TW202544219A - Red phosphor powder, luminescent element and luminescent device - Google Patents

Abstract

This invention provides a red phosphor powder with high luminescence efficiency despite its small particle size, as well as a light-emitting element and a light-emitting device having the aforementioned red phosphor powder. The red phosphor powder has main components comprising strontium (Sr), sulfur (S), and euthanasia (Eu), and the average primary particle size observed by SEM is less than 2.7 μm, and the crystallite diameter is less than 155 nm.

Description

Red phosphor powder, luminescent element and luminescent device

This invention relates to a red phosphor powder, a light-emitting element, and a light-emitting device.

Light-emitting elements that use light-emitting diodes (LEDs) that emit near-ultraviolet or blue light as light sources (excitation sources) and combine phosphors on them are widely used in various light-emitting devices such as lighting, backlighting of mobile terminals, and display devices (monitors).

In this light-emitting device, the phosphor absorbs the light emitted by the LED (emitted light) and emits light with a wavelength different from the absorbed light. Therefore, it can emit light with a different tone than the LED emitted light. For example, green light and/or red light can be obtained by combining a blue LED with a green phosphor and/or a red phosphor. Light-emitting elements with this configuration are used in displays and other applications. Furthermore, a phosphor refers to a substance that emits light (mainly visible light) during the process of returning to its ground state (a easing process) from a state excited by excitation light, electron beam, or other methods.

In recent years, with the advancement of display technology, mini LED displays and micro LED displays have attracted much attention. μLED displays consist of independent μLEDs as sub-pixels, representing red (R), green (G), and blue (B). Each package (unit) corresponding to a sub-pixel is separated by partitions (package walls) to prevent color mixing of light from adjacent packages. The package reflects the size of the sub-pixel and is extremely small, for example, less than 1000 μm on one side. An excitation source such as an LED is disposed on the bottom surface of the package, and a phosphor layer is disposed on top of it. The phosphor layer is manufactured by filling the package with phosphor powder.

Furthermore, the emitted light of a luminescent material varies depending on its composition. (Ca, Sr)S:Eu compounds have been proposed as red luminescent materials. Also, luminescent materials are mostly used in powder form, and powdered luminescent materials (luminescent powder) are generally synthesized using solid-state methods.

As a document disclosing this technology, Patent 1 discloses the following: Regarding the red luminescent material represented by the general formula (Ca _{_1-x}Sr_x )S:Eu (where 0 < x ≦ 1), CaCO _₃, SrCO _₃ and BaCO_₃ are wet-mixed and dried, then calcined at 850°C in a hydrogen sulfide atmosphere, followed by the addition of Eu _₂O, and calcined at 1000°C in an argon atmosphere to obtain the red luminescent powder represented by the general formula (Ca _{_{1- x}}Sr_{_x} )S:Eu, Ba (Please 2 of Patent 1, paragraphs [0011] and [0060], etc.).

On the other hand, a method for synthesizing phosphor powder using a liquid-phase method has also been proposed. As a document disclosing this technology, Patent 2 discloses a method for manufacturing a phosphor, comprising: a precursor formation step, which forms the phosphor precursor by a liquid-phase method; and a calcination step, which forms the phosphor by calcining the precursor (claim 1 of Patent 2). It also describes that: in the liquid-phase method, phosphors with high stoichiometric purity are easily obtained; even without a pulverization step, particles with small particle sizes can be obtained (paragraph [0028] of Patent 2). [Prior Art Documents][Patent Documents]

[Patent Document 1] International Publication No. 2013/021990 [Patent Document 2] Japanese Patent Application Publication No. 2007-106831

[Problem to be solved by the invention] It is known from the prior art that phosphor powders such as red phosphor powders can be synthesized by solid-phase or liquid-phase methods, and that the synthesized phosphor powders can be applied to applications such as μLED displays.

However, after investigation, the inventors found that there is room for improvement in the existing phosphor powder. Specifically, in displays such as μLED displays, each sub-pixel uses a different phosphor, namely, a red phosphor or a green phosphor. Therefore, a phosphor layer is made by filling each package corresponding to each sub-pixel with different phosphor powders.

