Fabry-Perot tunable filters, are pro- vided. Other examples use integrated tunable sources combining one or multiple diodes, such as superluminescent light emitting diodes (SLED), and a Fabry Perot tunable filter or etalon. Furthermore, US 5,475,221 A describes an optical device which uses an array of light emitting diodes, controlled by multiplexing schemes, to replace conventional broad band light sources in devices such as spectrometers. Generally, spectrometer devices are subject to various internal and external influences, such as environmental influences, which may have an impact on the results of the spectroscopic meas- urements. In order to correct and/or compensate for these influences, various calibration and/or correction methods are known. These calibration methods may be performed once or several times, such as under laboratory conditions, e.g. by the manufacturer. However, also a plurality of on-line calibration techniques are known which may be performed by performing one or more correction and/or calibration steps in between two spectroscopic measurements or even during the measurements. US 09360366 B1 discloses a self-referencing spectrometer that simultaneously auto-calibrate and measure optical spectra of physical object utilizing shared aperture as optical inputs. The concurrent measure and self-calibrate capabilities makes it possible as an attachment spec- trometer on a mobile computing device without requiring an off-line calibration with an external reference light source. Through the mobile computing device, the obtained spectral information and imagery captured can be distributed through the wireless communication networks. DE 102014013848 B4 discloses a microspectrometer, in particular a NIR microspectrometer for mobile applications in battery-operated terminals, to overcome the nonminiaturization and handheld limitations of the aforementioned system configurations, a microspectrometer system, and a calibration method. The miniaturized NIR spectrometer is to be designed without active temperature stabilization. Instead, according to the invention, the spectral sensitivity function is recorded on several levels in the expected working temperature range as part of a factory tem- perature calibration step (QEλ = f(T); measured with an integrated temperature sensor). WO 2019/191698 A2 relates to a self-referenced spectrometer for providing simultaneous measurement of a background or reference spectral density and a sample or other spectral density. The self-referenced spectrometer includes an interferometer optically coupled to re- ceive an input beam and to direct the input beam along a first optical path to produce a first in- terfering beam and a second optical path to produce a second interfering beam, where each in- terfering beam is produced prior to an output of the interferometer. The spectrometer further in- cludes a detector optically coupled to simultaneously detect a first interference signal produced
from the first interfering beam and a second interference signal produced from the second inter- fering beam, and a processor configured to process the first interference signal and the second interference signal and to utilize the second interference signal as a reference signal in pro- cessing the first interference signal. US 20210293620 A1 discloses a spectrometer, comprising: an illumination device for illuminat- ing a spectrometric measurement region; a detection unit for detecting electromagnetic radiation coming from the spectrometric measurement region; and a spectral element, which is arranged in the beam path between the illumination device and the detection unit. The illumination device comprises: a light emitting diode having a first central wavelength, which is designed to emit first electromagnetic radiation having a first spectrum; and a luminescent element for converting a first component of the first electromagnetic radiation having the first spectrum into second elec- tromagnetic radiation having a second spectrum. The first central wavelength is 550 nm or 3000 nm or has a value between 550 nm and 3000 nm. The first spectrum and the second spectrum have an overlap. US 06667802 B2 discloses a method of calibrating a spectrographic inspection system. The method comprises providing a plurality of packages, each of the plurality of packages containing a group of items, wherein each of the groups of items has a known composition, measuring the reflectance value of each of the groups of items and thereby obtaining a reference reflectance value set, normalizing the reference reflectance value set and thereby creating a normalized ref- erence reflectance value set, and storing the normalized reference reflectance value set. US 06717669 B2 discloses auto-calibrating spectrometers and methods that measure transmis- sion or reflection versus wavelength of a sample without need for calibration for long periods of time. Reflection and transmission spectrometers along with auto-calibrating methods for use therewith are disclosed. Light is focused onto a sample using a lens or similar optical element that transmits light towards the sample reflects light impinging upon it, and transmits light re- flected from the sample. If one monitors the light reflected from the first lens and sample, very useful information is available related to the system response versus time. The reflected light is monitored from the first lens and sample, and the system changes over time are corrected for using this reflected light. US 09448114 B2 discloses a spectrometer which comprises a plurality of isolated optical chan- nels comprising a plurality of isolated optical paths. The isolated optical paths decrease cross- talk among the optical paths and allow the spectrometer to have a decreased length with in- creased resolution. In many embodiments, the isolated optical paths comprise isolated parallel optical paths that allow the length of the device to be decreased substantially. In many embodi- ments, each isolated optical path extends from a filter of a filter array, through a lens of a lens array, through a channel of a support array, to a region of a sensor array. Each region of the sensor array comprises a plurality of sensor elements in which a location of the sensor element corresponds to the wavelength of light received based on an angle of light received at the loca- tion, the focal length of the lens and the central wavelength of the filter.
EP 3318854 A1 discloses a spectrometer including a plurality of light sources configured to emit light to a target object, a plurality of wavelength controllers installed on one surface of each of the plurality of light sources and configured to adjust a peak wavelength band of each of the light sources, and a detection unit configured to detect light returning from the target object. Veeramani Rajendran et. al. describe in Super Broadband Near-Infrared Phosphors with High Radiant Flux as Future Light Sources for Spectroscopy Applications, ACS ENERGY LETTERS, vol.3, no.11 of 8 October 2018 that the near-infrared (NIR) light source is desirable for realtime nondestructive examination applications, which include the analysis of foodstuffs, health moni- toring, iris recognition, and infrared cameras. The emission spectra of such an infrared light source should also be as broad as possible for effective performance, in view of the fact that the broad absorption and reflection of light by the organic elements present in foodstuffs and human health fall in the blue and NIR regions of the electromagnetic spectrum, respectively. A blue light-emitting diode (LED) excitable super broadband NIR phosphor light source is developed with a high fwhm of 330 nm and radiant flux of 18.2 mW for the first time. Marie Anne van de Haar et al. describe in Saturation Mechanisms in Common LED Phosphors, ACS PHOTONICS, vol.8, no.6 of 17 May 2021 that commercial lighting for ambient and dis- play applications is mostly based on blue light-emitting diodes (LEDs) combined with phosphor materials that convert some of the blue light into green, yellow, orange, and red. Not many phosphor materials can offer stable output under high incident light intensities for thousands of operating hours. Despite the advantages achieved by known methods and devices, several technical challenges remain in the field of spectroscopy and spectroscopic devices, specifically for spectroscopy in the near-infrared range. Thus, specifically, calibration techniques correcting for various influ- ences are desirable, specifically for on-line correction of these influences in the field, at the loca- tion of the spectroscopic measurement. Specifically, the temperature is known to have a signifi- cant impact on the results and the precision of the spectroscopic measurements. Temperature changes may arise due to external influences, such as to changes of the environmental temper- ature. Additionally or alternatively, temperature changes may arise due to internal influences, such as electrical currents and electrical resistances within the spectroscopic devices, e.g. due to electrical power dissipation. These temperature changes may arise on a short timescale and/or may arise in the form of long-term drifts. Further, it has to be taken into account that tem- perature changes do not necessarily have to take place on a global scale and/or with the entire spectrometer device being at a thermal equilibrium. Thus, local temperature changes may oc- cur, specifically at locations which are difficult to monitor, such as at locations within the spec- trometer device and/or at interfaces within components of the spectrometer device, e.g. at semi- conductor interfaces. In addition, temperature dependency of the system may change. For ex- ample, the system may exhibit a different behavior after some time, even if the temperature re- mains constant, e.g. due to degradation, aging, or changes of the optical or electrical interfaces due to frequent usage.
Problem to be solved It is therefore desirable to provide methods and devices, which at least partially address the above-mentioned technical challenges and at least substantially avoid the disadvantages of known methods and devices. In particular, it is an object of the present invention to provide a spectrometer device for obtaining spectroscopic information on at least one object, and to a method of obtaining spectroscopic information on at least one object, which are capable of in- creasing the resolution of the spectrometer device. Summary This problem is addressed by a spectrometer device for obtaining spectroscopic information on at least one object, a corresponding method, a computer program, a computer-readable storage medium and a non-transient computer-readable medium, with the features of the independent claims. Advantageous embodiments which might be realized in an isolated fashion or in any ar- bitrary combinations are listed in the dependent claims as well as throughout the specification. In a first aspect, a spectrometer device for obtaining spectroscopic information on at least one object is disclosed. The term “spectrometer device” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a spe- cial or customized meaning. The term specifically may refer, without limitation, to an optical de- vice configured for acquiring at least one item of spectral information on at least one object. Specifically, the at least one item of spectral information may refer to at least one optical prop- erty or optically measurable property which is determined as a function of a wavelength, for one or more different wavelengths. More specifically, the optical property or optically measurable property, as well as the at least one item of spectral information, may relate to at least one prop- erty characterizing at least one of a transmission, an absorption, a reflection and an emission of the at least one object, either by itself or after illumination with external light. The at least one optical property may be determined for one or more wavelengths. The spectrometer device spe- cifically may form an apparatus which is capable of recording a signal intensity with respect to the corresponding wavelength of a spectrum or a partition thereof, such as a wavelength inter- val, wherein the signal intensity may, specifically, be provided as an electrical signal which may be used for further evaluation. The spectrometer device, as an example, may be or may comprise a device which allows for a measurement of at least one spectrum, e.g. for the measurement of a spectral flux, specifically as a function of a wavelength or detection wavelength. The spectrum may be acquired, as an example, in absolute units or in relative units, e.g. in relation to at least one reference measure- ment. Thus, as an example, the acquisition of the at least one spectrum specifically may be per- formed either for a measurement of the spectral flux (unit W/nm) or for a measurement of a
spectrum relative to at least one reference material (unit 1), which may describe the property of a material, e.g., reflectance over wavelength. Additionally or alternatively, the reference meas- urement may be based on a reference light source, an optical reference path, a calculated refer- ence signal, e.g. a calculated reference signal from literature, and/or on a reference device. Specifically, the at least one spectrometer device may be a diffusive reflective spectrometer de- vice configured for acquiring spectral information from the light which is diffusively reflected by the at least one object, e.g. the at least one sample. Additionally or alternatively, the at least one spectrometer device may be or may comprise an absorption- and/or transmission spectrometer. In particular, measuring a spectrum with the spectrometer device may comprise measuring ab- sorption in a transmission configuration. Specifically, the spectrometer device may be config- ured for measuring absorption in a transmission configuration. As outlined above, however, other types of spectrometer devices are also feasible. The at least one spectrometer device, specifically and as will be outlined in further detail below, may comprise at least one light source which, as an example, may be at least one of a tunable light source, a light source having at least one fixed emission wavelength and a broadband light source. The spectrometer device, as will be outlined in further detail below, further comprises at least one detector device configured for detecting light, such as light which is at least one of transmitted, reflected or emitted from the at least one object. The spectrometer device further may comprise, as will be outlined in further detail below, at least one wavelength-selective ele- ment, such as at least one of a grating, a prism and a filter, e.g. a length variable filter having varying transmission properties over its lateral extension. The wavelength-selective element may be used for separating incident light into a spectrum of constituent wavelength signals whose respective intensities are determined by employing a detector such as a detector having a detector array as described below in more detail. The spectrometer device, specifically, may be a portable spectrometer device. The term “porta- ble” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to the property of at least one object of being moved by human force, such as by a single user. Specifically, the object characterized by the term “portable” may have a weight not exceeding 10 kg, specifically not exceeding 5 kg, more specifically not exceeding 1 kg or even not exceeding 500 g. Additionally or alternatively, the di- mensions of the object characterized by the term “portable” may be such that the object extends by no more than 0.3 m into any dimension, specifically by no more than 0.2 m into any dimen- sion. The object, specifically, may have a volume of no more than 0.03 m³, specifically of no more than 0.01 m³, more specifically no more than 0.001 m³ or even no more than 500 mm
3. In particular, as an example, the portable spectrometer device may have dimensions of e.g.10 mm by 10 mm by 5 mm. Specifically, the portable spectrometer device may be part of a mobile device or may be attachable to a mobile device, such as a notebook computer, a tablet, a cell phone, such as a smart phone, a smartwatch and/or a wearable computer, also referred to as “wearable”, e.g. a body borne computer such as a wrist band or a watch. In particular, the a
weight of the spectrometer device, specifically the portable spectrometer device, may be in the range from 1 g to 100 g, more specifically in the range from 1 g to 10 g. The term “spectroscopic information”, also referred to as “spectral information” or as “an item of spectral information”, as used herein is a broad term and is to be given its ordinary and custom- ary meaning to a person of ordinary skill in the art and is not to be limited to a special or cus- tomized meaning. The term specifically may refer, without limitation, to an item of information, e.g. on at least one object and/or radiation emitted by at least one object, characterizing at least one optical property of the object, more specifically at least one item of information characteriz- ing, e.g. qualifying and/or quantifying, at least one of a transmission, an absorption, a reflection and an emission of the at least one object. As an example, the at least one item of spectral in- formation may comprise at least one intensity information, e.g. information on an intensity of light being at least one of transmitted, absorbed, reflected or emitted by the object, e.g. as a function of a wavelength or wavelength sub-range over one or more wavelengths, e.g. over a range of wavelengths. Specifically, the intensity information may correspond to or be derived from the signal intensity, specifically the electrical signal, recorded by the spectrometer device with respect to a wavelength or a range of wavelengths of the spectrum. The spectrometer device specifically may be configured for acquiring at least one spectrum or at least a part of a spectrum of detection light propagating from the object to the spectrometer. The spectrum may describe the radiometric unit of spectral flux, e.g. given in units of watt per nanometer (W / nm), or other units, e.g. as a function of the wavelength of the detection light. Thus, the spectrum may describe the optical power of light, e.g. in the NIR spectral range, in a specific wavelength band. The spectrum may contain one or more optical variables as a func- tion of the wavelength, e.g. the power spectral density ^^^, electric signals derived by optical measurements and the like. The spectrum may indicate, as an example, the power spectral density ^^^ and/or the spectral flux of the object, e.g. of a sample, e.g. relative to a reference sample, such as a transmittance and/or a reflectance of the object, specifically of the sample. The spectrum, as an example, may comprise at least one measurable optical variable or prop- erty of the detection light and/or of the object, specifically as a function of the illumination light and/or the detection light. As an example, the at least one measurable optical variable or prop- erty may comprise at least one at least one radiometric quantity, such as at least one of a spec- tral density, a power spectral density ^^^, a spectral flux, a radiant flux, a radiant intensity, a spectral radiant intensity, an irradiance, a spectral irradiance. Specifically, as an example, the spectrometer device, specifically the detector, may measure the irradiance in Watt per square meter (W / m
2), more specifically the spectral irradiance in Watt per square meter per nanome- ter (W / m
2 / nm). Based on the measured quantity the spectral flux in Watt per nanometer (W / nm) and/or the radiant flux in Watt (W) may be determined, e.g. calculated, by taking into ac- count an area of the detector. The term “object” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized
meaning. The term specifically may refer, without limitation, to an arbitrary body, chosen from a living object and a non-living object. Thus, as an example, the at least one object may comprise one or more articles and/or one or more parts of an article, wherein the at least one article or the at least one part thereof may comprise at least one component which may provide a spec- trum suitable for investigations. Additionally or alternatively, the object may be or may comprise one or more living beings and/or one or more parts thereof, such as one or more body parts of a human being, e.g. a user, and/or an animal. The object specifically may comprise at least one sample which may fully or partially be analyzed by spectroscopic methods. As an example, the object may be or may comprise at least one of: human or animal skin; edibles, such as fruits; plastics and textile. The spectrometer device comprises: (i) at least one light source configured for generating illumination light for illuminating the object, the light source comprising at least one light-emitting diode and at least one luminescent material for light-conversion of primary light generated by the light- emitting diode, wherein the spectrometer device is configured for driving the light source in a manner that the driving state of the light source is changed at least one time; (ii) at least one detector configured for detecting detection light from the object and, thereby, generating at least one detector signal when the driving state of the light source is changed, wherein the detector signal is time-resolved; (iii) at least one evaluation unit configured for evaluating the detector signal generated by the detector for deriving the spectroscopic information on the object, and further configured for considering a plurality of known time constants ^ of the light source describing a property of the light source when the driving state is changed for deter- mining a contribution of signal intensities of a plurality of wavelength intervals to the detector signal when the spectroscopic information on the object is derived. The spectrometer device comprises at least one light source configured for generating illumina- tion light for illuminating the object, the light source comprising at least one light-emitting diode and at least one luminescent material for light-conversion of primary light generated by the light- emitting diode, wherein the spectrometer device is configured for driving the light source in a manner that the driving state of the light source is changed at least one time. As further used herein, the term “light” as used herein is a broad term and is to be given its ordi- nary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to electro- magnetic radiation in one or more of the infrared, the visible and the ultraviolet spectral range. Herein, the term “ultraviolet spectral range”, generally, refers to electromagnetic radiation hav- ing a wavelength of 1 nm to 380 nm, preferably of 100 nm to 380 nm. Further, in partial accord- ance with standard ISO-21348 in a valid version at the date of this document, the term “visible spectral range”, generally, refers to a spectral range of 380 nm to 760 nm. The term “infrared spectral range” (IR) generally refers to electromagnetic radiation of 760 nm to 1000 µm, wherein the range of 760 nm to 1.5 µm is usually denominated as “near infrared spectral range” (NIR)
while the range from 1.5 µ to 15 µm is denoted as “mid infrared spectral range” (MidIR) and the range from 15 µm to 1000 µm as “far infrared spectral range” (FIR). Preferably, light used for the typical purposes of the present invention is light in the infrared (IR) spectral range, more preferred, in the near infrared (NIR) and/or the mid infrared spectral range (MidIR), especially the light having a wavelength of 1 µm to 5 µm, preferably of 1 µm to 3 µm. This is due to the fact that many material properties or properties on the chemical constitution of many objects may be derived from the near infrared spectral range. It shall be noted, however, that spectroscopy in other spectral ranges is also feasible and within the scope of the present invention. Consequently, the term “light source”, also referred to as an “illumination source”, as used herein is a broad term and is to be given its ordinary and customary meaning to a person of or- dinary skill in the art and is not to be limited to a special or customized meaning. The term spe- cifically may refer, without limitation, to an arbitrary device configured for generating or providing light in the sense of the above-mentioned definition. The light source specifically may be or may comprise at least one electrical light source, such as an electrically driven light source. As will be outlined in further detail below, the light source generally can be embodied in various ways. Thus, the light source can be for example part of the spectrometer device in a housing of the spectrometer device. Alternatively or additionally, however, the at least one light source can also be arranged outside a housing, for example as a separate light source. The light source can be arranged separately from the object and illuminate the object from a distance. In spectroscopy, various sources and paths of light are to be distinguished. In the context of the present invention, a nomenclature is used which, firstly, denotes light propagating from the light source to the object as “illuminating light” or “illumination light”. Secondly, light propagating from the object to the detector is denoted as “detection light”. The detection light may comprise at least one of illumination light reflected by the object, illumination light scattered by the object, illumination light transmitted by the object, luminescence light generated by the object, e.g. phosphorescence or fluorescence light generated by the object after optical, electrical or acous- tic excitation of the object by the illumination light or the like. Thus, the detection light may di- rectly or indirectly be generated through the illumination of the object by the illumination light. Further, as will be outlined in detail below, within the light source itself, a distinction may be made between various light sources, such as primary light sources and secondary light sources. Thus, as will be outlined in further detail below, “primary light”, also referred to as “pump light”, may be generated by a primary light source such as at least one light-emitting diode and may subsequently be transformed into “secondary light”, such as by using light conversion, e.g. through one or more phosphor materials. The illumination light may be or may comprise at least one of the primary light or a part thereof, the secondary light or a part thereof, or a mixture of both. Consequently, the term “illuminate”, as used herein, is a broad term and is to be given its ordi- nary and customary meaning to a person of ordinary skill in the art and is not to be limited to a
special or customized meaning. The term specifically may refer, without limitation, to the pro- cess of exposing at least one element to light. As outlined above, the light source comprises at least one light-emitting diode and at least one luminescent material for light-conversion of primary light generated by the light-emitting diode, wherein, specifically, the illumination light may be a combination of the primary light and light generated by the light-conversion by the luminescent material or light generated by the light conversion of the luminescent material, also referred to as secondary light. The term “light-emitting diode” or briefly “LED”, as used herein, is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an optoelectronic semiconductor device capable of emitting light when an electrical current flows through the device. The optoelectronic semiconductor device may be configured for gen- erating the light due to various physical processes, including one or more of spontaneous emis- sion, induced emission, decay of metastable excited states and the like. Thus, as an example, the light-emitting diode, may comprise one or more of: a light-emitting diode based on sponta- neous emission of light, in particular an organic light emitting diode, a light-emitting diode based on superluminescence (sLED), or a laser diode (LD) In the following, without narrowing the pos- sible embodiments of the light-emitting diode to any of the before-mentioned physical principles or setups, the abbreviation “LED” will be used for any type of light-emitting diode. Specifically, the LED may comprise at least two layers of semiconductor material, wherein light may be gen- erated at at least one interface between the at least two layers of semiconductor material, spe- cifically due to a recombination of positive and negative electrical charges, e.g. due to electron- hole recombination. The at least two layers of semiconductor material may have differing electri- cal properties, such as at least one of the layers being an n-doped semiconductor material and at least one of the layers being a p-doped semiconductor material. Thus, as an example, the LED may comprise at least one pn-junction and/or at least one pin-set up. It shall be noted, however, that other device structures are feasible, too. The at least one semiconductor material may specifically be or may comprise at least one inorganic semiconducting material. It shall be noted, however, that organic semiconducting materials may be used additionally or alterna- tively. Generally, the LED may convert electrical current into light, specifically into the primary light, more specifically into blue primary light, as will be outlined in further detail below. The LED, thus, specifically may be a blue LED. The LED may be configured for generating the primary light, also referred to as the “pump light”. Thus, the LED may also be referred to as the “pump LED”. The LED specifically may comprise at least one LED chip and/or at least one LED die. Thus, the semiconductor element of the LED may comprise an LED bare chip. Various types of LEDs suitable for generating the primary light are known to the skilled person and may also be applied in the present invention. Specifically, p-n-diodes may be used. As an example, one or more LEDs selected from the group of an LED on the basis of indium gallium
nitride (InGaN), an LED on the basis of GaN, an LED on the basis of InGaN/GaN alloys or com- binations thereof and/or other LEDs may be used. Additionally or alternatively, quantum well LEDs may also be used, such as one or more quantum well LEDs on the basis of InGaN. Addi- tionally or alternatively, Superluminescence LEDs (sLED) and/or Quantum cascade lasers may be used. The term “luminescence” as used herein is a broad term and is to be given its ordinary and cus- tomary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to the process of spon- taneous emission of light by a substance not resulting from heat. Specifically, luminescence may refer to a cold-body radiation. More specifically, the luminescence may be initiated or ex- cited by irradiation of light, in which case the luminescence is also referred to as “photolumines- cence”. The property of a material being capable of performing luminescence, in the context of the present invention, is referred to by the adjective “luminescent”. The at least one luminescent material specifically may be a photoluminescent material, i.e. a material which is capable of emitting light after absorption of photons or excitation light. Specifically, the luminescent mate- rial may have a positive Stokes shift, which generally may refer to the fact that the secondary light is red-shifted with respect to the primary light. The at least one luminescent material, thus, may form at least one converter, also referred to as a light converter, transforming primary light into secondary light having different spectral proper- ties as compared to the primary light. Specifically, a spectral width of the secondary light may be larger than a spectral width of the primary light, and/or a center of emission of the secondary light may be shifted, specifically red-shifted, compared to the primary light. Specifically, the at least one luminescent material may have an absorption in the ultraviolet and/or blue spectral range and an emission in the near-infrared and/or infrared spectral range. Thus, generally, the luminescent material or converter may form at least one component of the phosphor LED con- verging primary light or pump light, specifically in the blue spectral range, into light having a longer wavelength, e.g. in the near-infrared or infrared spectral range. Various types of conversion and/or luminescence are known and may be used in the context of the present invention. Thus, specifically, the conversion can occur via a dipole-allowed transi- tion in the luminescent material, also referred to as fluorescence, and/or via a dipole-forbidden, thus long-lived, transition in the luminescent material, often also referred to as phosphores- cence. The luminescent material, specifically, may, thus, form at least one converter or light converter. The luminescent material may form at least one of a converter platelet, a luminescent and spe- cifically a fluorescent coating on the LED and phosphor coating on the LED. The luminescent material may, as an example, comprise one or more of the following materials: Cerium-doped YAG (YAG:Ce
3+, or Y3Al5O12:Ce
3+); rare-earth-doped Sialons; copper- and aluminium-doped zinc sulfide (ZnS:Cu,Al).
