Phosphor powder, composition containing phosphor, light-emitting element and light-emitting device

Abstract

This invention provides a phosphor powder with sufficiently high absorption rate and high internal quantum efficiency, a composition containing phosphor, a light-emitting element, and a light-emitting device. The phosphor powder, measured by laser diffraction particle size distribution method, has a total volume frequency of particles with a diameter less than 2.5 μm of 10% or more, and a total volume frequency of particles with a diameter between 2.5 μm and 10 μm of 10% or more but less than 90%, resulting in a cumulative 50% particle size (D50) of 10.0 μm or less in the volume particle size distribution.

Description

Technical Field

[0001] This invention relates to a phosphor powder, a composition containing phosphor, a light-emitting element, and a light-emitting device. Prior Technology

[0002] Light-emitting diodes (LEDs) that emit near-ultraviolet or blue light are used as light sources (excitation sources) and combined with phosphors. These light-emitting elements are widely used in various light-emitting devices such as lighting, backlighting of mobile terminals, and displays.

[0003] 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, light with a hue different from the emitted light can be obtained. For example, by combining a blue LED with a yellow phosphor, white light can be obtained. Light-emitting elements emitting this type of white light (white LEDs) are often used in lighting applications. Furthermore, by combining a blue LED with a green or red phosphor, green or red light can be obtained; such light-emitting elements are used in displays and other applications.

[0004] As a phosphor material for LEDs, for example, Patent Document 1 discloses a green phosphor containing: an element comprising one or more combinations of Sr, Ba, and Ca, a parent crystal of Ga and S; and a light-emitting center (claim 1 of Patent Document 1). Furthermore, it describes the use of this green phosphor for lighting or display purposes (claim 1 of Patent Document 1). Also, Patent Document 2 discloses a β-type silane with Eu dissolved in it, represented by the general formula Si 6-zAl zO zN 8-z, which can be used in light-emitting devices such as light-emitting diodes that utilize blue or ultraviolet light (claims 1 and

[0001] of Patent Document 2).

[0005] In recent years, with the advancement of display technology, small LED displays and micro LED displays have received increasing attention. In micro LED displays, the R (red), G (green), and B (blue) sub-pixels are each composed of independent light-emitting diodes (LEDs). Compared to LCD panels, micro LED displays have the advantages of achieving higher brightness and higher contrast ratio images with faster response times and lower power consumption. Furthermore, compared to organic EL (electroluminescence) displays, they are characterized by the ability to display images with higher brightness and without image retention caused by image degradation.

[0006] Patent Document 3 discloses a micro-LED display device comprising a micro-LED driving substrate and a micro-LED panel (claim 1 of Patent Document 3). Furthermore, Patent Document 3 describes that the micro-LED panel includes a light-emitting structure (a plurality of micro-LED pixels), a growth substrate on the light-emitting structure, a plurality of spacers on the growth substrate, and R / G / B color conversion material located between the spacers. The R / G / B color conversion material (or R / G / B phosphor) is disposed between the spacers to convert the wavelength of light emitted by each light-emitting element (pixel) (

[0022] and

[0034] of Patent Document 3). [Previous Technical Documents] [Patent Literature]

[0007] [Patent Document 1] International Publication No. 2009 / 136505 [Patent Document 2] Japanese Patent Application Publication No. 2012-056804 [Patent Document 3] Japanese Patent Application Publication No. 2018-182282 Summary of the Invention

[0008] [The problem the invention aims to solve]

[0009] Phosphors for LEDs, especially those for micro LED displays, require high luminous intensity and excellent color emission. High luminous intensity enables efficient color conversion of the LED emitted light. Therefore, high internal quantum efficiency (IQE) and external quantum efficiency (EQE) are important. Furthermore, to obtain excellent color emission, a narrow emission spectrum is important to prevent blue light from passing through; therefore, a high absorptivity (Abs) is sought. Here, external quantum efficiency refers to the efficiency of converting light irradiated by the phosphor into other colors, while internal quantum efficiency refers to the efficiency of converting light absorbed by the phosphor into other colors. Absorptivity is the ratio of light absorbed by the phosphor in the irradiated light. External quantum efficiency (EQE), internal quantum efficiency (IQE), and absorptivity (Abs) satisfy the following relationship (1).

[0010] [Number 1]

[0011] As shown in equation (1) above, the external quantum efficiency (EQE) of a phosphor is represented by the product of the internal quantum efficiency (IQE) and the absorptivity (Abs). Therefore, in order to obtain an excellent phosphor, it is ideal to improve both the internal quantum efficiency and the absorptivity of the phosphor.

[0012] In particular, compared to previous white LED phosphors, phosphors for micro-LED displays are crucial in simultaneously improving quantum efficiency and absorptivity. Specifically, in previous white LEDs, which combined a blue LED with a phosphor layer containing a yellow phosphor, as shown in Figure 1, a portion of the LED's emitted light passes through the phosphor, thus producing white light. Furthermore, the phosphor layer is relatively thick, several millimeters, and does not need to absorb all the LED's emitted light, therefore the absorptivity does not need to be excessively high. In contrast, for phosphors used in micro-LED displays, a more ideal approach is as shown in Figures 2A and 2B, where color conversion occurs by having all the blue light emitted by the LED absorbed and excited by phosphor layers containing green and red phosphors. Furthermore, the phosphor layer is relatively thin, ranging from tens to hundreds of micrometers. That is, even with a thinner phosphor layer, sufficient absorption of emitted light is still required; therefore, improving the phosphor's absorptivity is crucial.