On the other hand, the demand for high precision in displays has led to continuous miniaturization of package sizes. Correspondingly, this necessitates the miniaturization of phosphor powder. This is because coarse phosphor powder is difficult to uniformly fill into tiny packages. By using fine phosphor powder, it is possible to uniformly fill tiny packages and manufacture high-precision displays. Furthermore, using fine phosphor powder also offers the advantage of using inkjet printing processes, which can reduce costs.

However, conventional phosphor powders suffer from a problem where luminous efficiency decreases as particle size decreases. Therefore, it was previously difficult to obtain phosphor powders with both small particle size and high luminous efficiency. When the luminous efficiency of the phosphor powder is low, it cannot emit high-brightness light in light-emitting devices such as displays.

The inventors have conducted intensive research in view of this problem. As a result, they discovered a specific relationship between crystallite diameter and luminous efficiency in regions where the particle size of a red phosphor powder with a specified composition is relatively small. Moreover, they obtained the insight that even with a small particle size, luminous efficiency can be improved by reducing the crystallite diameter.

This invention is based on this understanding, and its objective is to provide a red phosphor powder with relatively small particle size but high luminous efficiency, as well as a light-emitting element and a light-emitting device comprising the aforementioned red phosphor powder. [Technical means for solving the problem]

This invention includes the following states (1) to (6). Furthermore, in this specification, the expression "~" includes the numerical values at both ends. That is, "X~Y" has the same meaning as "X or more, Y or less". Also, in this specification, any combination of preferred states can be used as long as technical matching can be achieved. For example, one of the preferred numerical ranges can be arbitrarily combined with the other.

(1) A red phosphor powder having main components including strontium (Sr), sulfur (S) and monium (Eu), with an average primary particle size of less than 2.7 μm and a crystallite diameter of less than 155 nm as observed by SEM.

(2) The red phosphor powder as described in (1) above, wherein the main component has a composition represented by the general formula (Ca _{1-x- y} Sr _x )S:Eu _y (where 0＜x≦1－y, 0＜y≦0.01).

(3) The red phosphor powder as described in (1) or (2) above, wherein the main component has a composition represented by the general formula (Ca _1-xy Sr _x )S:Eu _y (where 0＜x＜1－y, 0＜y≦0.01).

(4) The red phosphor powder of any of (1) to (3) above has an internal quantum efficiency (IQE) of 40% or more.

(5) A light-emitting element having a light source for generating excitation light and a red phosphor powder as described in any one of (1) to (4) above.

(6) A light-emitting device having a light-emitting element as described in (5) above. [Effects of the Invention]

According to the present invention, a red phosphor powder with small particle size but high luminous efficiency is provided, as well as a light-emitting element and a light-emitting device having the above-mentioned red phosphor powder.

The specific embodiments of the present invention (hereinafter referred to as "the embodiments") are described below. However, the present invention is not limited to the following embodiments, and various changes may be made without altering the spirit of the present invention.

<<1. Red Phosphor Powder>> The red phosphor powder (sometimes simply referred to as "phosphor powder") of this embodiment has a main component comprising strontium (Sr), sulfur (S), and eu. The main component preferably has a composition represented by the general formula (Ca _{_{1-x -y}}Sr_{_x} )S:Eu _{_y} (wherein 0 < x ≦ 1 - y, 0 < y ≦ 0.01), and more preferably has a composition represented by the general formula (Ca _{_1-xy}Sr_{_x})S:Eu_{_y} (wherein 0 < x < 1 - y, 0 < y ≦ 0.01). That is, the red phosphor powder is not limited, but preferably comprises a compound represented by the above general formula (the main component compound) as the main component. The main component compound has a rock salt-type crystal structure. Furthermore, in this specification, "main component" refers to a component (compound) present in the luminescent powder at a content of 50% by mass or more. The content of the main component may be 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more. Also, the luminescent powder may contain components other than Ca, Sr, S, and Eu. There are no limitations on such components; examples include at least one alkali metal from the group consisting of sodium (Na) and potassium (K).