The LED and the luminescent material, together, may form a so-called “phosphor LED”. Conse- quently, the term “phosphor light-emitting diode” or briefly “phosphor LED”, as used herein, is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a combination of at least one light-emitting diode configured for gen- erating primary light or pump light, and at least one luminescent material, also referred to as a “phosphor”, configured for light-conversion of the primary light generated by the light-emitting diode. The phosphor LED may form a packaged LED light source, including the LED die, e.g. a blue LED emitting blue pump light, as well as the phosphor, which, as an example, fully or par- tially coats the LED, which is, as an example, configured for converting the primary light or blue light into light having differing spectral properties, specifically into near-infrared light. Generally, the phosphor LED may be packaged in one housing or may be unpackaged. Thus, the LED and the at least one luminescent material for light-conversion of the primary light generated by the light-emitting diode may specifically be housed in a common housing. Alternatively, however, the LED may also be an unhoused or bare LED which may fully or partially be covered with the luminescent material, such as by disposing one or more layers of the luminescent material on the LED die. The phosphor LED, generally, may form an emitter or light source by itself. In the light source, specifically the phosphor LED, the at least one luminescent material specifi- cally may be located with respect to the light-emitting diode such that a heat transfer from the light-emitting diode to the luminescent material is possible. More specifically, the luminescent material may be located such that a heat transfer by one or both of thermal radiation and heat conduction is possible, more preferably by heat conduction. Thus, as an example, the lumines- cent material may be in thermal contact and/or in physical contact with the light-emitting diode. As an example, the luminescent material may form one or more coatings or layers in contact with or in close proximity to the light-emitting diode, such as with one or more of the semicon- ductor materials of the light-emitting diode. Thereby, generally, a temperature of the lumines- cent material and a temperature of the light-emitting diode may be coupled. The at least one luminescent material specifically may form at least one layer. Generally, vari- ous alternatives of positioning the luminescent material with respect to the light-emitting diode are feasible, alone or in combination. Firstly, the luminescent material, e.g., at least one layer of the luminescent material, such as the phosphor, may be positioned directly on the light-emitting diode, which is also referred to as a “direct attach”, e.g. with no material in between the LED and the luminescent material or with one or more transparent materials in between, such as with one or more transparent materials, specifically transparent for the primary light, in between the LED and the luminescent material. Thus, as an example, a coating of the luminescent mate- rial may be placed directly or indirectly on the LED. Additionally or alternatively, the luminescent material, as an example, may form at least one converter body, such as at least one converter disk, which may be placed on top of the LED, e.g. by adhesive attachment of the converter body to the LED. Additionally or alternatively, the luminescent material may also be placed in a re- mote fashion, such that the primary light from the LED has to pass an intermediate optical path before reaching the luminescent material. This placement may also be referred to as a “remote
placement” or as a “remote phosphor”. Again, as an example, the luminescent material in the remote placement may form a solid body or converter body, such as a disk or converter disk. Further, in case of the remote placement, the luminescent material may also be a coating. In particular, an object which is transmitting light, e.g. a thin glass substrate, module window, com- prising and/or being made of glass or plastics, may be coated with the phosphor. Alternatively, a reflective surface may be coated with the phosphor. This could be a flat or rough mirror, which may comprise and/or be made of a high-reflective index material substrate, e.g. silicon, or a gold, silver, aluminum or chromium coated flat or rough surface, e.g. glass, or a plastic. In the intermediate optical path, one or more optical elements may be placed, such as one or more of a lens, a prism, a grating, a mirror, an aperture or a combination thereof. Thus, specifically, an optical system having imaging properties may be placed in between the LED and the lumines- cent material, in the intermediate optical path. Thereby, as an example, the primary light may be focused, or bundled onto the converter body. The term “to drive” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. For driving the at least one light source, the spectrometer device may comprise a driv- ing unit. The term specifically may refer, without limitation, to the process of providing one or both of at least one control parameter and/or electrical power to another device. Consequently, the term “driving unit” as used herein is a broad term and is to be given its ordinary and custom- ary meaning to a person of ordinary skill in the art and is not to be limited to a special or cus- tomized meaning. The term specifically may refer, without limitation, to an arbitrary device or a combination of devices configured for providing one or both of at least one control parameter and/or electrical power to another device, such as, in the present case, to the at least one light source. For example, the driving unit specifically may be configured for at least one of measur- ing and controlling one or more electrical parameters of an electrical power provided to the light source, specifically to the at least one light-emitting diode. As an example, the driving unit may be configured for providing an electrical current to the LED, specifically for controlling an electri- cal current through the LED. Therein, as an example, the driving unit may be configured for adapting and measuring a voltage provided to the LED, the voltage being required for achieving a specific electrical current through the LED. The driving unit, specifically, may comprise one or more of: a current source, a voltage source, a current measurement device, such as an Am- père-meter, a voltage measurement device, such as a Volt-meter, a power measurement de- vice. Specifically, the driving unit may comprise at least one current source for providing at least one predetermined current to the LED, wherein the current source specifically may be config- ured for adjusting or controlling a voltage applied to the LED in order to generate the predeter- mined current. The driving unit, as an example, may comprise one or more electrical compo- nents, such as integrated circuits, for driving the light source. The driving unit may fully or par- tially be integrated into the light source or may be separated from the light source. The term “driving state” as used herein is a broad term and is to be given its ordinary and cus- tomary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to at least one specific
condition under which the light source is operated. The at least one specific condition may be directly and/or indirectly related to at least one and/or any specific electrical parameter of the electrical power provided to the light source. Alternatively, the at least one specific condition may be the at least one and/or any specific electrical parameter of the electrical power provided to the light source. The driving state may be changed by changing the specific condition, specifi- cally the at least one and/or any specific electrical parameter of the electrical power provided to the light source. Thereby, the light source may be driven at a first specific condition and then at a second specific condition that is different from the first specific condition. The driving state may further be influenced by at least one pressure and/or at least one temperature associated with the light source. Also optical feedback may have an effect on the light source. The driving state may be changed due to modulating the light source, specifically the light emitting-diode, particularly by applying a pulse modulation scheme, specifically a pulse width modulation scheme. As further outlined above, the spectrometer device is further comprising the at least one detec- tor configured for detecting detection light from the object and, thereby, generating at least one detector signal when the driving state of the light source is changed, wherein the detector signal is time-resolved. As further outlined above, the spectrometer device comprises at least one detector configured for detecting the detection light from the object, such as diffusely reflected light. The verb “to de- tect” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to the process of at least one of determining, measuring and monitoring at least one parameter, qualitatively and/or quantitatively, such as at least one of a physical parameter, a chemical parameter and a biological parameter. Specifi- cally, the physical parameter may be or may comprise an electrical parameter. Consequently, the term “detector” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an arbitrary device configured for detecting, i.e. for at least one of determining, measuring and monitoring, at least one parameter, qualitatively and/or quantitatively, such as at least one of a physical parameter, a chemical pa- rameter and a biological parameter. The detector may be configured for generating at least one detector signal, more specifically at least one electrical detector signal, such as an analogue and/or a digital detector signal, the detector signal providing information on the at least one pa- rameter measured by the detector. The detector signal may directly or indirectly be provided by the detector to the evaluation unit, such that the detector and the evaluation unit may be directly or indirectly connected. The detector signal may be used as a “raw” detector signal and/or may be processed or preprocessed before further used, e.g. by filtering and the like. Thus, the detec- tor may comprise at least one processing device and/or at least one preprocessing device, such as at least one of an amplifier, an analogue/digital converter, an electrical filter and a Fourier transformation.
In the present case, the detector is configured for detecting light propagating from the object to the spectrometer device or more specifically to the detector of the spectrometer device, which, according to the above-mentioned nomenclature, is referred to as “detection light”. Thus, specif- ically, the detector may be or may comprise at least one optical detector. The optical detector may be configured for determining at least one optical parameter, such as an intensity and/or a power of light by which at least one sensitive area of the detector is irradiated. More specifically, the optical detector may comprise at least one photosensitive element and/or at least one opti- cal sensor, such as at least one of a photodiode, a photocell, a photosensitive resistor, a photo- transistor, a thermophile sensor, a photoacoustic sensor, a pyroelectric sensor, a photomulti- plier and a bolometer. The detector, thus, may be configured for generating at least one detec- tor signal, more specifically at least one electrical detector signal, in the above-mentioned sense, providing information on at least one optical parameter, such as the power and/or inten- sity of light by which the detector or a sensitive area of the detector is illuminated. The detector may comprise one single optically sensitive element or area or a plurality of opti- cally sensitive elements or areas. Specifically, the detector may be or may comprise at least one detector array, more specifically an array of photosensitive elements, as will be outlined in further detail below. Each of the photosensitive elements may comprise at least a photosensi- tive area which may be adapted for generating an electrical signal depending on the intensity of the incident light, wherein the electrical signal may, in particular, be provided to the evaluation unit, as will be outlined in further detail below. The photosensitive area as comprised by each of the optically sensitive elements may, espe- cially, be a single, uniform photosensitive area which is configured for receiving the incident light which impinges on the individual optically sensitive elements. However, other arrangements of the optically sensitive elements may also be conceivable. The array of optically sensitive elements may be designed to generate detector signals, prefera- bly electronic signals, associated with the intensity of the incident light which impinges on the individual optically sensitive elements. The detector signal may be an analogue and/or a digital signal. The electronic signals for adjacent pixelated sensors can, accordingly, be generated simultaneously or else in a temporally successive manner. By way of example, during a row scan or line scan, it is possible to generate a sequence of electronic signals, which correspond to the series of the individual optically sensitive elements which are arranged in a line. In addi- tion, the individual optically sensitive elements may, preferably, be active pixel sensors, which may be adapted to amplify the electronic signals prior to providing it to the evaluation unit. For this purpose, the detector may comprise one or more signal processing devices, such as one or more filters and/or analogue-digital-converters for processing and/or preprocessing the elec- tronic signals. In case the detector comprises an array of optically sensitive elements, the detector, as an ex- ample, may be selected from any known pixel sensor, in particular, from a pixelated organic camera element, preferably, a pixelated organic camera chip, or from a pixelated inorganic
camera element, preferably, a pixelated inorganic camera chip, more preferably from a CCD chip or a CMOS chip, which are, commonly, used in various cameras nowadays. As an alterna- tive, the detector generally may be or comprise a photoconductor, in particular an inorganic photoconductor, especially PbS, PbSe, Ge, InGaAs, ext. InGaAs, InSb, or HgCdTe. As a further alternative it may comprise at least one of pyroelectric, bolometer or thermophile detector ele- ments. Thus, a camera chip having a matrix of 1 x N pixels or of M x N pixels may be used here, wherein, as an example, M may be < 10 and N may be in the range from 1 to 50, preferably from 2 to 20, more preferred from 5 to 10. Further, a monochrome camera element, preferably a monochrome camera chip, may be used, wherein the monochrome camera element may be dif- ferently selected for each optically sensitive element, especially, in accordance with the varying wavelength along the series of the optical sensors. Thus, the array may be adapted to provide a plurality of the electrical signals which may be gen- erated by the photosensitive areas of the optically sensitive elements comprised by the array. The electrical signals as provided by the array of the spectrometer device may be forwarded to the evaluation unit. The term “time resolved detector signal”, as used herein, is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a detec- tor signal that captures a temporal evolution of at least one process, particularly in a manner that the process may be decomposed in time. The time resolved detector signal may be config- ured for monitoring the at least one change in the operating parameter, particularly by monitor- ing the at least one illumination light generated by the light source, particularly at least indirectly. As further outlined above, the spectrometer device further comprises at least one evaluation unit configured for evaluating the detector signal generated by the detector for deriving the spectroscopic information on the object, and further configured for considering a plurality of known time constants ^ of the light source describing a property of the light source when the driving state is changed for determining a contribution of signal intensities of a plurality of wave- length intervals to the detector signal when the spectroscopic information on the object is de- rived. As further described above, the spectrometer device comprises the at least one evaluation unit for evaluating at least one detector signal generated by the detector and for deriving the spec- troscopic information on the object from the detector signal. The term “to evaluate”, as used herein, is a broad term and is to be given its ordinary and customary meaning to a person of or- dinary skill in the art and is not to be limited to a special or customized meaning. The term spe- cifically may refer, without limitation, to the process of processing at least one first item of infor- mation in order to generate at least one second item of information thereby. Consequently, the term “evaluation unit”, as used herein, is a broad term and is to be given its ordinary and cus- tomary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an arbitrary device or
a combination of devices configured to evaluate or process at least one first item of information, in order to generate at least one second item of information thereof. Thus, specifically, the eval- uation unit may be configured for processing at least one input signal and to generate at least one output signal thereof. The at least one input signal, as an example, may comprise at least one detector signal provided directly or indirectly by the at least one detector. As an example, the evaluation unit may be or may comprise one or more integrated circuits, such as one or more application-specific integrated circuits (ASICs), and/or one or more data processing devices, such as one or more of computers, digital signal processors (DSP), field programmable gate arrays (FPGA) preferably one or more microcomputers and/or microcontrol- lers. Additional components may be comprised, such as one or more preprocessing devices and/or data acquisition devices, such as one or more devices for receiving and/or preprocessing of the detector signals, such as one or more AD-converters and/or one or more filters. Further, the evaluation unit may comprise one or more data storage devices. Further, the evaluation unit may comprise one or more interfaces, such as one or more wireless interfaces and/or one or more wire-bound interfaces. The at least one evaluation unit may be adapted to execute at least one computer program, such as at least one computer program performing or supporting the step of generating the items of information. As an example, one or more algorithms may be implemented which, by us- ing the at least one detector signal, such as the time resolved detector signal and/or the spec- troscopic detector signal, as input variables, may perform a predetermined transformation for deriving the spectroscopic information on the object, such as for deriving at least one spectro- scopic information describing at least one property of the object. For this purpose, the evalua- tion unit may, particularly, comprise at least one data processing device, also referred to as a processor, in particular an electronic data processing device, which can be designed to gener- ate the desired information by evaluating the detector signal. The evaluation unit may use an arbitrary process for generating the required information, such as by calculation and/or using at least one stored and/or known relationship. The evaluation unit specifically may be configured for performing at least one digital signal processing (DSP) technique on the primary detector signal or any secondary detector signal derived thereof, in particular at least one Fourier trans- formation. Additionally or alternatively, the evaluation unit may be configured for performing one or more further digital signal processing techniques on the primary detector signal or any sec- ondary detector signal derived thereof, e.g. windowing, filtering, Goertzel algorithm, crosscorre- lation and autocorrelation. Besides the detector signal, one or a plurality of further parameters and/or items of information can influence said relationship. The relationship can be determined or determinable empirically, analytically or else semi-empirically. As an example, the relation- ship may comprise at least one of a model or calibration curve, at least one set of calibration curves, at least one function or a combination of the possibilities mentioned. One or a plurality of calibration curves can be stored for example in the form of a set of values and the associated function values thereof, for example in a data storage device and/or a table. Alternatively or ad- ditionally, however, the at least one calibration curve can also be stored for example in parame- terized form and/or as a functional equation. Separate relationships for processing the detector
signals into the items of information may be used. Alternatively, at least one combined relation- ship for processing the detector signals is feasible. Various possibilities are conceivable and can also be combined. As an example, the detector signal may comprise a plurality of detector signals being at least a function of the wavelength of the detection light, and, optionally, also of time, specifically for time-dependent detector signals. This plurality of detector signals, such as the spectroscopic detector signal, may form a spectrum, including the option of a digital or an analogue spectrum. Thus, as an example, each of the detector signals may summarize information from a predeter- mined spectral range being defined by a spectral resolution of the detector. As will be outlined in further detail below, the detector may comprise exactly one or a plurality of photosensitive ele- ments, each of the photosensitive elements being sensitive in a different spectral range and/or being exposed to a different part of the spectrum of the detection light. The entirety of the detec- tor signals of the photosensitive elements may form the detector signal, or in the entirety, as an example, defines the spectral information, a part thereof, or a predecessor thereof. Since the spectral range of sensitivity of each of the photosensitive elements may be known, particularly from considering the time resolved detector signal, the intensity of the detection light as a func- tion of the detection wavelength may be derived by this detector signal, by combining the data pairs of the photosensitive elements, each data pair comprising the respective signal of the pho- tosensitive element and the wavelength of sensitivity. It shall be noted, however, that other ways of generating spectral information are also feasible, such as by sequentially exposing one and the same detector to different spectral portions of the detection light, e.g. by using a scan- nable wavelength-selective element. As an example, the detector may be configured for generating a plurality of detector signals for at least one spectral range, specifically for at least two differing spectral ranges of the light from the object, specifically at least one of sequentially and simultaneously. For example, the detec- tor, as outlined above, may comprise an array of photosensitive elements, wherein each photo- sensitive element may be sensitive in a different spectral range and/or may be exposed to light in a different spectral range. A plurality of detector signals sensitive to differing spectral ranges may be combined for generating the detector signal that is evaluated for deriving the spectro- scopic information on the object. The term “time constant ^”, as used herein, is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a typical time interval describing a reorganization of the states of equilibrium when changing the at least one operat- ing parameter. The time constant ^ may describe a delay that occurs between the absorption of the at least one primary photon by the luminescent material and the emission of the at least one secondary photon by the luminescent material. This delay may be characterized by the so- called “characteristic time constant” ^, also referred to as the “time constant”, the “decay time” or the “saturation time”. When used in the context of processes in which a rate or probability of a process, such as emission of a photon, is proportional to the population of one or more states or
process states, the population typically changes exponentially. The time constant ^, in these processes, may determine the 1/e-time of the process. For the luminescent material or con- verter, specifically for the phosphor, two different time constants may occur. Firstly, a first time constant may describe the typical time for reaching a saturation of the emission of converted light, such as the “growth constant”. Secondly, a second time constant may describe the typical time of an afterglow of the luminescent material or converter, such as the “decay constant” or “decay”. The time constant ^ may be related to a property of the light source, specifically a material char- acteristic of the light source, more specifically of the luminescent material used in the light source. The term “property of the light source”, as used herein, is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to at least one characteristic of a material of the light source, specifically of the luminescent mate- rial. The “property” of the light source may, thus, be a “material property” of the light source, specifically of the luminescent material. The property of the material of the light source may be related to a structure of at least one molecule of the light source, specifically of the luminescent material. The property of the light source may be described by using temperature coefficients. The temperature coefficients may differ for different wavelengths, thereby the temperature coef- ficients may depend on the wavelength. Temperature coefficients related to a specific wave- length may be positive or negative and may vary in their absolute value based on the distribu- tion of various energy states and Einstein coefficients. The at least one time constant of the light source, typically, depends on the light-emitting diode and the luminescent material. The time constant of the light source ^
^^^^, ^
^^, ^
^^^ may be de- rived by considering the time constants of the light-emitting diode ^
^^^^, ^
^^^ and the lumines- cent material Any one of these time constants ^
^ (^, ^
^ ) is dependent on the respec- tive
wavelength. Typically ^
^^^^, ^
^^^ is much smaller than ^
^^^^, ^
^^^ in a manner that ^
^^^^, ^
^^^ is dominated by ^
^^^^, ^
^^^ on minor time scales. The determination of the time scales in this regime is of particular interest. Therefore, the time constant of the light source ^
^^^^, ^
^^, ^
^^^ may be derived from a convolu- tion of the time constants of the light-emitting diode ^
^^^^, ^
^^^ and the luminescent material ^
^^^^, ^
^^^, such as by determining * may be dominated by ^
^^^^, ^
^^^,
^
^^^^, ^
^^, ^
^^^. Typical time constants ^
^^^^, ^
^^^ of phosphor converters are in the range of 0.1 ms to < 10 ms. The at least one detector may be configured for generating a time resolved detector signal for monitoring these time constants. Typically, a time resolution of the detector may be less than 1ms, more preferred, less than 0.1 ms.
The time constants typically differ between different phosphor LEDs and/or between different types of the luminescent material or phosphor. Typically, shorted wavelengths emitting phos- phor exhibit smaller time constants. Additionally, decay ^
^ and growth constant ^
^ may depend on the wavelength. The time constants typically are extracted from step response of the optical signal by applying / shutting off the forward current required for driving the light source in a man- ner that primary light is being generated by the light-emitting diode. After turning off the forward current, the signal or emission typically decays according to equa- tion (1): ^
/^^
After turning on the forward current, the signal or emission typically grows according to equation (2): ^ ^
^
For both equations (1) and (2), ^
^ is the optical signal level at ^
^, when the forward current is ap- plied/shut off. ^
^^^ is the reached optical signal level as ^ ≫ 5. As described above, time constants ^ of the light source that are known, such as being available and/or being provided to the spectrometer device, specifically the evaluation unit, are consid- ered for deriving the spectroscopic information on the object. As the time constants ^ are, typi- cally, wavelength dependent, the contribution of a plurality of specific signal intensities of a plu- rality of specific wavelength intervals to the detector signal is derived by evaluating a temporal change in the detector signal, particularly after turning of the forward current and/or after turning on the forward current. Thereby, the resolution of the spectrometer device may be increased. The resolution of a spectrum in terms of the wavelengths may, generally, be limited, particularly due the setup of the spectrometer device, particularly limited in a manner that a specific detec- tor signal is comprises information on range of different wavelengths. The resolution may be in- creased by evaluating the contribution of the plurality of specific signal intensities of the plurality of specific wavelength intervals, particularly comprised by the range of different wavelengths, to the detector signal. This may be performed by considering the difference in the temporal change of the signal intensities related to the specific wavelength intervals. In that manner the detector signal may be decomposed into a plurality of specific signal intensities of a plurality of specific wavelength intervals. Thereby, even a spectrometer device comprising only one or ex- actly one detector generating only one or exactly one detector signal may used for generating spectroscopic information, particularly even when no or a wavelength-selective element having a fixed transmission spectrum is used. The light-emitting diode may have a primary emission range at least partially located in the spectral range of 420 nm to 460 nm, more specifically in the range of 440 nm to 455 nm, more specifically at 440 nm. The luminescent material may be phosphor. The illumination light may
have a spectral range at least partially located in the near-infrared spectral range, specifically in the spectral range from 1 to 3 µm, preferably from 1.3 to 2.5 µm, more preferably from 1.5 to 2.2 µm. The driving state of the light source may be at least one of: a first driving state in which the light- emitting diode is generating the primary light; or a second driving state in which the light-emit- ting diode is not generating primary light. For switching between the first driving state and the second driving state, the driving unit may switch the electrical current and/or voltage, such as the forward voltage, provided to the LED. When it is switched into the first driving state the light-emitting diode may be illuminating the lu- minescent material. Thereby, excited states in the luminescent material may be populated, as described by the growth constant ^
^ of excited states in the luminescent material. When it is switched into the second driving state from the first driving state the light-emitting diode may no longer be illuminating the luminescent material. Thereby, excited states in the luminescent ma- terial may be depopulated, as described by the decay constant ^
^ of excited states in the lumi- nescent material. The at least one light source may be configured for operating in a pulsed mode in a manner that the driving state of the light source changes repeatedly, particularly changes repeatedly be- tween the first driving state and the second driving state. The term “pulsed mode”, as used herein, is a broad term and is to be given its ordinary and customary meaning to a person of or- dinary skill in the art and is not to be limited to a special or customized meaning. The term spe- cifically may refer, without limitation, to driving the light source in a manner that the illumination light is generated in a plurality of pulses having a predetermined duration at a predetermined repetition rate. The at least one spectrometer device may be configured for operating the light source in a, par- ticularly specific, driving state, particularly the first driving state and/or the second driving state, for a predetermined time span larger than the time constant ^, particularly at least 5 times or at least 10 times larger than the time constant ^. A pulse duration, particularly when the light source is operated in a pulsed mode, may be larger than the time constant ^, particularly at least 5 times; or at least 10 times larger than the time constant ^. Typically, a pulse duration may be between 0.5 ms and 100 ms, depending on time constant ^ associated with the lumi- nescent material. The detector signal may configured for comprising information on the plurality of wavelength in- tervals, particularly by covering a range of wavelengths. The detector signal may be configured for comprising the spectroscopic information from the detected detection light. The detector may comprise exactly one photosensitive element, which may be particularly pre- ferred, or at least one photosensitive element configured for generating the detector signal com- prising information on the plurality of wavelength intervals.
