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

Abstract

To provide a phosphor powder that can be uniformly filled even in a minute package rib and enables fabrication of a light-emitting element showing a high EQE, and to provide a phosphor-containing composition, a phosphor, a light-emitting element, and a light-emitting device including such a phosphor powder.SOLUTION: A phosphor powder contains a plurality of phosphor particles, wherein the phosphor powder has a cumulative 80% diameter (D80) of 30 μm or less in a volume particle size distribution measured by a laser diffraction scattering particle size distribution measurement method, and wherein the phosphor powder has a particle cage evaluation value of 10 μm or more and 50 μm or less as measured in accordance with JIS K5600-2-5:1999 for a slurry obtained by adding the phosphor powder at a proportion of 40 pts.mass relative to 100 pts.mass of a silicone resin and mixing the mixture using a revolution-rotation stirring and defoaming apparatus.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a phosphor powder, a phosphor-containing composition, a phosphor, a light-emitting element, and a light-emitting device. [Background technology]

[0002] Light-emitting devices that use light-emitting diodes (LEDs) that emit near-ultraviolet or blue light as a light source (excitation source) and combine this with phosphors are widely used in various light-emitting devices such as lighting, backlights for mobile devices, and displays.

[0003] In this light-emitting device, the phosphor absorbs the light emitted by the LED (radiated light) and emits light of a different wavelength from the absorbed light. This makes it possible to obtain light emission of a different color tone from the LED-radiated light. For example, by combining a blue LED with a green phosphor and / or red phosphor, green light and / or red light can be obtained, and light-emitting devices with this configuration are used in displays and other applications.

[0004] Phosphors are produced by kneading phosphor powder with a binder resin to form a paste, and then coating or molding the resulting paste. For example, Patent Document 1 discloses preparing a phosphor paste by dispersing and kneading phosphor powder, binder resin, and an organic solvent using a triple-roll mill or a homogenizer, and then coating, drying, and firing the resulting phosphor paste to produce a phosphor layer for a display panel component such as a plasma display (see paragraphs

[0027] and

[0030] of Patent Document 1). Patent Document 2 also discloses a method for producing an inorganic powder-containing paste by kneading using a predetermined kneader, in which the inorganic powder is phosphor powder (see claims 1 and

[0024] of Patent Document 2).

[0005] In recent years, advances in display technology have drawn attention to micro LED (μLED) displays. Compared to LCD panels, μLED displays have the advantage of being able to produce images with higher brightness and a higher contrast ratio, with a faster response time and lower power consumption. Furthermore, compared to OLED displays, they are characterized by their ability to display images with higher brightness and no burn-in caused by deterioration.

[0006] A μLED display is composed of independent μLEDs for each of the R (red), G (green), and B (blue) subpixels. Each package (cell) corresponding to the subpixel is separated by a partition called a package rib, which prevents color mixing due to light from adjacent package ribs. The package rib is very small, measuring, for example, 1000 μm or less on a side, reflecting the size of the subpixel. An excitation source such as an LED is provided on the bottom of the package rib, and a phosphor layer is provided above it.

[0007] As an example of such technology, Patent Document 3 discloses a μLED display device comprising a μLED drive substrate and a μLED panel (claim 1 of Patent Document 3). Specifically, it describes that the μLED panel includes a light-emitting structure (plurality of μLED pixels), a growth substrate on the light-emitting structure, a plurality of partitions on the growth substrate, and an R / G / B color conversion material positioned between the partitions, and that the R / G / B color conversion material (or R / G / B phosphor) converts the wavelength of light emitted from each light-emitting element (pixel) (paragraphs

[0022] and

[0034] of Patent Document 3). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-171663 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-279374 [Patent Document 3] Japanese Patent Application Publication No. 2018-182282 Summary of the Invention [Problem to be solved by the invention]

[0009] While expectations for μLED displays are high, conventional phosphor powders, when used in the phosphor layer of μLED displays, have the problem of poor external quantum efficiency (EQE), one of the light-emitting characteristics. This issue is explained using Figure 1, which illustrates the manufacturing process for phosphor layers. Figure 1 shows an example of the manufacturing process for phosphor layers. First, phosphor powder (particles) is prepared (Step A), and the prepared phosphor powder is dispersed in a resin solution to form an ink, creating a phosphor paste (phosphor dispersion) (Step B). This paste contains the phosphor powder, resin, and solvent, or molten resin. The resulting paste is then filled (coated) into a package rib with an excitation source on the bottom, and the resulting filler is then dried and / or cured to create the phosphor layer (Step C). When manufacturing the phosphor layer, it is important to fill the package rib uniformly with the phosphor paste. Uneven filling can result in variations in the amount of phosphor per cell, which can lead to a decrease in EQE.

