ES2940565T3 - Security feature based on luminescent substances, verifiable by smartphone and provision for verification - Google Patents

Abstract

The invention relates to a smartphone verifiable security feature (01) containing a luminescent material that can be excited to luminescence by visible electromagnetic radiation generated by a smartphone and, after completion of excitation, exhibits a emission that can be detected by means of a smartphone image capture unit during a decay time in the range of 1 ms to 100 ms. The invention also relates to a set for verifying a security document (02) comprising such a security feature (01). (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Security feature based on luminescent substances, verifiable by smartphone and provision for verification

The present invention relates to a security feature with a luminescent substance, which can be verified with the help of a commercially available smartphone. The invention further relates to an arrangement for checking a security document with such a security feature.

The use of security features provided with luminescent substances (luminescent substances) for the protection and authentication of valuable and security documents has been known for a long time from the prior art. They are mainly used as so-called Level 2 features. Their presence can be detected through the emission of luminescent substances which can be excited by simple portable devices (UV or IR radiation sources) and which takes place mainly in the visible spectral region. They also serve as copy protection. On the other hand, luminescent security features having particularly high counterfeiting security are, however, also used as machine-readable level 3 features. Verification of the authenticity of such features is as a rule associated with a high level of technical expense.

Both in the area of security and value documents and in the area of product protection, there is a growing interest in the use of authenticity features that present a high level of security (level 2+ or level 3 feature), however they can be tested with little technical effort.

Thus, from the document WO 2012/083469 A1 a device for the authentication of documents marked with photochromic systems is known. The photochromic safety feature shows a change in color and/or a change in shape under flash excitation. It is further described that the security feature is formed on the basis of a retinal protein.

From DE 102015219395 A1 an identification feature is known with at least two identification elements arranged on a defined limited area for the identification of an object. Upon irradiation of the surface with visible light, a first identification element consisting of printer ink becomes visually visible and a second identification element does not become visually visible.

EP 0091 184 A1 names a sulphide phosphor which emits green to orange light with a long glow time. This luminescent substance has been described by the general formula (Zn ¹ -x,CdX)S:eMI', fMm', gX', where Mr has been selected from copper and gold, Mm' has been selected from gallium and indium, and X' has been selected from chlorine, bromine, iodine, fluorine and aluminum.

The document WO 02/071347 A1 describes a method and a device for the authentication of documents or security objects that have a luminescent compound. The compound can be excited by excitation light.

From US Pat. No. 7,079,230 B1 a method as well as an authentication device for detecting an authentication marking is known.

EP 1672568 A1 describes tamper-proof security labels as well as an optical scanner for illuminating, detecting and sorting a sample or the security label.

In US 2010/0102250 A1 a method and an apparatus for the authentication of a photoluminescent security feature have been described.

US 2016/0314374 A1 describes a device for a portable smart device as well as a method for authenticating an object to be authenticated.

From US 2013/0153789 A1 a luminescent material and objects with this material are known. In addition, a method for authenticating the objects with the luminescent material has been described. The material consists of a first particle of a first inorganic host network with at least one first substance and a second particle of a second inorganic host network with at least one second substance.

WO 2018/007444 A1 describes a method for authenticating a security marking as well as the security marking and a reading device that can carry out the method. The security marking can emit a long luminescent luminescent light. The reading apparatus with CPU unit and memory unit, for example a smartphone, is used for generating and recording the broadcast.

Document WO 2013/012656 A1 discloses different luminescent substance compositions comprising one or more emitting ions as well as one or more impurity ions. An emitting ion is characterized by a first decay time constant in the undisturbed state. Impurity ions lead to a predetermined quenching behavior with a modified quenching time that is greater than zero and less than the undisturbed quenching time. An authentication system is configured for the measurement of the extinction time, when this phosphor composition has been applied to an article.

WO 2013/034471 A1 and DE 10 2011 082 174 A1 describe a device for recognizing a document that has a phosphor-based security feature with so-called wavelength conversion properties. For this, a light-generating device (for example, an LED flash unit) is provided, which irradiates the security feature with excitation light, as well as an image recording device (for example, a digital camera from a mobile communication device), which must register the light emitted by the security feature. However, it has been shown that the regularly reported luminescent substances have extinction times which do not allow evaluation of the emission with widely used devices, in particular an authenticity check with the aid of commercially available smartphones.

WO 2013/034603 A1 describes a method for verifying a security document with a security feature in the form of a fluorescent printing element. The method provides that the printing element is excited by means of a light source and, as a result of this excitation, emits electromagnetic radiation that can be detected at a later stage by means of a detector. The recorded data is evaluated by comparison with predetermined data. In a later stage, the verification result is output depending on the comparison result. In particular, the method must be performed with a smartphone, where the flash module of the smartphone is used as the drive source and the photodetector of the smartphone camera is used as the detection unit. As luminescent substances for the pigment-like fluorescent printing element are mentioned inorganic luminescent substances, namely nitride luminescent substances; europium-doped alkaline earth orthosilicate and oxyorthosilicate luminescent substances; cerium-doped rare earth metal and gallium aluminum garnet luminescent substances; (Ca,Sr)S:Eu2+ which emits red light; and SrGa2S4:Eu2+ which emits green light. The proposed luminescent substances are so-called LED conversion luminescent substances which extinguish extremely quickly. However, it has been shown that it is practically not possible to reliably detect the luminescence signals of these rapidly extinguishing luminescent substances directly during flash excitation, because the luminescence signals have too low an intensity compared to the excitation light and are covered by the high intensity exciting flash of the smart phone.