The spectrometer device may further comprise at least one wavelength-selective element, wherein the wavelength-selective element may be disposed in at least one of: - a beam path of the illumination light; or - a beam path of the detection light. The wavelength-selective element may be configured such that each of the photosensitive ele- ments may be exposed to an individual spectral range of the light from the object. The term “in- dividual”, as used herein, is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized mean- ing. The term specifically may refer, without limitation, to the photosensitive elements being ex- posed to differing spectral range of the light from the object. The wavelength-selective element may be configured such that the at least one of the photo- sensitive elements is exposed to a further individual spectral range of the light from the object, wherein the individual spectral range and the further individual range are distant from each other. As used herein, the term “distant” is a broad term and is to be given its ordinary and cus- tomary meaning to a person of ordinary skill in the art and are not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to the intervals are spaced from each other with respect to their wavelength. Accordingly, there may be an interme- diate interval between the spaced intervals. No information about the intermediate interval may be available. The photosensitive elements may be exposed to at least one additional individual spectral range. That additional individual spectral range may be distant from at least one of: the individual spectral range; or the further spectral range. The wavelength-selective element may be selected from the group of a tunable wavelength-se- lective element and a wavelength-selective element having a fixed transmission spectrum. The wavelength-selective element may be or may comprise at least one filter element, particularly wherein the filter element is an absorption filter element, specifically a bandpass filter element. As outlined above, the photosensitive elements may be sensitive to differing spectral ranges of the light from the object. The differing spectral sensitivity may be implemented by using photo- sensitive elements having inherently differing spectral sensitivities, such as by using differing integrated filters and/or differing sensitive materials, such as semiconductor materials. Addition- ally or alternatively, the differing spectral sensitivity may be achieved by using one or more wavelength-selective elements in one or more beam paths of the detection light, such as one or more of a filter, a grating, a prism or the like, configured to allow forward differing spectral por- tions of the detection light from the object to reach the individual photosensitive elements, se- quentially or simultaneously. Thus, generally, the spectrometer device may further comprise at least one wavelength-selec- tive element. As used herein, the term “wavelength-selective element” is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to
be limited to a special or customized meaning. The term specifically may refer, without limita- tion, to an arbitrary optical element which interacts with differing spectral portions of incident light in a different manner, e.g. by having at least one wavelength-dependent optical property, such as at least one wavelength-dependent optical property selected from the list consisting of a degree of reflection, a direction of reflection, a degree of refraction, a direction of refraction, an absorption, a transmission, an index of refraction. Therein, the wavelength selection by the at least one wavelength-selective element may take place in the at least one beam path of the illumination light, thereby selecting and/or modifying a wavelength of the illumination of the object, and/or in the detection beam path of the detection light, thereby selecting and/or modifying a wavelength of detection, e.g. for the detector in gen- eral and/or for each of the photosensitive elements. Thus, as an example, the at least one wavelength-selective element may comprise at least one of a wavelength-selective element dis- posed in a beam path of the illumination light and a wavelength-selective element disposed in a beam path of the detection light. The wavelength-selective element, specifically may be selected from the group of a tunable wavelength-selective element and a wavelength-selective element having a fixed transmission spectrum. By using a tunable wavelength selective element, as an example, differing wave- length ranges may be selected sequentially, whereas, by using a wavelength-selective element having a fixed transmission spectrum, the selection of the wavelength ranges may be fixed and may, however, be dependent e.g. on a detection position, thereby allowing, as an example, in the detection light beam path, for simultaneously exposing different detectors and/or different photosensitive elements of the detector to differing spectral ranges of light. Thus, as outlined above and as an example, the at least one wavelength-selective element may comprise at least one of a filter, a grating, a prism, a plasmonic filter, a diffractive optical ele- ment and a metamaterial. More specifically, the spectrometer device may comprise at least one filter element disposed in a beam path of the light from the object, i.e. in the beam path of the detection light, wherein the filter element, specifically may be configured such that each of the photosensitive elements is exposed to an individual spectral range of the light from the object. As an example, a variable filter element may be used, the transmission of which depends on a position on the filter element, such that, when the variable filter element is placed on top of the array of photosensitive elements, the individual photosensitive elements are exposed to differ- ing spectral ranges of the incident light, specifically the detection light from the object. Addition- ally or alternatively the at least one wavelength-selective element may comprise at least one of the following elements: an array of individual bandpass filters, an array of patterned filters, an MEMS-Interferometer, an MEMS-Fabry Perot interferometer. Further elements are feasible. The spectrometer device may comprise at least one filter element disposed in a beam path of the light from the object, wherein the filter element may be configured such that the photosensi- tive element may be exposed to the individual spectral range of the light from the object. The spectrometer device may comprise at least one further filter element disposed in a beam path of
the light from the object, wherein the further filter element may be configured such that the pho- tosensitive element may be exposed to the further individual spectral range of the light from the object. The detector may configured for generating a plurality of detector signals for at least two differ- ing spectral ranges of the light from the object, specifically at least one of sequentially and sim- ultaneously. The detector may comprise an array of photosensitive elements, wherein each of the photosensitive elements is configured for generating at least one detector signal. The spec- trometer device may be configured such that the photosensitive elements are sensitive to differ- ing spectral ranges of the light from the object. A plurality of the spectrometer device may be configured such that the photosensitive elements are sensitive to differing spectral ranges of the light from the object. A plurality of detector signals sensitive to differing spectral ranges may combined for generating the detector signal evaluated for deriving the spectroscopic information on the object. The time constants ^ may be at least one of: - a decay constant ^
^ of excited states in the luminescent material; or - a growth constant ^
^ of excited states in the luminescent material. The term “decay constant” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a constant describing a decay of the signal and/or emission, particularly of the luminescent material until no more sig- nal is generated. The term “growth constant” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be lim- ited to a special or customized meaning. The term specifically may refer, without limitation, to a constant describing a growth of the signal and/or emission until a saturation is reached, particu- larly of the luminescent material. The time constants ^ may depend on at least one of: the wavelength ^ of the illumination light; or the temperature ^ of the light source, specifically the luminescent material. The growth con- stant ^
^ may depend on the intensity of pump light. The plurality of time constants ^ may consid- ered for determining the contribution of the signal intensities of the plurality of wavelength inter- vals to the detector signal by performing a regression algorithm, particularly a fit, on the detector signal configured for comprising information on the plurality of wavelength intervals. As gener- ally used, the term “regression” refers to a statistical analysis tool that aims to determine a rela- tionship between an input, such as the detector signal, and a statistical model to determine an output, such as the spectroscopic information. In this process, the statistical model may be fitted onto the input data. The statistical model may consider the contribution of the signal intensities of the plurality of wavelength intervals to the detector signal. The regression algorithm, particu- larly the fit, may consider a function describing the contribution of the signal intensities of the plurality of wavelength intervals to the detector signal. Therefore, a function ^
^^^(^) may be assumed with
^^^^ ( ^ ) = ^^ ( ^ ) + ^^ ( ^ ) + ⋯ , wherein ^
with ^
^ being the signal intensity of a wavelength intervals ^, and ^
^ being the respective time constant ^ assigned to the wavelength intervals ^, ^ being the time and ^
^ being the time when the driving state of the light source is changed. For performing the fit a least square |^
^^^(^) − ^
^^^(^)|
^ may be minimized, particularly by opti- mizing the parameters ^
^. The signal ^
^ (^ = ^
^ ) = ^
^ may provide the spectroscopic information on the object. Alternatively, a function ^
^^^ (^
) may be assumed with ^
^^^ (^
) = ^
^ (^
) + ^
^ (^
) + ⋯ + ^
^^^^^ (^, ^
), wherein ^
^^^^^ (^, ^
) is the noise signal, particularly assuming a normally distributed noise with a center at 0. The fit may be performed by an algorithm of at least one of: Levenberg-Marquardt-; steepest decent; or orthogonal decent. There may be further options for performing the fit. A further plurality of known time constants ^ of wavelengths comprised by a specific wavelength interval may be combined, particularly by averaging, for determining an overall time constant ^ that is considered for determining the contribution of the signal intensity of the specific wave- length interval to the detector signal. In a further aspect, a method of obtaining spectroscopic information on at least one object is disclosed. The method comprises the following steps that may be performed in the given order. However, a different order may also be possible. In particular, one, more than one or even all of the method steps may be performed once or repeatedly. Further, the method steps may be per- formed successively or, alternatively, one or more of the method steps may be performed in a timely overlapping fashion or even in a parallel fashion and/or in a combined fashion. The method may further comprise additional method steps that are not listed. The method comprises the following steps: (a) illuminating the object with illumination light generated by at least one light source, the light source comprising at least one light-emitting diode and at least one lumi- nescent material for light-conversion of primary light generated by the light-emitting diode, and driving the light source in a manner that an driving state of the light source is changed at least one time at least one time;
(b) detecting detection light from the object by using at least one detector and, thereby, generating at least one detector signal when the driving state of the light source is changed, wherein the detector signal is time-resolved; and (c) evaluating, by using at least one evaluation unit, the detector signal generated by the detector for deriving the spectroscopic information on the object, and further considering a plurality of known time constants ^ of the light source describing a property of the light source when the driving state is changed for determining a con- tribution of signal intensities of a plurality of wavelength intervals to the detector sig- nal when the spectroscopic information on the object is derived. As further outlined above, the method described above and/or according to any one of the Em- bodiments described in further detail below, may fully or partially be at least one of computer- controlled, computer-implemented, and computer-assisted, e.g. by using one or more computer programs running on at least one processor, e.g., at least one processor of the spectrometer device, e.g. of at least one processor integrated within the detector and/or within the evaluation unit. Specifically, as outlined above, at least step (c) of the method may be at least one of com- puter-controlled, computer-implemented, and computer-assisted. It shall be noted, however, that other steps of the method may also fully or partially be at least one of computer-controlled, computer-implemented, and computer-assisted, such as one or more of steps (a), (b), and (c). The method may be performed on-line in the field. The spectrometer device, specifically, may be a portable spectrometer device which specifically may be used in the field. In particular, the spectrometer device may be part of a mobile device or may be attachable to a mobile device, such as a notebook computer, a tablet, a cell phone, such as a smart phone, a smartwatch and/or a wearable computer, also referred to as “wearable”, e.g. a body borne computer.The method according to the preceding claim, wherein a spectrometer device according to any one of the preceding claims referring to a spectrometer device is used. A computer program comprising instructions which, when the instructions are executed by the evaluation unit of the spectrometer device, cause the evaluation unit to perform the method. A computer-readable storage medium comprising instructions which, when the instructions are ex- ecuted by the evaluation unit of the spectrometer device, cause the evaluation unit to perform the method. A non-transient computer-readable medium including instructions that, when exe- cuted by the evaluation unit of the spectrometer device, cause the evaluation unit to perform the method. As used herein, the terms “computer-readable data carrier”, “computer-readable stor- age medium” and “non-transient computer-readable medium” are broad term and are to be given their ordinary and customary meaning to a person of ordinary skill in the art and are not to be limited to a special or customized meaning. The terms specifically may refer, without limita- tion, to data storage means, specifically non-transitory data storage means, such as a hardware storage medium having stored thereon computer-executable instructions. The computer-reada- ble data carrier or storage medium or computer-readable medium specifically may be or may comprise a storage medium such as a random-access memory (RAM) and/or a read-only memory (ROM).
As used herein, the terms “have”, “comprise” or “include” or any arbitrary grammatical variations thereof are used in a non-exclusive way. Thus, these terms may both refer to a situation in which, besides the feature introduced by these terms, no further features are present in the en- tity described in this context and to a situation in which one or more further features are present. As an example, the expressions “A has B”, “A comprises B” and “A includes B” may both refer to a situation in which, besides B, no other element is present in A (i.e. a situation in which A solely and exclusively consists of B) and to a situation in which, besides B, one or more further elements are present in entity A, such as element C, elements C and D or even further ele- ments. Further, it shall be noted that the terms “at least one”, “one or more” or similar expressions indi- cating that a feature or element may be present once or more than once typically are used only once when introducing the respective feature or element. In most cases, when referring to the respective feature or element, the expressions “at least one” or “one or more” are not repeated, notwithstanding the fact that the respective feature or element may be present once or more than once. Further, as used herein, the terms "preferably", "more preferably", "particularly", "more particu- larly", "specifically", "more specifically" or similar terms are used in conjunction with optional fea- tures, without restricting alternative possibilities. Thus, features introduced by these terms are optional features and are not intended to restrict the scope of the claims in any way. The inven- tion may, as the skilled person will recognize, be performed by using alternative features. Simi- larly, features introduced by "in an embodiment of the invention" or similar expressions are in- tended to be optional features, without any restriction regarding alternative embodiments of the invention, without any restrictions regarding the scope of the invention and without any re- striction regarding the possibility of combining the features introduced in such way with other optional or non-optional features of the invention. The spectrometer device and the method according to the present invention, in one or more of the above-mentioned embodiments and/or in one or more of the embodiments described in fur- ther detail below, provide a large number of advantages over known devices and methods of similar kind. Specifically, by using exactly one detector, a detector drift may be compensated more easily. Using a single detector setup may further enable a reduction of the technical com- plexity compared to the use of individual detectors for each different wavelength range. Besides practical advantages, the simultaneous detection of multiple wavelengths by a single detector may allow compensating for a drift of the detector signal, particularly the DC signal, as well as the detectors responsivity. In particular, a reference signal may be recoded on the de- tector simultaneously to the measurement of a sample signal. This may enables an on-line sys- tem calibration.
Further, the use of phosphor LEDs instead of or in addition to conventional thermal emitters such as incandescent lamps with a tungsten wire as a light source, may provide for several ad- vantages. Thus, in general, even though thermal emitters may provide for a flat spectrum, low temperature dependency and a high power spectral density ^^^ even at long wavelengths, such as in the NIR range, thermal emitters typically are not well-suited for large-volume spec- trometer production. Thus, typically, a high complexity of the manufacturing process, a low con- version efficiency from electrical to optical power and physical limitations in miniaturization are to be noted as disadvantages for thermal emitters. By using LEDs, specifically phosphor LEDs, these disadvantages may be overcome. LEDs have proven to be reliable light sources, such as standardized light sources in the visible light regime. In the context of the present invention, broadband light sources may be provided by using one or more phosphor LEDs in the spectrometer device, comprising the at least one light-emitting diode and the at least one luminescent material or phosphor. Thereby, as an example, a white light source may be created and/or a broadband light source in the infrared range, specifically in the NIR range. The phosphor may convert photons having a shorter wavelength, and, thus, a higher energy, into photons having a longer wavelength or lower energy, e.g. by transferring a portion of the primary photon energy to the phosphor material, such as to the phosphor lattice. The remaining lower energy may lead to an emission of a long-wavelength photon. Consequently, the luminescent material may be configured for absorbing one or more primary photons generated by the light-emitting diode and may, in reaction to this absorption, emit one or more secondary photons. The emission of the secondary photons may take place instantane- ously or after a delay or decay time. Thus, as outlined above, the luminescent material may be or may comprise at least one of a phosphorescent and a fluorescent material. The phosphores- cence may lead to the effect that after turning off the primary light, such as the short-wavelength or high energy pump light, the luminescent material may emit the secondary light, such as the long wavelength light, for a characteristic life time ^ (tau), e.g., due to a forbidden quantum-opti- cal transition or forbidden dipole transition. Thus, specifically, in the luminescent material, the emission of the secondary light may take place over a forbidden transition, such as a forbidden dipole transition, having a longer lifetime than e.g. spontaneous dipole allowed transition, as may be the case in many fluorescent materials. Specifically, as outlined above, a luminescent material may be used, specifically a phosphores- cent material, having an absorption in the blue spectral range and an emission in the infrared spectral range. As an example, luminescent materials may be used capable of converting blue primary light or pump light, having a wavelength of e.g.440 nm, into near-infrared secondary light, e.g. secondary light having a wavelength in the range of 1 to 3 µm, preferably from 1.3 to 2.5 µm, more preferably from 1.5 to 2.2 µm. Additionally or alternatively, the primary light or pump light may generated by an infrared LED with a wavelength in the range from 850 nm to 940 nm, which may then be converted by the luminescent material into near-infrared secondary light having a wavelength in the range of 1 to 3 µm, preferably from 1.3 to 2.5 µm, more prefera- bly from 1.5 to 2.2 µm.
The phosphor LED, comprising the at least one light-emitting diode and the at least one lumi- nescent material, may be embodied as a single element. Thus, on a technical level, the phos- phor LED may comprise multiple sub-components. First of all, the phosphor LED may comprise one or more functional components, such as the LED die comprising at least one junction between at least two semiconductor regions, such as at least one p-n-transition. In the LED die, the primary light may be generated, such as the short-wavelength pump light, e.g. in the blue spectral range. Further, the phosphor LED may comprise the at least one luminescent material, specifically the at least one phosphorescent material, which may, specifically, be placed directly on top of the LED die and which may convert the primary light, specifically the pump light, into the secondary light, specifically into the long-wavelength near-infrared light. Further, the phosphor LED may comprise one or more substrates, specifically one or more elec- trically insulating substrates. Thus, as an example, the phosphor LED may comprise one or more ceramic substrates. The at least one substrate may be configured for holding the at least one LED die and the at least one luminescent material. Further, the at least one substrate may hold or comprise one or more components of electrical connectivity, such as one or more con- tact pads and/or one or more electrical leads, such as one or more metallic contacts and/or one or more metallic leads. Furthermore, the substrate, such as the ceramic substrate, may be con- figured to serve as a heat sink. Heat may be generated both in the LED die and in the lumines- cent material, such as due to a limited conversion of electrical energy into photonic energy, as well as in the luminescent material, e.g. during the conversion process. Said heat may be dissi- pated in the substrate, such as in ceramic substrate. The spectrometer device using the at least one LED may be configured for applying a continu- ous wave (CW) mode and/or, preferably, at least one modulation driving scheme for improving precision and reliability of the measurement. Thus, for example, the at least one driving unit may be configured for applying a modulation driving scheme to the LED, and the evaluation de- vice may be configured for taking into account the modulation driving scheme for deriving the at least one spectroscopic information from the at least one detector signal. As an example, Lock- In-techniques, filter techniques, and the like may be applied, as known to the skilled person. Thus, the spectrometer device may be configured for applying a modulation driving scheme to the LED for compensating for DC background of the detector and/or in order to reduce the de- tector noise. Thus, as an example, a band pass filter may be applied to the detector signal, in order to eliminate DC components. The illumination light generated by the light source, specifically the phosphor LED, may be di- rected to illuminate the sample. For directing the illumination light, as an example, one or more mirrors, may optionally be used. The detection light from the object, e.g. reflected light, may be
directed to the detector, wherein, optionally, one or more optical components may be used. As an example, one or more wavelength-selective elements may be used, such as one or more dispersive elements, e.g. for splitting the detection light into its spectral components. By the detector, one or more detector signals may be recorded, e.g. by using a readout elec- tronics, comprised by the spectrometer device, specifically by one or both of the detector and the evaluation device. The readout electronics, as an example, may comprise one or more sig- nal processing devices. Thus, as outlined above, for evaluation by the evaluation device, the “raw” detector signal may be used, and/or one or more secondary detector signals derived thereof, such as one or more filtered detector signals. Further, the at least one detector signal, primary or secondary, may also be combined with further information, such as information on a wavelength, e.g. derived from a number of the photosensitive element of an array of photosen- sitive elements from which the detector signal is derived, which is known to be exposed to a specific wavelength of a wavelength range. In the context of the present invention, specifically in the context of the evaluation of the detector signal by the evaluation unit, the option of evaluat- ing the raw detector signal, and/or the option of evaluating a secondary detector signal, such as a preprocessed detector signal, a processed detector signal, or a combined detector signal, is feasible. Still, however, the invention specifically is interesting for determining the “raw” detector signal, specifically a detector signal, indicating a signal intensity as a function of the detection wavelength. Other options, however, are also feasible. As an example, the detector signal, e.g. by the detector itself and/or by the evaluation unit, may be processed or preprocessed into a secondary detector signal, by applying one or more Fou- rier transformations. As an example, a Fast Fourier Transformation may be applied. From the processed, secondary detector signal, the at least one spectroscopic information may be de- rived, such as by a software being executed by the evaluation unit. Thus, as an example, the Fourier transform of the detector signal may be read out by the software of the spectroscopic device, specifically of the evaluation device, and post-processed into the spectroscopic infor- mation on the object. LEDs and phosphor LEDs, as outlined above, may, thus, provide for an efficient light source, which may be modulated in order to perform specific evaluation schemes and in order to reduce noise and artifacts. By using considering the at least one time constant ^ of the light source de- scribing a property of the light source when the driving state is changed, temperature variations within the light source, specifically within the luminescent material, may fully or partially be com- pensated for. Thus, for typical LEDs, as used herein, when operating with the maximum voltage and current that the LED can withstand, the temperatures of the various components of the light source, specifically of the LED, may vary over a large temperature range. As an example, standard operation currents may range from 2 mA to 1000 mA, typically from 10 mA to 300 mA. As an example, forward voltages may be in the range from 1.5 V to 3.5 V, typically from 2.25 V to 3 V. Thus, as an example, under maximum operating conditions, the emitter junction temper- ature may be 135 °C. The operating case temperature may vary from -40 °C to 135 °C and the emitter storage temperature may vary from -40 °C to 125 °C. The ESD sensitivity of the LED
may be 250 V under the standard ANSI/ESDA/JEDEC JS-001-2012. These typical parameters show the large range of temperature variation, which may have an impact on spectroscopic in- formation on the object derived by the spectrometer device. It shall be noted that other parame- ters and other parameter ranges are feasible, too. It is generally known that, with different compositions of the luminescent material, such as differ- ent compositions of phosphors, the phosphor LEDs generate different spectra. Typically, each phosphor LED has multiple peaks in the spectrum, wherein the spectrum typically is spread over a wide wavelength range. However, even giving the same current to the phosphor LED, the spectral properties or the spectrum may change with temperature. These changes may in- clude shifts of the emission peaks, broadening or narrowing of the spectrum, increases or de- creases of the emission and the like. In many cases, however, the emission at some wave- lengths is affected to a larger extent than the emission at other wavelengths. Thus, typically, within the spectrum, there is a specific central wavelength, where the power, specifically the power spectral density ^^^, typically does not change with temperature. Each wavelength therefore typically has its own temperature coefficient, regarding to the increment/decrement of the power. Therefore, the shape of the spectrum changes with temperature. By using the at least one time constant ^, an individual temperature of the spectrum at the different wavelengths may be generated. Thus, as outlined above, the evaluation unit may be configured for individu- ally determining the detector signals in differing spectral ranges and for combining the individual detector signals for deriving the spectroscopic information. More specifically, as also outlined above, this may be performed by using an array of photosensitive elements, wherein each of the photosensitive elements may be configured for generating at least one detector signal. Fi- nally, the corrected detector signals may be combined for deriving the spectroscopic infor- mation. Temperature changes as well as individual properties of the phosphor LEDs may be deter- mined. Thus, as an example, when applying the same current to the LED, the forward voltage of the LED typically decreases while temperature increases. Each type of the LED has its own characteristic forward voltage to temperature curve. Typically, the forward voltage of the LED linearly decreases with rising temperature, such as with a slope in the range of 1 ∙ 10
^^ to 1 ∙ 10
^^ V/K. A further characteristic of the LED is the light output power as a function of the forward current. Thus, generally, by increasing the input current, the power admitted by the LED is increased. The shape, e.g. the slope, of the curve of the light output as a function of the forward current is characteristic to the individual LED. As outlined above, using the at least one time constant ^ as a control parameter for spectro- scopic purposes, an efficient and reliable on-line correction or on-line calibration is feasible. Thereby, various challenges of typical spectrometers and their respective calibration may be overcome. Specifically, in typical spectroscopic processes, reference measurements with the
spectrometer allow for calibrating instrument response, so the measurement provides infor- mation on the sample only. If, however, an optical component of the spectrometer device changes between the reference measurement and the sample measurement, the sample infor- mation is affected by the system change, so the information on the sample may be falsified. In particular, when the optical spectrum ^
^^(^) of the light source changes between the reference measurement, during which the light source has an optical spectrum ^
^^,^^^ (^
), and the actual sample measurement, during which the light source has an optical spectrum ^
^^,^^^^^^ (^
), the spectroscopic information on the object or sample is falsified, since the spectrum typically devi- ates by the ratio of both spectra phosphor LEDs, the situation is typically even more complex, since the
LED is a combination of the spectrum of the LED and the luminescent material. Both components of the phosphor LED may be af- fected by temperature changes in a different way. Thus, for phosphor LEDs, the spectrum typi- cally may be described by equation (3):
Therein, ^
^^^^, ^
^^, ^
^^ denotes the spectrum of the light source LS as a function of the wave- length ^, the p-n-junction temperature of the LED ^
^^, and the temperature of the phosphor ^
^. ^
^^^^^^, ^
^^^ denotes the spectrum of the LED, e.g. the blue LED, and ^
^^^^^^^^^^, ^
^^ denotes the spectrum of the luminescent material, e.g. the phosphor. Both sub-components, the LED and the luminescent material, show an individual temperature response. Thus, a system temperature change or shift or an ambient temperature change or shift, specifically between a reference measurement and a sample measurement, typically af- fects the spectrum by affecting both the LED junction and the luminescent material. Summarizing and without excluding further possible embodiments, the following embodiments may be envisaged: Embodiment 1: A spectrometer device for obtaining spectroscopic information on at least one object, the spectrometer device comprising: (i) at least one light source configured for generating illumination light for illuminating the object, the light source comprising at least one light-emitting diode and at least one luminescent material for light-conversion of primary light generated by the light- emitting diode, wherein the spectrometer device is configured for driving the light source in a manner that the driving state of the light source is changed at least one time; (ii) at least one detector configured for detecting detection light from the object and, thereby, generating at least one detector signal when the driving state of the light source is changed, wherein the detector signal is time-resolved; (iii) at least one evaluation unit configured for evaluating the detector signal generated by the detector for deriving the spectroscopic information on the object, and further configured for considering a plurality of known time constants ^ of the light source
describing a property of the light source when the driving state is changed for deter- mining a contribution of signal intensities of a plurality of wavelength intervals to the detector signal when the spectroscopic information on the object is derived. Embodiment 2: The spectrometer device according to any one of the preceding Embodiments, wherein the light-emitting diode has a primary emission range at least partially located in the spectral range of 420 nm to 460 nm, more specifically in the range of 440 nm to 455 nm, more specifically at 440 nm. Embodiment 3: The spectrometer device according to any one of the preceding Embodiments, wherein the luminescent material is phosphor. Embodiment 4: The spectrometer device according to any one of the preceding Embodiments, wherein the illumination light has a spectral range at least partially located in the near-infra- red spectral range, specifically in the spectral range from 1 to 3 µm, preferably from 1.3 to 2.5 µm, more preferably from 1.5 to 2.2 µm. Embodiment 5: The spectrometer device according to any one of the preceding Embodiments, wherein the driving state of the light source is at least one of: - a first driving state in which the light-emitting diode is generating the primary light; or - a second driving state in which the light-emitting diode is not generating primary light. Embodiment 6: The spectrometer device according to any one of the preceding Embodiments, wherein the at least one light source is configured for operating in a pulsed mode in a man- ner that the driving state of the light source changes repeatedly, particularly changes repeat- edly between the first driving state and the second driving state. Embodiment 7: The spectrometer device according to any one of the preceding Embodiments, wherein the at least one spectrometer device is configured for operating the light source in a specific driving state, particularly the first driving state and/or the second driving state, for a predetermined time span larger than the time constant ^, particularly at least 5 times; or at least 10 times larger than the time constant ^. Embodiment 8: The spectrometer device according to any one of the preceding Embodiments, wherein the detector signal is configured for comprising information on the plurality of wave- length intervals. Embodiment 9: The spectrometer device according to any one of the preceding Embodiments, wherein the detector signal is configured for comprising the spectroscopic information from the detected detection light.
Embodiment 10: The spectrometer device according to any one of the preceding Embodiments, wherein the detector comprises exactly one photosensitive element or at least one photo- sensitive element configured for generating the detector signal comprising information on the plurality of wavelength intervals. Embodiment 11: The spectrometer device according to any one of the preceding Embodiments, the spectrometer device further comprising at least one wavelength-selective element, wherein the wavelength-selective element is disposed in at least one of: - a beam path of the illumination light; or - a beam path of the detection light. Embodiment 12: The spectrometer device according to any one of the preceding Embodiments, wherein the wavelength-selective element is configured such that each of the photosensitive elements is exposed to an individual spectral range of the light from the object. Embodiment 13: The spectrometer device according to any one of the preceding Embodiments, wherein the wavelength-selective element is configured such that the at least one of the photosensitive elements is exposed to a further individual spectral range of the light from the object, wherein the individual spectral range and the further individual range are distant from each other. Embodiment 14: The spectrometer device according to any one of the preceding Embodiments, wherein the wavelength-selective element is selected from the group of a tunable wave- length-selective element and a wavelength-selective element having a fixed transmission spectrum. Embodiment 15: The spectrometer device according to any one of the preceding Embodiments, wherein the wavelength-selective element is or comprises at least one filter element, partic- ularly wherein the filter element is an absorption filter element, specifically a bandpass filter element. Embodiment 16: The spectrometer device according to any one of the preceding Embodiments, wherein the detector is configured for generating a plurality of detector signals for at least two differing spectral ranges of the light from the object, specifically at least one of sequen- tially and simultaneously. Embodiment 17: The spectrometer device according to any one of the preceding Embodiments, wherein the detector comprises an array of photosensitive elements, wherein each of the photosensitive elements is configured for generating at least one detector signal. Embodiment 18: The spectrometer device according to any one of the preceding Embodiments, wherein the spectrometer device is configured such that the photosensitive elements are sensitive to differing spectral ranges of the light from the object.