[0013] However, it is previously known that for fluorescent powders, the larger the particle size of the particles contained in the powder, the higher the internal quantum efficiency and absorption rate. Therefore, techniques for removing microparticles have been proposed. For example, Patent Document 1 describes that by limiting D10 to 4.5 μm or more, the absorption rate of fluorescent particles can be made to 70% or more, thereby improving the external quantum efficiency of fluorescent particles (Patent Document 1

[0013] ). Furthermore, Patent Document 2 describes that the average particle diameter D50 is preferably 5 μm or more and 30 μm or less. If the average particle diameter D50 is too small, the luminous efficiency will be low. And by performing water fractionation after particle size adjustment, microparticles smaller than 5 μm are removed (Patent Document 2

[0023] and

[0031] ).

[0014] However, the inventors discovered that while coarse particles in the pure powder state result in higher phosphor absorption, fine particles can also improve absorption when the phosphor-containing composition, formed by dispersing the particles in resin, is filled into an LED package (unit). Further research by the inventors yielded the following insight: filling the LED package with a phosphor-containing composition that includes medium-diameter particles in addition to fine particles can significantly improve absorption and internal quantum efficiency.

[0015] The present invention was made based on this insight, and the objective is to provide a phosphor powder with sufficiently high absorption rate and high internal quantum efficiency, a composition containing phosphor, a light-emitting element, and a light-emitting device. [Technical means to solve the problem]

[0016] The present invention provides a phosphor powder in which the total volume frequency of particles with a diameter less than 2.5 μm, as measured by laser diffraction particle size distribution method, is 10% or more, and the total volume frequency of particles with a diameter between 2.5 μm and 10.0 μm is 10% or more and less than 90%, thereby the cumulative 50% particle size (D50) in the volume particle size distribution is less than 10.0 μm.

[0017] Furthermore, the present invention provides a composition containing a phosphor, which comprises the above-mentioned phosphor powder.

[0018] Furthermore, in this specification, the expression "~" includes both ends. That is, "X~Y" has the same meaning as "X above and Y below". [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a phosphor powder with sufficiently high absorption rate and high internal quantum efficiency, a composition containing phosphor, a light-emitting element, and a light-emitting device. Simple Explanation of the Diagram

[0020] Figure 1 is a diagram illustrating the phosphor used in the previous white LED. Figure 2 is a diagram illustrating phosphors used in micro LEDs. Figure 3 shows the particle size distribution (volume frequency distribution curve) of the phosphor powder (Example 1 and Comparative Example 1). Figure 4 shows the particle size distribution (volume frequency distribution curve) of the phosphor powder (Example 2 and Comparative Example 1). Figure 5 shows the particle size distribution (volume frequency distribution curve) of the phosphor powder (Example 3 and Comparative Example 1). Figure 6 shows the particle size distribution (volume frequency distribution curve) of the phosphor powder (Example 4 and Comparative Example 1). Figure 7 shows the particle size distribution (volume frequency distribution curve) of the phosphor powder (Example 5 and Comparative Example 1). Figure 8 shows the particle size distribution (volume frequency distribution curve) of the phosphor powder (Example 6 and Comparative Example 1). Figure 9 shows the particle size distribution (volume frequency distribution curve) of the phosphor powder (Example 7 and Comparative Example 1). Figure 10 shows the particle size distribution (volume frequency distribution curve) of the phosphor powder (Example 8 and Comparative Example 1). Figure 11 shows the particle size distribution (volume frequency distribution curve) of the phosphor powder (Example 9 and Comparative Example 1). Figure 12 shows the particle size distribution (volume frequency distribution curve) of the phosphor powder (Example 10 and Comparative Example 1). Figure 13 shows the particle size distribution (volume frequency distribution curve) of the phosphor powder (Example 11 and Comparative Example 1). Figure 14 shows the particle size distribution (volume frequency distribution curve) of the phosphor powder (Example 12 and Comparative Example 1). Implementation

[0021] Specific embodiments of the present invention (hereinafter referred to as "this embodiment") will be described. Furthermore, the present invention is not limited to the following embodiments, and various modifications can be made without altering the spirit of the invention.

[0022] <<1. Fluorescent Powder>> In this embodiment, the total volume frequency of particles with a diameter less than 2.5 μm (hereinafter, sometimes referred to as "fine particles") in the phosphor powder, as measured by laser diffraction particle size distribution method, is 10% or more, and the total volume frequency of particles with a diameter of 2.5 μm to 10 μm (hereinafter, sometimes referred to as "medium-diameter particles") is 10% to 90% or less. Furthermore, the cumulative 50% particle size (D50) in the volume particle size distribution of this phosphor powder is 10.0 μm or less. The phosphor powder of this embodiment contains fine particles and medium-diameter particles in an appropriate ratio.

[0023] The phosphor powder has a small D50 and a relatively wide particle size distribution. This, in turn, improves the absorption rate and internal quantum efficiency. Furthermore, in this specification, "powder" refers to an aggregate of multiple particles that exhibit overall fluidity. It can also be described as a powder composed of multiple particles.