In the practical application of the luminescent substances described in the aforementioned prior art, two hitherto unresolved problems have emerged. These previously known luminescent substances are regularly used as so-called conversion luminescent substances for the production of white LEDs, so that these luminescent substances are as a rule also contained as radiation conversion constituents in the flash LEDs of smartphones. common in the market.

This means that the excitation radiation from smartphone flash units used as excitation source exhibits with high probability the same luminescence signals as expected from the security feature to be examined. A reliable proof of the authenticity of valuable and security documents endowed with such security features has already been excluded for this reason.

A second problem results from the fact that the luminescent substances mentioned in the prior art for use as safety features generally have short extinction times in the range from ns to ps, just like those that can also be applied for Flash LED for the reasons mentioned. In the case of a smartphone flash excitation, the emissions from the safety feature are either completely overlapped by the flash or are already extinguished before the image recording takes place.

Proceeding from the state of the art, an object of the present invention is to provide an improved security feature based on luminescent substances that can only be verified with the aid of a smartphone or a comparable multifunctional, widely used data processing device. Another object of the present invention is to provide an arrangement for verification of such a security feature.

According to the invention, the solution of the objective is realized by means of a security feature based on luminescent substances, verifiable with a smartphone according to the appended claim 1 as well as by means of an arrangement for the verification of such a security feature according to the attached independent claim 9.

A general solution idea for the mentioned aim, which the invention implements, consists first of all in that a security feature is provided with a specific luminescent substance which avoids the problems described above. For this purpose, this luminescent substance must be configured in such a way that it can be activated on the one hand by a light source from a smartphone or a similar mobile data processing device, that is to say, in particular, a flash LED from a smartphone. At the same time, the luminescent substance must have a luminescence characteristic such that it allows the luminescence signals to be detected with still high reliability with the aid of the image recording unit of the same smartphone (mobile data processing device) as well. after completion of the excitation process. In addition to a high efficiency of the spectral excitability and a high luminescence yield, this primarily requires an extinction time of the luminescent substance according to the invention adapted to the exceptional speed of the image recording unit of the smartphone.

By means of the invention, a reliably evaluable security feature is provided, which allows unique luminescence properties, such as the spectral emission and extinction characteristic of the luminescent substances used for the creation of the security feature, to be included in the test, as a criterion of authenticity. Furthermore, it is a great advantage that the extinguishing luminescence signals of the safety feature according to the invention are not visible to the human eye either during or after the excitation has ended. It has been shown that the possibilities of choice to provide suitable luminescent substances to realize the inventive solution shown are severely limited. This applies in particular to the required extinguishing characteristic.

The invention provides a level 3 feature or at least a feature with level 2+ functionality, as can be used in security and value documents for authenticity verification. Such features are generally invisible to the human eye, for example also after excitation with UV or IR light sources. Until now, its features could only be tested with great technical effort, for example with the help of high-speed sorting machines. By means of the present invention a check of the authenticity of such exclusive features is enabled for the first time with the aid of commercially available smartphones.

The security feature according to the invention can be applied on or in a valuable or security document and comprises a luminescent substance that can be excited to luminesce with electromagnetic radiation of predetermined wavelength, such as can be generated by a lighting unit. of a smartphone, whereupon the luminescent substance emits radiation detectable by the camera device of a smartphone. The emission of the luminescent substance has an extinction time in the range of ms. According to the invention, the decay times have been selected in the range between 1 and 100 ms, preferably in the range between 5 and 50 ms, again preferably between 10 and 30 ms.

The quenching event (quenching process) basically characterizes the time-dependent decrease in the intensity of the radiation emitted by a luminescent substance. In this regard, the extinction curve can often be described by a simple exponential equation of the form I = Iüe-(t/t). The extinction constant t contains in it designates the length of time up to which the intensity of the emission has decreased by 36.79% (= 1/etel) of the starting intensity after the excitation source has been switched off . However, it has turned out that not all luminescent substances have a monoexponential extinction. Rather, multi-exponential (eg bi- or tri-exponential) extinction curves result, if appropriate, from the superimposition of different relaxation processes.

As a particularly suitable class of luminescent substances for the safety feature, silicate garnet luminescent substances co-doped with Ce3+ and Mn2+ (CSS) have emerged, which can be described by the formula:

Ca3Sc2Si3Ü12:Ce3+,Mn2+.

Luminescent substances of this type are characterized by a high absorption intensity at 450 nm, a high luminescence intensity and by efficient energy transfer between Ce3+ and Mn2+ ions.

According to an alternative way of writing the luminescent substance can be described with the formula:

(Ca1-xCex)3(Sc1-zMnz)2Si3Ü12,

where based on the ionic radii known in the technical literature, it is often assumed that Ce3+ ions are preferentially incorporated into Ca2+ lattice positions and Mn2+ ions preferentially into Sc3+ lattice positions.