Embodiment 19: The spectrometer device according to any one of the preceding Embodiments, wherein a plurality of detector signals sensitive to differing spectral ranges is combined for generating the detector signal evaluated for deriving the spectroscopic information on the object. Embodiment 20: The spectrometer device according to any one of the preceding Embodiments, wherein the time constants ^ are at least one of: - a decay constant ^
^ of excited states in the luminescent material; or - a growth constant ^
^ of excited states in the luminescent material. Embodiment 21: The spectrometer device according to any one of the preceding Embodiments, wherein the time constant ^ depends on at least one of: the wavelength ^ of the illumination light; or the temperature ^ of the light source, specifically the luminescent material. Embodiment 22: The spectrometer device according to any one of the preceding Embodiments, wherein the plurality of time constants ^ is considered for determining the contribution of the signal intensities of the plurality of wavelength intervals to the detector signal by performing a regression algorithm, particularly a fit, on the detector signal configured for comprising in- formation on the plurality of wavelength intervals. Embodiment 23: The spectrometer device according to any one of the preceding Embodiments, wherein the regression algorithm, particularly the fit, considers a function describing the con- tribution of the signal intensities of the plurality of wavelength intervals to the detector signal. Embodiment 24: The spectrometer device according to any one of the preceding Embodiments, wherein a further plurality of known time constants ^ of wavelengths comprised by a specific wavelength interval is combined for determining an overall time constant ^ that is considered for determining the contribution of the signal intensity of the specific wavelength interval to the detector signal. Embodiment 25: A method of obtaining spectroscopic information on at least one object, the method comprising: (a) illuminating the object with illumination light generated by at least one light source, the light source comprising at least one light-emitting diode and at least one lumi- nescent material for light-conversion of primary light generated by the light-emitting diode, and driving the light source in a manner that an driving state of the light source is changed at least one time at least one time; (b) detecting detection light from the object by using at least one detector and, thereby, generating at least one detector signal when the driving state of the light source is changed, wherein the detector signal is time-resolved; and (c) evaluating, by using at least one evaluation unit, the detector signal generated by the detector for deriving the spectroscopic information on the object, and further
considering a plurality of known time constants ^ of the light source describing a property of the light source when the driving state is changed for determining a con- tribution of signal intensities of a plurality of wavelength intervals to the detector sig- nal when the spectroscopic information on the object is derived. Embodiment 26: The method according to the preceding Embodiment, wherein a spectrometer device according to any one of the preceding Embodiments referring to a spectrometer de- vice is used. Embodiment 27: The method according to any one of the preceding method Embodiments, wherein the method is performed on-line in the field. Embodiment 28: The method according to any one of the preceding method Embodiments, wherein at least step c. of the method is computer-implemented. Embodiment 29: A computer program comprising instructions which, when the instructions are executed by the evaluation unit of the spectrometer device according to any one of the pre- ceding Embodiments referring to a spectrometer device, cause the evaluation unit to per- form the method according to any one of the preceding Embodiments referring to a method, particularly at least step (c) of the method. Embodiment 30: A computer-readable storage medium comprising instructions which, when the instructions are executed by the evaluation unit of the spectrometer device according to any one of the preceding Embodiments referring to a spectrometer device, cause the evaluation unit to perform the method according to any one of the preceding Embodiments referring to a method, particularly at least step (c) of the method. Embodiment 31: A non-transient computer-readable medium including instructions that, when executed by the evaluation unit of the spectrometer device according to any one of the pre- ceding Embodiments referring to a spectrometer device, cause the evaluation unit to per- form the method according to any one of the preceding Embodiments referring to a method, particularly at least step (c) of the method. Short description of the Figures Further optional features and embodiments will be disclosed in more detail in the subsequent description of embodiments, preferably in conjunction with the dependent claims. Therein, the respective optional features may be realized in an isolated fashion as well as in any arbitrary feasible combination, as the skilled person will realize. The scope of the invention is not re- stricted by the preferred embodiments. The embodiments are schematically depicted in the Fig- ures. Therein, identical reference numbers in these Figures refer to identical or functionally comparable elements.
In the Figures: Figure 1 shows a schematic overview of a spectrometer device; Figure 2 shows schematic cross-sectional view of a light source; Figure 3 shows a schematic flowchart illustrating generating and processing a de- tector signal; Figure 4 shows a diagram representing a superposition of spectra of infrared radia- tion of a phosphor LED at various temperatures; Figure 5 shows a diagram representing a change in emission power change as a function of temperature for a selected number of wavelengths; Figure 6 shows a diagram of a forward voltage as a function of temperature for a selected current; Figures 7A and 7B show spectra of two different types of phosphor LEDs; Figures 8A and 8B show diagrams representing decay constants (Figure 8A) and growth con- stants (Figure 8B) as a function of wavelength for a phosphor LED emit- ting between 1.3 µm and 2 µm; Figure 9A and 9B show diagrams representing decay constants (Figure 9A) and growth con- stants (Figure 9B) as a function of wavelength for a phosphor LED emit- ting between 1.6 µm and 2.1 µm; Figure 10 shows a diagram representing normalized light output as a function of a forward current; Figure 11 shows a heatmap indicating the performance of the present invention; Figure 12 shows three adjoining wavelength intervals; Figure 13 shows three distant wavelength intervals; and Figure 14 shows a method of obtaining spectroscopic information on at least one object. Detailed description of the embodiments
In Figure 1, a schematic overview of a spectrometer device 110 for obtaining spectroscopic in- formation on at least one object 112 is shown. The spectrometer device 110 may comprise a plurality of components as illustrated in Figure 1. Possible components of the spectrometer de- vice 110 and their interplay will be described in the following, specifically with reference to Fig- ure 1. The spectrometer device 110 comprises at least one light source 114 for generating illu- mination light 116 for illuminating the object 112. The light source 114 may be at least one of a tunable light source, a light source having at least one fixed emission wavelength and a broad- band light source. The light source 114 specifically may be or may comprise at least one electri- cal light source. The light source 114 comprises at least one light-emitting diode 118 and at least one luminescent material 120 for light-conversion of primary light generated by the light- emitting diode 118. As an example, the light-emitting diode 118, may comprise one or more of: a light-emitting diode (LED) based on spontaneous emission of light, a light-emitting diode based on superluminescence (sLED), a laser diode (LLED). The LED 118 may specifically comprise at least two layers of semiconductor material 121, wherein light may be generated at at least one interface between the at least two layers of semi- conductor material 121, specifically due to a recombination of positive and negative electrical charges. The at least two layers of semiconductor material 121 may have differing electrical properties, such as at least one of the layers being an n-doped semiconductor material 121 and at least one of the layers being a p-doped semiconductor material 121. Thus, as an example, the LED 118 may comprise at least one pn-junction and/or at least one pin-set up. It shall be noted, however, that other device structures are feasible, too. The light-emitting diode 118 may generate primary light, which may also be referred to as “pump light”. The primary light may subsequently be transformed into “secondary light”, such as by using light conversion, e.g. through one or more luminescent materials 120, such as phos- phor materials. The at least one luminescent material 120, thus, may form at least one con- verter, also referred to as a light converter, transforming primary light into secondary light hav- ing different spectral properties as compared to the primary light. Specifically, a spectral width of the secondary light may be larger than a spectral width of the primary light, and/or a center of emission of the secondary light may be shifted, specifically red-shifted, compared to the primary light. Specifically, the at least one luminescent material 120 may have an absorption in the ultra- violet and/or blue spectral range and an emission in the near-infrared and/or infrared spectral range. The illumination light 116 may be or may comprise at least one of the primary light or a part thereof, the secondary light or a part thereof, or a mixture of both. As indicated in Figure 1, the light source 114 may specifically comprise a phosphor light-emit- ting diode 122, also referred to as phosphor LED 122. The phosphor LED 122 may be a combi- nation of at least one light-emitting diode 118 configured for generating primary light or pump light, and at least one luminescent material 120, also referred to as a “phosphor”, configured for light-conversion of the primary light generated by the light-emitting diode 118. The phosphor LED 122 may form a packaged LED light source, including an LED die 124, e.g. a blue LED emitting blue pump light, as well as the phosphor, which, as an example, fully or partially coats
the LED 118, which is, as an example, configured for converting the primary light or blue light into light having differing spectral properties, specifically into near-infrared light. Figure 2 shows a more detailed view of the light source 114 embodied as a phosphor LED 122. Generally, the light source 114 can be embodied in various ways. Thus, the light source 114 can, for example, be part of the spectrometer device 110 in a housing 126 of the spectrometer device 110, as illustrated in Figure 1. Alternatively or additionally, however, the at least one light source 114 can also be arranged outside the housing 126, for example as a separate light source 114 (not shown). The light source 114 can be arranged separately from the object 110 and illuminate the object 110 from a distance, as indicated in Figure 1. Illumination light 116 as generated by the light source 114 may propagate from the light source 114 to the object 112. In Figure 1, the illumination light 116 generated by the light source 114 and propagating to the object 112 is illustrated by an arrow. The object 112 specifically may comprise at least one sample, which may fully or partially be analyzed by spectroscopic meth- ods. As apparent from Figure 1, the spectrometer device 110 further comprises at least one detector 128 configured for detecting detection light 130 from the object 112. While light propagating from the light source 114 to the object 112 may be referred to as illumination light 116, light propagating from the object 112 to the detector 128 may be denoted as “detection light” 130. In Figure 1, the detection light 130 is illustrated by an arrow. The detection light 130 may comprise at least one of illumination light 116 reflected by the object 112, illumination light 116 scattered by the object 112, illumination light 116 transmitted by the object 112, luminescence light gener- ated by the object 112, e.g. phosphorescence or fluorescence light generated by the object 112 after optical, electrical or acoustic excitation of the object 112 by the illumination light 116 or the like. Thus, the detection light 130 may directly or indirectly be generated through the illumination of the object 112 by the illumination light 116. The detector 128 may be further configured for detecting detection light 130 and, thereby, gen- erating at least one detector signal. This detector signal may be time-resolved may be gener- ated when the driving state of the light source 114 may be changed. The detector signal may be configured for comprising the spectroscopic information from the detected detection light 130. The detector signal may be configured for comprising information exactly one wavelength inter- val 236. For such a purpose, the detector 128 may comprise exactly one photosensitive ele- ment 133 or at least one photosensitive element 133 configured for generating the detector sig- nal comprising information on the plurality of wavelength intervals. In addition, the spectrometer device 110 may comprise at least one wavelength-selective element 152. The spectrometer device 110 may comprise at least one wavelength-selective element 152, wherein the wavelength-selective element 152 may be disposed in at least one of: - a beam path of the illumination light 116; or
- a beam path of the detection light 130. The detector signal may be configured for comprising information a plurality of wavelength inter- vals 236. For such a purpose, the detector 128 may comprise exactly one photosensitive ele- ment 133 or at least one photosensitive element 133 configured for generating the detector sig- nal comprising information on the plurality of wavelength intervals 236. Alternatively or in addi- tion, the spectrometer device 110 may comprise a plurality of wavelength-selective elements 152. The wavelength-selective element 152 may be configured such that each of the photosen- sitive elements 133 may be exposed to an individual spectral range of the light from the object 112. The wavelength-selective element 152 may be configured such that the at least one of the pho- tosensitive elements 133 may be exposed to a further individual spectral range of the light from the object, wherein the individual spectral range and the further individual range are distant from each other. For this purpose, a plurality of filter elements 150, particularly absorption and/or bandpass filter elements 150, may be configured such that the photosensitive element 133 is exposed to the individual spectral range and the further individual spectral range of the light from the object. In general, the wavelength-selective element 152 may be selected from the group of a tunable wavelength-selective element 152 and a wavelength-selective element 152 having a fixed trans- mission spectrum. The wavelength-selective element 152 may be or may comprise at least one filter element 150, particularly wherein the filter element 150 may be an absorption filter ele- ment, specifically a bandpass filter element 150. The detector 128 may be configured for generating a plurality of detector signals for at least two differing spectral ranges of the light from the object 112, specifically at least one of sequentially and simultaneously. The detector 128 may comprise an array of photosensitive elements 134, wherein each of the photosensitive elements 133 is configured for generating at least one de- tector signal. The spectrometer device 110 may be configured such that the photosensitive ele- ments 133 are sensitive to differing spectral ranges of the light from the object 112. A plurality of different detector signals, particularly generated by the photosensitive elements 133 that are sensitive to differing spectral ranges of the light from the object 112, may be combined for gen- erating the detector signal evaluated for deriving the spectroscopic information on the object 112. The detector 128 may be or may comprise at least one optical detector 132. The optical detec- tor 132 may be configured for determining at least one optical parameter, such as an intensity and/or a power of light by which at least one sensitive area of the detector 132 is irradiated. More specifically, the optical detector 132 may comprise exactly one, which may be preferred, or at least one photosensitive element 133 and/or at least one optical sensor, such as at least one of a photodiode, a photocell, a photosensitive resistor, a phototransistor, a thermophile sen-
sor, a photoacoustic sensor, a pyroelectric sensor, a photomultiplier and a bolometer. The de- tector 128, thus, may be configured for generating at least one detector signal, more specifically at least one electrical detector signal, in the above-mentioned sense, providing information on at least one optical parameter, such as the power and/or intensity of light by which the detector 128 or a sensitive area of the detector 128 is illuminated. The detector 128 may comprise one single optically sensitive element or area, which may be preferred, or a plurality of optically sensitive elements or areas. As indicated in Figure 1, the de- tector 130 may comprise at least one detector array, more specifically an array of photosensi- tive elements 134. Each of the photosensitive elements 133 may be configured for generating at least one detector signal. In particular, each of the photosensitive elements 133134 may com- prise at least a photosensitive area, which may be adapted for generating an electrical signal depending on the intensity of the incident light, wherein the electrical signal may, in particular, be provided to an evaluation unit 136 of the spectrometer device, as will be outlined in further detail below. In case the detector 128 comprises the array of optically sensitive elements 134, the detector 128, may e.g. be selected from any known pixel sensor, specifically from a CCD chip or a CMOS chip. As an alternative, the detector 128 generally may be or comprise a photoconduc- tor, in particular an inorganic photoconductor, especially PbS, PbSe, Ge, InGaAs, ext. InGaAs, InSb, or HgCdTe. As a further alternative, it may comprise at least one of pyroelectric, bolome- ter or thermopile detector elements. The spectrometer device 110 comprises at least one evaluation unit 136 for evaluating at least one detector signal generated by the detector 128, such as the time-resolved detector signal, and for deriving the spectroscopic information on the object 112 from the detector signal. The detector 128 may directly or indirectly provide the detector signals to the evaluation unit 136. Thus, the detector 128 and the evaluation unit 136 may be directly or indirectly connected, as indicated by arrows in Figure 1. The detector signal may be used as a “raw” detector signal and/or may be processed or preprocessed before further use, e.g. by filtering and the like. Thus, the detector 128 may comprise at least one processing device and/or at least one prepro- cessing device, such as at least one of an amplifier, an analogue/digital converter, an electrical filter and a Fourier transformation. As shown in Figure 1, the spectrometer device 110 further comprises at least one driving unit 138 for electrically driving the light source 114. The spectrometer device 110 comprises at least one measurement unit 139 for generating at least one item of information on an electronic value, specifically on the light source 114, particularly for determining a temperature of the light source. The item of information on the electronic characteristic may be considered for determin- ing a power spectral density ^^^ of the light source, specifically the light-emitting diode. The measurement unit 139 may be an element of the driving unit 138, as indicated in Figure 1. Par- ticularly, the driving unit 138 may be configured for providing an electrical current to the LED
118, specifically for controlling an electrical current through the LED 118. Therein, as an exam- ple, the driving unit 138 may be configured for adapting and measuring a voltage provided to the LED 118, the voltage being required for achieving a specific electrical current through the LED 118. The driving unit 138, specifically, may comprise one or more of: a current source 140, a voltage source, a current measurement device, such as an Ampère-meter, a voltage meas- urement device 142, such as a Volt-meter, a power measurement device. Specifically, the driv- ing unit 138 may comprise at least one current source 140 for providing at least one predeter- mined current to the LED 118, wherein the current source 140 specifically may be configured for adjusting or controlling a voltage applied to the LED 118 in order to generate the predetermined current. The driving unit 138, as an example, may comprise one or more electrical components, such as integrated circuits, for driving the light source 114. The driving unit 138 may be fully or partially integrated into the light source 114 or may be separated from the light source 114, the latter configuration being illustrated in Figure 1. A forward voltage may be applied to the LED in the forward direction, i.e. as with a positive con- tact of a voltage or current source 140 applied to a p-layer of the LED 118 and a negative con- tact applied to the n-layer of the LED 118, in order to generate a predetermined electrical cur- rent through the LED 118. Thereby, the LED may generate the primary light. As an example, the predetermined current defining the forward voltage may be a current, which is known to generate a predetermined light output of the light source 114 and/or of the light-emitting diode 118. The spectrometer device 110 may configured for driving the light source 114 in a manner that the driving state of the light source 114 is changed at least one time. The driving state of the light source 114 may be at least one of: - a first driving state in which the light-emitting diode 118 is generating the primary light; or - a second driving state in which the light-emitting diode 118 is not generating primary light. The at least one light source 114 may be configured for operating in a pulsed mode in a manner that the driving state of the light source 114 changes repeatedly, particularly changes repeat- edly between the first driving state and the second driving state. The at least one spectrometer device 110 may be configured for operating the light source 114 in a specific driving state, par- ticularly the first driving state and/or the second driving state, for a predetermined time span larger than the time constant ^, particularly at least 5 times; or at least 10 times larger than the time constant ^. As outlined above, and as shown in Figure 1, the spectrometer device 110 may comprise the at least one evaluation unit 136 for evaluating the at least one detector signal, such as the time re- solved detector signal, generated by the detector 128 for deriving the spectroscopic information on the object 112 from the detector signal. The evaluation unit 136 may be configured for con- sidering a plurality of known time constants ^ of the light source 114 describing a property of the
light source 114 when the driving state is changed for determining a contribution of signal inten- sities of a plurality of wavelength intervals 236 to the detector signal when the spectroscopic in- formation on the object 112 is derived. The time constants ^ may at least one of: - a decay constant ^
^ of excited states in the luminescent material 120; or - a growth constant ^
^ of excited states in the luminescent material 120. The time constants ^ may depend on at least one of: the wavelength ^ of the illumination light; or the temperature ^ of the light source 114, specifically the luminescent material 120. The plu- rality of time constants ^ may be considered for determining the contribution of the signal inten- sities of the plurality of wavelength intervals to the detector signal by performing a regression algorithm, particularly a fit, on the detector signal configured for comprising information on the plurality of wavelength intervals 236. The regression algorithm, particularly the fit, may consider a function describing the contribution of the signal intensities of the plurality of wavelength inter- vals to the detector signal. Specifically, the evaluation unit 136 may be configured for processing at least one input signal and to generate at least one output signal thereof. The at least one input signal, as an example, may comprise at least one detector signal provided directly or indirectly by the at least one de- tector 128. The arrows between the driving unit 138, which comprises the measurement unit 139 in the embodiment illustrated in Figure 1, and the evaluation unit 136 in Figure 1 illustrate the process of providing to the evaluation unit 136 and/or retrieving by the evaluation unit 136 the signal comprising the at least one item of information on the electronic characteristic. The evaluation unit 136 may be or may comprise one or more integrated circuits, such as one or more application-specific integrated circuits (ASICs), and/or one or more data processing de- vices 144, such as one or more of computers, digital signal processors (DSP), field programma- ble gate arrays (FPGA), preferably one or more microcomputers and/or microcontrollers. Addi- tional components may be comprised, such as one or more preprocessing devices 146 and/or data acquisition devices, such as one or more devices for receiving and/or preprocessing of the detector signals, such as one or more AD-converters and/or one or more filters. Further, the evaluation unit may comprise one or more data storage devices 148, as shown in Figure 1. Fur- ther, the evaluation unit 136 may comprise one or more interfaces, such as one or more wire- less interfaces and/or one or more wire-bound interfaces. As described above in more detail, the detector 128 may specifically comprise an array of pho- tosensitive elements 134. Each of the photosensitive elements 133 may be configured for gen- erating at least one detector signal. The evaluation unit 136 may be configured for considering each of the detector signals for deriving the spectroscopic information. The spectrometer device 110 may be configured such that the photosensitive elements 133 of the detector 128 are sensi- tive to differing spectral ranges of the light from the object 112. In particular, the detector 128 may be configured for generating detector signals for at least two differing spectral ranges of the
light from the object, specifically at least one of sequentially and simultaneously. The spectrom- eter 110 specifically may comprise at least one filter element 150 disposed in a beam path of the light from the object. The filter element 150 specifically may be configured such that each of the photosensitive elements 133 is exposed to an individual spectral range of the light from the object 112. As already discussed, the spectrometer device 110 further may comprise one or more optical components 151, e.g. such as one or more of at least one mirror, at least one lens, at least one aperture and at least one wavelength-selective element 152. Specifically, the one or more opti- cal components 151 may be arranged in at least one of the beam path of the illumination light 116 and the beam path of the detection light 130. The spectrometer device 110 may in particu- lar comprise the at least one wavelength-selective element 152. The wavelength-selective ele- ment 152 specifically may be selected from the group of a tunable wavelength-selective ele- ment 152 and a wavelength-selective element 152 having a fixed transmission spectrum. By us- ing a tunable wavelength-selective element 152, as an example, differing wavelength ranges may be selected sequentially, whereas, by using a wavelength-selective element 152 having a fixed transmission spectrum, the selection of the wavelength ranges may be fixed and may, however, be dependent e.g. on a detector position. The wavelength-selective element 152 may be used for separating incident light into a spectrum of constituent wavelength signals whose respective intensities are determined by employing a detector, e.g. the detector 128 of the spec- trometer device 110, which may comprise the array of photosensitive elements 134. The at least one wavelength-selective element 152 may e.g. comprise at least one of a filter, a grating and a prism. The wavelength-selective element 152 may specifically comprise at least one of a wavelength-selective element 152 disposed in the beam path of the illumination light 116 and a wavelength-selective element 152 disposed in the beam path of the detection light 130. Figure 1 illustrates an embodiment of the spectrometer device 110 with one wavelength-selective ele- ment 152 arranged in the beam path of the illumination light 116, and one wavelength-selective element 152 arranged in the beam path of the detection light 130. The spectrometer device 110 as represented in a schematic fashion in Figure 1 is configured for obtaining spectroscopic information on the at least one object 112. In particular, the spectrome- ter device may be configured for obtaining an item of information, e.g. on at least one object and/or radiation emitted by at least one object, characterizing at least one optical property of the object, more specifically at least one item of information characterizing, e.g. qualifying and/or quantifying, at least one of a transmission, an absorption, a reflection and an emission of the at least one object. As an example, the at least one item of spectral information may comprise at least one intensity information, e.g. information on an intensity of light being at least one of transmitted, absorbed, reflected or emitted by the object, e.g. as a function of a wavelength or wavelength sub-range over one or more wave-lengths, e.g. over a range of wavelengths. Thus, the spectrometer device 110 may be configured for acquiring at least one spectrum or at least a part of a spectrum of detection light 130 propagating from the object 112 to the detector 128. The spectrum may describe the radiometric unit of spectral flux, e.g. given in units of watt per nanometer (W / nm), or other units, e.g. as a function of the wavelength of the detection light.