[0024] Regarding the phosphor powder, the total volume frequency of particles with a diameter of less than 2.5 μm (fine particles) is limited to 10% or more. Increasing the proportion of fine particles improves the absorption rate of the phosphor-containing composition filled into the LED package. Conversely, if the proportion of fine particles is less than 10%, the absorption rate is low, and phosphors with excellent emission color cannot be obtained. The total volume frequency of fine particles is preferably 20% or more, more preferably 30% or more, and even more preferably 40% or more. On the other hand, if the proportion of fine particles is too high, the proportion of medium-diameter particles may decrease, potentially reducing internal quantum efficiency. The total volume frequency of fine particles is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less. Furthermore, the total volume frequency of fine particles can be calculated by measuring the particle size distribution of the phosphor powder, obtaining the frequency distribution curve based on the volume (mass) standard, and then summing the frequencies of particles with a diameter of less than 2.5 μm in the frequency distribution curve.

[0025] Regarding the phosphor powder, the total volume frequency of particles with a diameter of 2.5 μm to 10 μm (medium-diameter particles) is limited to 10% to 90%. Increasing the proportion of medium-diameter particles to a certain level improves the internal quantum efficiency during LED package filling. Conversely, if the proportion of medium-diameter particles is less than 10%, the internal particle efficiency decreases, making it difficult to improve the phosphor's luminous intensity. The total volume frequency of medium-diameter particles is preferably 15% or more, more preferably 20% or more, and even more preferably 30% or more. On the other hand, if the proportion of medium-diameter particles is too high, the proportion of fine particles may decrease, leading to a reduction in absorption rate. The total volume frequency of medium-diameter particles is preferably 80% or less, more preferably 70% or less, and even more preferably 60% or less.

[0026] Regarding the phosphor powder, the total volume frequency of particles with a diameter exceeding 10 μm (coarse particles) is preferably between 0% and 50%. By setting the proportion of coarse particles to 50% or less, the filling performance of the LED package is better, and the uniformity of the phosphor powder filling is better guaranteed. The total volume frequency of coarse particles is preferably below 40%, more preferably below 30%, and particularly preferably below 20%.

[0027] The D50 of the phosphor powder in the volumetric particle size distribution is limited to 10.0 μm or less. In previous technologies, quantum efficiency was improved by removing smaller particles from the phosphor powder to achieve a particle size distribution containing only larger particles. In contrast, the phosphor powder in this embodiment is densely formed in the composition when the phosphor-containing composition is prepared by reducing the average particle size and widening the particle size distribution. This improves the absorption rate and internal quantum efficiency when the LED package is filled. Furthermore, it is easier to manufacture a thinner design that meets the requirements of small LED or micro LED display applications. If D50 exceeds 10.0 μm, there is a risk of reduced absorption rate. D50 is preferably 9.0 μm or less, more preferably 8.0 μm or less, and even more preferably 7.0 μm or less. On the other hand, if D50 is too small, the proportion of medium-diameter particles decreases, and the internal quantum efficiency decreases. D50 is preferably 1.0 μm or more, more preferably 2.0 μm or more, and even more preferably 3.0 μm or more. Furthermore, D50 can be used to determine the cumulative distribution curve of the phosphor powder based on the volume (mass) ratio, and is used as the 50% particle size in the cumulative distribution curve.

[0028] Preferably, when the volume frequency distribution curve is normalized with the common logarithm of particle size as the horizontal axis and volume frequency as the vertical axis, and the maximum volume frequency is 1, the area enclosed by the volume frequency distribution curve and the horizontal axis, i.e., the peak area, is 12 or more, more preferably 13 or more. Here, the peak area represents the width of the particle size distribution. The smaller the peak area, the narrower the particle size distribution; conversely, the larger the peak area, the wider the particle size distribution. By widening the particle size distribution of the phosphor powder, particles of sizes other than the desired particle size can be included in the phosphor powder, and when filling the LED package, both absorption rate and internal quantum efficiency can be obtained to a greater extent. From the point of view of absorption rate and quantum efficiency, the larger the peak area, the better. The peak area is preferably 16 or more, and more preferably 18 or more. Regarding the upper limit of the peak area, considering both absorption rate and internal quantum efficiency, it is preferably 80.

[0029] Furthermore, the peak area can be calculated as follows. First, obtain the frequency distribution curve of the phosphor powder based on volume. This frequency distribution curve is plotted with the common logarithm of particle size (unit: μm) (base 10 logarithm) on the horizontal axis and the frequency based on volume (volume frequency) on the vertical axis. Then, it is standardized so that the maximum value of the frequency distribution curve is 1. Next, the area enclosed by the frequency distribution curve and the horizontal axis is calculated and taken as the peak area.

[0030] Preferably, the particle size distribution ratio ((D80-D20) / D50) representing the cumulative 20% particle size (D20), cumulative 50% particle size (D50), and cumulative 80% particle size (D80) in the volumetric particle size distribution measured by laser diffraction scattering particle size distribution method is 0.7 or higher, more preferably greater than 0.8. Here, the particle size distribution ratio ((D80-D20) / D50) is a standard indicating the width of the particle size distribution. The smaller the particle size distribution ratio, the narrower the particle size distribution; conversely, the larger the particle size distribution ratio, the wider the particle size distribution. From the viewpoint of absorption rate and quantum efficiency, a larger particle size distribution ratio is more desirable. The particle size distribution ratio is preferably 1.0 or higher, and more preferably 1.2 or higher.

[0031] Regarding the aforementioned D20, it is preferably less than D50 or D80, and more preferably 1 μm or more and 5 μm or less, and even more preferably 1.5 μm or more and 3 μm or less. Furthermore, regarding D80, it is preferably greater than D20 or D50, and more preferably 3 μm or more and 13 μm or less, and even more preferably 5 μm or more and 10 μm or less.