In experimental investigations, it was surprisingly found that highly effective and particularly stable phase-pure Ca3Sc2Si3Ü12:Ce3+,Mn2+ luminescent substances are formed above all when calculating the weights of the starting substances it is assumed that the Mn2+ ions are incorporated into the lattice at both Ca2+ sites and also at Sc3+ sites. Particularly good results are achieved when weight calculations are made with the assumption that about 75% of the Mn2+ coactivators replace Ca2+ ions and about 25% Sc3+ ions as lattice constituent parts.

With particular preference, the luminescent substance according to the invention can be described by the following general chemical formula:

(Ca1 -x-yCexM ny)3(Sc1-zM nz)2Si3Ü1 ²

with 0<x<0.1; 0<y<0.8; 0<z<0.8

where a y/z ratio of = 2 is preferred.

Taking stoichiometric factors into account, this corresponds to the ratio specified for the occupancy of the Ca2+ or Sc3+ lattice sites by coactivating Mn2+ ions.

The described Ca ³ Sc ² Si ³ O ¹² :Ce3+,Mn2+ materials provide particularly advantageous luminescent substances according to the invention, which have emissions with decay times between 5 and 30 ms and whose luminescence signals can be detected with high security using commercially available smartphone camera modules even after flash excitation has ended.

The emission spectra of the luminescent substances according to the invention consist of three bands in each case, which can be assigned to the direct luminescence of the activating Ce3+ ions (band with an Amax of approx. 505 nm) as well as the emissions allowed through the transfer of energy from Ce3+ -Mn2+ from the Mn2+ coactivators positioned in the different lattice sites. The maxima of the last-mentioned emission bands lie at about 570 nm (Mn2+ at Ca2+ site) and at about 700 nm (Mn2+ at Sc3+ site).

The relative intensities of the different emission bands can be varied and adjusted through the concentrations of the activating and coactivating ions and through the respective concentration ratios. Furthermore, individual emissions exhibit different spectral extinction times. While the quenching time of the Ce3+ emission allowed from the quantum mechanical point of view is in the range of nanoseconds, for the two Mn2+ emission bands resulting from the optical transitions it is prohibited from the mechanical point of view Quantum extinction times are achieved in the single-digit millisecond interval (Mn2+ at Ca2+ site) or in the double-digit millisecond interval (Mn2+ at Sc3+ site).

The fact that the emission bands lying in the green spectral region with maxima at about 505 and 570 nm largely overlap due to their comparatively large half-widths also leads to an overlap of the extinction curves of these emissions. However, modified CSS luminescent substances are characterized by different spectral extinction curves with differentiable extinction times. On the other hand, it results from this constellation that if the entire visible spectral region is detected in the extinction measurements, a significant color shift of the extinguishing luminescence of the luminescent substances results. Furthermore, it has been shown that the individual emission bands do not exhibit monoexponential extinction curves due to their characteristic overlaps. Rather, bi- or tri-exponential extinction curves are characteristic.

The described special quenching behavior contributes to a large extent to the uniqueness of the Ca3Sc2Si3O12:Ce3+,Mn2+ phosphors according to the invention. Added to this are other properties that recommend these luminescent substances for use in luminescent security features, the presence and authenticity of which can be verified with the help of common smartphones on the market. On the one hand, the mentioned luminescent substances cannot be excited practically in the ultraviolet spectral region and, on the other hand, the body color of the corresponding luminescent pigments has been achieved in such a way that it can be easily adapted to the color design of security documents. and of value that are going to be protected (banknotes, identity documents, passports, driving licenses, etc.) or can be hidden by the inks used to manufacture these documents. This means that the presence of CSS:Ce3+,Mn2+ luminescent substances introduced as security features in security documents cannot be recognized by the observer either with the naked eye or with the aid of usual UV excitation sources.

On the other hand, a special embodiment of the invention is that, during UV excitation, luminescent substances with effective luminescence, which extinguish quickly, are added to luminescent substances with a delayed extinguishing behavior, which emit almost exclusively in the spectral region. visible, preferably excitable at 450 nm. The stationary photoluminescence of the corresponding additional components, clearly perceptible under UV excitation, can serve as a security-enhancing masking of security features embedded in security documents.

Even if the possibilities of choice for providing the luminescent substances required for the realization of the shown inventive solution are severely limited, in addition to the luminescent substances of Ca3Sc2Si3O12:Ce3+,Mn2+ there are however some other materials that could be used for the production of lighting characteristics. security due to their extinction behavior, however they are not in the scope of protection of the claims. Some of the luminescent substance compositions tested for suitability according to the invention as well as non-inventive phosphor compositions have been summarized in the following table, including luminescent properties relevant to the inventive application.

In particular, the table contains data regarding the measured maxima of the respective emission bands and regarding the extinction times. Verbal scale was used to assess luminescence performance and spectral excitability at 450 nm.

The luminescent substances mentioned are essentially silicate garnets or germanate garnets codoped with Ce3+ and Mn2+, complex silicate or phosphatic base networks activated with Mn2+ ions and optionally additionally coactivated with certain rare earth ions (Ce3+, Eu2+, Dy3+), Cr3-activated gallate compounds as well as the Mn4+-activated phosphors BaGeF6:Mn4+ and K ² SiF ⁶ :Mn4+.