[0010] In this regard, conventional phosphor powders have been insufficient for obtaining a phosphor layer with excellent EQE. Conventional phosphor powders contain large particles, such as large primary particles or secondary particles (aggregated particles or agglomerated particles) formed by the coagulation or aggregation of primary particles. The presence of these particles in the paste leads to uneven filling of the package ribs. In this regard, as proposed in Patent Documents 1 and 2, methods are known in which the phosphor powder is strongly crushed or the phosphor paste is strongly dispersed to produce a paste in which fine phosphor powder is uniformly dispersed. However, these methods severely damage the phosphor powder, which is likely to result in a decrease in EQE.

[0011] The present inventors have conducted extensive research to solve these problems, and as a result have discovered that by using the cumulative 80% diameter in the volumetric particle size distribution and the particle cage evaluation value as indicators for controlling the phosphor powder, it is possible to uniformly fill even minute package ribs with a paste containing phosphor powder, and furthermore, to manufacture a light-emitting device that exhibits a high EQE.

[0012] The present invention was completed based on these findings, and aims to provide a phosphor powder that can be uniformly filled even in minute package ribs and that enables the fabrication of light-emitting devices that exhibit a high EQE. Another aim of the present invention is to provide a phosphor-containing composition, a phosphor, a light-emitting device, and a light-emitting device that contain such a phosphor powder. [Means for solving the problem]

[0013] The present invention includes the following aspects (1) to (8). In this specification, the expression "to" includes the numerical values ​​on both ends. In other words, "X to Y" is synonymous with "at least X and at most Y."

[0014] (1) A phosphor powder containing a plurality of phosphor particles, the phosphor powder has a cumulative 80% diameter (D80) of 30 μm or less in a volume particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method; The phosphor powder is added in a ratio of 40 parts by mass to 100 parts by mass of silicone resin, and then mixed using an orbital rotation type stirring and degassing device to obtain a slurry, which has a particle size evaluation value of 10 μm or more and 50 μm or less when measured in accordance with JIS K5600-2-5:1999.

[0015] (2) The phosphor powder of (1) above includes a host crystal containing at least one metal element selected from the group consisting of barium (Ba), strontium (Sr), and calcium (Ca), gallium (Ga), and sulfur (S), and a host crystal containing at least one metal element selected from the group consisting of strontium (Sr) and calcium (Ca), and sulfur (S), and a luminescent center.

[0016] (3) A phosphor-containing composition comprising the phosphor powder of (1) or (2) above and a resin, wherein the content of the phosphor powder relative to 100 parts by mass of the resin is 5 parts by mass or more and 70 parts by mass or less.

[0017] (4) A phosphor comprising the phosphor-containing composition of (3) above.

[0018] (5) A light-emitting device comprising the phosphor of (4) above and an excitation source.

[0019] (6) The light-emitting device according to (5) above, wherein the phosphor and the excitation source are filled in an internal gap of a frame-shaped package rib, and the internal gap of the package rib has a diameter of 1000 μm or less.

[0020] (7) A light-emitting device comprising the light-emitting element of (5) or (6) above.

[0021] (8) The light-emitting device of (7) above, which is a μLED display. [Effects of the Invention]

[0022] The present invention provides a phosphor powder that can be uniformly filled even in minute package ribs and that can be used to fabricate light-emitting devices that exhibit a high EQE. The present invention also provides a phosphor-containing composition, a phosphor, a light-emitting device, and a light-emitting device that contain such a phosphor powder. [Brief explanation of the drawings]

[0023] [Figure 1]1 is a diagram illustrating a manufacturing process of a phosphor layer. DETAILED DESCRIPTION OF THE INVENTION

[0024] A specific embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described. Note that the present invention is not limited to the following embodiment, and various modifications are possible within the scope of the present invention.