Thus, the spectrum may describe the optical power of light, e.g. in the NIR spectral range, in a specific wavelength band. The spectrum may contain one or more optical variables as a func- tion of the wavelength, e.g. the power spectral density ^^^, electric signals derived by optical measurements and the like. Examples of spectra are shown e.g. in Figures 4, 7A and 7B. The spectrometer device 110 may specifically be a portable spectrometer device 110, which may in particular be used in the field. In Figure 2, a schematic cross-sectional view of a light source 114 is shown. The at least one light source 114 of the spectrometer device 110 may be configured for generating or providing to electromagnetic radiation in one or more of the infrared, the visible and the ultraviolet spectral range. Due to the fact that many material properties or properties on the chemical constitution of many objects 112 may be derived from the near infrared spectral range, light used for the typi- cal purposes of the present invention is light in the infrared (IR) spectral range, more preferred, in the near infrared (NIR) and/or the mid infrared spectral range (MidIR), especially the light having a wavelength of 1 µm to 5 µm, preferably of 1 µm to 3 µm. The light source 114 com- prises the at least one light-emitting diode 118 and the at least one luminescent material 120 for light-conversion of primary light generated by the light-emitting diode 118. The LED 118 and the luminescent material 120, together, may form the phosphor LED 122, as described above. The phosphor LED 122 as illustrated in Figure 2 may comprise one or more functional compo- nents. Specifically, the phosphor LED 122 may comprise one or more substrates 154, specifi- cally one or more electrically insulating substrates 154. In particular, the phosphor LED 122 may comprise one or more ceramic substrates 156, as shown in Figure 2. The substrate 154 may be configured for holding the at least one LED die 124 and the at least one luminescent material 120. Further, the at least one substrate 154 may hold or comprise one or more components of electrical connectivity, such as one or more contact pads 158 as shown in Figure 2 and/or one or more electrical leads, such as one or more metallic contacts and/or one or more metallic leads. The substrate 154 may be configured to serve as a heat sink. Heat may be generated in the LED die 124, such as due to a limited conversion of electrical energy into photonic energy, as well as in the luminescent material 120, e.g. during the conversion process. Said heat may be dissipated in the substrate 154, such as in ceramic substrate. As shown in Figure 2, the phosphor LED 122 may comprise the light-emitting diode 118. The light-emitting diode 118 may be configured for converting electrical current into primary light, such as blue primary light, using at least one LED chip and/or the at least one LED die 124 as illustrated in Figure 2. Specifically, p-n-diodes may be used. As an example, one or more LEDs 118 selected from the group of an LED 118 on the basis of indium gallium nitride (InGaN), an LED 118 on the basis of GaN, an LED 118 on the basis of InGaN/GaN alloys or combinations thereof and/or other LEDs 118 may be used. Additionally or alternatively, quantum well LEDs 118 may also be used, such as one or more quantum well LEDs 118 on the basis of InGaN. Ad- ditionally or alternatively, Superluminescence LEDs (sLED) and/or Quantum cascade lasers may be used. As further apparent from Figure 2, the phosphor LED may comprise the at least one luminescent material 120 configured for light-conversion of the primary light generated by
the light-emitting diode 118. Various types of conversion and/or luminescence are known and may be used in the context of the present invention. Specifically, the luminescent material 120 may comprise at least one of: Cerium-doped YAG (YAG:Ce3
+, or Y3Al5O12:Ce
3+); rare-earth- doped Sialons; copper- and alu-minium-doped zinc sulfide (ZnS:Cu,Al). The luminescent material 120 specifically may form at least one layer. Generally, various alter- natives of positioning the luminescent material 120 with respect to the light-emitting diode118 are feasible, alone or in combination. Firstly, the luminescent material 120, e.g., at least one layer of the luminescent material 120, such as the phosphor, may be positioned directly on the light-emitting diode 118, e.g. with no material in between the LED 118 and the luminescent ma- terial 120 or with one or more transparent materials in between, such as with one or more trans- parent materials, specifically transparent for the primary light, in between the LED and the lumi- nescent material 120. Thus, as an example, a coating of the luminescent material 120 may be placed directly or indirectly on the LED 118 (not shown). Additionally or alternatively, the lumi- nescent material 120, as an example, may form at least one converter body 160, such as at least one converter disk, which may also be referred to as converter platelet. The converter body 160 may be placed on top of the LED 118, e.g. by adhesive attachment of the converter body 160 to the LED 118, as illustrated in Figure 2. Additionally or alternatively, the luminescent material 120 may also be placed in a remote fashion, such that the primary light from the LED 118 has to pass an intermediate optical path before reaching the luminescent material 120 (not shown). Again, as an example, the luminescent material in the remote placement may form a solid body or converter body 160, such as a disk or converter disk. In the intermediate optical path, one or more optical elements may be placed, such as one or more of a lens, a prism, a grating, a mirror, an aperture or a combination thereof. Thus, specifically, an optical system hav- ing imaging properties may be placed in between the LED 118 and the luminescent material 120, in the intermediate optical path. Thereby, as an example, the primary light may be focused, or bundled onto the converter body 160. In the light source 114, specifically the phosphor LED 122, the at least one luminescent material 120 may be located with respect to the light-emitting diode 118 such that a heat transfer from the light-emitting diode 118 to the luminescent material 120 is possible. More specifically, the luminescent material 120 may be located such that a heat transfer by one or both of thermal ra- diation and heat conduction is possible, more preferably by heat conduction. Thus, as an exam- ple, the luminescent material 120 may be in thermal contact and/or in physical contact with the light-emitting diode 118 as illustrated in Figure 2. Thereby, generally, a temperature of the lumi- nescent material 120 and a temperature of the light-emitting diode 118 may be coupled. As illustrated in Figure 2, the light source 114, specifically the phosphor LED 122, may comprise further components such as at least one side coat 162 covering at least one side, such as a top side, a bottom side and/or one or more lateral sides of at least of: the substrate 154, the contact pad 158, the light-emitting diode 118 and the luminescent material 120. Specifically, the side coat 162 may cover gaps and/or interspaces that may be present in the layered set-up of the light source 114 as shown in Figure 2. Further components of the light source 114, specifically
components, which are not shown in Figure 2, are feasible. Generally, the light source 114, in particular the phosphor LED 122, may be packaged in one housing (not shown in Figure 2) or may be unpackaged. Thus, the LED 118 and the at least one luminescent material 120 for light- conversion of the primary light generated by the light-emitting diode 118 may specifically be housed in a common housing. Alternatively, however, the LED 118 may also be an unhoused or bare LED 118, as illustrated in Figure 2. The schematic flowchart of Figure 3 illustrates the process of generating the detector signal as well as processing of the detector signal. Specifically, hardware components 164, which may take part in the process or generating and/or preprocessing the detector signal as well as soft- ware components 166, which may take part in processing the detector signal, are illustrated in Figure 3. The hardware components 164, also simply referred to as “hardware” 164, may spe- cifically comprise the at least one light-emitting diode 118 of the spectrometer device 110, in particular a blue LED 118, configured for emitting blue primary light. The hardware components 164 may further comprise the luminescent material 120, also referred to as LED phosphor, the object 112 as well as one or more optical components 151, e.g. the at least one wavelength-se- lective element 152, and the detector 128. The evaluation unit 136 may consider temperature changes, even local temperature changes within the light source 114, which may have an impact on the emission characteristics of the light source 114. In addition to the hardware components 164, temperatures for selected hard- ware components 164 are indicated in Figure 3. The hardware components 164 may have dif- fering or identical temperatures, e.g. depending on an arrangement of the hardware compo- nents 164, such as their relative positions and distances in the spectrometer device 110. Specif- ically, as described above, the temperature of the luminescent material 120 and the tempera- ture of the light-emitting diode 118 may be coupled, e.g. due to heat transfer by one or both of thermal radiation and heat conduction between the light-emitting diode 118 and the luminescent material 120. Thus, in particular, the temperature of the LED 118, which may also be referred to as “T
pn”, and the temperature of the luminescent material 120, which may also be referred to as “TPh”, may be similar. In Figure 3, the temperature of the LED 118 is indicated with reference sign 168, the temperature of the luminescent material 120 is indicated with reference sign 170, and the temperature of the detector 128, also referred to as “T
D”, is indicated with reference sign 172. The LED 118 may emit primary light when an electrical current flows through the LED 118, e.g. as a result of an appropriate voltage applied to the LED by the driving unit 138 in order to gener- ate a specific electrical current, such as a predetermined electrical current. A target signal St may be provided as indicated in Figure 3 by reference sign 174, e.g. to the driving unit 138, to drive the LED 118 to emit blue primary light. The target signal S
t 174 may in particular be a pre- determined current value that is to be generated through the LED 118, e.g. by applying an ap- propriate voltage. The predetermined current value may in particular be in the range from 10 mA to 500 mA, more specifically in the range from 100 mA to 300 mA, e.g. a current value of 50 mA. Thus, the predetermined current may be known to generate a predetermined light output of
the LED 118, such as blue primary light. The LED 118 may be at the temperature “T
pn” indicated by reference sign 168. The blue primary light may be converted by the luminescent material 120 into secondary light, such as into light in the infrared spectral range. The luminescent material 120 may be at the temperature “T
ph” indicated by reference sign 170. The illumination light 116 generated by the light source 114, which may comprise at least one of the primary light or a part thereof, the secondary light or a part thereof, or a mixture of both, may illuminate the object 112. For directing the illumination light 116, one or more optical components 151, such as one or more mirrors, lenses, wavelength selective elements 152 or other optical components 151 may be used, e.g. by placing the optical components 151 in the beam path of the illumination light 116. The detection light from the object 112, e.g. reflected light, may be directed to the detector 128. In the beam path of the detection light 130, again, optionally, one or more optical compo- nents 151 may be used. As an example, one or more wavelength-selective elements 152 may be used, such as one or more dispersive elements, e.g. for splitting the detection light 130 into its spectral components. As described above in more detail, the detector 128 may e.g. comprise an array of photosensi- tive elements 134. Specifically, the detector 128 may be or may comprise a pixel sensor, such as a CCD chip or a CMOS chip, comprising a plurality of pixels arranged on the chip. As an ex- ample, each of the pixels may correspond to a predetermined spectral range, e.g. by being sen- sitive to the predetermined spectral range. The detector 128 may thus generate a detector sig- nal S
px,i 176, as indicated in Figure 3 by reference sign 176, comprising a plurality of detector signals. Thus, each of the plurality of detector signals may correspond to an electronic signal generated by one of the plurality of pixels of the detector 128. Each of the plurality of detector signals may e.g. be given as a numerical value corresponding to a number of counts of the re- spective pixel as measured e.g. during a predetermined time span. Thus, the detector signal S
px,i 176 may specifically be a function of the wavelength of the detection light 130, as indicated by the index “px”. The signal Spx,i 176 may further be a function of time, e.g. in the case of time- dependent detector signals or time resolved detector signals, as indicated by the index “i”. The plurality of signals comprised by the detector signal Spx,i 176 may be generated simultane- ously or in a temporally successive manner. The detector signal S
px,i 176 may be determined using readout electronics 178 as indicated in Figure 3. The detector signal S
px,i 176 may be pro- cessed, e.g. as part of the preprocessing and/or as part of further processing steps. As an ex- ample, the pixels comprised by the detector 128 may specifically be active pixel sensors, which may be adapted to amplify the electronic detector signal S
px,i 176, e.g. as part of a prepro- cessing process prior to further processing that may e.g. be performed by one or more of the software components 166. The signal S
px,i 176 as generated by the detector 128 may also be referred to as “Frame signal Spx,i 176”. Figure 3 illustrates the process of providing the signal Spx,i 176 to one of the software components 166 with an arrow. Specifically, the software components 166 configured for pro- cessing the detector signal S
px,i, 176 may comprise at least one first software 180, which may also be referred to as “software 1”, and at least one second software 182, which may also be
referred to as “software 2”. The first software 180 may be configured for performing at least one first processing step 184, also referred to as “processing 1”, on the detector signal Spx,i 176, such as by applying at least one algorithm to the detector signal Spx,i 176. Specifically, the first processing step 184 may comprise at least one correction of transient or time-dependent ef- fects. Thus, as an example, the first processing step 184 may comprise one or more of the fol- lowing: a correction of the dark signal; a correction of dark signal drift; a correction of fluctuation effects; a correction of photodetector response for individual detector elements or individual time steps; a correction of environment-induced, e.g., temperature-induced changes of the pho- todetector response; an extraction of information for subsequent processing; an addition or mul- tiplication with a parameter, which was generated from information on the at least one electrical value and/or on device temperature. The first software 180 may be configured for performing at least one further step comprising at least one fast Fourier transform 186 to the detector signal. Thus, as a result of applying the first processing step 184 and/or the fast Fourier transform 186 to the detector signal S
px,i 176, a signal S
px 188, also referred to as “pixel signal S
px 188”, may be generated, which may no longer be a function of time. Specifically, the time dependency of the frame signal Spx,i 176 may be eliminated by one or more of the steps forming part of the first software component 1 while the wavelength dependency may still be present in the on signal S
px 188 as indicated by the index “pn”. Figure 3 further illustrates the process of providing the signal S
px 188 to the second software 182 with an arrow. The second software 182 may be con- figured for performing at least one second processing step 190, also referred to as “processing 2”, on the signal S
px 188, such as by applying at least one algorithm to the signal S
px 188, thereby generating at least one corrected signal S
px, corr 191. Specifically, the second processing step 190 may comprise one or more of the following: a correction of the dark signal; a correction of dark signal drift; a correction of fluctuation effects; a correction of photodetector response for individual detector elements or individual time steps; a correction of environment-induced, e.g., temperature-induced changes of the photodetector response; an extraction of information for subsequent processing; an addition or multiplication with a parameter, which was generated from information on the at least one electrical value and/or on device temperature. In particular, the corrected signal S
px, corr 191 may comprise a plurality of corrected signals, such as a plurality of corrected electronic signals. Each of the plurality of corrected signals may specifically corre- spond to a corrected number of counts of the respective pixel. Both the light-emitting diode 118 and the luminescent material 120 may be based on different materials and/or different compositions of materials, e.g. as described in more detail above, which, generally, may affect and influence the spectrum 192 of the phosphor LED 122. How- ever, the spectrum 192 or the spectral properties of a specific phosphor LED 122 may change with temperature, even when being operated at a specific, predetermined current. These changes may include shifts of the emission peaks 193, broadening or narrowing of the spectrum 192, increases or decreases of the emission and the like. In many cases, however, the emission at some wavelengths is affected to a larger extent than the emission at other wavelengths. This effect is illustrated by the diagram shown in Figure 4, which represents a superposition of spec- tra 192 of infrared radiation of a phosphor LED 122 at various temperatures. Specifically, the di-
agram in Figure 4 shows the power spectral density ^^^ 194 in units of microwatt per nanome- ter (µW/nm) on the y-axis 196 as a function of the wavelength 198 given in nanometers on the x-axis 200. For the represented spectra 192 the temperature of the phosphor LED 122 generat- ing the illumination light 116 ranges from 25°C to 50°C. Typically, there is within the spectrum 192, a specific central wavelength, where the power spectral density ^^^ typically does not change with temperature. Each wavelength therefore typically has its own temperature coeffi- cient, regarding to the increment/decrement of the power. Therefore, the shape of the spectrum 192 changes with temperature as apparent from Figure 4. To visualize this effect even more clearly, a number of four specific wavelength intervals, each centering around one of four spe- cific wavelengths ranging across the spectrum 192 are indicated in Figure 4. The wavelength intervals are delimited by dashed lines. Specifically, the following four wavelengths and their re- spective intervals are marked with the following reference signs: 1643 nm is indicated by refer- ence sign 202, 1750 nm is indicated by reference sign 204, 1802 nm is indicated by reference sign 206, and 1950 nm is indicated by reference sign 208,. For each of these wavelengths, the emission power change normalized to the emission power change at 25°C is shown in the dia- gram in Figure 5 as a function of temperature over a temperature range from 25°C to 50°C. In the diagram of Figure 5 the emission power change normalized to the emission power change at 25°C given in percent is shown on the y-axis 196 and represented by reference sign 219, while the temperature in °C, represented by reference sign 220, is indicated on the x-axis 200. The lines in the diagram in Figure 5 indicate fitted curves 236. As apparent from Figure 5, the emission power at the central wavelength of 1802 nm may change very little over the observed temperature range (that is, the emission power change is zero or close to zero), while the emis- sion power change may change considerably for other wavelengths, e.g. for 1643 nm or 1953 nm. When generating a specific current through a light-emitting diode 118, such as an electrical cur- rent at a specific, predefined value by applying to the light-emitting diode 118 a forward voltage, the appropriate forward voltage may be a function of the temperature of the light-emitting diode 118. Thus, when applying the same current to the light-emitting diode 118, the forward voltage of the LED 118 typically decreases while temperature increases. Each type of the LED 118 has its own characteristic forward voltage to temperature curve. Typically, the forward voltage of the LED 118 linearly decreases with rising temperature, such as with a slope in the range of 1 ∙ 10
^^ to 1 ∙ 10
^^ V/K. Figure 6 illustrates this relationship for a specific LED 118. In particular, the dia- gram of Figure 6 shows the forward voltage applied to an LED 118 for the generation of a direct current of 150 mA through the LED 118 as a function of the temperature of the LED 118. The forward voltage in the units of Volt is represented by reference sign 224 on the y-axis 196. The temperature in °C is indicated by reference sign 220 on the x-axis 200. As apparent from Figure 6, the forward voltage, in this case, decreases linearly with increasing temperature. The curve in Figure 5, may be described by the following equation: ^ ^
^ = −0.00059 2.98
wherein ^
^represents the forward voltage and ^ represents the Temperature. In the diagram in Figure 6, measuring points 221 represented by grey, filled circles are shown as well as a dashed line corresponding to the above given fitted curve 236. Instead of a relation and/or curve between the forward voltage and the temperature as described in an exemplary fashion above, a relation between another electrically measurable quantity required for driving the light source and the temperature may be used, e.g. a fed in electrical power; a current, resistance, induct- ance, capacitance and the like. For deriving the spectroscopic information on the object 112, specifically a spectrum, the spec- trometer device 110, in particular the evaluation unit 136, may specifically take into account the characteristics of the luminescent material 120 used in the light source 114. As outlined in more detail above, the luminescent material 120 may be configured for absorbing primary photons generated by the light-emitting diode 118 and may, as a reaction, emit secondary photons in- stantaneously or after a delay or decay time. The signal or emission of the phosphor LED 122 after turning off the forward current may be described using equations (1) and (2) as described above. Thus, characteristic for the luminescent material 120 may in particular be the decay constant ^
^ 228, which may describe the typical time of an afterglow of the luminescent material 120, as well as the growth constant ^
^, which may describe the typical time for reaching a saturation of the emission of converted light. The time constants ^
^ and ^
^ typically differ between different phosphor LEDs 122 and/or between different types of the luminescent material 120. Addition- ally, decay constant ^
^ and growth constant ^
^ may depend on the wavelength. The time con- stants typically are extracted from step response of the optical signal by applying / shutting off the forward current. Figures 7A and 7B show spectra 192 of two different types of phosphor LEDs 122, which emit light in the near infrared range. Specifically the power spectral density ^^^ is shown as a function of the wavelength, which is given in nm. As apparent from Figures 7A and 7B the spectra 192 of the two different phosphor LEDs 122 differ. Thus, as an example, the spectrum 192 shown in Figure 7A reflects a high emission in the range from 1400 nm to 1600 nm, while the emission in this region is negligible for the phosphor LED 122, whose spec- trum 192 is shown in Figure 7B. The decay constant ^
^ and the growth constant ^
^ of the phos- phor LED 122, whose spectrum is shown in Fig 7A,
given as a function of the wavelength in Figures 8A and 8B, respectively. The decay constant ^
^ and the growth constant ^
^ of the phos- phor LED 122, whose spectrum is shown in Fig 7B, are given as a function of the wavelength in Figures 9A and 9B, respectively. Specifically, Figures 8A and 9A show the respective decay constants ^
^ in ms, indicated by reference sign 228, on the y-axis 196 versus the wavelength in nm 198 on the x-axis 200; and Figures 8B and 9B show the respective growth constants ^
^ in ms, indicated by reference sign 230, on the y-axis 196 versus the wavelength in nm 198 on the x-axis 200. Data points from different repetition measurements are marked in different shades of grey. A further characteristic of the LED 118 is the light output power as a function of the forward cur- rent. Thus, generally, by increasing the forward current, specifically the input current, the power
emitted by the LED 118 is increased. The shape, e.g. the slope, of the curve of the light output as a function of the forward current is characteristic to the individual LED 118. Figure 10 shows an example of such a curve. Specifically, in the diagram in Figure 10, the normalized light out- put 232 of a phosphor LED is shown as a function of the forward current 234, which is given in Ampere. Figure 11 illustrates a heat map 238 indicating the performance of the present invention. On the horizontal axis 240, the noise level in units of the signal amplitude is shown. Thus, the horizon- tal axis 240 shows the relative noise level. On the vertical axis 242 the number of contributing signal intensities of the plurality of wavelength intervals 236 to the detector signal is illustrated. The heat map 238 indicates the mean deviation of the fitted signal amplitudes to the real signal amplitudes. Thus, the heat map 238 indicates the relative error of the described method.. As may be derived from the Figure 11, the number of contributing signal intensities of the plurality of wavelength intervals 236 to the detector signal and noise level influence the performance. Particularly, for a low noise level a high number of contributing signal intensities of the plurality of wavelength intervals 236 to the detector signal may be considered. In Figure 12, a graph 244 illustrating three adjoining wavelength intervals are depicted. On the horizontal axis 246 the wavelength is depicted. On the vertical axis 248 the time constant ^ may be depicted. As may be derived from Figure 12, the time constant ^ within a wavelength interval 236 may fluctuate strongly. For compensating this fluctuation, a further plurality of known time constants ^ of wavelengths comprised by a specific wavelength interval 236 may be combined for determining an overall time constant ^ that is considered for determining the contribution of the signal intensity of the specific wavelength interval 236 to the detector signal. In Figure 13, a graph 250 illustrating three distant wavelength intervals 236 are depicted. On the horizontal axis 240 the wavelength is depicted. On the vertical axis 242 the time constant ^ ^is depicted. The distant or separate wavelength intervals 236 may particularly be recorded by us- ing exactly one detector 128 having exactly one photosensitive area and a wavelength-selective element 152 that transmits only wavelengths comprised by the separate wavelength intervals 236 onto the photosensitive area. Further wavelengths may be blocked and/or strongly attenu- ated. A method 256 of obtaining spectroscopic information on at least one object 112 is displayed in Figure 14. The method is comprising: (a) illuminating the object 112 with illumination light 116, in a step (a) 258, generated by at least one light source 114, the light source 114 comprising at least one light-emit- ting diode 118 and at least one luminescent material 120 for light-conversion of pri- mary light generated by the light-emitting diode 114, and driving the light source 114 in a manner that an driving state of the light source 114 is changed at least one time at least one time; (b) detecting detection light 130 from the object 112, in a step (b) 260, by using at least one detector 128 and, thereby, generating at least one detector signal when the
driving state of the light source 114 is changed, wherein the detector signal 114 is time-resolved; and (c) evaluating, by using at least one evaluation unit 136, the detector signal, in a step (c) 262, generated by the detector 128 for deriving the spectroscopic information on the object 112, and further considering a plurality of known time constants ^ of the light source 114 describing a property of the light source 114 when the driving state is changed for determining a contribution of signal intensities of a plurality of wave- length intervals 236 to the detector signal when the spectroscopic information on the object 112 is derived. A spectrometer device 110 as described may be used for performing the method 256. The method 256 may be performed on-line in the field. At least step (c) 262 of the method 256 may be computer-implemented.
List of reference numbers spectrometer device object light source illumination light light-emitting diode luminescent material semiconductor material phosphor light-emitting diode LED die housing detector detection light optical detector photosensitive element array of photosensitive elements evaluation unit driving unit measurement unit current source voltage measurement device data processing devices preprocessing devices data storage devices filter element optical component wavelength-selective element substrate ceramic substrate contact pad converter body side coat hardware components software components temperature of the LED temperature of the luminescent material
temperature of the detector target signal St electronic detector signal Spx,i readout electronics software 1 software 2 first processing step fast Fourier transformation pixel signal Spx second processing step signal Spx, corr spectrum peak power spectral density ^^^ in microwatt per nanometer y-axis wavelength in nm x-axis 1643nm 1750nm 1802nm 1950nm emission power change normalized to 25°C (given in percent) temperature in °C measuring points forward voltage in Volt signal in number of counts decay constant ^^ in ms growth constant ^^ in ms normalized light output forward current in Ampere wavelength interval heatmap indicating the performance of the present invention horizontal axis vertical axis graph illustrating three adjoining wavelength horizontal axis vertical axis
graph illustrating three adjoining wavelength horizontal axis vertical axis method of obtaining spectroscopic information step (a) step (b) step (c)
wavelength. Typically ^^^^^, ^^^^ is much smaller than ^^^^^, ^^^^ in a manner that ^^^^^, ^^^^ is dominated by ^^^^^, ^^^^ on minor time scales. The determination of the time scales in this regime is of particular interest. Therefore, the time constant of the light source ^^^^^, ^^^, ^^^^ may be derived from a convolu- tion of the time constants of the light-emitting diode ^^^^^, ^^^^ and the luminescent material ^^^^^, ^^^^, such as by determining * may be dominated by ^^^^^, ^^^^,
^^^^^, ^^^, ^^^^. Typical time constants ^^^^^, ^^^^ of phosphor converters are in the range of 0.1 ms to < 10 ms. The at least one detector may be configured for generating a time resolved detector signal for monitoring these time constants. Typically, a time resolution of the detector may be less than 1ms, more preferred, less than 0.1 ms.
The time constants typically differ between different phosphor LEDs and/or between different types of the luminescent material or phosphor. Typically, shorted wavelengths emitting phos- phor exhibit smaller time constants. Additionally, decay ^^ and growth constant ^^ may depend on the wavelength. The time constants typically are extracted from step response of the optical signal by applying / shutting off the forward current required for driving the light source in a man- ner that primary light is being generated by the light-emitting diode. After turning off the forward current, the signal or emission typically decays according to equa- tion (1): ^ /^^
After turning on the forward current, the signal or emission typically grows according to equation (2): ^ ^^
For both equations (1) and (2), ^^ is the optical signal level at ^^, when the forward current is ap- plied/shut off. ^^^^ is the reached optical signal level as ^ ≫ 5. As described above, time constants ^ of the light source that are known, such as being available and/or being provided to the spectrometer device, specifically the evaluation unit, are consid- ered for deriving the spectroscopic information on the object. As the time constants ^ are, typi- cally, wavelength dependent, the contribution of a plurality of specific signal intensities of a plu- rality of specific wavelength intervals to the detector signal is derived by evaluating a temporal change in the detector signal, particularly after turning of the forward current and/or after turning on the forward current. Thereby, the resolution of the spectrometer device may be increased. The resolution of a spectrum in terms of the wavelengths may, generally, be limited, particularly due the setup of the spectrometer device, particularly limited in a manner that a specific detec- tor signal is comprises information on range of different wavelengths. The resolution may be in- creased by evaluating the contribution of the plurality of specific signal intensities of the plurality of specific wavelength intervals, particularly comprised by the range of different wavelengths, to the detector signal. This may be performed by considering the difference in the temporal change of the signal intensities related to the specific wavelength intervals. In that manner the detector signal may be decomposed into a plurality of specific signal intensities of a plurality of specific wavelength intervals. Thereby, even a spectrometer device comprising only one or ex- actly one detector generating only one or exactly one detector signal may used for generating spectroscopic information, particularly even when no or a wavelength-selective element having a fixed transmission spectrum is used. The light-emitting diode may have a primary emission range at least partially located in the spectral range of 420 nm to 460 nm, more specifically in the range of 440 nm to 455 nm, more specifically at 440 nm. The luminescent material may be phosphor. The illumination light may
have a spectral range at least partially located in the near-infrared spectral range, specifically in the spectral range from 1 to 3 µm, preferably from 1.3 to 2.5 µm, more preferably from 1.5 to 2.2 µm. The driving state of the light source may be at least one of: a first driving state in which the light- emitting diode is generating the primary light; or a second driving state in which the light-emit- ting diode is not generating primary light. For switching between the first driving state and the second driving state, the driving unit may switch the electrical current and/or voltage, such as the forward voltage, provided to the LED. When it is switched into the first driving state the light-emitting diode may be illuminating the lu- minescent material. Thereby, excited states in the luminescent material may be populated, as described by the growth constant ^^ of excited states in the luminescent material. When it is switched into the second driving state from the first driving state the light-emitting diode may no longer be illuminating the luminescent material. Thereby, excited states in the luminescent ma- terial may be depopulated, as described by the decay constant ^^ of excited states in the lumi- nescent material. The at least one light source may be configured for operating in a pulsed mode in a manner that the driving state of the light source changes repeatedly, particularly changes repeatedly be- tween the first driving state and the second driving state. The term “pulsed mode”, as used herein, is a broad term and is to be given its ordinary and customary meaning to a person of or- dinary skill in the art and is not to be limited to a special or customized meaning. The term spe- cifically may refer, without limitation, to driving the light source in a manner that the illumination light is generated in a plurality of pulses having a predetermined duration at a predetermined repetition rate. The at least one spectrometer device may be configured for operating the light source in a, par- ticularly specific, driving state, particularly the first driving state and/or the second driving state, for a predetermined time span larger than the time constant ^, particularly at least 5 times or at least 10 times larger than the time constant ^. A pulse duration, particularly when the light source is operated in a pulsed mode, may be larger than the time constant ^, particularly at least 5 times; or at least 10 times larger than the time constant ^. Typically, a pulse duration may be between 0.5 ms and 100 ms, depending on time constant ^ associated with the lumi- nescent material. The detector signal may configured for comprising information on the plurality of wavelength in- tervals, particularly by covering a range of wavelengths. The detector signal may be configured for comprising the spectroscopic information from the detected detection light. The detector may comprise exactly one photosensitive element, which may be particularly pre- ferred, or at least one photosensitive element configured for generating the detector signal com- prising information on the plurality of wavelength intervals.