This list is not conclusive.

In this context, it should be considered extremely advantageous to modify the luminescent substances that seem suitable by deliberately changing their chemical composition, i.e. by substitutions carried out in a targeted manner in the partial lattice of cations and/or anions, so that their luminescence properties, in particularly their characteristic extinction times, clearly differ from the data described in the technical literature. In this way, the exclusivity of delayed-extinguishing luminescent materials and the security against counterfeiting of the corresponding security features can be clearly increased.

Another embodiment of the invention is characterized in that mixtures of luminescent substances are used to create the security features, the individual, preferably exclusive, components of which have different extinction times and can be distinguished by detectors. In this case, too, an increase in the protection against counterfeiting of the security features according to the invention results.

The luminescent substance preferably has an extinction time in the range of more than one or two digits, so that the emission of the luminescent substance can be detected with an image recording unit, in particular with a smartphone camera. Currently known smartphone cameras have a frame rate in the range of 240 fps (frames per second) up to 960 fps. Higher frame rates are conceivable, above all, in future apparatuses, which however does not preclude the use of the invention described herein. With currently known frame rates, a first image can be recorded by the smartphone camera after approximately 4.2 ms or, in exceptional cases, after 1 ms.

The frame rate of the image detector used (in particular a smartphone camera) determines a lower limit for the decay time of the luminescent substances that can be used within the meaning of the invention. In the event that the human eye is not to recognize the security feature in the sense of realizing a particularly high level of security, the physiology of human vision predetermines an upper limit. In particular, the extinguishing time of the phosphor should be less than 1 s in this case, since a luminescence of the phosphor lasting longer than 1 s can be perceived by a normal human observer.

According to the invention, the phosphor is a silicate garnet phosphor doped with Ce3+ or Mn2+. When excited with light from LEDs emitting white light, preferably with a maximum wavelength of 450 nm, the stationary luminescence of the phosphor exhibits a broadband emission spectrum with several emission maxima in the visible spectral region. These maxima are located at about

505 nm (assignable to Ce3+ ion emission at dodecahedral Ca2+ sites),

570 nm (assignable to sensitized emission of Mn2+ ions at dodecahedral Ca2+ sites),

700 nm (assignable to sensitized emission of Mn2+ ions at octahedral Sc3+ sites).

The spectral decay times of the different emission bands are in the order mentioned in the interval of ns, in the interval of ms of one digit or of two digits.

The extinguishing time of the luminescent substance of the security feature is preferably in the range from 1 ms to 50 ms. The luminescent substance of the security feature particularly preferably has an extinction time of 10 ms to 30 ms.

So that the security feature can only be detected by means of a smartphone, the luminescent substance is configured in such a way that it can be excited in the visible spectral region, in particular in the blue spectral region, so that the flash source of the smartphone can supply this exciting radiation. In addition, the luminescent substance is configured so that it emits in the visible spectral region to ensure that it can be detected with the camera module of a commercially available smartphone. In addition, the luminescent substance is configured so that its luminescence is extinguished within ms after the flash drive is completed, so that a safe verification is possible after the drive is finished.

The white light from a smartphone lighting unit is generated by an LED, which consists of an LED semiconductor chip emitting at about 450 nm, for example, and one or more LED conversion phosphors placed on top of the LED semiconductor chip. . These conversion luminescent substances are capable of proportionally converting blue LED emission into longer wave visible luminescence radiation (broadband emissions in the green, yellow and red spectral region) with an emission maximum of eg approx. 560 nm . The white light of the LED, which is available as a lighting unit of commercially available smartphones, results from the additive color mixing of the individual luminescent components described, with the blue spectral ratio having the clearly highest intensity. This means that the luminescent substance that can be used to provide the security feature according to the invention should preferably be configured so that it has a high spectral excitability efficiency, particularly in the range between 420 nm and 470 nm. The maximum of the spectral excitability of the phosphor is particularly preferably at about 450 nm.

The smartphone camera is available as an image recording unit for detecting the luminescence signals of the luminescent substance. The image recording unit is preferably equipped with a CMOS detector and an IR filter. As a result, it has a spectral sensitivity that covers the entire visible spectral region up to approximately 750 nm. By means of the image recording unit, individual images, image series or video recordings can be recorded. For the luminescent substance used to create the security feature, this means that it must be configured in such a way that, after excitation has been carried out, it emits with the highest possible intensity, preferably in the spectral region between 480 nm and 750 nm.

The mobile terminal device used according to the invention for verification of the security feature is preferably a conventional smartphone. It is understandable to a person skilled in the art that the same functionality can also be integrated into a tablet or similar multifunctional data processing device, for which it must be equipped with a camera with image recording unit and/or lighting unit. as well as a data processing unit. Apparatus of this type having the same effect should also be included in the invention. The data processing unit is preferably a processor, in particular a microprocessor.