The main component compounds of the phosphor powder include SrS-based compounds or (Ca,Sr)S-based compounds as the host crystals, and eutectic (Eu) as the luminescence center. When the compound is excited by irradiation light with wavelengths between 420 nm and 500 nm, it emits red light.

The host crystal must contain strontium (Sr). Alternatively, it can contain both calcium (Ca) and strontium (Sr) as essential components. However, the ratio of Ca to Sr is not limited. By adjusting the ratio of Ca to Sr in the host crystal, the maximum emission wavelength (peak emission wavelength) of the emitted light can be controlled. Specifically, when the host crystal is a CaS-based compound (x = 0), the maximum emission wavelength is 655 nm. When the host crystal is an SrS-based compound (x = 1 - y), the maximum emission wavelength is 620 nm. Therefore, by adjusting x within the range above 0 and below 1 - y, the maximum emission wavelength can be controlled within the range above 620 nm but below 655 nm.

Eu acts as the luminescent center. By appropriately including Eu, concentration quenching that would reduce luminescence intensity can be prevented, and higher luminescence efficiency can be obtained. From this perspective, the ideal Eu content, y, is greater than 0 and less than 0.01 (0 < y ≤ 0.01).

The average primary particle size of the red phosphor powder in this embodiment, as observed by SEM, is 2.7 μm or less. By reducing the particle size, miniaturization of the package and the resulting high precision of the display can be achieved. Furthermore, when filling the phosphor powder into the package, an inkjet process that reduces manufacturing costs can be used. In contrast, if the phosphor powder particle size is larger, it is difficult to fill it into the small package of the display and to use an inkjet process. The average primary particle size is preferably 2.2 μm or less, and more preferably 1.8 μm or less. On the other hand, by appropriately increasing the particle size of the phosphor powder, particle aggregation is suppressed, thereby improving the treatment efficiency of the phosphor powder. The average primary particle size is preferably 0.05 μm or more, and more preferably 0.1 μm or more. The average primary particle size is preferably 0.05 μm or more and 2.2 μm or less, and more preferably 0.1 μm or more and 1.8 μm or less.

The crystallite diameter of the red luminescent powder in this embodiment is 155 nm or less. According to the inventors, in the region where the average primary particle size of the red luminescent powder is small (2.7 μm or less), the luminescence efficiency increases with a smaller crystallite diameter. This should not be interpreted restrictively; it is speculated that the smaller the crystallite diameter, the fewer impurities in the luminescent powder. Furthermore, it is believed that the smaller the crystallite diameter and the greater the lattice strain, the less susceptible it is to the effects of temperature quenching. The crystallite diameter is preferably 150 nm or less, and more preferably 130 nm or less. On the other hand, powders with excessively small crystallite diameters may have lower luminescence efficiency. The crystallite diameter is preferably 90 nm or greater, and more preferably 100 nm or greater. From the perspective of improving luminescence efficiency, the crystallite diameter is preferably 90 nm or greater and 150 nm or less, and more preferably 100 nm or greater and 130 nm or less. Furthermore, the crystallite diameter is determined by analyzing the phosphor powder using X-ray diffraction.

Preferably, the internal quantum efficiency (IQE) of the phosphor powder is 40% or higher. Internal quantum efficiency is the efficiency with which a phosphor converts absorbed light into other types of light; it is a standard for luminous efficiency. By using phosphor powder with a higher IQE, the luminous intensity of light-emitting devices such as displays can be improved. An IQE of 45% or higher is preferred, and even more preferably 50% or higher. There is no upper limit to the IQE value.

The sphericity of phosphor powder is not limited, but it is preferably between 0.60 and 0.75, and more preferably between 0.63 and 0.72. Sphericity is an indicator of the roundness (sphericity) of the particles (phosphor particles) constituting the phosphor powder. If the particles constituting the phosphor powder have a shape close to a true sphere, the sphericity is close to 1; if they have a shape far from a true sphere, the sphericity is close to 0. By appropriately increasing the sphericity, the flowability of the powder is improved. Therefore, miniaturization of the package and high precision of the display can be achieved at a higher level. On the other hand, phosphor powder with excessively high sphericity may lead to increased manufacturing costs. By appropriately reducing the sphericity, manufacturing costs can be reduced.