The spectrometer device may further comprise at least one wavelength-selective element, wherein the wavelength-selective element may be disposed in at least one of: - a beam path of the illumination light; or - a beam path of the detection light. The wavelength-selective element may be configured such that each of the photosensitive ele- ments may be exposed to an individual spectral range of the light from the object. The term “in- dividual”, as used herein, is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized mean- ing. The term specifically may refer, without limitation, to the photosensitive elements being ex- posed to differing spectral range of the light from the object. The wavelength-selective element may be configured such that the at least one of the photo- sensitive elements is exposed to a further individual spectral range of the light from the object, wherein the individual spectral range and the further individual range are distant from each other. As used herein, the term “distant” is a broad term and is to be given its ordinary and cus- tomary meaning to a person of ordinary skill in the art and are not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to the intervals are spaced from each other with respect to their wavelength. Accordingly, there may be an interme- diate interval between the spaced intervals. No information about the intermediate interval may be available. The photosensitive elements may be exposed to at least one additional individual spectral range. That additional individual spectral range may be distant from at least one of: the individual spectral range; or the further spectral range. The wavelength-selective element may be selected from the group of a tunable wavelength-se- lective element and a wavelength-selective element having a fixed transmission spectrum. The wavelength-selective element may be or may comprise at least one filter element, particularly wherein the filter element is an absorption filter element, specifically a bandpass filter element. As outlined above, the photosensitive elements may be sensitive to differing spectral ranges of the light from the object. The differing spectral sensitivity may be implemented by using photo- sensitive elements having inherently differing spectral sensitivities, such as by using differing integrated filters and/or differing sensitive materials, such as semiconductor materials. Addition- ally or alternatively, the differing spectral sensitivity may be achieved by using one or more wavelength-selective elements in one or more beam paths of the detection light, such as one or more of a filter, a grating, a prism or the like, configured to allow forward differing spectral por- tions of the detection light from the object to reach the individual photosensitive elements, se- quentially or simultaneously. Thus, generally, the spectrometer device may further comprise at least one wavelength-selec- tive element. As used herein, the term “wavelength-selective element” is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to
be limited to a special or customized meaning. The term specifically may refer, without limita- tion, to an arbitrary optical element which interacts with differing spectral portions of incident light in a different manner, e.g. by having at least one wavelength-dependent optical property, such as at least one wavelength-dependent optical property selected from the list consisting of a degree of reflection, a direction of reflection, a degree of refraction, a direction of refraction, an absorption, a transmission, an index of refraction. Therein, the wavelength selection by the at least one wavelength-selective element may take place in the at least one beam path of the illumination light, thereby selecting and/or modifying a wavelength of the illumination of the object, and/or in the detection beam path of the detection light, thereby selecting and/or modifying a wavelength of detection, e.g. for the detector in gen- eral and/or for each of the photosensitive elements. Thus, as an example, the at least one wavelength-selective element may comprise at least one of a wavelength-selective element dis- posed in a beam path of the illumination light and a wavelength-selective element disposed in a beam path of the detection light. The wavelength-selective element, specifically may be selected from the group of a tunable wavelength-selective element and a wavelength-selective element having a fixed transmission spectrum. By using a tunable wavelength selective element, as an example, differing wave- length ranges may be selected sequentially, whereas, by using a wavelength-selective element having a fixed transmission spectrum, the selection of the wavelength ranges may be fixed and may, however, be dependent e.g. on a detection position, thereby allowing, as an example, in the detection light beam path, for simultaneously exposing different detectors and/or different photosensitive elements of the detector to differing spectral ranges of light. Thus, as outlined above and as an example, the at least one wavelength-selective element may comprise at least one of a filter, a grating, a prism, a plasmonic filter, a diffractive optical ele- ment and a metamaterial. More specifically, the spectrometer device may comprise at least one filter element disposed in a beam path of the light from the object, i.e. in the beam path of the detection light, wherein the filter element, specifically may be configured such that each of the photosensitive elements is exposed to an individual spectral range of the light from the object. As an example, a variable filter element may be used, the transmission of which depends on a position on the filter element, such that, when the variable filter element is placed on top of the array of photosensitive elements, the individual photosensitive elements are exposed to differ- ing spectral ranges of the incident light, specifically the detection light from the object. Addition- ally or alternatively the at least one wavelength-selective element may comprise at least one of the following elements: an array of individual bandpass filters, an array of patterned filters, an MEMS-Interferometer, an MEMS-Fabry Perot interferometer. Further elements are feasible. The spectrometer device may comprise at least one filter element disposed in a beam path of the light from the object, wherein the filter element may be configured such that the photosensi- tive element may be exposed to the individual spectral range of the light from the object. The spectrometer device may comprise at least one further filter element disposed in a beam path of
the light from the object, wherein the further filter element may be configured such that the pho- tosensitive element may be exposed to the further individual spectral range of the light from the object. The detector may configured for generating a plurality of detector signals for at least two differ- ing spectral ranges of the light from the object, specifically at least one of sequentially and sim- ultaneously. The detector may comprise an array of photosensitive elements, wherein each of the photosensitive elements is configured for generating at least one detector signal. The spec- trometer device may be configured such that the photosensitive elements are sensitive to differ- ing spectral ranges of the light from the object. A plurality of the spectrometer device may be configured such that the photosensitive elements are sensitive to differing spectral ranges of the light from the object. A plurality of detector signals sensitive to differing spectral ranges may combined for generating the detector signal evaluated for deriving the spectroscopic information on the object. The time constants ^ may be at least one of: - a decay constant ^^ of excited states in the luminescent material; or - a growth constant ^^ of excited states in the luminescent material. The term “decay constant” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a constant describing a decay of the signal and/or emission, particularly of the luminescent material until no more sig- nal is generated. The term “growth constant” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be lim- ited to a special or customized meaning. The term specifically may refer, without limitation, to a constant describing a growth of the signal and/or emission until a saturation is reached, particu- larly of the luminescent material. The time constants ^ may depend on at least one of: the wavelength ^ of the illumination light; or the temperature ^ of the light source, specifically the luminescent material. The growth con- stant ^^ may depend on the intensity of pump light. The plurality of time constants ^ may consid- ered for determining the contribution of the signal intensities of the plurality of wavelength inter- vals to the detector signal by performing a regression algorithm, particularly a fit, on the detector signal configured for comprising information on the plurality of wavelength intervals. As gener- ally used, the term “regression” refers to a statistical analysis tool that aims to determine a rela- tionship between an input, such as the detector signal, and a statistical model to determine an output, such as the spectroscopic information. In this process, the statistical model may be fitted onto the input data. The statistical model may consider the contribution of the signal intensities of the plurality of wavelength intervals to the detector signal. The regression algorithm, particu- larly the fit, may consider a function describing the contribution of the signal intensities of the plurality of wavelength intervals to the detector signal. Therefore, a function ^^^^(^) may be assumed with
^^^^ ( ^ ) = ^^ ( ^ ) + ^^ ( ^ ) + ⋯ , wherein ^
with ^^ being the signal intensity of a wavelength intervals ^, and ^^ being the respective time constant ^ assigned to the wavelength intervals ^, ^ being the time and ^^ being the time when the driving state of the light source is changed. For performing the fit a least square |^^^^(^) − ^^^^(^)|^ may be minimized, particularly by opti- mizing the parameters ^^. The signal ^^ (^ = ^^ ) = ^^ may provide the spectroscopic information on the object. Alternatively, a function ^^^^ (^) may be assumed with ^^^^ (^) = ^^ (^) + ^^ (^) + ⋯ + ^^^^^^ (^, ^), wherein ^^^^^^ (^, ^) is the noise signal, particularly assuming a normally distributed noise with a center at 0. The fit may be performed by an algorithm of at least one of: Levenberg-Marquardt-; steepest decent; or orthogonal decent. There may be further options for performing the fit. A further plurality of known time constants ^ of wavelengths comprised by a specific wavelength interval may be combined, particularly by averaging, for determining an overall time constant ^ that is considered for determining the contribution of the signal intensity of the specific wave- length interval to the detector signal. In a further aspect, a method of obtaining spectroscopic information on at least one object is disclosed. The method comprises the following steps that may be performed in the given order. However, a different order may also be possible. In particular, one, more than one or even all of the method steps may be performed once or repeatedly. Further, the method steps may be per- formed successively or, alternatively, one or more of the method steps may be performed in a timely overlapping fashion or even in a parallel fashion and/or in a combined fashion. The method may further comprise additional method steps that are not listed. The method comprises the following steps: (a) illuminating the object with illumination light generated by at least one light source, the light source comprising at least one light-emitting diode and at least one lumi- nescent material for light-conversion of primary light generated by the light-emitting diode, and driving the light source in a manner that an driving state of the light source is changed at least one time at least one time;
(b) detecting detection light from the object by using at least one detector and, thereby, generating at least one detector signal when the driving state of the light source is changed, wherein the detector signal is time-resolved; and (c) evaluating, by using at least one evaluation unit, the detector signal generated by the detector for deriving the spectroscopic information on the object, and further considering a plurality of known time constants ^ of the light source describing a property of the light source when the driving state is changed for determining a con- tribution of signal intensities of a plurality of wavelength intervals to the detector sig- nal when the spectroscopic information on the object is derived. As further outlined above, the method described above and/or according to any one of the Em- bodiments described in further detail below, may fully or partially be at least one of computer- controlled, computer-implemented, and computer-assisted, e.g. by using one or more computer programs running on at least one processor, e.g., at least one processor of the spectrometer device, e.g. of at least one processor integrated within the detector and/or within the evaluation unit. Specifically, as outlined above, at least step (c) of the method may be at least one of com- puter-controlled, computer-implemented, and computer-assisted. It shall be noted, however, that other steps of the method may also fully or partially be at least one of computer-controlled, computer-implemented, and computer-assisted, such as one or more of steps (a), (b), and (c). The method may be performed on-line in the field. The spectrometer device, specifically, may be a portable spectrometer device which specifically may be used in the field. In particular, the spectrometer device may be part of a mobile device or may be attachable to a mobile device, such as a notebook computer, a tablet, a cell phone, such as a smart phone, a smartwatch and/or a wearable computer, also referred to as “wearable”, e.g. a body borne computer.The method according to the preceding claim, wherein a spectrometer device according to any one of the preceding claims referring to a spectrometer device is used. A computer program comprising instructions which, when the instructions are executed by the evaluation unit of the spectrometer device, cause the evaluation unit to perform the method. A computer-readable storage medium comprising instructions which, when the instructions are ex- ecuted by the evaluation unit of the spectrometer device, cause the evaluation unit to perform the method. A non-transient computer-readable medium including instructions that, when exe- cuted by the evaluation unit of the spectrometer device, cause the evaluation unit to perform the method. As used herein, the terms “computer-readable data carrier”, “computer-readable stor- age medium” and “non-transient computer-readable medium” are broad term and are to be given their ordinary and customary meaning to a person of ordinary skill in the art and are not to be limited to a special or customized meaning. The terms specifically may refer, without limita- tion, to data storage means, specifically non-transitory data storage means, such as a hardware storage medium having stored thereon computer-executable instructions. The computer-reada- ble data carrier or storage medium or computer-readable medium specifically may be or may comprise a storage medium such as a random-access memory (RAM) and/or a read-only memory (ROM).
As used herein, the terms “have”, “comprise” or “include” or any arbitrary grammatical variations thereof are used in a non-exclusive way. Thus, these terms may both refer to a situation in which, besides the feature introduced by these terms, no further features are present in the en- tity described in this context and to a situation in which one or more further features are present. As an example, the expressions “A has B”, “A comprises B” and “A includes B” may both refer to a situation in which, besides B, no other element is present in A (i.e. a situation in which A solely and exclusively consists of B) and to a situation in which, besides B, one or more further elements are present in entity A, such as element C, elements C and D or even further ele- ments. Further, it shall be noted that the terms “at least one”, “one or more” or similar expressions indi- cating that a feature or element may be present once or more than once typically are used only once when introducing the respective feature or element. In most cases, when referring to the respective feature or element, the expressions “at least one” or “one or more” are not repeated, notwithstanding the fact that the respective feature or element may be present once or more than once. Further, as used herein, the terms "preferably", "more preferably", "particularly", "more particu- larly", "specifically", "more specifically" or similar terms are used in conjunction with optional fea- tures, without restricting alternative possibilities. Thus, features introduced by these terms are optional features and are not intended to restrict the scope of the claims in any way. The inven- tion may, as the skilled person will recognize, be performed by using alternative features. Simi- larly, features introduced by "in an embodiment of the invention" or similar expressions are in- tended to be optional features, without any restriction regarding alternative embodiments of the invention, without any restrictions regarding the scope of the invention and without any re- striction regarding the possibility of combining the features introduced in such way with other optional or non-optional features of the invention. The spectrometer device and the method according to the present invention, in one or more of the above-mentioned embodiments and/or in one or more of the embodiments described in fur- ther detail below, provide a large number of advantages over known devices and methods of similar kind. Specifically, by using exactly one detector, a detector drift may be compensated more easily. Using a single detector setup may further enable a reduction of the technical com- plexity compared to the use of individual detectors for each different wavelength range. Besides practical advantages, the simultaneous detection of multiple wavelengths by a single detector may allow compensating for a drift of the detector signal, particularly the DC signal, as well as the detectors responsivity. In particular, a reference signal may be recoded on the de- tector simultaneously to the measurement of a sample signal. This may enables an on-line sys- tem calibration.
Further, the use of phosphor LEDs instead of or in addition to conventional thermal emitters such as incandescent lamps with a tungsten wire as a light source, may provide for several ad- vantages. Thus, in general, even though thermal emitters may provide for a flat spectrum, low temperature dependency and a high power spectral density ^^^ even at long wavelengths, such as in the NIR range, thermal emitters typically are not well-suited for large-volume spec- trometer production. Thus, typically, a high complexity of the manufacturing process, a low con- version efficiency from electrical to optical power and physical limitations in miniaturization are to be noted as disadvantages for thermal emitters. By using LEDs, specifically phosphor LEDs, these disadvantages may be overcome. LEDs have proven to be reliable light sources, such as standardized light sources in the visible light regime. In the context of the present invention, broadband light sources may be provided by using one or more phosphor LEDs in the spectrometer device, comprising the at least one light-emitting diode and the at least one luminescent material or phosphor. Thereby, as an example, a white light source may be created and/or a broadband light source in the infrared range, specifically in the NIR range. The phosphor may convert photons having a shorter wavelength, and, thus, a higher energy, into photons having a longer wavelength or lower energy, e.g. by transferring a portion of the primary photon energy to the phosphor material, such as to the phosphor lattice. The remaining lower energy may lead to an emission of a long-wavelength photon. Consequently, the luminescent material may be configured for absorbing one or more primary photons generated by the light-emitting diode and may, in reaction to this absorption, emit one or more secondary photons. The emission of the secondary photons may take place instantane- ously or after a delay or decay time. Thus, as outlined above, the luminescent material may be or may comprise at least one of a phosphorescent and a fluorescent material. The phosphores- cence may lead to the effect that after turning off the primary light, such as the short-wavelength or high energy pump light, the luminescent material may emit the secondary light, such as the long wavelength light, for a characteristic life time ^ (tau), e.g., due to a forbidden quantum-opti- cal transition or forbidden dipole transition. Thus, specifically, in the luminescent material, the emission of the secondary light may take place over a forbidden transition, such as a forbidden dipole transition, having a longer lifetime than e.g. spontaneous dipole allowed transition, as may be the case in many fluorescent materials. Specifically, as outlined above, a luminescent material may be used, specifically a phosphores- cent material, having an absorption in the blue spectral range and an emission in the infrared spectral range. As an example, luminescent materials may be used capable of converting blue primary light or pump light, having a wavelength of e.g.440 nm, into near-infrared secondary light, e.g. secondary light having a wavelength in the range of 1 to 3 µm, preferably from 1.3 to 2.5 µm, more preferably from 1.5 to 2.2 µm. Additionally or alternatively, the primary light or pump light may generated by an infrared LED with a wavelength in the range from 850 nm to 940 nm, which may then be converted by the luminescent material into near-infrared secondary light having a wavelength in the range of 1 to 3 µm, preferably from 1.3 to 2.5 µm, more prefera- bly from 1.5 to 2.2 µm.
The phosphor LED, comprising the at least one light-emitting diode and the at least one lumi- nescent material, may be embodied as a single element. Thus, on a technical level, the phos- phor LED may comprise multiple sub-components. First of all, the phosphor LED may comprise one or more functional components, such as the LED die comprising at least one junction between at least two semiconductor regions, such as at least one p-n-transition. In the LED die, the primary light may be generated, such as the short-wavelength pump light, e.g. in the blue spectral range. Further, the phosphor LED may comprise the at least one luminescent material, specifically the at least one phosphorescent material, which may, specifically, be placed directly on top of the LED die and which may convert the primary light, specifically the pump light, into the secondary light, specifically into the long-wavelength near-infrared light. Further, the phosphor LED may comprise one or more substrates, specifically one or more elec- trically insulating substrates. Thus, as an example, the phosphor LED may comprise one or more ceramic substrates. The at least one substrate may be configured for holding the at least one LED die and the at least one luminescent material. Further, the at least one substrate may hold or comprise one or more components of electrical connectivity, such as one or more con- tact pads and/or one or more electrical leads, such as one or more metallic contacts and/or one or more metallic leads. Furthermore, the substrate, such as the ceramic substrate, may be con- figured to serve as a heat sink. Heat may be generated both in the LED die and in the lumines- cent material, such as due to a limited conversion of electrical energy into photonic energy, as well as in the luminescent material, e.g. during the conversion process. Said heat may be dissi- pated in the substrate, such as in ceramic substrate. The spectrometer device using the at least one LED may be configured for applying a continu- ous wave (CW) mode and/or, preferably, at least one modulation driving scheme for improving precision and reliability of the measurement. Thus, for example, the at least one driving unit may be configured for applying a modulation driving scheme to the LED, and the evaluation de- vice may be configured for taking into account the modulation driving scheme for deriving the at least one spectroscopic information from the at least one detector signal. As an example, Lock- In-techniques, filter techniques, and the like may be applied, as known to the skilled person. Thus, the spectrometer device may be configured for applying a modulation driving scheme to the LED for compensating for DC background of the detector and/or in order to reduce the de- tector noise. Thus, as an example, a band pass filter may be applied to the detector signal, in order to eliminate DC components. The illumination light generated by the light source, specifically the phosphor LED, may be di- rected to illuminate the sample. For directing the illumination light, as an example, one or more mirrors, may optionally be used. The detection light from the object, e.g. reflected light, may be
directed to the detector, wherein, optionally, one or more optical components may be used. As an example, one or more wavelength-selective elements may be used, such as one or more dispersive elements, e.g. for splitting the detection light into its spectral components. By the detector, one or more detector signals may be recorded, e.g. by using a readout elec- tronics, comprised by the spectrometer device, specifically by one or both of the detector and the evaluation device. The readout electronics, as an example, may comprise one or more sig- nal processing devices. Thus, as outlined above, for evaluation by the evaluation device, the “raw” detector signal may be used, and/or one or more secondary detector signals derived thereof, such as one or more filtered detector signals. Further, the at least one detector signal, primary or secondary, may also be combined with further information, such as information on a wavelength, e.g. derived from a number of the photosensitive element of an array of photosen- sitive elements from which the detector signal is derived, which is known to be exposed to a specific wavelength of a wavelength range. In the context of the present invention, specifically in the context of the evaluation of the detector signal by the evaluation unit, the option of evaluat- ing the raw detector signal, and/or the option of evaluating a secondary detector signal, such as a preprocessed detector signal, a processed detector signal, or a combined detector signal, is feasible. Still, however, the invention specifically is interesting for determining the “raw” detector signal, specifically a detector signal, indicating a signal intensity as a function of the detection wavelength. Other options, however, are also feasible. As an example, the detector signal, e.g. by the detector itself and/or by the evaluation unit, may be processed or preprocessed into a secondary detector signal, by applying one or more Fou- rier transformations. As an example, a Fast Fourier Transformation may be applied. From the processed, secondary detector signal, the at least one spectroscopic information may be de- rived, such as by a software being executed by the evaluation unit. Thus, as an example, the Fourier transform of the detector signal may be read out by the software of the spectroscopic device, specifically of the evaluation device, and post-processed into the spectroscopic infor- mation on the object. LEDs and phosphor LEDs, as outlined above, may, thus, provide for an efficient light source, which may be modulated in order to perform specific evaluation schemes and in order to reduce noise and artifacts. By using considering the at least one time constant ^ of the light source de- scribing a property of the light source when the driving state is changed, temperature variations within the light source, specifically within the luminescent material, may fully or partially be com- pensated for. Thus, for typical LEDs, as used herein, when operating with the maximum voltage and current that the LED can withstand, the temperatures of the various components of the light source, specifically of the LED, may vary over a large temperature range. As an example, standard operation currents may range from 2 mA to 1000 mA, typically from 10 mA to 300 mA. As an example, forward voltages may be in the range from 1.5 V to 3.5 V, typically from 2.25 V to 3 V. Thus, as an example, under maximum operating conditions, the emitter junction temper- ature may be 135 °C. The operating case temperature may vary from -40 °C to 135 °C and the emitter storage temperature may vary from -40 °C to 125 °C. The ESD sensitivity of the LED
may be 250 V under the standard ANSI/ESDA/JEDEC JS-001-2012. These typical parameters show the large range of temperature variation, which may have an impact on spectroscopic in- formation on the object derived by the spectrometer device. It shall be noted that other parame- ters and other parameter ranges are feasible, too. It is generally known that, with different compositions of the luminescent material, such as differ- ent compositions of phosphors, the phosphor LEDs generate different spectra. Typically, each phosphor LED has multiple peaks in the spectrum, wherein the spectrum typically is spread over a wide wavelength range. However, even giving the same current to the phosphor LED, the spectral properties or the spectrum may change with temperature. These changes may in- clude shifts of the emission peaks, broadening or narrowing of the spectrum, increases or de- creases of the emission and the like. In many cases, however, the emission at some wave- lengths is affected to a larger extent than the emission at other wavelengths. Thus, typically, within the spectrum, there is a specific central wavelength, where the power, specifically the power spectral density ^^^, typically does not change with temperature. Each wavelength therefore typically has its own temperature coefficient, regarding to the increment/decrement of the power. Therefore, the shape of the spectrum changes with temperature. By using the at least one time constant ^, an individual temperature of the spectrum at the different wavelengths may be generated. Thus, as outlined above, the evaluation unit may be configured for individu- ally determining the detector signals in differing spectral ranges and for combining the individual detector signals for deriving the spectroscopic information. More specifically, as also outlined above, this may be performed by using an array of photosensitive elements, wherein each of the photosensitive elements may be configured for generating at least one detector signal. Fi- nally, the corrected detector signals may be combined for deriving the spectroscopic infor- mation. Temperature changes as well as individual properties of the phosphor LEDs may be deter- mined. Thus, as an example, when applying the same current to the LED, the forward voltage of the LED typically decreases while temperature increases. Each type of the LED has its own characteristic forward voltage to temperature curve. Typically, the forward voltage of the LED linearly decreases with rising temperature, such as with a slope in the range of 1 ∙ 10^^ to 1 ∙ 10^^ V/K. A further characteristic of the LED is the light output power as a function of the forward current. Thus, generally, by increasing the input current, the power admitted by the LED is increased. The shape, e.g. the slope, of the curve of the light output as a function of the forward current is characteristic to the individual LED. As outlined above, using the at least one time constant ^ as a control parameter for spectro- scopic purposes, an efficient and reliable on-line correction or on-line calibration is feasible. Thereby, various challenges of typical spectrometers and their respective calibration may be overcome. Specifically, in typical spectroscopic processes, reference measurements with the
spectrometer allow for calibrating instrument response, so the measurement provides infor- mation on the sample only. If, however, an optical component of the spectrometer device changes between the reference measurement and the sample measurement, the sample infor- mation is affected by the system change, so the information on the sample may be falsified. In particular, when the optical spectrum ^^^(^) of the light source changes between the reference measurement, during which the light source has an optical spectrum ^^^,^^^ (^), and the actual sample measurement, during which the light source has an optical spectrum ^^^,^^^^^^ (^), the spectroscopic information on the object or sample is falsified, since the spectrum typically devi- ates by the ratio of both spectra phosphor LEDs, the situation is typically even more complex, since the
LED is a combination of the spectrum of the LED and the luminescent material. Both components of the phosphor LED may be af- fected by temperature changes in a different way. Thus, for phosphor LEDs, the spectrum typi- cally may be described by equation (3):
Therein, ^^^^^, ^^^, ^^^ denotes the spectrum of the light source LS as a function of the wave- length ^, the p-n-junction temperature of the LED ^^^, and the temperature of the phosphor ^^. ^^^^^^^, ^^^^ denotes the spectrum of the LED, e.g. the blue LED, and ^^^^^^^^^^^, ^^^ denotes the spectrum of the luminescent material, e.g. the phosphor. Both sub-components, the LED and the luminescent material, show an individual temperature response. Thus, a system temperature change or shift or an ambient temperature change or shift, specifically between a reference measurement and a sample measurement, typically af- fects the spectrum by affecting both the LED junction and the luminescent material. Summarizing and without excluding further possible embodiments, the following embodiments may be envisaged: Embodiment 1: A spectrometer device for obtaining spectroscopic information on at least one object, the spectrometer device comprising: (i) at least one light source configured for generating illumination light for illuminating the object, the light source comprising at least one light-emitting diode and at least one luminescent material for light-conversion of primary light generated by the light- emitting diode, wherein the spectrometer device is configured for driving the light source in a manner that the driving state of the light source is changed at least one time; (ii) at least one detector configured for detecting detection light from the object and, thereby, generating at least one detector signal when the driving state of the light source is changed, wherein the detector signal is time-resolved; (iii) at least one evaluation unit configured for evaluating the detector signal generated by the detector for deriving the spectroscopic information on the object, and further configured for considering a plurality of known time constants ^ of the light source
describing a property of the light source when the driving state is changed for deter- mining a contribution of signal intensities of a plurality of wavelength intervals to the detector signal when the spectroscopic information on the object is derived. Embodiment 2: The spectrometer device according to any one of the preceding Embodiments, wherein the light-emitting diode has a primary emission range at least partially located in the spectral range of 420 nm to 460 nm, more specifically in the range of 440 nm to 455 nm, more specifically at 440 nm. Embodiment 3: The spectrometer device according to any one of the preceding Embodiments, wherein the luminescent material is phosphor. Embodiment 4: The spectrometer device according to any one of the preceding Embodiments, wherein the illumination light has a spectral range at least partially located in the near-infra- red spectral range, specifically in the spectral range from 1 to 3 µm, preferably from 1.3 to 2.5 µm, more preferably from 1.5 to 2.2 µm. Embodiment 5: The spectrometer device according to any one of the preceding Embodiments, wherein the driving state of the light source is at least one of: - a first driving state in which the light-emitting diode is generating the primary light; or - a second driving state in which the light-emitting diode is not generating primary light. Embodiment 6: The spectrometer device according to any one of the preceding Embodiments, wherein the at least one light source is configured for operating in a pulsed mode in a man- ner that the driving state of the light source changes repeatedly, particularly changes repeat- edly between the first driving state and the second driving state. Embodiment 7: The spectrometer device according to any one of the preceding Embodiments, wherein the at least one spectrometer device is configured for operating the light source in a specific driving state, particularly the first driving state and/or the second driving state, for a predetermined time span larger than the time constant ^, particularly at least 5 times; or at least 10 times larger than the time constant ^. Embodiment 8: The spectrometer device according to any one of the preceding Embodiments, wherein the detector signal is configured for comprising information on the plurality of wave- length intervals. Embodiment 9: The spectrometer device according to any one of the preceding Embodiments, wherein the detector signal is configured for comprising the spectroscopic information from the detected detection light.