Preferably, the luminescent substance is arranged on the security feature so as to form a pattern. Luminescent substance pigments have preferably been applied to a support as a defined pattern. The pattern may be arranged as a shape, for example a triangle or a star. Alternatively, the pattern formed by the luminescent substance of the security feature itself may contain data and may be arranged as a code, eg a QR code. Luminescent pigments have been printed as a security feature, eg on a security document. The printing or application can be carried out using known printing methods, such as gravure printing, flexographic printing, offset printing or screen printing. Furthermore, the luminescent substance can be applied to the security document or introduced into the security document by coating processes or laminating processes. The grain size distribution of the luminescent substance pigments is preferably adapted to the respective printing and application process.

The security feature, in particular the luminescent substance, preferably has a high processing stability. In particular, the phosphor has a high thermal and mechanical stability. The luminescent substance preferably has a high aging resistance against environmental influences. Stability and resistance to aging are necessary to ensure that the security feature can be reliably verified throughout the entire life cycle of the security document.

An advantage of the security feature according to the invention, which comprises a luminescent substance, can be seen in the fact that the security feature can be aroused by means of a flash from a smartphone due to the specially configured luminescence characteristics of the luminescent substance and its emission can be detected by the smartphone's camera, allowing for simple, fast and easy-to-use verification of the security feature. An authenticity check and/or integrity check may be performed. It has proven to be advantageous to select a special luminescent substance with decay times in the ms range to provide the safety feature, whose luminescence signals can still be reliably measured even after the end of the excitation process. The verification advantageously does not refer exclusively to the detection of the presence of the security feature, it also includes the emission spectrum, the specific shape of the extinction curve (extinction characteristic) and the pattern formed by the phosphor pigments in authenticity checking as authenticity criteria. Another advantage of the security feature is that humans cannot visually perceive it.

The arrangement according to the invention comprises a security feature according to the invention in one of the embodiments described above, which is applied on a valuable or security document or embedded in a valuable or security document. Furthermore, the arrangement comprises a smartphone, which comprises a lighting unit, an image recording unit and a data processing unit.

It has turned out that an advantageous solution approach to be able to reliably measure the quenching luminescence of luminescent substances after completion of the excitation process is to use a combination of single flashes and serial or video recordings as detection methods, where the duration of the serial or video recordings must clearly exceed that of the exciting flash.

At the same time, the recording duration must be adapted to the extinction time of the luminescent substance used. In the last recording, ie in the last frame, the emission intensity of the luminescent substance must be zero, as it was before the flash excitation. This frame can be used as a reference to calculate the image differences (B ¹ -R; B ² -R;...Bn-R). The analysis of image differences, the contrast adjustment to be performed and the consideration and inclusion of other procedures for image analysis (histogram analysis of the different color channels) can be considered as an essential prerequisite to not only detect the presence of a selected inventive luminescent substance with the help of the smartphone, but also at the same time checking the spectral emission characteristic and the exclusive extinction characteristic.

Furthermore, it has proven to be extremely advantageous to keep the distance between the smartphone and the security feature to be checked as small as possible when verifying the authenticity of the security document. In this way, the intensity of the flash excitation can be increased and the disturbing influence of extraneous light can be significantly reduced. In particular, the distance between the detection device and the security document can be selected to be less than the adjustment range of the axis of the smartphone; sharp images are not required for the exception and verification of diffuse luminescence signals.

For example, the smartphone must be configured with an App in such a way that at least the following steps are performed for verification of the security feature:

In a first method step, the security feature is excited to luminescence by means of the lighting unit of the smartphone, preferably by triggering a single flash of the LED flash module, so that the security feature emits electromagnetic radiation. in the visible spectral region.

In a second method step, parallel to the single-flash excitation, the luminescent signals of the luminescent substance of the security feature according to the invention, which extinguish after the end of the excitation, are detected by means of the image registration unit, that is, with the help of the smartphone camera module.

In another stage of the method, the luminescence features in the recorded images are evaluated by the data processing unit and compared with reference data to verify the security feature and confirm the authenticity of the security document.

Other details, advantages and refinements of the invention result from the following description of preferred embodiments of the invention, with reference to the drawing. Show:

1 is a schematic representation of an embodiment of a security feature according to the invention in a security document in the form of a banknote;

2 a schematic representation of components of an arrangement according to the invention for the security feature verification;

3 is a schematic representation of the rise and fall behavior of a luminescent substance of the safety feature with flash excitation;

figure 4 a flowchart for performing security feature verification with the arrangement according to the invention;

5 is an excitation spectrum of the 700 nm emission band of a luminescent substance according to the invention according to exemplary embodiment 1;

6 is an emission spectrum of the stationary photoluminescence excited at 450 nm of the luminescent substance according to exemplary embodiment 1;

Figure 7 Spectral extinction curves of the different emission bands of an inventive luminescent substance described in Embodiment Example 1;

8 a color shift of the luminescence of the extinguishing luminescent substance, detected over the entire visible spectral region according to exemplary embodiment 1, represented by means of the time course of the x-y color coordinates in the color table CIE standard;

Figure 9 Emission spectra of the stationary photoluminescence of the luminescent substances excited at 450 nm according to Embodiment Examples 2 and 3;

figure 10 extinction curves of the main emission bands of the excited luminescent substances at 450 nm according to embodiment examples 2 and 3;

1 shows a security feature 01 according to the invention, which is applied to a valuable document, namely a security document 02 in the form of a banknote, which is represented in symbol form. The security feature is used to detect the authenticity of the security document 02. The security feature 01 is here in the shape of a star. It is placed under a visible feature 03, in this case the face value of the banknote. The security feature 01 consists of a luminescent substance that can be excited by means of the illumination unit of a smartphone, preferably in the blue spectral region, to give the luminescence that extinguishes in the interval of ms, as previously disclosed. in the context of the description of the invention.