[0032] The fluorescent powder in this embodiment only needs to exhibit fluorescence, and its material composition is not limited. Fluorescent materials consist of a matrix crystal and luminescent centers (activators), and are mostly formed by dissolving a few percent of luminescent centers in a suitable matrix crystal. As fluorescent materials, oxide-based, sulfide-based, oxysulfide-based, nitride-based, and oxynitride-based materials are known, and any of these materials can be used.

[0033] For example, as oxide-based fluorescent materials, examples include: (Y,Gd,Lu)3(Al,Ga)5O12:Ce3+, (Ba,Sr,Ca)2SiO4:Eu2+, (Ba,Sr,Ca)3MgSi2O8:Eu2+, CaAl12O19:Mn4+, Ca3Sc2Si3O12:Ce3+, CaSc2O4:Ce3+, (Ba,Sr)3SiO5:Eu2+, Li2SrSiO4:Eu2+, Ba9Sc2Si6O24:Eu2+, Ca3Si2O7:Eu2+, LiSrPO4:Eu2+, CaLa4Si3O13:Eu3+, Ba2Gd3Li 3Mo 8O 32:Eu 3+ and BaMgAl 10O 17:Eu 2+, Mn 2+, etc.

[0034] Examples of sulfide-based fluorescent materials include: (Ba,Sr,Ca)Ga₂S₄:Eu²⁺, (Ba,Sr,Ca)Ga₂S₄:Ce³⁺, (Sr,Ca)S:Eu²⁺, (Sr,Cd)S:Eu²⁺, and ZnS:Cu.

[0035] Examples of oxysulfide-based fluorescent materials include (La,Y)₂O₂S:Eu³⁺, La(Ca,Sr)Ga₃S₆O:Eu²⁺, and La₂O₃S:Eu³⁺.

[0036] Examples of nitride-based fluorescent materials include: (Ba,Sr,Ca)₂Si₅N₈:Eu²⁺, (Ba,Ca,Sr)AlSiN₃:Eu²⁺, La₃Si₆N₁₁:Ce³⁺, (Ba,Sr,Ca)LiAl₃N₄:Eu²⁺, Sr(Mg₃SiN₄):Eu²⁺, and (Ba,Sr)₂Si₅N₈:Eu²⁺.

[0037] Examples of nitrogen oxide-based fluorescent materials include: α-type silane containing Eu, β-type silane containing Eu, Ba 9Sc 3Si 6O 21N 3:Eu 2+, Ba 3Si 6O 12N 2:Eu 2+, BaSi 2O 2N 2:Eu 2+, and (Ba,Sr,Ca)AlSi(ON) 3:Eu 2+, etc.

[0038] Other examples of fluorescent materials include Sr10(PO4)6C12:Eu2+ and K2(Si,Ge,Ti)F6:Mn4+.

[0039] According to a preferred embodiment, as shown in the composition listed above as a sulfide-based fluorescent material, the phosphor powder comprises: a parent crystal containing at least one metallic element selected from the group consisting of barium (Ba), strontium (Sr), and calcium (Ca), and gallium (Ga) and sulfur (S); and a luminescent center. The luminescent center preferably comprises at least one element selected from the group consisting of europium (Eu), cerium (Ce), manganese (Mn), and samarium (Sm). From the viewpoint of further improving the internal quantum efficiency under the excitation of blue light generated by the LED, the luminescent center preferably contains Eu, more preferably contains divalent Eu ions (Eu²⁺), and even more preferably contains only Eu²⁺. More preferably, the phosphor powder comprises crystals represented by the general formula: MGa₂S₄:Eu²⁺ (wherein M is at least one element selected from the group consisting of Ba, Sr, and Ca). Phosphor powders with this composition exhibit green luminescence when excited by light in the near-ultraviolet to blue region (around 300 nm to 510 nm).

[0040] According to a preferred embodiment, as shown in the compositions listed above for sulfide-based fluorescent materials, the phosphor powder comprises: a parent crystal containing at least one metallic element selected from the group consisting of barium (Ba), strontium (Sr), and calcium (Ca), and sulfur (S); and a luminescent center. Preferably, the luminescent center comprises at least one element selected from the group consisting of europium (Eu), cerium (Ce), manganese (Mn), and samarium (Sm). More preferably, the phosphor powder comprises crystals represented by the general formula: MS:Eu²⁺ (where M represents at least one element selected from the group consisting of Ba, Sr, and Ca). The phosphor powder having this composition exhibits red luminescence upon excitation with light of wavelengths (approximately 250 nm to 610 nm) in the ultraviolet to visible light region.

[0041] Regarding the ratio of luminescent centers in the phosphor powder, from the viewpoint of thereby improving luminescence intensity, the ratio (XA / (XM+XA)) of the molar amount XA of element A (a luminescent element) to the sum of the molar amounts XM of element M and XA of element A contained in the phosphor powder (XM+XA) is preferably 0.05 or more, more preferably 0.07 or more, and more preferably 0.10 or more. Furthermore, from the viewpoint of preventing concentration quenching, XA / (XM+XA) is preferably 0.30 or less, more preferably 0.25 or less, and more preferably 0.20 or less.