Embodiment 10: The spectrometer device according to any one of the preceding Embodiments, wherein the detector comprises exactly one photosensitive element or at least one photo- sensitive element configured for generating the detector signal comprising information on the plurality of wavelength intervals. Embodiment 11: The spectrometer device according to any one of the preceding Embodiments, the spectrometer device further comprising at least one wavelength-selective element, wherein the wavelength-selective element is disposed in at least one of: - a beam path of the illumination light; or - a beam path of the detection light. Embodiment 12: The spectrometer device according to any one of the preceding Embodiments, wherein the wavelength-selective element is configured such that each of the photosensitive elements is exposed to an individual spectral range of the light from the object. Embodiment 13: The spectrometer device according to any one of the preceding Embodiments, wherein the wavelength-selective element is configured such that the at least one of the photosensitive elements is exposed to a further individual spectral range of the light from the object, wherein the individual spectral range and the further individual range are distant from each other. Embodiment 14: The spectrometer device according to any one of the preceding Embodiments, wherein the wavelength-selective element is selected from the group of a tunable wave- length-selective element and a wavelength-selective element having a fixed transmission spectrum. Embodiment 15: The spectrometer device according to any one of the preceding Embodiments, wherein the wavelength-selective element is or comprises at least one filter element, partic- ularly wherein the filter element is an absorption filter element, specifically a bandpass filter element. Embodiment 16: The spectrometer device according to any one of the preceding Embodiments, wherein the detector is configured for generating a plurality of detector signals for at least two differing spectral ranges of the light from the object, specifically at least one of sequen- tially and simultaneously. Embodiment 17: The spectrometer device according to any one of the preceding Embodiments, wherein the detector comprises an array of photosensitive elements, wherein each of the photosensitive elements is configured for generating at least one detector signal. Embodiment 18: The spectrometer device according to any one of the preceding Embodiments, wherein the spectrometer device is configured such that the photosensitive elements are sensitive to differing spectral ranges of the light from the object.
Embodiment 19: The spectrometer device according to any one of the preceding Embodiments, wherein a plurality of detector signals sensitive to differing spectral ranges is combined for generating the detector signal evaluated for deriving the spectroscopic information on the object. Embodiment 20: The spectrometer device according to any one of the preceding Embodiments, wherein the time constants ^ are at least one of: - a decay constant ^^ of excited states in the luminescent material; or - a growth constant ^^ of excited states in the luminescent material. Embodiment 21: The spectrometer device according to any one of the preceding Embodiments, wherein the time constant ^ depends on at least one of: the wavelength ^ of the illumination light; or the temperature ^ of the light source, specifically the luminescent material. Embodiment 22: The spectrometer device according to any one of the preceding Embodiments, wherein the plurality of time constants ^ is considered for determining the contribution of the signal intensities of the plurality of wavelength intervals to the detector signal by performing a regression algorithm, particularly a fit, on the detector signal configured for comprising in- formation on the plurality of wavelength intervals. Embodiment 23: The spectrometer device according to any one of the preceding Embodiments, wherein the regression algorithm, particularly the fit, considers a function describing the con- tribution of the signal intensities of the plurality of wavelength intervals to the detector signal. Embodiment 24: The spectrometer device according to any one of the preceding Embodiments, wherein a further plurality of known time constants ^ of wavelengths comprised by a specific wavelength interval is combined for determining an overall time constant ^ that is considered for determining the contribution of the signal intensity of the specific wavelength interval to the detector signal. Embodiment 25: A method of obtaining spectroscopic information on at least one object, the method comprising: (a) illuminating the object with illumination light generated by at least one light source, the light source comprising at least one light-emitting diode and at least one lumi- nescent material for light-conversion of primary light generated by the light-emitting diode, and driving the light source in a manner that an driving state of the light source is changed at least one time at least one time; (b) detecting detection light from the object by using at least one detector and, thereby, generating at least one detector signal when the driving state of the light source is changed, wherein the detector signal is time-resolved; and (c) evaluating, by using at least one evaluation unit, the detector signal generated by the detector for deriving the spectroscopic information on the object, and further
considering a plurality of known time constants ^ of the light source describing a property of the light source when the driving state is changed for determining a con- tribution of signal intensities of a plurality of wavelength intervals to the detector sig- nal when the spectroscopic information on the object is derived. Embodiment 26: The method according to the preceding Embodiment, wherein a spectrometer device according to any one of the preceding Embodiments referring to a spectrometer de- vice is used. Embodiment 27: The method according to any one of the preceding method Embodiments, wherein the method is performed on-line in the field. Embodiment 28: The method according to any one of the preceding method Embodiments, wherein at least step c. of the method is computer-implemented. Embodiment 29: A computer program comprising instructions which, when the instructions are executed by the evaluation unit of the spectrometer device according to any one of the pre- ceding Embodiments referring to a spectrometer device, cause the evaluation unit to per- form the method according to any one of the preceding Embodiments referring to a method, particularly at least step (c) of the method. Embodiment 30: A computer-readable storage medium comprising instructions which, when the instructions are executed by the evaluation unit of the spectrometer device according to any one of the preceding Embodiments referring to a spectrometer device, cause the evaluation unit to perform the method according to any one of the preceding Embodiments referring to a method, particularly at least step (c) of the method. Embodiment 31: A non-transient computer-readable medium including instructions that, when executed by the evaluation unit of the spectrometer device according to any one of the pre- ceding Embodiments referring to a spectrometer device, cause the evaluation unit to per- form the method according to any one of the preceding Embodiments referring to a method, particularly at least step (c) of the method. Short description of the Figures Further optional features and embodiments will be disclosed in more detail in the subsequent description of embodiments, preferably in conjunction with the dependent claims. Therein, the respective optional features may be realized in an isolated fashion as well as in any arbitrary feasible combination, as the skilled person will realize. The scope of the invention is not re- stricted by the preferred embodiments. The embodiments are schematically depicted in the Fig- ures. Therein, identical reference numbers in these Figures refer to identical or functionally comparable elements.
In the Figures: Figure 1 shows a schematic overview of a spectrometer device; Figure 2 shows schematic cross-sectional view of a light source; Figure 3 shows a schematic flowchart illustrating generating and processing a de- tector signal; Figure 4 shows a diagram representing a superposition of spectra of infrared radia- tion of a phosphor LED at various temperatures; Figure 5 shows a diagram representing a change in emission power change as a function of temperature for a selected number of wavelengths; Figure 6 shows a diagram of a forward voltage as a function of temperature for a selected current; Figures 7A and 7B show spectra of two different types of phosphor LEDs; Figures 8A and 8B show diagrams representing decay constants (Figure 8A) and growth con- stants (Figure 8B) as a function of wavelength for a phosphor LED emit- ting between 1.3 µm and 2 µm; Figure 9A and 9B show diagrams representing decay constants (Figure 9A) and growth con- stants (Figure 9B) as a function of wavelength for a phosphor LED emit- ting between 1.6 µm and 2.1 µm; Figure 10 shows a diagram representing normalized light output as a function of a forward current; Figure 11 shows a heatmap indicating the performance of the present invention; Figure 12 shows three adjoining wavelength intervals; Figure 13 shows three distant wavelength intervals; and Figure 14 shows a method of obtaining spectroscopic information on at least one object. Detailed description of the embodiments
In Figure 1, a schematic overview of a spectrometer device 110 for obtaining spectroscopic in- formation on at least one object 112 is shown. The spectrometer device 110 may comprise a plurality of components as illustrated in Figure 1. Possible components of the spectrometer de- vice 110 and their interplay will be described in the following, specifically with reference to Fig- ure 1. The spectrometer device 110 comprises at least one light source 114 for generating illu- mination light 116 for illuminating the object 112. The light source 114 may be at least one of a tunable light source, a light source having at least one fixed emission wavelength and a broad- band light source. The light source 114 specifically may be or may comprise at least one electri- cal light source. The light source 114 comprises at least one light-emitting diode 118 and at least one luminescent material 120 for light-conversion of primary light generated by the light- emitting diode 118. As an example, the light-emitting diode 118, may comprise one or more of: a light-emitting diode (LED) based on spontaneous emission of light, a light-emitting diode based on superluminescence (sLED), a laser diode (LLED). The LED 118 may specifically comprise at least two layers of semiconductor material 121, wherein light may be generated at at least one interface between the at least two layers of semi- conductor material 121, specifically due to a recombination of positive and negative electrical charges. The at least two layers of semiconductor material 121 may have differing electrical properties, such as at least one of the layers being an n-doped semiconductor material 121 and at least one of the layers being a p-doped semiconductor material 121. Thus, as an example, the LED 118 may comprise at least one pn-junction and/or at least one pin-set up. It shall be noted, however, that other device structures are feasible, too. The light-emitting diode 118 may generate primary light, which may also be referred to as “pump light”. The primary light may subsequently be transformed into “secondary light”, such as by using light conversion, e.g. through one or more luminescent materials 120, such as phos- phor materials. The at least one luminescent material 120, thus, may form at least one con- verter, also referred to as a light converter, transforming primary light into secondary light hav- ing different spectral properties as compared to the primary light. Specifically, a spectral width of the secondary light may be larger than a spectral width of the primary light, and/or a center of emission of the secondary light may be shifted, specifically red-shifted, compared to the primary light. Specifically, the at least one luminescent material 120 may have an absorption in the ultra- violet and/or blue spectral range and an emission in the near-infrared and/or infrared spectral range. The illumination light 116 may be or may comprise at least one of the primary light or a part thereof, the secondary light or a part thereof, or a mixture of both. As indicated in Figure 1, the light source 114 may specifically comprise a phosphor light-emit- ting diode 122, also referred to as phosphor LED 122. The phosphor LED 122 may be a combi- nation of at least one light-emitting diode 118 configured for generating primary light or pump light, and at least one luminescent material 120, also referred to as a “phosphor”, configured for light-conversion of the primary light generated by the light-emitting diode 118. The phosphor LED 122 may form a packaged LED light source, including an LED die 124, e.g. a blue LED emitting blue pump light, as well as the phosphor, which, as an example, fully or partially coats
the LED 118, which is, as an example, configured for converting the primary light or blue light into light having differing spectral properties, specifically into near-infrared light. Figure 2 shows a more detailed view of the light source 114 embodied as a phosphor LED 122. Generally, the light source 114 can be embodied in various ways. Thus, the light source 114 can, for example, be part of the spectrometer device 110 in a housing 126 of the spectrometer device 110, as illustrated in Figure 1. Alternatively or additionally, however, the at least one light source 114 can also be arranged outside the housing 126, for example as a separate light source 114 (not shown). The light source 114 can be arranged separately from the object 110 and illuminate the object 110 from a distance, as indicated in Figure 1. Illumination light 116 as generated by the light source 114 may propagate from the light source 114 to the object 112. In Figure 1, the illumination light 116 generated by the light source 114 and propagating to the object 112 is illustrated by an arrow. The object 112 specifically may comprise at least one sample, which may fully or partially be analyzed by spectroscopic meth- ods. As apparent from Figure 1, the spectrometer device 110 further comprises at least one detector 128 configured for detecting detection light 130 from the object 112. While light propagating from the light source 114 to the object 112 may be referred to as illumination light 116, light propagating from the object 112 to the detector 128 may be denoted as “detection light” 130. In Figure 1, the detection light 130 is illustrated by an arrow. The detection light 130 may comprise at least one of illumination light 116 reflected by the object 112, illumination light 116 scattered by the object 112, illumination light 116 transmitted by the object 112, luminescence light gener- ated by the object 112, e.g. phosphorescence or fluorescence light generated by the object 112 after optical, electrical or acoustic excitation of the object 112 by the illumination light 116 or the like. Thus, the detection light 130 may directly or indirectly be generated through the illumination of the object 112 by the illumination light 116. The detector 128 may be further configured for detecting detection light 130 and, thereby, gen- erating at least one detector signal. This detector signal may be time-resolved may be gener- ated when the driving state of the light source 114 may be changed. The detector signal may be configured for comprising the spectroscopic information from the detected detection light 130. The detector signal may be configured for comprising information exactly one wavelength inter- val 236. For such a purpose, the detector 128 may comprise exactly one photosensitive ele- ment 133 or at least one photosensitive element 133 configured for generating the detector sig- nal comprising information on the plurality of wavelength intervals. In addition, the spectrometer device 110 may comprise at least one wavelength-selective element 152. The spectrometer device 110 may comprise at least one wavelength-selective element 152, wherein the wavelength-selective element 152 may be disposed in at least one of: - a beam path of the illumination light 116; or
- a beam path of the detection light 130. The detector signal may be configured for comprising information a plurality of wavelength inter- vals 236. For such a purpose, the detector 128 may comprise exactly one photosensitive ele- ment 133 or at least one photosensitive element 133 configured for generating the detector sig- nal comprising information on the plurality of wavelength intervals 236. Alternatively or in addi- tion, the spectrometer device 110 may comprise a plurality of wavelength-selective elements 152. The wavelength-selective element 152 may be configured such that each of the photosen- sitive elements 133 may be exposed to an individual spectral range of the light from the object 112. The wavelength-selective element 152 may be configured such that the at least one of the pho- tosensitive elements 133 may be exposed to a further individual spectral range of the light from the object, wherein the individual spectral range and the further individual range are distant from each other. For this purpose, a plurality of filter elements 150, particularly absorption and/or bandpass filter elements 150, may be configured such that the photosensitive element 133 is exposed to the individual spectral range and the further individual spectral range of the light from the object. In general, the wavelength-selective element 152 may be selected from the group of a tunable wavelength-selective element 152 and a wavelength-selective element 152 having a fixed trans- mission spectrum. The wavelength-selective element 152 may be or may comprise at least one filter element 150, particularly wherein the filter element 150 may be an absorption filter ele- ment, specifically a bandpass filter element 150. The detector 128 may be configured for generating a plurality of detector signals for at least two differing spectral ranges of the light from the object 112, specifically at least one of sequentially and simultaneously. The detector 128 may comprise an array of photosensitive elements 134, wherein each of the photosensitive elements 133 is configured for generating at least one de- tector signal. The spectrometer device 110 may be configured such that the photosensitive ele- ments 133 are sensitive to differing spectral ranges of the light from the object 112. A plurality of different detector signals, particularly generated by the photosensitive elements 133 that are sensitive to differing spectral ranges of the light from the object 112, may be combined for gen- erating the detector signal evaluated for deriving the spectroscopic information on the object 112. The detector 128 may be or may comprise at least one optical detector 132. The optical detec- tor 132 may be configured for determining at least one optical parameter, such as an intensity and/or a power of light by which at least one sensitive area of the detector 132 is irradiated. More specifically, the optical detector 132 may comprise exactly one, which may be preferred, or at least one photosensitive element 133 and/or at least one optical sensor, such as at least one of a photodiode, a photocell, a photosensitive resistor, a phototransistor, a thermophile sen-
sor, a photoacoustic sensor, a pyroelectric sensor, a photomultiplier and a bolometer. The de- tector 128, thus, may be configured for generating at least one detector signal, more specifically at least one electrical detector signal, in the above-mentioned sense, providing information on at least one optical parameter, such as the power and/or intensity of light by which the detector 128 or a sensitive area of the detector 128 is illuminated. The detector 128 may comprise one single optically sensitive element or area, which may be preferred, or a plurality of optically sensitive elements or areas. As indicated in Figure 1, the de- tector 130 may comprise at least one detector array, more specifically an array of photosensi- tive elements 134. Each of the photosensitive elements 133 may be configured for generating at least one detector signal. In particular, each of the photosensitive elements 133134 may com- prise at least a photosensitive area, which may be adapted for generating an electrical signal depending on the intensity of the incident light, wherein the electrical signal may, in particular, be provided to an evaluation unit 136 of the spectrometer device, as will be outlined in further detail below. In case the detector 128 comprises the array of optically sensitive elements 134, the detector 128, may e.g. be selected from any known pixel sensor, specifically from a CCD chip or a CMOS chip. As an alternative, the detector 128 generally may be or comprise a photoconduc- tor, in particular an inorganic photoconductor, especially PbS, PbSe, Ge, InGaAs, ext. InGaAs, InSb, or HgCdTe. As a further alternative, it may comprise at least one of pyroelectric, bolome- ter or thermopile detector elements. The spectrometer device 110 comprises at least one evaluation unit 136 for evaluating at least one detector signal generated by the detector 128, such as the time-resolved detector signal, and for deriving the spectroscopic information on the object 112 from the detector signal. The detector 128 may directly or indirectly provide the detector signals to the evaluation unit 136. Thus, the detector 128 and the evaluation unit 136 may be directly or indirectly connected, as indicated by arrows in Figure 1. The detector signal may be used as a “raw” detector signal and/or may be processed or preprocessed before further use, e.g. by filtering and the like. Thus, the detector 128 may comprise at least one processing device and/or at least one prepro- cessing device, such as at least one of an amplifier, an analogue/digital converter, an electrical filter and a Fourier transformation. As shown in Figure 1, the spectrometer device 110 further comprises at least one driving unit 138 for electrically driving the light source 114. The spectrometer device 110 comprises at least one measurement unit 139 for generating at least one item of information on an electronic value, specifically on the light source 114, particularly for determining a temperature of the light source. The item of information on the electronic characteristic may be considered for determin- ing a power spectral density ^^^ of the light source, specifically the light-emitting diode. The measurement unit 139 may be an element of the driving unit 138, as indicated in Figure 1. Par- ticularly, the driving unit 138 may be configured for providing an electrical current to the LED
118, specifically for controlling an electrical current through the LED 118. Therein, as an exam- ple, the driving unit 138 may be configured for adapting and measuring a voltage provided to the LED 118, the voltage being required for achieving a specific electrical current through the LED 118. The driving unit 138, specifically, may comprise one or more of: a current source 140, a voltage source, a current measurement device, such as an Ampère-meter, a voltage meas- urement device 142, such as a Volt-meter, a power measurement device. Specifically, the driv- ing unit 138 may comprise at least one current source 140 for providing at least one predeter- mined current to the LED 118, wherein the current source 140 specifically may be configured for adjusting or controlling a voltage applied to the LED 118 in order to generate the predetermined current. The driving unit 138, as an example, may comprise one or more electrical components, such as integrated circuits, for driving the light source 114. The driving unit 138 may be fully or partially integrated into the light source 114 or may be separated from the light source 114, the latter configuration being illustrated in Figure 1. A forward voltage may be applied to the LED in the forward direction, i.e. as with a positive con- tact of a voltage or current source 140 applied to a p-layer of the LED 118 and a negative con- tact applied to the n-layer of the LED 118, in order to generate a predetermined electrical cur- rent through the LED 118. Thereby, the LED may generate the primary light. As an example, the predetermined current defining the forward voltage may be a current, which is known to generate a predetermined light output of the light source 114 and/or of the light-emitting diode 118. The spectrometer device 110 may configured for driving the light source 114 in a manner that the driving state of the light source 114 is changed at least one time. The driving state of the light source 114 may be at least one of: - a first driving state in which the light-emitting diode 118 is generating the primary light; or - a second driving state in which the light-emitting diode 118 is not generating primary light. The at least one light source 114 may be configured for operating in a pulsed mode in a manner that the driving state of the light source 114 changes repeatedly, particularly changes repeat- edly between the first driving state and the second driving state. The at least one spectrometer device 110 may be configured for operating the light source 114 in a specific driving state, par- ticularly the first driving state and/or the second driving state, for a predetermined time span larger than the time constant ^, particularly at least 5 times; or at least 10 times larger than the time constant ^. As outlined above, and as shown in Figure 1, the spectrometer device 110 may comprise the at least one evaluation unit 136 for evaluating the at least one detector signal, such as the time re- solved detector signal, generated by the detector 128 for deriving the spectroscopic information on the object 112 from the detector signal. The evaluation unit 136 may be configured for con- sidering a plurality of known time constants ^ of the light source 114 describing a property of the
light source 114 when the driving state is changed for determining a contribution of signal inten- sities of a plurality of wavelength intervals 236 to the detector signal when the spectroscopic in- formation on the object 112 is derived. The time constants ^ may at least one of: - a decay constant ^^ of excited states in the luminescent material 120; or - a growth constant ^^ of excited states in the luminescent material 120. The time constants ^ may depend on at least one of: the wavelength ^ of the illumination light; or the temperature ^ of the light source 114, specifically the luminescent material 120. The plu- rality of time constants ^ may be considered for determining the contribution of the signal inten- sities of the plurality of wavelength intervals to the detector signal by performing a regression algorithm, particularly a fit, on the detector signal configured for comprising information on the plurality of wavelength intervals 236. The regression algorithm, particularly the fit, may consider a function describing the contribution of the signal intensities of the plurality of wavelength inter- vals to the detector signal. Specifically, the evaluation unit 136 may be configured for processing at least one input signal and to generate at least one output signal thereof. The at least one input signal, as an example, may comprise at least one detector signal provided directly or indirectly by the at least one de- tector 128. The arrows between the driving unit 138, which comprises the measurement unit 139 in the embodiment illustrated in Figure 1, and the evaluation unit 136 in Figure 1 illustrate the process of providing to the evaluation unit 136 and/or retrieving by the evaluation unit 136 the signal comprising the at least one item of information on the electronic characteristic. The evaluation unit 136 may be or may comprise one or more integrated circuits, such as one or more application-specific integrated circuits (ASICs), and/or one or more data processing de- vices 144, such as one or more of computers, digital signal processors (DSP), field programma- ble gate arrays (FPGA), preferably one or more microcomputers and/or microcontrollers. Addi- tional components may be comprised, such as one or more preprocessing devices 146 and/or data acquisition devices, such as one or more devices for receiving and/or preprocessing of the detector signals, such as one or more AD-converters and/or one or more filters. Further, the evaluation unit may comprise one or more data storage devices 148, as shown in Figure 1. Fur- ther, the evaluation unit 136 may comprise one or more interfaces, such as one or more wire- less interfaces and/or one or more wire-bound interfaces. As described above in more detail, the detector 128 may specifically comprise an array of pho- tosensitive elements 134. Each of the photosensitive elements 133 may be configured for gen- erating at least one detector signal. The evaluation unit 136 may be configured for considering each of the detector signals for deriving the spectroscopic information. The spectrometer device 110 may be configured such that the photosensitive elements 133 of the detector 128 are sensi- tive to differing spectral ranges of the light from the object 112. In particular, the detector 128 may be configured for generating detector signals for at least two differing spectral ranges of the
light from the object, specifically at least one of sequentially and simultaneously. The spectrom- eter 110 specifically may comprise at least one filter element 150 disposed in a beam path of the light from the object. The filter element 150 specifically may be configured such that each of the photosensitive elements 133 is exposed to an individual spectral range of the light from the object 112. As already discussed, the spectrometer device 110 further may comprise one or more optical components 151, e.g. such as one or more of at least one mirror, at least one lens, at least one aperture and at least one wavelength-selective element 152. Specifically, the one or more opti- cal components 151 may be arranged in at least one of the beam path of the illumination light 116 and the beam path of the detection light 130. The spectrometer device 110 may in particu- lar comprise the at least one wavelength-selective element 152. The wavelength-selective ele- ment 152 specifically may be selected from the group of a tunable wavelength-selective ele- ment 152 and a wavelength-selective element 152 having a fixed transmission spectrum. By us- ing a tunable wavelength-selective element 152, as an example, differing wavelength ranges may be selected sequentially, whereas, by using a wavelength-selective element 152 having a fixed transmission spectrum, the selection of the wavelength ranges may be fixed and may, however, be dependent e.g. on a detector position. The wavelength-selective element 152 may be used for separating incident light into a spectrum of constituent wavelength signals whose respective intensities are determined by employing a detector, e.g. the detector 128 of the spec- trometer device 110, which may comprise the array of photosensitive elements 134. The at least one wavelength-selective element 152 may e.g. comprise at least one of a filter, a grating and a prism. The wavelength-selective element 152 may specifically comprise at least one of a wavelength-selective element 152 disposed in the beam path of the illumination light 116 and a wavelength-selective element 152 disposed in the beam path of the detection light 130. Figure 1 illustrates an embodiment of the spectrometer device 110 with one wavelength-selective ele- ment 152 arranged in the beam path of the illumination light 116, and one wavelength-selective element 152 arranged in the beam path of the detection light 130. The spectrometer device 110 as represented in a schematic fashion in Figure 1 is configured for obtaining spectroscopic information on the at least one object 112. In particular, the spectrome- ter device may be configured for obtaining an item of information, e.g. on at least one object and/or radiation emitted by at least one object, characterizing at least one optical property of the object, more specifically at least one item of information characterizing, e.g. qualifying and/or quantifying, at least one of a transmission, an absorption, a reflection and an emission of the at least one object. As an example, the at least one item of spectral information may comprise at least one intensity information, e.g. information on an intensity of light being at least one of transmitted, absorbed, reflected or emitted by the object, e.g. as a function of a wavelength or wavelength sub-range over one or more wave-lengths, e.g. over a range of wavelengths. Thus, the spectrometer device 110 may be configured for acquiring at least one spectrum or at least a part of a spectrum of detection light 130 propagating from the object 112 to the detector 128. The spectrum may describe the radiometric unit of spectral flux, e.g. given in units of watt per nanometer (W / nm), or other units, e.g. as a function of the wavelength of the detection light.