Figure 2 shows a schematic representation of an arrangement for checking the security feature 01, whereby the security feature is excited to luminescence by means of an illumination unit 04 of an image recording unit 06 of a mobile terminal device, namely a smartphone 07, in which the lighting unit 04 generates excitation light, in particular white LED flash 08 with a spectral maximum of approximately 450 nm. Flash 08 has an intensity I ^a . During excitation, the luminescent substance of security feature 01 emits stationary electromagnetic radiation in the visible spectral region, which dies out within ms after the end of excitation. The quenching emission I ^e of the luminescent substance is detected by a camera 09 of the image recording unit 06 of the smartphone 07 by triggering a serial or video recording. The camera 09, which functions as a detector, additionally detects an ambient radiation I ⁰ of daylight or ambient light, which hits the security feature 01 and the banknote 02 and is reflected there. The influence of ambient radiation I ⁰ can be kept small in the method according to the invention because a distance d between the security feature 01 and the smartphone 07 is kept small. Due to the small distance d, which is located preferably below the focus range of the image recording unit 06, the smartphone 07 shields the ambient radiation I ⁰ to a great extent. Clear image recordings are not specifically required for the reliable verification of the diffuse luminescence signals of the security feature.

Figure 3 shows a schematic representation of the rising and dying behavior of the luminescent substance, which is used in the security feature 01. An emission curve 11 of the security feature 01 excited to give the luminescence is represented in the diagram a along a time axis t.

In addition, a flash excitation curve 12 is plotted along the time axis. If the single flash is generated by means of the smartphone 07 (FIG. 2), the LED flash drive curve 12 rises sharply, holds its level for a short time, and then falls to zero in the range from ns to gs. The luminescent substance of the security feature 01 is excited to luminescence by the electromagnetic radiation of the flash, whereby its emission curve 11 increases almost simultaneously with the flash excitation curve 12. After completion of the flash excitation 12, the emission of the luminescent substance 11 extinguishes significantly slower than the excitation radiation of the lighting unit of the smartphone preferably equipped with white-emitting LEDs. According to the invention, the extinguishing time of the phosphor is in the range of ms.

The individual images 13 of the security feature 01 recorded by the detector 09 of the smartphone 07 (FIG. 2) are represented below the time axis in FIG. 3. The image records 13 show the extinguishing emission intensity of safety feature 01 by means of the luminosity of the star pattern used as an example, which becomes smaller over time. After essentially complete extinguishing of the emission of the luminescent substance, a reference image 14b can be recorded as the last image of the recorded image sequence. Depending on the evaluation method, an additional reference image 14a (initial image) can also be recorded before the activation of the excitation radiation (flash activation). In order to ensure the availability of a reference image required for calculating the image differences, a start image 14a can optionally be recorded as an additional reference image, if necessary already before the activation of serial or video recordings decisive for the detection of the extinguishing luminescence signals of the security feature.

Figure 4 shows, in simplified form, the main sequence of the verification of the security feature 01 using the arrangement represented in Figure 3. In a positioning step 41, the security document to be verified is positioned so that can be safely detected by the smartphone's image recording unit. In an optional reference check step 42, the start image 14a of the security feature is already generated before the flash drive of the smartphone is activated. In a detection step 43, a single flash is triggered with the help of the image recording unit of the illumination unit of the smartphone, and a serial image or video recording is performed to record the luminescence signals of the light. Luminescent substance used to create the security feature, which are present after completion of flash excitation and which extinguish within ms. Finally, in a broadcast analysis step 44, the recorded image series and the reference recordings are compared by means of the data processing unit. In addition to the calculation of the image differences and their analysis, other image processing methods such as contrast adjustment and histogram analysis of the different color channels are used in this regard in order to verify in this way both the spectral emission as well as the unique quenching characteristic of the phosphor used according to the invention. The authenticity of the checked security document can be confirmed in an unlocking step 45 by comparing the calculated parameters with the authenticity parameters of the security feature preferably stored in the data memory of the smartphone. In particular, the authenticity and integrity of the security document can be confirmed by checking the security feature in the security document.

5 shows an excitation spectrum 121 of the 700 nm emission band of a luminescent substance according to Embodiment Example 1. To produce this luminescent substance, 0.2822 g of CaC03, 0.5335 g of Sc2 are homogenized (C2O4)3*10.723H2O, 0.1803 g of SiÜ ² , 0.0052 g of CeÜ ² , and 0.0358 g of MnC2O4-2H2O completely by mortars with acetone addition. After evaporating the solvent, the dry powder mixture is transferred to a corundum crucible. The sample is first precalcined in a chamber furnace at 500 °C for 2 h in air atmosphere and then annealed in a tube furnace at 1400 °C for 4 h in an atmosphere of 5% H ^{2 /95} % CO. No. ² . The resulting product is then sieved. This luminescent substance has the formula (Ca2.82Ce0.03Mn0.15)(Sc1.95Mn0.05)Si3O12. The excitation spectrum illustrates that the exemplary inventive phosphor exhibits a maximum spectral excitability in the range 440 to 450 nm.