[0042] The phosphor powder may or may not have a surface coating. However, by providing a coating, durability such as moisture resistance can be improved. From the viewpoint of improving durability and maintaining the good luminescence properties of the phosphor, the coating is preferably one or more inorganic compounds including silicon dioxide (SiO2), zinc oxide (ZnO), aluminum oxide (Al2O3), titanium oxide (TiO2), and / or oxides containing boron (B), metal sulfates such as barium sulfate (BaSO4).

[0043] When the phosphor powder of this embodiment is filled into an LED package, it exhibits sufficiently high absorptivity and internal quantum efficiency. Therefore, the external quantum efficiency, which is the product of absorptivity and internal quantum efficiency, is high. Thus, a phosphor with high luminous intensity and excellent emission color can be obtained.

[0044] <<2. Manufacturing Method of Fluorescent Powder>> The phosphor powder of this embodiment only needs to meet the above requirements, and its manufacturing method is not limited. Preferably, it is produced by synthesizing coarse phosphor powder from raw materials, and then subjecting the coarse phosphor powder to particle size adjustment treatments such as crushing and grading. Hereinafter, an example of a preferred manufacturing method of phosphor powder will be described.

[0045] First, a raw material mixture is obtained by weighing and mixing at least one of strontium (Sr), barium (Ba), and calcium (Ca), as well as gallium (Ga), sulfur (S), and europium (Eu). As strontium (Sr), barium (Ba), and calcium (Ca) raw materials, oxides, complex oxides, and / or carbonates of each element can be used. As gallium (Ga) raw material, oxides (Ga₂O₃, GaO) can be used. As sulfur (S) raw material, strontium sulfide (SrS), barium sulfide (BaS), calcium sulfide (CaS), sulfur (S), silicon sulfide (SiS₂), cerium sulfide (Ce₂S₃), hydrogen sulfide (H₂S) gas, etc., can be used. As europium (Eu) raw material, europium compounds such as europium fluoride (EuF₃), europium oxide (Eu₂O₃), and europium chloride (EuCl₃) can be used.

[0046] To adjust the wavelength of phosphor powder or improve its luminous efficiency, rare earth elements such as Pr or Sm can be added to the raw material. Furthermore, to improve excitation efficiency, at least one element selected from rare earth elements such as scandium (Sc), lanthanum (La), thorium (Gd), and argon (Lu) can be added to the raw material as a sensitizer. Preferably, the amount of these elements added relative to strontium (Sr) is 5 mol% or less. If the content of these elements exceeds 5 mol%, there is a risk of precipitation of a large amount of heterogeneous phases, resulting in a significant decrease in brightness. Additionally, alkali metal elements, monovalent cations such as silver ions (Ag+), and halide ions such as chloride (Cl), fluorine (F), and iodine (I) can be added to the raw material as charge compensators. Regarding the amount added, in terms of charge compensation effect and brightness, it is preferably set to an amount equivalent to the content of aluminum group or rare earth elements.

[0047] There are no limitations on the mixing method of the raw materials. It can be carried out by either dry or wet mixing. In the case of dry mixing, for example, zirconia balls can be used as a medium, and the mixture can be mixed using a mixer such as a coating shaker or ball mill. Drying is then performed as needed to prepare the raw material mixture. In the case of wet mixing, for example, a solvent such as water can be added to the raw materials to form a suspension. Zirconia balls can be used as a medium, and the mixture can be mixed using a mixer such as a coating shaker or ball mill. The medium is then separated using a sieve, and the solvent is removed from the suspension by drying methods such as reduced pressure drying or vacuum drying.

[0048] The obtained raw material mixture is then fired to produce a fired product. Before firing, the raw material mixture may be crushed, graded, and / or dried as needed, or this may not be done.

[0049] Firing is preferably carried out at a temperature above 1000°C. At temperatures above 1000°C, thorough and uniform firing can be achieved. The upper limit of the firing temperature depends on the durability and formation temperature of the firing furnace, and therefore cannot be generalized. However, firing is preferably carried out at a temperature between 1000°C and 1200°C. Firing time is related to the firing temperature. However, it is preferably between 2 and 24 hours.

[0050] The firing environment can be an inert gas or a reducing gas. Examples include: argon environment, nitrogen environment, sulfur environment, argon environment containing hydrogen, nitrogen environment containing hydrogen, and hydrogen sulfide environment. Among these, firing in a hydrogen sulfide environment is preferred.

[0051] When the raw material mixture contains sulfur (S), calcination can be carried out in an environment containing hydrogen sulfide, carbon disulfide, or an inert gas. When using hydrogen sulfide or carbon disulfide, these substances become sulfur compounds during calcination, which has the effect of inhibiting the decomposition of the products. On the other hand, when the raw materials do not contain sulfur, calcination is preferably carried out in a sulfur-containing environment such as hydrogen sulfide or carbon disulfide.

[0052] The calcined material is then crushed to produce powder. Crushing can be performed using known crushers such as ball mills, pulverizers, jet mills, grinders, and / or paint vibrators. Furthermore, the crushed material can be graded as needed. Grading can be performed using known mechanisms such as sieves or air classifiers. In this way, fluorescent powders can be produced.

[0053] Furthermore, in this embodiment, it is preferable that the fine particles obtained by crushing or grading as described above are also effectively utilized. That is, by preparing a phosphor-containing composition that includes phosphors containing fine particles in addition to medium-diameter particles, the absorption rate can be significantly improved, and the internal quantum efficiency can be enhanced.

[0054] In the manufacturing method of this embodiment, it is important to control the particle size distribution of the phosphor powder obtained after crushing. Specifically, the particle size is adjusted such that the total volume frequency of fine particles is 10% or more, the total volume frequency of medium-diameter particles is 10% or more and 90% or less, and the D50 is 10.0 μm or less.