Furthermore, the roundness is determined by SEM observation of the luminescent powder and image analysis of the obtained SEM images. Specifically, for the multiple particles constituting the powder, the area S and perimeter L of each particle in the two-dimensional projection image are measured. Then, the roundness of each particle is calculated according to the following formula (1), and the arithmetic mean is determined as the roundness of the luminescent powder.

[Equation 1]

<<2. Method for Manufacturing Red Phosphor Powder>> The red phosphor powder of this embodiment is not particularly limited in its manufacturing method within the scope of satisfying the above requirements. It can be synthesized by a solid-state method or by a liquid-phase method. However, phosphor powder synthesized by a liquid-phase method has the characteristics of higher crystallinity despite its fineness. In addition, it has the characteristics of higher sphericity and excellent flowability. Therefore, phosphor powder synthesized by a liquid-phase method is particularly suitable for use in μLED displays.

The following describes an example of a liquid-phase method for manufacturing red phosphor powder. The method includes the following steps: dissolving starting materials containing a strontium (Sr) source, a molybdenum (Eu) source, a sulfur (S) source, and an alkaline metal source in a solvent to prepare a starting material solution (starting material mixing step); subjecting the obtained starting material solution to heat treatment and solid-liquid separation treatment to obtain phosphor precursor powder (reaction step); and calcining the obtained phosphor precursor powder (calcination step). Details of each step are explained below.

<Raw Material Mixing Step> In the raw material mixing step, starting materials including strontium (Sr) source, ammonium (Eu) source, sulfur (S) source, and alkali metal source are dissolved in a solvent to prepare a starting material solution. The starting material may include a calcium (Ca) source. Here, the alkali metal is selected from at least one of the groups consisting of sodium (Na) and potassium (K). Among the alkali metal elements, the ionic radius of Na or K is close to that of Ca or Sr. Therefore, even if a phenomenon of Eu ³⁺ ion generation and Ca ²⁺ ion disappearance (Shotter defect) occurs in the fluorescent powder, Na ⁺ or K ⁺ ions occupy Ca ²⁺ lattice sites to compensate for the Schottky defect. As a result, it has the effect of shortening the afterglow time of the phosphor powder. In addition, the alkali metal acts as a flux in the following baking step.

As Sr, Ca, Eu, and alkali metal sources, chlorides, sulfates, nitrates, etc., can be used. As a sulfur (S) source, sulfur, sodium sulfide, potassium sulfide, and/or aminosulfonic acids, etc., can be used. Sodium sulfide and potassium sulfide also function as alkali metal sources. As a solvent, hydrocarbon solvents such as _heptane ( _C7H16 ) can be used. Additives can also be added to the solvent. Examples of additives include reducing agents such as oleylamine ( _C18H37N ). The dissolution of _the starting materials can be carried out using known methods. For example, a stirrer can be used to stir the solvent containing the starting materials.

<Reaction Steps> In the reaction steps, the obtained starting material solution is subjected to heat treatment and solid-liquid separation to obtain phosphor precursor powder. Through heating, the starting material in the solution reacts to form precipitates. The heating treatment is preferably carried out in an inert gas atmosphere such as nitrogen ( _N2 ) at a temperature between 200°C and 300°C. Subsequently, the precipitates are recovered from the solution through solid-liquid separation to obtain the phosphor precursor powder. Solid-liquid separation can be carried out using known methods such as filtration or centrifugation. Furthermore, the precipitates recovered during solid-liquid separation can be washed.

<Caking Step> In the calcination step, the luminescent precursor powder is calcined. Calcination yields luminescent powder with improved crystallinity. The calcination conditions are not particularly limited. However, it is preferably carried out at a temperature between 500°C and 1200°C. This allows for the acquisition of highly crystalline and fine luminescent powder. Furthermore, calcination is also preferably carried out in a sulfur atmosphere. This allows for the replenishment of sulfur even when the sulfur content in the luminescent precursor powder is insufficient.