6 shows a corresponding emission spectrum 111 of the luminescent substance according to exemplary embodiment 1 at an excitation of 450 nm. It is shown that the specially configured luminescent substance due to the luminescent substance composition and the selected preparation conditions exhibits broadband emissions in the entire visible spectral region. Three emission bands with maxima at about 505 nm, 570 nm and about 700 nm are visible, with the band showing the highest relative intensity at a maximum of about 700 nm. As already described, these bands from the direct luminescence of Ce3+ activating ions (Ce3+ at the Ca2+ site) as well as the emissions allowed through Ce3+ - Mn2+ energy transfer can be assigned to the joint activators of Mn2+ positioned in the different network sites (Mn2+ in the Ca2+ site or Mn2+ in the Sc3+ site).

Figure 7 shows the spectral extinction curves of the individual emission bands. Curve 1311 is the extinction curve for emission at 505 nm, curve 1312 is the extinction curve for emission at 570 nm, and curve 1313 is the extinction curve for emission at 700 nm. It can be clearly recognized that the spectral extinction curves for the individual emissions differ significantly. As already explained, an extinction in the range of nanoseconds is determined for the emission with a maximum of about 505 nm, while the luminescence bands with maxima of about 570 or about 700 nm exhibit extinction times in the range either single-digit or double-digit milliseconds. Furthermore, it is clear to the person skilled in the art that individual extinction curves are highly unlikely to develop exponentially. Rather, the measured curves seem to exhibit multi-exponential decay characteristics.

Figure 8 illustrates the color shift that results when quenching luminescence is detected throughout the visible spectral region. In this connection, FIG. 8 firstly shows a schematic representation of a CIE standard color table 15 of the CIE standard valence system. The CIE standard valence system was defined in 1931 to establish a relationship between human color perception and the physical causes of the color stimulus and normally records the totality of all perceptible colors, where color perception is related to that of a defined normal observer. Each color or emission spectrum of a self-luminous object is represented by a unique xy coordinate in the CIE standard value table. The color coordinates of the signals Integrally measured luminescence as a function of the extinction time are represented in FIG. 8 by means of the elements with the reference numerals 140 to 147. At the same time, the data determined for a luminescent substance according to Embodiment Example 1 can be taken from the following table.

The color displacement that goes tendentially from the green to the red spectral region results from the superposition of the emission bands represented in figure 6 as well as from the differences and the superposition of the corresponding extinction curves represented in figure 7 of the luminescent substance according to exemplary embodiment 1. The described special quenching behavior makes a significant contribution to the uniqueness of the luminescent substance Ca3Sc2Si3O12:Ce3+,Mn2+ according to the invention.

Figure 9 shows the emission spectra 1123, 113 of the stationary photoluminescence of the luminescent substances excited at 450 nm according to embodiment examples 2 and 3. Figure 10 shows the associated extinction curves 132, 133 of the main bands emission of excited luminescent substances at 450 nm according to embodiment examples 2 and 3.

To produce the luminescent substance according to Embodiment Example 2, 0.2898 g CaCOa, 0.1362 g ScaOa, 0.1803 g SiOa, 0.0130 g Ce(NOa)3-6H2O, 0, are completely dissolved. 0.0179 g of MnC2O4-2HaO and 1.8170 g of tris(hydroxymethyl)aminomethane in a mixture of 10 ml of nitric acid and 100 ml of water with stirring and heating on a hot plate. The liquid is then evaporated until the remaining gel ignites and a black foam forms. This foam is first dried at 150 °C in a drying cabinet, then finely ground in a mortar and pestle and transferred to a porcelain crucible. In a first heating stage, the mixture is subjected to annealing for 2 h at 1000 °C in the air atmosphere of a chamber furnace in order to decompose the remaining organic residual constituent parts. The annealed material, which now has a white body color, is then mixed with 2% by mass boric acid and annealed again this time for 4 h at 1300 °C in a forming gas atmosphere at 5 %. The resulting luminescent substance has the composition (Ca2.895Ce0.03Mn0.075) (Sc1.975Mn0.025)Si3O12. Curve 112 of Figure 9 shows the emission spectrum of this luminescent substance. In FIG. 10, curve 132 designates the extinction curve of this luminescent substance, which preferentially emits in the green spectral region.