[0055] There are no limitations on how particle size distribution can be adjusted. However, it can be adjusted by controlling the conditions during crushing or grading. For example, when using a ball mill for crushing, the processing time, ball mill speed, media (ball) size, and media (ball) filling rate can be adjusted. Similarly, when using a jet mill for crushing, the crushing pressure and the type of gas supplied can be adjusted. Furthermore, when performing grading, the mesh size of the screen or the grading points (segmentation points) can be adjusted.

[0056] <<3. Compositions containing phosphors>> The phosphor-containing composition of this embodiment comprises the aforementioned phosphor powder. The phosphor-containing composition may also contain other components besides the phosphor powder. Preferably, these other components are resin and / or organic solvents. The phosphor-containing composition comprising phosphor powder and resin can be molded to obtain a light-emitting element. Furthermore, the phosphor-containing composition comprising phosphor powder and organic solvent can be coated onto the surface of an excitation source to directly mold a light-emitting element onto the excitation source.

[0057] As resins, one or more selected from thermoplastic resins, thermosetting resins, ionizing radiation-cured resins, and two-component mixed-curing resins can be used. Examples of thermoplastic resins include: polyolefin resins such as polyethylene or polypropylene; polyester resins such as polyethylene terephthalate or polybutylene terephthalate; polyacrylic resins such as polycarbonate resin, polyacrylic acid or its esters, or polymethacrylic acid or its esters; polyethylene resins such as polystyrene or polyvinyl chloride; cellulose resins such as triacetin cellulose; and polyurethane resins such as polyurethane. Examples of thermosetting resins include: silicone resins, phenolic resins, epoxy resins, melamine resins, urea resins, unsaturated polyester resins, alkyd resins, polyurethane resins, and polyimide resins. Examples of ionizing radiation-cured resins include: acrylic resins, polyurethane resins, vinyl ester resins, and polyester alkyd resins. In addition to polymers, oligomers and monomers can also be used in these resins. Epoxy resin is an example of a two-component curable resin.

[0058] <<4. Light-emitting elements>> The light-emitting element of this embodiment includes the phosphor and excitation source described above. The excitation source functions to excite the phosphor by emitting light toward it. Preferably, the excitation source is an LED with a wavelength of 250 nm to 510 nm. The light from the excitation source only needs to be incident on the phosphor; the arrangement of the phosphor and excitation source is not limited. However, it is preferable to place the phosphor directly above the excitation source. This allows all the light emitted from the excitation source to be absorbed by the phosphor, thus achieving color conversion. For example, when applying the light-emitting element to a micro-LED display, it is preferable to place the LED as the excitation source at the bottom of each package and the phosphor at the top.

[0059] The light-emitting element of this embodiment is characterized by high luminous intensity and excellent luminous color. Therefore, it is suitable for small LED displays or micro LED displays.

[0060] <<5. Light-emitting device>> The light-emitting device of this embodiment includes the aforementioned light-emitting element. The light-emitting element of the light-emitting device of this embodiment is characterized by high luminous intensity and excellent luminous color. Therefore, the light-emitting device of this embodiment is suitable as a small LED display or a micro LED display. [Example]

[0061] The invention will be further described in detail using the following embodiments. However, the invention is not limited to the following embodiments.

[0062] (1) Preparation of phosphor powder and composition containing phosphor [Example 1] Barium sulfide (BaS), strontium sulfide (SrS), europium sulfide (EuS), and gallium sulfide (Ga₂S₃) were prepared and weighed according to the molar ratios of Ba (0.22), Sr (0.65), Eu (0.13), and Ga (2.00). The weighed mixtures were then mixed for 100 minutes using zirconia balls with a diameter of 3 mm in a coating shaker to obtain a raw material composition. Subsequently, the raw material composition was calcined in a hydrogen sulfide (H₂S) environment at a heating rate of 5°C / min, a calcination temperature of 1100°C, and a calcination time of 6 hours to obtain the product.

[0063] 50 g of the obtained product and 50 g of ethanol were added to a 500 ml alumina crucible to obtain a mixture with a solid content of 50% by mass. Subsequently, wet crushing was performed using a ball mill to obtain crushed material. The balls used were zirconia balls with diameters of any one of 15 mm, 10 mm, 7 mm, and 3 mm. The ball mill rotation speed was set to 300 rpm. The crushing process is shown in Table 1. The obtained crushed material was evaluated as a fluorescent powder.

[0064] Subsequently, the obtained phosphor powder was mixed at a ratio of 10 parts by mass relative to 100 parts by mass of silicone resin, and then kneaded and dispersed to prepare a dispersion composition. A coating film with a thickness of 100 μm was then prepared from the obtained dispersion composition, and this was evaluated as a phosphor-containing composition.

[0065] [Examples 2-6 and 8] The crushing process is shown in Table 1. Otherwise, the same procedures as in Example 1 were followed to prepare phosphor powder and compositions containing phosphors, and these were evaluated.

[0066] [Example 7] The crushing process was performed using a jet mill (Dec Group, MC DecJet (registered trademark) 30). The gas pressure was set to 0.4 MPa, and the supply gas was N2. Otherwise, the process was the same as in Example 1 to prepare fluorescent powder and compositions containing fluorescent materials, and these were evaluated.