<<3. Light-emitting element>> The light-emitting element of this embodiment includes a light source (excitation source) for generating excited light and the aforementioned red phosphor powder. The light source has the function of emitting light to the phosphor powder to excite the phosphor. As a light source, a blue light-emitting LED with a wavelength of 420 nm to 500 nm is more suitable. The arrangement of the phosphor powder and the light source is not limited, as long as the light from the light source is incident on the phosphor powder. For example, when the light-emitting element is applied to a μLED display, it is preferable to arrange the LED as the light source at the bottom of each package and fill the upper part with phosphor powder.

The light-emitting element may be a single powder containing red phosphor powder. Alternatively, it may contain red phosphor powder and other known phosphor powders. For example, it may contain red phosphor powder and green phosphor powder. It may also be a mixture of phosphor powders such as red phosphor powder and resin. As the resin, for example, one or more selected from thermoplastic resins, thermosetting resins, free radiation-curing resins, and two-component mixed-curing resins may be used.

<<4. Light-emitting device>> The light-emitting device of this embodiment includes the aforementioned light-emitting element. There is no limitation on the light-emitting element; examples include known applications such as lighting, backlighting for mobile terminals, and displays (display devices). Among these, μLED displays or small LED displays are particularly suitable, especially μLED displays. [Example]

The invention is further illustrated in detail using the following embodiments and comparative examples. However, the invention is not limited to the following embodiments.

(1) Synthesis of Fluorescent Powder [Comparative Example 1] In Comparative Example 1, fluorescent powder was synthesized by a solid-state method. Specifically, calcium carbonate ( _CaCO3 ) was calcined at 850°C for 4 hours in a hydrogen sulfide ( _H2S ) atmosphere to obtain calcium sulfide (CaS). Subsequently, the obtained calcium sulfide (CaS) was dry-mixed with _molybdenum oxide ( _Eu2O3 ) and molybdenum fluoride ( _EuF3 ), and the mixture was calcined at 1000°C for 4 hours in an argon (Ar) atmosphere to obtain a calcined product. The argon (Ar) flow rate during calcination was set to 1.0 L/min. The obtained calcined material was pulverized and classified using a jet mill (manufactured by Dec) under a fluid pressure of 12 MPa to obtain a fluoropolymer powder composed of CaS:Eu.

[Comparative Example 2] Except that the fluid pressure of the jet mill was changed to 0.3 MPa, the fluorescent powder of Comparative Example 2 was obtained in the same manner as Comparative Example 1.

[Comparative Example 3] In Comparative Example 3, luminescent powder was synthesized using a liquid-phase method. Specifically, strontium chloride ( _SrCl₂ ), calcium chloride ( _CaCl₂ ), sulfur (S), rum chloride ( _EuCl₃ ), and sodium chloride (NaCl) were prepared as starting materials. _Heptane ( _C₇H₁₆ ) and _oleylamine ( _{C₁₈H₃₇N} ) were prepared as solvents, and the starting materials were dissolved in the solvents to prepare a starting material solution. Furthermore, the amount of starting materials was adjusted to obtain luminescent powder having the composition shown in Table 2 below. The ratio of starting materials ( _SrCl₂ to NaCl) to solvents (heptane and oleylamine) was adjusted to 1000 parts by mass relative to 100 parts by mass of the total starting materials. Furthermore, the mixing ratio of heptane and oleylamine was adjusted to 150 parts by mass relative to 100 parts by mass of heptane.

Next, the obtained starting material solution was heated at 250°C for 0.5 hours under a nitrogen ( _N2 ) gas stream. Heating caused a reaction, forming a precipitate in the solution. The heated starting material solution was then subjected to solid-liquid separation using a centrifuge, and the obtained precipitate was washed with ethanol to obtain phosphor precursor powder.