To produce the luminescent substance according to Embodiment Example 3 with the composition (Ca2.745Ce0.03Mn0.225) (Sc1.925Mn0.075)Si3O12, 0.2747 g of CaCO3, 0.1327 g of Sc2O3, 0 0.1803 g of SiO ² , 0.0130 g of Ce(NO3)3-6H2O, 0.0537 g of MnC2O4-2H2O and 1.8170 g of tris(hydroxymethyl)aminomethane in a mixture of 10 ml of nitric acid and 100 ml of water with stirring and heating. The liquid is then evaporated until the resulting gel ignites. The produced black foam is dried in a drying cabinet at 150°C, then finely ground in a mortar and pestle and transferred to a porcelain crucible. After an initial annealing of two hours at 1000 °C in the air atmosphere of a chamber furnace as well as the subsequent addition of two percent by mass of boric acid to the cooled annealed material, a new heat treatment is carried out. four hours at 1100°C in a 5% formation gas atmosphere. The emission spectrum of the obtained luminescent substance, measured at 450 nm excitation, is represented by curve 113 of FIG. 9, the associated extinction curve can be deduced from curve 133 of FIG. 10.

The two exemplary embodiments and the associated figures show once more clearly that the luminescent substances Ca3Sc2Si3O12:Ce3+,Mn2+ are a particularly suitable class of luminescent substances for the formation of a security feature according to with the invention. By varying the phosphor composition and the preparation conditions, numerous unique phosphor compositions with different quenching behavior and distinguishable emission spectra can be created and, for this reason, with a remarkably high level of security and authenticity. The unique properties of luminescent substances that can be used to protect valuable and security documents in the form of security features can be reliably verified with the help of commercially available smartphones.

Reference number list

01 security feature

02 security document / bank note

03 face value

04 lighting unit

05 -06 image registration unit

07 smartphone

08 flash

09 camera / detector

10 -11 emission curve

12 flash drive curve

13 security feature image record 01

14th start image

14b reference image

15 CIE standard color table

41 - 45 steps of the procedure

111 emission spectrum of the luminescent substance according to exemplary embodiment 1 112 emission spectrum of the luminescent substance according to exemplary embodiment 2 113 emission spectrum of the luminescent substance according to exemplary embodiment 3 121 spectrum excitation curve of the luminescent substance according to exemplary embodiment 1 1311 extinction curve for the emission at 505 nm of the luminescent substance according to exemplary embodiment 1

1312 extinction curve for emission at 570 nm of the luminescent substance according to exemplary embodiment 1

1313 extinction curve for emission at 700 nm of the luminescent substance according to exemplary embodiment 1

132 extinction curve of the predominantly green emission of the luminescent substance according to exemplary embodiment 2

133 extinction curve of the predominantly green emission of the luminescent substance according to exemplary embodiment 3

140 - 147 x-y color coordinates of the extinguishing integral luminescence of the luminescent substance according to exemplary embodiment 1

Claims (11)

1. Smartphone verifiable security feature with a luminescent substance that can be excited to luminescence by means of visible electromagnetic radiation generated by a smartphone and displays an emission that can be detected by means of an image recording unit of the smartphone, wherein the luminescent substance has been selected from the following group: - (Ca1-x-yCexMny)3(Sc1-z/Mnz)2Si3O12; with 0<x<0.1; 0<y<0.8; and 0<z<0.8; yy/z=2; - Ca3Sc2Si3O12:Ce3+,Mn2+; and where after termination of excitation, the luminescent substance shows emission for a decay time in the range of 1 ms to 100 ms. Safety feature according to claim 1, characterized in that after excitation the luminescent substance has an extinction time of 1 ms to 50 ms, preferably an extinction time of 10 ms to 30 ms, in which its emission in the visible spectral region exhibits a luminescence characteristic that can be detected by the image recording unit of the smartphone. Security feature according to claim 1 or 2, characterized in that the luminescent substance can be excited to luminescence by means of a white light-emitting flash LED of the smartphone. Security feature according to one of Claims 1 to 3, characterized in that during the extinction time the luminescent substance emits in the spectral region between 480 nm and 750 nm. Safety feature according to one of Claims 1 to 4, characterized in that the luminescent substance is configured as a luminescent substance mixture, the luminescent substance components of which have different extinction times that can be differentiated by detectors after the end of excitation. Security feature according to claim 5, characterized in that the luminescent substance mixture contains a rapidly extinguishing, UV-excited luminescent luminescent substance whose stationary, visually perceptible photoluminescence acts as a mask for the emission of the luminescent substance which serves as a security feature. Security feature according to one of Claims 1 to 6, characterized in that the phosphor is formed as phosphor pigments that can be processed in a printing process. Security feature according to claim 7, characterized in that the phosphor pigments represent a predetermined pattern in the security feature. 9. Arrangement for the verification of a security document (02), which includes: - a security feature (01), which has been applied in the security document (02), contains a luminescent substance that can be excited to emit and is designed according to one of claims 1 to 8, - a smartphone (07) with a lighting unit (04) for excitation of the luminescent substance of the security feature, with a camera (09) for detecting the emission of the luminescent substance after excitation has ended for a duration of predetermined quenching by recording a series of images and with a data processing unit for evaluation of the series of images, wherein the detected emission during the quenching time is compared with stored reference values to verify the security document. Arrangement according to claim 9, characterized in that an application (App) has been installed on the smartphone (07), which controls the lighting unit (04), the camera (09) and the data processing unit. Arrangement according to one of Claims 9 to 10, characterized in that the distance between the smartphone and the security document to be checked is selected to be less than or equal to the focus range of the smartphone.