[0067] [Examples 9-12] Calcium carbonate (CaCO3) was weighed, pulverized using a bead mill, dried, and then calcined at 850°C for 4 hours in a hydrogen sulfide atmosphere. Then, europium oxide (Eu2O3) was added, and calcination was carried out in an argon atmosphere at a heating rate of 5°C / min, a calcination temperature of 1000°C, and a calcination time of 4 hours to obtain the product represented by the general formula CaS:Eu. The amount of raw materials was adjusted so that the europium (Eu) concentration (XA / (XM+XA)) was 0.3 mol%.

[0068] 50 g of the obtained product and 50 g of ethanol were added to a 500 ml alumina crucible to obtain a mixture with a solid content of 50% by mass. Subsequently, wet crushing was performed using a ball mill to obtain crushed material. The balls used were zirconia balls with diameters of any one of 15 mm, 10 mm, 7 mm, and 3 mm. The ball mill rotation speed was set to 300 rpm. The crushing process is shown in Table 1. The obtained crushed material was evaluated as a fluorescent powder.

[0069] [Comparative Example 1] Microparticles smaller than 3 μm were removed from the crushed material obtained in Example 8 by wet classification. Otherwise, the same procedure as in Example 8 was followed to prepare phosphor powder and compositions containing phosphors, and these were evaluated.

[0070] (2) Evaluation The phosphor powders obtained in Examples 1-12 and Comparative Example 1 were evaluated for various properties in the following order.

[0071] <Particle size distribution> The particle size distribution of fluorescent powder was determined using a laser diffraction particle size analyzer (Microtrac BEL Co., Ltd., MT3300EXII). First, the circulating system of the apparatus was filled with a 99.5% ethanol solution, and the sample (fluorescent powder) was introduced with a transmittance of 95-60%. During introduction, the sample was dispersed using ultrasonic dispersion (40 W, 180 seconds). Then, the particle size was measured while the particles were circulated in the solvent within the measurement unit. Based on the measurements, a volume-based frequency particle size distribution curve and a cumulative particle size distribution curve were obtained. From these, the total volume frequency of particles with a diameter less than 2.5 μm (fine particles) and the total volume frequency of particles with a diameter between 2.5 μm and 10 μm (medium-diameter particles) were calculated. Furthermore, the cumulative 20% particle size (D20), cumulative 50% particle size (D50), and cumulative 80% particle size (D80) were calculated, and the particle size distribution ratio ((D80-D20) / D50) was determined. Moreover, the particle size determination was performed under the conditions described below.

[0072] - Flow rate: 80% - Ultrasound: 40 W, 180 seconds - Reset time: 10 seconds - Measurement time: 30 seconds -Number of measurements: 1 -Transparency: Transmission - Particle refractive index: 2.46 (in the cases of Examples 1-8 and Comparative Example 1) 1.59 (in the case of Examples 9-12) -Particle shape: Non-spherical - Solvent refractive index: 1.36

[0073] Furthermore, in the volume frequency curve with the common logarithm of particle size as the horizontal axis and volume frequency as the vertical axis, the curve is standardized so that the maximum value of the volume frequency is 1, and the area enclosed by the volume frequency curve and the horizontal axis (peak area) is calculated.

[0074] <Fluorescence properties (absorption rate, external quantum efficiency, internal quantum efficiency)> For the obtained phosphor-containing composition, the internal quantum efficiency (IQE), external quantum efficiency (EQE), and absorptivity (Abs) were measured. The measurement was performed by irradiating one side of the phosphor-containing composition with 460 nm LED light, and measuring the light transmitted from the other side using a spectrometer (Ocean Insight, USB4000).

[0075] The formulas for calculating the absorptivity, internal quantum efficiency, and external quantum efficiency of a phosphor when the excitation light is set to 460 nm are shown below.

[0076] Let P1(λ) be the LED light spectrum at 460 nm, and P2(λ) be the sample spectrum. According to equation (i), calculate the area L1 enclosed by the spectrum P1(λ) within the excitation wavelength range of 440 nm to 488 nm, and take the obtained value as the excitation intensity. According to equation (ii), calculate the area L2 enclosed by the spectrum P2(λ) within the excitation wavelength range of 440 nm to 488 nm, and take the obtained value as the sample scattering intensity. According to equation (iii), calculate the area E2 enclosed by the spectrum P2(λ) within the excitation wavelength range of 489 nm to 800 nm, and take the obtained value as the sample fluorescence intensity.

[0077] [Number 2]

[0078] The absorptivity (Abs) is the ratio of the reduction in excitation light caused by the sample to the incident light, calculated according to equation (iv) below. Furthermore, the external quantum efficiency (EQE) is the value obtained by dividing the number of photons Nem of fluorescence emitted from the sample by the number of photons Nex of excitation light irradiating the sample, calculated according to equation (v) below. Moreover, the internal quantum efficiency (IQE) is the value obtained by dividing the number of photons Nem of fluorescence emitted from the sample by the number of photons Nabs of excitation light absorbed by the sample, calculated according to equation (vi) below.

[0079] [Number 3]

[0080] (3) Evaluation Results The particle size distribution and fluorescence properties of the phosphor powders of Examples 1-12 and Comparative Example 1 are summarized in Table 2. Furthermore, the particle size distribution (volume frequency distribution curve) of the phosphor powders is shown in Figures 3-14.

[0081] Examples 1-12, in which the ratio of fine to medium-diameter particles meets the range of this embodiment, exhibit higher absorption rates and internal quantum efficiencies. In contrast, Comparative Example 1, in which fine particles were removed, shows a lower absorption rate than Examples 1-12.