The obtained phosphor precursor powder was placed together with sulfur (S) in a calcination furnace and calcined at 900°C for 2 hours under a nitrogen atmosphere. The nitrogen ( _N2 ) flow rate during calcination was set to 0.2 L/min. Phonogeneous powder was synthesized in this manner. Furthermore, the manufacturing conditions of the phosphor powder are shown in Table 1 below, and the characteristics of the phosphor powder are shown in Table 2 below.

[Examples 1-8 and Comparative Example 4] The manufacturing conditions of the luminescent powder were changed as shown in Tables 1 and 2 below. Otherwise, the luminescent powder was synthesized in the same manner as in Comparative Example 3. Furthermore, in Example 7, although an Sr source ( _SrCl₂ ) was used, a Ca source ( _CaCl₂ ) was not used.

[Table 1] Table 1 Manufacturing conditions of phosphor powder synthesis Ca/Sr Mörgüe Roasting conditions Temperature-Time gas flow Comparative example 1 solid phase method 10/0 1000℃ for 4 hours 1.0 L/min Comparative example 2 solid phase method 10/0 1000℃ for 4 hours 1.0 L/min Comparative example 3 Liquid phase method 5/5 900℃ for 2 hours 0.2 L/min Implementation Example 1 Liquid phase method 5/5 900℃ for 2 hours 0.2 L/min Implementation Example 2 Liquid phase method 6/4 950℃ for 1 hour 0.2 L/min Implementation Example 3 Liquid phase method 5/5 900℃ for 2 hours 0.5 L/min Implementation Example 4 Liquid phase method 5/5 900℃ for 2 hours 1.0 L/min Comparative example 4 Liquid phase method 5/5 900℃ for 2 hours 0.2 L/min Implementation Example 5 Liquid phase method 5/5 850℃ for 3 hours 0.2 L/min Implementation Example 6 Liquid phase method 5/5 900℃ for 2 hours 0.2 L/min Implementation Example 7 Liquid phase method 0/10 800℃ for 2 hours 1.0 L/min Implementation Example 8 Liquid phase method 0.5/9.5 700℃ for 2 hours 2.0 L/min

(2) Evaluation of phosphor powder The phosphor powders obtained in Examples 1 to 8 and Comparative Examples 1 to 4 were used as samples and their various characteristics were evaluated as follows.

<ICP Luminescence Analysis> The sample was completely dissolved using the acid decomposition method, and the content of each element was confirmed by the calibration curve method using an ICP emission spectrometry analyzer (Hitachi High-Tech Science, PS3520UVDDII).

<SEM Observation (Average First-Order Particle Size)> The average first-order particle size (SEM diameter) of the fluorescent powder was determined. First, the fluorescent powder was observed using a scanning electron microscope (SEM) to obtain SEM images. Observation was performed at magnifications of 1000–3000x. Next, the SEM images were analyzed using image-resolution particle size distribution measurement software (MOUNTECH, Mac-View, Version 4, File Version: v 1.0.0.14) to determine the particle size (Heywood diameter) of the particles constituting the powder. At this stage, at least 300 particles were selected from areas where they did not overlap for analysis. Next, based on the obtained particle size, a volume-based particle size distribution is obtained. Then, the particle size at the center of the particle size distribution is determined as the average first-order particle size (D50).

<SEM Observation (Roundness)> The roundness of the phosphor powder is determined based on the SEM image obtained during the first particle size measurement. Specifically, the SEM image is analyzed using image resolution particle size distribution measurement software to measure the area S and perimeter L of the two-dimensional projection image of the particles constituting the powder. At this time, more than 300 particles are selected for measurement in areas where the particles do not overlap. Then, the roundness of each particle is calculated according to the above formula (1), and the arithmetic mean is determined as the roundness of the phosphor powder.

<XRD Analysis (Crystal Diameter, Lattice Strain)> The phosphor powder was analyzed by X-ray diffraction (XRD) to obtain the XRD pattern. The XRD analysis was performed under the following conditions.