Thus, the spectrum may describe the optical power of light, e.g. in the NIR spectral range, in a specific wavelength band. The spectrum may contain one or more optical variables as a func- tion of the wavelength, e.g. the power spectral density ^^^, electric signals derived by optical measurements and the like. Examples of spectra are shown e.g. in Figures 4, 7A and 7B. The spectrometer device 110 may specifically be a portable spectrometer device 110, which may in particular be used in the field. In Figure 2, a schematic cross-sectional view of a light source 114 is shown. The at least one light source 114 of the spectrometer device 110 may be configured for generating or providing to electromagnetic radiation in one or more of the infrared, the visible and the ultraviolet spectral range. Due to the fact that many material properties or properties on the chemical constitution of many objects 112 may be derived from the near infrared spectral range, light used for the typi- cal purposes of the present invention is light in the infrared (IR) spectral range, more preferred, in the near infrared (NIR) and/or the mid infrared spectral range (MidIR), especially the light having a wavelength of 1 µm to 5 µm, preferably of 1 µm to 3 µm. The light source 114 com- prises the at least one light-emitting diode 118 and the at least one luminescent material 120 for light-conversion of primary light generated by the light-emitting diode 118. The LED 118 and the luminescent material 120, together, may form the phosphor LED 122, as described above. The phosphor LED 122 as illustrated in Figure 2 may comprise one or more functional compo- nents. Specifically, the phosphor LED 122 may comprise one or more substrates 154, specifi- cally one or more electrically insulating substrates 154. In particular, the phosphor LED 122 may comprise one or more ceramic substrates 156, as shown in Figure 2. The substrate 154 may be configured for holding the at least one LED die 124 and the at least one luminescent material 120. Further, the at least one substrate 154 may hold or comprise one or more components of electrical connectivity, such as one or more contact pads 158 as shown in Figure 2 and/or one or more electrical leads, such as one or more metallic contacts and/or one or more metallic leads. The substrate 154 may be configured to serve as a heat sink. Heat may be generated in the LED die 124, such as due to a limited conversion of electrical energy into photonic energy, as well as in the luminescent material 120, e.g. during the conversion process. Said heat may be dissipated in the substrate 154, such as in ceramic substrate. As shown in Figure 2, the phosphor LED 122 may comprise the light-emitting diode 118. The light-emitting diode 118 may be configured for converting electrical current into primary light, such as blue primary light, using at least one LED chip and/or the at least one LED die 124 as illustrated in Figure 2. Specifically, p-n-diodes may be used. As an example, one or more LEDs 118 selected from the group of an LED 118 on the basis of indium gallium nitride (InGaN), an LED 118 on the basis of GaN, an LED 118 on the basis of InGaN/GaN alloys or combinations thereof and/or other LEDs 118 may be used. Additionally or alternatively, quantum well LEDs 118 may also be used, such as one or more quantum well LEDs 118 on the basis of InGaN. Ad- ditionally or alternatively, Superluminescence LEDs (sLED) and/or Quantum cascade lasers may be used. As further apparent from Figure 2, the phosphor LED may comprise the at least one luminescent material 120 configured for light-conversion of the primary light generated by
the light-emitting diode 118. Various types of conversion and/or luminescence are known and may be used in the context of the present invention. Specifically, the luminescent material 120 may comprise at least one of: Cerium-doped YAG (YAG:Ce3+, or Y3Al5O12:Ce3+); rare-earth- doped Sialons; copper- and alu-minium-doped zinc sulfide (ZnS:Cu,Al). The luminescent material 120 specifically may form at least one layer. Generally, various alter- natives of positioning the luminescent material 120 with respect to the light-emitting diode118 are feasible, alone or in combination. Firstly, the luminescent material 120, e.g., at least one layer of the luminescent material 120, such as the phosphor, may be positioned directly on the light-emitting diode 118, e.g. with no material in between the LED 118 and the luminescent ma- terial 120 or with one or more transparent materials in between, such as with one or more trans- parent materials, specifically transparent for the primary light, in between the LED and the lumi- nescent material 120. Thus, as an example, a coating of the luminescent material 120 may be placed directly or indirectly on the LED 118 (not shown). Additionally or alternatively, the lumi- nescent material 120, as an example, may form at least one converter body 160, such as at least one converter disk, which may also be referred to as converter platelet. The converter body 160 may be placed on top of the LED 118, e.g. by adhesive attachment of the converter body 160 to the LED 118, as illustrated in Figure 2. Additionally or alternatively, the luminescent material 120 may also be placed in a remote fashion, such that the primary light from the LED 118 has to pass an intermediate optical path before reaching the luminescent material 120 (not shown). Again, as an example, the luminescent material in the remote placement may form a solid body or converter body 160, such as a disk or converter disk. In the intermediate optical path, one or more optical elements may be placed, such as one or more of a lens, a prism, a grating, a mirror, an aperture or a combination thereof. Thus, specifically, an optical system hav- ing imaging properties may be placed in between the LED 118 and the luminescent material 120, in the intermediate optical path. Thereby, as an example, the primary light may be focused, or bundled onto the converter body 160. In the light source 114, specifically the phosphor LED 122, the at least one luminescent material 120 may be located with respect to the light-emitting diode 118 such that a heat transfer from the light-emitting diode 118 to the luminescent material 120 is possible. More specifically, the luminescent material 120 may be located such that a heat transfer by one or both of thermal ra- diation and heat conduction is possible, more preferably by heat conduction. Thus, as an exam- ple, the luminescent material 120 may be in thermal contact and/or in physical contact with the light-emitting diode 118 as illustrated in Figure 2. Thereby, generally, a temperature of the lumi- nescent material 120 and a temperature of the light-emitting diode 118 may be coupled. As illustrated in Figure 2, the light source 114, specifically the phosphor LED 122, may comprise further components such as at least one side coat 162 covering at least one side, such as a top side, a bottom side and/or one or more lateral sides of at least of: the substrate 154, the contact pad 158, the light-emitting diode 118 and the luminescent material 120. Specifically, the side coat 162 may cover gaps and/or interspaces that may be present in the layered set-up of the light source 114 as shown in Figure 2. Further components of the light source 114, specifically
components, which are not shown in Figure 2, are feasible. Generally, the light source 114, in particular the phosphor LED 122, may be packaged in one housing (not shown in Figure 2) or may be unpackaged. Thus, the LED 118 and the at least one luminescent material 120 for light- conversion of the primary light generated by the light-emitting diode 118 may specifically be housed in a common housing. Alternatively, however, the LED 118 may also be an unhoused or bare LED 118, as illustrated in Figure 2. The schematic flowchart of Figure 3 illustrates the process of generating the detector signal as well as processing of the detector signal. Specifically, hardware components 164, which may take part in the process or generating and/or preprocessing the detector signal as well as soft- ware components 166, which may take part in processing the detector signal, are illustrated in Figure 3. The hardware components 164, also simply referred to as “hardware” 164, may spe- cifically comprise the at least one light-emitting diode 118 of the spectrometer device 110, in particular a blue LED 118, configured for emitting blue primary light. The hardware components 164 may further comprise the luminescent material 120, also referred to as LED phosphor, the object 112 as well as one or more optical components 151, e.g. the at least one wavelength-se- lective element 152, and the detector 128. The evaluation unit 136 may consider temperature changes, even local temperature changes within the light source 114, which may have an impact on the emission characteristics of the light source 114. In addition to the hardware components 164, temperatures for selected hard- ware components 164 are indicated in Figure 3. The hardware components 164 may have dif- fering or identical temperatures, e.g. depending on an arrangement of the hardware compo- nents 164, such as their relative positions and distances in the spectrometer device 110. Specif- ically, as described above, the temperature of the luminescent material 120 and the tempera- ture of the light-emitting diode 118 may be coupled, e.g. due to heat transfer by one or both of thermal radiation and heat conduction between the light-emitting diode 118 and the luminescent material 120. Thus, in particular, the temperature of the LED 118, which may also be referred to as “Tpn”, and the temperature of the luminescent material 120, which may also be referred to as “TPh”, may be similar. In Figure 3, the temperature of the LED 118 is indicated with reference sign 168, the temperature of the luminescent material 120 is indicated with reference sign 170, and the temperature of the detector 128, also referred to as “TD”, is indicated with reference sign 172. The LED 118 may emit primary light when an electrical current flows through the LED 118, e.g. as a result of an appropriate voltage applied to the LED by the driving unit 138 in order to gener- ate a specific electrical current, such as a predetermined electrical current. A target signal St may be provided as indicated in Figure 3 by reference sign 174, e.g. to the driving unit 138, to drive the LED 118 to emit blue primary light. The target signal St 174 may in particular be a pre- determined current value that is to be generated through the LED 118, e.g. by applying an ap- propriate voltage. The predetermined current value may in particular be in the range from 10 mA to 500 mA, more specifically in the range from 100 mA to 300 mA, e.g. a current value of 50 mA. Thus, the predetermined current may be known to generate a predetermined light output of
the LED 118, such as blue primary light. The LED 118 may be at the temperature “Tpn” indicated by reference sign 168. The blue primary light may be converted by the luminescent material 120 into secondary light, such as into light in the infrared spectral range. The luminescent material 120 may be at the temperature “Tph” indicated by reference sign 170. The illumination light 116 generated by the light source 114, which may comprise at least one of the primary light or a part thereof, the secondary light or a part thereof, or a mixture of both, may illuminate the object 112. For directing the illumination light 116, one or more optical components 151, such as one or more mirrors, lenses, wavelength selective elements 152 or other optical components 151 may be used, e.g. by placing the optical components 151 in the beam path of the illumination light 116. The detection light from the object 112, e.g. reflected light, may be directed to the detector 128. In the beam path of the detection light 130, again, optionally, one or more optical compo- nents 151 may be used. As an example, one or more wavelength-selective elements 152 may be used, such as one or more dispersive elements, e.g. for splitting the detection light 130 into its spectral components. As described above in more detail, the detector 128 may e.g. comprise an array of photosensi- tive elements 134. Specifically, the detector 128 may be or may comprise a pixel sensor, such as a CCD chip or a CMOS chip, comprising a plurality of pixels arranged on the chip. As an ex- ample, each of the pixels may correspond to a predetermined spectral range, e.g. by being sen- sitive to the predetermined spectral range. The detector 128 may thus generate a detector sig- nal Spx,i 176, as indicated in Figure 3 by reference sign 176, comprising a plurality of detector signals. Thus, each of the plurality of detector signals may correspond to an electronic signal generated by one of the plurality of pixels of the detector 128. Each of the plurality of detector signals may e.g. be given as a numerical value corresponding to a number of counts of the re- spective pixel as measured e.g. during a predetermined time span. Thus, the detector signal Spx,i 176 may specifically be a function of the wavelength of the detection light 130, as indicated by the index “px”. The signal Spx,i 176 may further be a function of time, e.g. in the case of time- dependent detector signals or time resolved detector signals, as indicated by the index “i”. The plurality of signals comprised by the detector signal Spx,i 176 may be generated simultane- ously or in a temporally successive manner. The detector signal Spx,i 176 may be determined using readout electronics 178 as indicated in Figure 3. The detector signal Spx,i 176 may be pro- cessed, e.g. as part of the preprocessing and/or as part of further processing steps. As an ex- ample, the pixels comprised by the detector 128 may specifically be active pixel sensors, which may be adapted to amplify the electronic detector signal Spx,i 176, e.g. as part of a prepro- cessing process prior to further processing that may e.g. be performed by one or more of the software components 166. The signal Spx,i 176 as generated by the detector 128 may also be referred to as “Frame signal Spx,i 176”. Figure 3 illustrates the process of providing the signal Spx,i 176 to one of the software components 166 with an arrow. Specifically, the software components 166 configured for pro- cessing the detector signal Spx,i, 176 may comprise at least one first software 180, which may also be referred to as “software 1”, and at least one second software 182, which may also be
referred to as “software 2”. The first software 180 may be configured for performing at least one first processing step 184, also referred to as “processing 1”, on the detector signal Spx,i 176, such as by applying at least one algorithm to the detector signal Spx,i 176. Specifically, the first processing step 184 may comprise at least one correction of transient or time-dependent ef- fects. Thus, as an example, the first processing step 184 may comprise one or more of the fol- lowing: a correction of the dark signal; a correction of dark signal drift; a correction of fluctuation effects; a correction of photodetector response for individual detector elements or individual time steps; a correction of environment-induced, e.g., temperature-induced changes of the pho- todetector response; an extraction of information for subsequent processing; an addition or mul- tiplication with a parameter, which was generated from information on the at least one electrical value and/or on device temperature. The first software 180 may be configured for performing at least one further step comprising at least one fast Fourier transform 186 to the detector signal. Thus, as a result of applying the first processing step 184 and/or the fast Fourier transform 186 to the detector signal Spx,i 176, a signal Spx 188, also referred to as “pixel signal Spx 188”, may be generated, which may no longer be a function of time. Specifically, the time dependency of the frame signal Spx,i 176 may be eliminated by one or more of the steps forming part of the first software component 1 while the wavelength dependency may still be present in the on signal Spx 188 as indicated by the index “pn”. Figure 3 further illustrates the process of providing the signal Spx 188 to the second software 182 with an arrow. The second software 182 may be con- figured for performing at least one second processing step 190, also referred to as “processing 2”, on the signal Spx 188, such as by applying at least one algorithm to the signal Spx 188, thereby generating at least one corrected signal Spx, corr 191. Specifically, the second processing step 190 may comprise one or more of the following: a correction of the dark signal; a correction of dark signal drift; a correction of fluctuation effects; a correction of photodetector response for individual detector elements or individual time steps; a correction of environment-induced, e.g., temperature-induced changes of the photodetector response; an extraction of information for subsequent processing; an addition or multiplication with a parameter, which was generated from information on the at least one electrical value and/or on device temperature. In particular, the corrected signal Spx, corr 191 may comprise a plurality of corrected signals, such as a plurality of corrected electronic signals. Each of the plurality of corrected signals may specifically corre- spond to a corrected number of counts of the respective pixel. Both the light-emitting diode 118 and the luminescent material 120 may be based on different materials and/or different compositions of materials, e.g. as described in more detail above, which, generally, may affect and influence the spectrum 192 of the phosphor LED 122. How- ever, the spectrum 192 or the spectral properties of a specific phosphor LED 122 may change with temperature, even when being operated at a specific, predetermined current. These changes may include shifts of the emission peaks 193, broadening or narrowing of the spectrum 192, increases or decreases of the emission and the like. In many cases, however, the emission at some wavelengths is affected to a larger extent than the emission at other wavelengths. This effect is illustrated by the diagram shown in Figure 4, which represents a superposition of spec- tra 192 of infrared radiation of a phosphor LED 122 at various temperatures. Specifically, the di-
agram in Figure 4 shows the power spectral density ^^^ 194 in units of microwatt per nanome- ter (µW/nm) on the y-axis 196 as a function of the wavelength 198 given in nanometers on the x-axis 200. For the represented spectra 192 the temperature of the phosphor LED 122 generat- ing the illumination light 116 ranges from 25°C to 50°C. Typically, there is within the spectrum 192, a specific central wavelength, where the power spectral density ^^^ typically does not change with temperature. Each wavelength therefore typically has its own temperature coeffi- cient, regarding to the increment/decrement of the power. Therefore, the shape of the spectrum 192 changes with temperature as apparent from Figure 4. To visualize this effect even more clearly, a number of four specific wavelength intervals, each centering around one of four spe- cific wavelengths ranging across the spectrum 192 are indicated in Figure 4. The wavelength intervals are delimited by dashed lines. Specifically, the following four wavelengths and their re- spective intervals are marked with the following reference signs: 1643 nm is indicated by refer- ence sign 202, 1750 nm is indicated by reference sign 204, 1802 nm is indicated by reference sign 206, and 1950 nm is indicated by reference sign 208,. For each of these wavelengths, the emission power change normalized to the emission power change at 25°C is shown in the dia- gram in Figure 5 as a function of temperature over a temperature range from 25°C to 50°C. In the diagram of Figure 5 the emission power change normalized to the emission power change at 25°C given in percent is shown on the y-axis 196 and represented by reference sign 219, while the temperature in °C, represented by reference sign 220, is indicated on the x-axis 200. The lines in the diagram in Figure 5 indicate fitted curves 236. As apparent from Figure 5, the emission power at the central wavelength of 1802 nm may change very little over the observed temperature range (that is, the emission power change is zero or close to zero), while the emis- sion power change may change considerably for other wavelengths, e.g. for 1643 nm or 1953 nm. When generating a specific current through a light-emitting diode 118, such as an electrical cur- rent at a specific, predefined value by applying to the light-emitting diode 118 a forward voltage, the appropriate forward voltage may be a function of the temperature of the light-emitting diode 118. Thus, when applying the same current to the light-emitting diode 118, the forward voltage of the LED 118 typically decreases while temperature increases. Each type of the LED 118 has its own characteristic forward voltage to temperature curve. Typically, the forward voltage of the LED 118 linearly decreases with rising temperature, such as with a slope in the range of 1 ∙ 10^^ to 1 ∙ 10^^ V/K. Figure 6 illustrates this relationship for a specific LED 118. In particular, the dia- gram of Figure 6 shows the forward voltage applied to an LED 118 for the generation of a direct current of 150 mA through the LED 118 as a function of the temperature of the LED 118. The forward voltage in the units of Volt is represented by reference sign 224 on the y-axis 196. The temperature in °C is indicated by reference sign 220 on the x-axis 200. As apparent from Figure 6, the forward voltage, in this case, decreases linearly with increasing temperature. The curve in Figure 5, may be described by the following equation: ^ ^^ = −0.00059 2.98
wherein ^^represents the forward voltage and ^ represents the Temperature. In the diagram in Figure 6, measuring points 221 represented by grey, filled circles are shown as well as a dashed line corresponding to the above given fitted curve 236. Instead of a relation and/or curve between the forward voltage and the temperature as described in an exemplary fashion above, a relation between another electrically measurable quantity required for driving the light source and the temperature may be used, e.g. a fed in electrical power; a current, resistance, induct- ance, capacitance and the like. For deriving the spectroscopic information on the object 112, specifically a spectrum, the spec- trometer device 110, in particular the evaluation unit 136, may specifically take into account the characteristics of the luminescent material 120 used in the light source 114. As outlined in more detail above, the luminescent material 120 may be configured for absorbing primary photons generated by the light-emitting diode 118 and may, as a reaction, emit secondary photons in- stantaneously or after a delay or decay time. The signal or emission of the phosphor LED 122 after turning off the forward current may be described using equations (1) and (2) as described above. Thus, characteristic for the luminescent material 120 may in particular be the decay constant ^^ 228, which may describe the typical time of an afterglow of the luminescent material 120, as well as the growth constant ^^, which may describe the typical time for reaching a saturation of the emission of converted light. The time constants ^^ and ^^ typically differ between different phosphor LEDs 122 and/or between different types of the luminescent material 120. Addition- ally, decay constant ^^ and growth constant ^^ may depend on the wavelength. The time con- stants typically are extracted from step response of the optical signal by applying / shutting off the forward current. Figures 7A and 7B show spectra 192 of two different types of phosphor LEDs 122, which emit light in the near infrared range. Specifically the power spectral density ^^^ is shown as a function of the wavelength, which is given in nm. As apparent from Figures 7A and 7B the spectra 192 of the two different phosphor LEDs 122 differ. Thus, as an example, the spectrum 192 shown in Figure 7A reflects a high emission in the range from 1400 nm to 1600 nm, while the emission in this region is negligible for the phosphor LED 122, whose spec- trum 192 is shown in Figure 7B. The decay constant ^^ and the growth constant ^^ of the phos- phor LED 122, whose spectrum is shown in Fig 7A,
given as a function of the wavelength in Figures 8A and 8B, respectively. The decay constant ^^ and the growth constant ^^ of the phos- phor LED 122, whose spectrum is shown in Fig 7B, are given as a function of the wavelength in Figures 9A and 9B, respectively. Specifically, Figures 8A and 9A show the respective decay constants ^^ in ms, indicated by reference sign 228, on the y-axis 196 versus the wavelength in nm 198 on the x-axis 200; and Figures 8B and 9B show the respective growth constants ^^ in ms, indicated by reference sign 230, on the y-axis 196 versus the wavelength in nm 198 on the x-axis 200. Data points from different repetition measurements are marked in different shades of grey. A further characteristic of the LED 118 is the light output power as a function of the forward cur- rent. Thus, generally, by increasing the forward current, specifically the input current, the power
emitted by the LED 118 is increased. The shape, e.g. the slope, of the curve of the light output as a function of the forward current is characteristic to the individual LED 118. Figure 10 shows an example of such a curve. Specifically, in the diagram in Figure 10, the normalized light out- put 232 of a phosphor LED is shown as a function of the forward current 234, which is given in Ampere. Figure 11 illustrates a heat map 238 indicating the performance of the present invention. On the horizontal axis 240, the noise level in units of the signal amplitude is shown. Thus, the horizon- tal axis 240 shows the relative noise level. On the vertical axis 242 the number of contributing signal intensities of the plurality of wavelength intervals 236 to the detector signal is illustrated. The heat map 238 indicates the mean deviation of the fitted signal amplitudes to the real signal amplitudes. Thus, the heat map 238 indicates the relative error of the described method.. As may be derived from the Figure 11, the number of contributing signal intensities of the plurality of wavelength intervals 236 to the detector signal and noise level influence the performance. Particularly, for a low noise level a high number of contributing signal intensities of the plurality of wavelength intervals 236 to the detector signal may be considered. In Figure 12, a graph 244 illustrating three adjoining wavelength intervals are depicted. On the horizontal axis 246 the wavelength is depicted. On the vertical axis 248 the time constant ^ may be depicted. As may be derived from Figure 12, the time constant ^ within a wavelength interval 236 may fluctuate strongly. For compensating this fluctuation, a further plurality of known time constants ^ of wavelengths comprised by a specific wavelength interval 236 may be combined for determining an overall time constant ^ that is considered for determining the contribution of the signal intensity of the specific wavelength interval 236 to the detector signal. In Figure 13, a graph 250 illustrating three distant wavelength intervals 236 are depicted. On the horizontal axis 240 the wavelength is depicted. On the vertical axis 242 the time constant ^ ^is depicted. The distant or separate wavelength intervals 236 may particularly be recorded by us- ing exactly one detector 128 having exactly one photosensitive area and a wavelength-selective element 152 that transmits only wavelengths comprised by the separate wavelength intervals 236 onto the photosensitive area. Further wavelengths may be blocked and/or strongly attenu- ated. A method 256 of obtaining spectroscopic information on at least one object 112 is displayed in Figure 14. The method is comprising: (a) illuminating the object 112 with illumination light 116, in a step (a) 258, generated by at least one light source 114, the light source 114 comprising at least one light-emit- ting diode 118 and at least one luminescent material 120 for light-conversion of pri- mary light generated by the light-emitting diode 114, and driving the light source 114 in a manner that an driving state of the light source 114 is changed at least one time at least one time; (b) detecting detection light 130 from the object 112, in a step (b) 260, by using at least one detector 128 and, thereby, generating at least one detector signal when the
driving state of the light source 114 is changed, wherein the detector signal 114 is time-resolved; and (c) evaluating, by using at least one evaluation unit 136, the detector signal, in a step (c) 262, generated by the detector 128 for deriving the spectroscopic information on the object 112, and further considering a plurality of known time constants ^ of the light source 114 describing a property of the light source 114 when the driving state is changed for determining a contribution of signal intensities of a plurality of wave- length intervals 236 to the detector signal when the spectroscopic information on the object 112 is derived. A spectrometer device 110 as described may be used for performing the method 256. The method 256 may be performed on-line in the field. At least step (c) 262 of the method 256 may be computer-implemented.