[0082] [Table 1] Table 1. Crushing conditions for phosphor powders ball mill Jet mill Micro powder removal Ball input (g) Ball mill time (h) Gas pressure (MPa) Gas supply 15 mm in diameter 10 mm in diameter 7 mm in diameter 3 mm in diameter Example 1 0 0 300 400 4 - - none Example 2 0 0 400 300 2 - - none Example 3 0 400 0 300 5 - - none Example 4 0 350 0 350 7 - - none Example 5 0 0 700 0 1.5 - - none Example 6 0 0 700 0 20 - - none Example 7 - - - - - 0.4 N 2 none Example 8 500 0 0 200 5 - - none Example 9 0 0 400 300 1.5 - - none Example 10 0 0 300 400 2 - - none Example 11 0 400 0 300 1.5 - - none Example 12 0 0 500 200 15 - - none Comparative Example 1 500 0 0 200 5 - - Removal of particles smaller than 3 μm

[0083] [Table 2] Table 2. Particle size distribution and fluorescent properties of phosphor powders Particle size distribution Fluorescence properties Total volume frequency of fine particles (%) Total volume frequency of medium diameter particles (%) Total volume frequency of coarse particles (%) Peak area D20 (μm) D50 (μm) D80 (μm) (D80-D20) / D50 Absorption rate Abs Internal quantum efficiency IQE External quantum efficiency EQE Example 1 34 59 7 19 1.7 3.0 5.5 1.3 56 65 37 Example 2 twenty three 66 11 twenty one 2.1 4.1 7.3 1.2 52 67 35 Example 3 31 54 15 twenty three 1.4 4.2 8.0 1.6 66 52 35 Example 4 52 38 10 31 0.9 2.2 6.4 2.5 66 49 32 Example 5 11 74 15 15 3.1 5.4 8.4 0.96 52 58 31 Example 6 82 16 2 20 0.7 1.1 2.2 1.4 72 43 31 Example 7 48 50 1 15 1.3 2.4 3.6 0.97 51 58 30 Example 8 10 44 46 17 3.8 8.7 14 1.2 49 65 31 Example 9 11 85 4 13 3.0 4.8 6.8 0.8 45 66 30 Example 10 17 80 3 13 2.6 4.3 6.1 0.8 46 63 29 Example 11 20 74 6 15 2.3 4.5 6.8 1.0 42 65 27 Example 12 45 54 1 16 0.7 2.5 3.9 1.3 51 49 25 Comparative Example 1 0.79 48 52 12 6.3 9.4 13 0.75 33 72 twenty four

Claims

1. A fluorescent powder, wherein the total volume frequency of particles with a diameter less than 2.5 μm, as measured by laser diffraction particle size distribution method, is 10% or more, and the total volume frequency of particles with a diameter of 2.5 μm to 10 μm is 10% to 90%, and the cumulative 50% particle size (D50) in the volume particle size distribution is 10.0 μm or less, wherein the fluorescent powder comprises a parent crystal and a luminescent center, the parent crystal being any one of the following parent crystals: a parent crystal comprising at least one metal element selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca) and gallium (Ga) and sulfur (S); and a parent crystal comprising at least one metal element selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca) and sulfur (S).

2. The fluorescent powder of claim 1, wherein when the volume frequency distribution curve is normalized such that the maximum value of the volume frequency is 1, the area enclosed by the volume frequency distribution curve and the horizontal axis, i.e., the peak area, is 12 or more.

3. For the fluorescent powder of claim 1 or 2, the particle size distribution ratio ((D80-D20) / D50) represented by the cumulative 20% particle size (D20), cumulative 50% particle size (D50), and cumulative 80% particle size (D80) in the volume particle size distribution measured by laser diffraction particle size distribution method is 0.7 or more.

4. A composition containing a phosphor, comprising phosphor powder, wherein the total volume frequency of particles with a diameter less than 2.5 μm, as determined by laser diffraction particle size distribution measurement, is 10% or more, and the total volume frequency of particles with a diameter between 2.5 μm and 10 μm is 10% to 90%, and the cumulative 50% particle size (D50) in the volume particle size distribution is 10.0 μm or less, wherein the phosphor powder comprises a parent crystal and a luminescent center, the parent crystal being any one of the following parent crystals: a parent crystal comprising at least one metal element selected from the group consisting of barium (Ba), strontium (Sr), and calcium (Ca), and gallium (Ga) and sulfur (S); and a parent crystal comprising at least one metal element selected from the group consisting of barium (Ba), strontium (Sr), and calcium (Ca), and sulfur (S).

5. As in claim 4, the composition containing a phosphor, wherein, regarding the phosphor powder, when the volume frequency distribution curve is normalized such that the maximum value of the volume frequency is 1, the area enclosed by the volume frequency distribution curve and the horizontal axis, i.e., the peak area, is 12 or more.

6. The composition containing phosphor as claimed in claim 4 or 5, wherein the particle size distribution ratio ((D80-D20) / D50) of the cumulative 20% particle size (D20), cumulative 50% particle size (D50), and cumulative 80% particle size (D80) in the volume particle size distribution measured by laser diffraction particle size distribution method is 0.7 or more.

7. A light-emitting element comprising a phosphor-containing composition as described in any one of claims 4 to 6 and an excitation source.

8. A light-emitting device comprising a light-emitting element as claimed in claim 7.

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