- X-ray diffraction apparatus: Multifunctional horizontal high-output X-ray diffraction apparatus (RIGAKU Corporation, RINT-TTRIII) - Radiation source: CuKα (X-ray wavelength: 0.154056 nm) - Detector: D/teX Ultra 2 - Scanning axis: 2θ/θ - Scanning range: 5–120 degrees - Step size: 0.01 degrees - Scanning speed: 1 degree/minute - Entrance slit: 2/3° - Tube voltage: 50 kV - Tube current: 300 mA

Furthermore, SRM660a (compound name: LaB6) manufactured by NIST (National Institute of Standards and Technology) was measured under the same conditions. The obtained XRD patterns were analyzed using integrated powder X-ray analysis software (RIGAKU Inc., PDXL) in the following order: First, the software's automatic search function was used to identify LaB6, and the peak shape model function was the "segmented PearsoVII function". Next, from the "Basic" column, "Precision Parameter Settings" → "Method" → "Intensity Decomposition" was selected. Then, refinement was performed. During refinement, various parameters were set before convergence. This was saved as a width standard data file.

Next, the crystallite diameter and lattice strain were calculated based on the XRD patterns obtained from each phosphor powder. The analysis was performed using integrated powder X-ray analysis software (RIGAKU Inc., PDXL) in the following order: First, the crystalline phase was identified using the software's automatic search function. Next, intensity decomposition was performed using WPPF. As a line correction, a width standard data file was selected to correct the peak angle and width. The peak shape model function used was the "segmented PearsoVII function". Next, from the "Basic" column, "Precision Parameter Settings" → "Method" → "Intensity Decomposition" was selected. Then, refinement was performed. During refinement, various parameters were set before convergence.

<Luminescence Properties (Absorptivity, Quantum Efficiency)> Using a fluorescence spectrophotometer (JASCO, FP-8700DS), the absorptivity (Abs) and internal quantum efficiency (IQE) of the luminescent powder were calculated according to the quantum efficiency calculation program. The calculation formulas for absorptivity and internal quantum efficiency are shown below.

P1(λ) is taken as the LED light spectrum at 450 nm, and P2(λ) is taken as the sample spectrum. The area L1 enclosed by spectrum P1(λ) within the excitation wavelength range of 430 nm to 500 nm is calculated according to equation (i), and the obtained value is taken as the excitation intensity. The area L2 enclosed by spectrum P2(λ) within the excitation wavelength range of 430 nm to 500 nm is calculated according to equation (ii), and the obtained value is taken as the sample scattering intensity. The area E2 enclosed by spectrum P2(λ) within the excitation wavelength range of 500 nm to 850 nm is calculated according to equation (iii), and the obtained value is taken as the sample fluorescence intensity.

[Equation 2]

The absorptivity (Abs) is the ratio of the amount of incident light reduced due to the sample in the excitation light, and is calculated according to the following formula (iv). Furthermore, the internal quantum efficiency (IQE) is the value obtained by dividing the number of lattice particles (Nem) of the fluorescence emitted by the sample by the number of photons (Nabs) of the excitation light absorbed by the sample, and is calculated according to the following formula (v).

[Equation 3]

(3) Evaluation results Regarding the phosphor powders of Examples 1 to 8 and Comparative Examples 1 to 4, the evaluation results obtained are summarized in Table 2 below.

The luminescent powders of Examples 1 to 8 meet the composition (0 < x ≦ 1 - y, 0 < y ≦ 0.01), average primary particle size (2.7 μm or less), and crystallite diameter (155 nm or less) specified in this embodiment. These luminescent powders emit red light with a peak emission wavelength of 627.0–650.6 nm. Furthermore, they exhibit a high internal quantum efficiency (IQE) of 40% or more. In particular, Examples 1, 2, 4, 5, 7, and 8, with crystallite diameters of 150 nm or less, have an IQE of 48% or more, while Examples 2, 4, 5, and 8, with crystallite diameters of 130 nm or less, have an IQE of 50% or more.

In contrast, Comparative Example 1 does not contain Sr and does not meet the composition specified in this embodiment. Comparative Examples 2 and 3 have larger average primary particle size and crystallite diameter, which do not meet the range specified in this embodiment. Therefore, Comparative Examples 2 and 3 have lower IQE, ranging from 36% to 37%.

On the other hand, Comparative Example 4, which has a larger average primary particle size and crystal diameter, has a relatively high IQE of 47%. However, due to the larger average primary particle size, it may be difficult to uniformly fill the tiny packages. Therefore, it is not ideal in terms of achieving high precision in displays.

[Table 2] Characteristics of Phosphor Powder Elemental analysis Composition SEM observation XRD Luminescence properties Ca (mol%) Sr (mol%) Eu (mol%) x y Average primary particle size (μm) Roundness Microcrystal diameter (nm) Peak wavelength (nm) Abs (%) IQE (%) Comparative example 1 99.63 0 0.37 0 0.0037 1.288 0.58 42.2 655.0 53 9 Comparative example 2 99.63 0 0.37 0 0.0037 8.800 0.60 86.4 655.0 76 37 Comparative example 3 43.84 55.82 0.35 0.5582 0.0035 1.309 0.62 155.9 644.0 65 36 Implementation Example 1 45.26 54.44 0.30 0.5444 0.0030 1.679 0.68 135.7 643.6 62 48 Implementation Example 2 60.00 39.69 0.31 0.3969 0.0031 2.003 0.65 128.0 646.6 59 50 Implementation Example 3 56.79 42.92 0.29 0.4292 0.0029 2.047 0.70 150.6 650.0 43 40 Implementation Example 4 57.83 41.89 0.28 0.4189 0.0028 1.314 0.66 110.5 647.0 50 59 Comparative example 4 54.41 45.25 0.35 0.4525 0.0035 4.471 0.73 163.2 647.4 76 47 Implementation Example 5 62.68 36.95 0.37 0.3695 0.0037 1.388 0.63 126.9 650.6 62 53 Implementation Example 6 58.30 41.41 0.29 0.4141 0.0029 2.692 0.72 151.4 646.6 62 49 Implementation Example 7 0.00 99.82 0.18 0.9982 0.0018 0.996 0.68 147.2 627.0 55 52 Implementation Example 8 16.79 82.86 0.35 0.8286 0.0035 1.115 0.83 96.4 629.0 82 59 Note 1) The elemental analysis value (unit: moles%) is the value obtained by dividing the wt% of the ICP result by the atomic weight.

SEM images of the luminescent powders of Comparative Example 1 and Example 5 are shown in Figures 1 and 2, respectively. The primary particle size of the luminescent powder of Comparative Example 1 synthesized by the solid-phase method and the luminescent powder of Example 5 synthesized by the liquid-phase method are both about 1 μm. However, the particle shape of the luminescent powder of Comparative Example 1 is relatively amorphous, while the particle shape of the luminescent powder of Example 5 is close to that of a sphere.

From the above results, it can be understood that, according to this embodiment, a red phosphor powder with a small particle size but high luminous efficiency is provided, as well as a light-emitting element and a light-emitting device having the above-mentioned red phosphor powder.

Figure 1 shows an SEM image of the phosphor powder (Comparative Example 1). Figure 2 shows an SEM image of the phosphor powder (Example 5).

Claims (6)

A red phosphor powder containing strontium (Sr), sulfur (S) and monium (Eu) as its main components, with an average primary particle size of less than 2.7 μm and a crystallite diameter of less than 155 nm as observed by SEM. The red phosphor powder of claim 1, wherein the main component has a composition represented by the general formula (Ca _{1-x -y} Sr _x )S:Eu _y (where 0＜x≦1－y, 0＜y≦0.01). The red phosphor powder of claim 1 or 2, wherein the main component has a composition represented by the general formula (Ca _{1-x -y} Sr _x )S:Eu _y (where 0＜x＜1－y, 0＜y≦0.01). For example, the red phosphor powder in Request 1 or 2 has an internal quantum efficiency (IQE) of 40% or higher. A light-emitting element comprising a light source for generating excitation light and a red phosphor powder as claimed in claim 1 or 2. A light-emitting device having a light-emitting element as claimed in claim 5.