[0025] <<1. Phosphor powder>> The phosphor powder of this embodiment contains a plurality of phosphor particles. In other words, it is an aggregate of a plurality of particles. It can also be said that a plurality of phosphor particles constitute the phosphor powder. In this specification, the term "powder" refers to a substance that is composed of a plurality of particles and exhibits fluidity as a whole. Even if some particles are bonded or bound to each other, it is still called a powder as long as it exhibits fluidity as a whole.

[0026] Furthermore, the phosphor powder of this embodiment is limited to a cumulative 80% diameter (D80) of 30 μm or less in the volume particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method. Powders with a D80 of more than 30 μm contain coarse particles, which may act as barriers during filling and hinder uniform filling. From the viewpoint of promoting uniform filling, D80 is more preferably 20 μm or less, and even more preferably 15 μm or less. The lower limit of D80 is not particularly limited. However, if the phosphor powder is too fine, the viscosity of the phosphor paste (phosphor-containing composition) made from this powder may become too high, making filling difficult. D80 is preferably 0.1 μm or more from the viewpoint of ensuring sufficient EQE as a light-emitting element. D80 may also be 2.5 μm or more.

[0027] Furthermore, the phosphor powder of this embodiment has a particle size rating of 10 μm or more and 50 μm or less. The particle size rating is a measurement obtained by adding 40 parts by mass of phosphor powder to 100 parts by mass of silicone resin, mixing them using a revolution-rotation type agitator / deaerator to prepare a slurry, and then coating and evaluating the resulting slurry on a particle size rating according to JIS K5600-2-5:1999. By using the particle size rating of the phosphor powder slurried using the revolution-rotation type agitator / deaerator as an index, it is possible to examine the particle size and dispersion state while minimizing damage to the particles contained in the phosphor powder. Moreover, particle size and dispersion can be evaluated in the presence of the resin.

[0028] To explain this point, a revolution-rotation type agitation / deaeration apparatus is an apparatus that rotates a container that contains a slurry while revolving it around its axis, thereby applying centrifugal force and shear force to the slurry to agitate, degas, and disperse it. The revolution-rotation type agitation / deaeration apparatus does not have a forced agitation function such as an agitating blade or media. Therefore, it is possible to gently disperse the slurry, and damage to the particles in the obtained slurry is minimized.

[0029] On the other hand, a grain gauge is a device used to evaluate the size and dispersibility of particles contained in a powder, and is also called a grind gauge or particle size gauge. A grain gauge has a roughly rectangular steel body with grooves on the surface of the body. The depth of these grooves gradually decreases from one side to the other. When a slurry containing powder is squeegeeed on the grain gauge, linear or granular marks are left at locations with depths corresponding to the size of the particles contained in the powder. By measuring the depth of the grooves where linear or granular marks are left, the size of the particles and their dispersion state can be investigated.

[0030] Furthermore, particle size distribution analysis can be used to examine the particle size and dispersibility of phosphor powder particles in a resin mixture similar to the mounting environment for μLEDs. In contrast, particle size distribution analysis, which measures phosphor powder dispersed in a dispersant such as water or alcohol, cannot examine the tendency of the powder to aggregate in the resin mixture. Even fine powders measured by particle size distribution analysis can aggregate into coarse aggregates when mixed with resin. Such powders can cause problems in uniformly filling the micro-packaging ribs. In other words, particle size distribution analysis can detect powders with a high tendency to aggregate in resin. Furthermore, particle size distribution analysis can also detect small amounts of coarse particles.

[0031] In this way, by evaluating using a combination of a revolution-type stirring device and particle gauge evaluation values, it is possible to examine the size of particles and their dispersion state while allowing them to coexist with the resin and minimizing damage.

[0032] In this embodiment, by limiting the particle gauge evaluation value of the phosphor powder to 10 μm or more and 50 μm or less, it is possible to improve the EQE while more reliably ensuring uniform filling into a micro package. That is, phosphor powder that satisfies the above conditions can have a relatively small particle size and be highly dispersible while maintaining a state in which damage is suppressed. Because damage is suppressed, there are few particle defects. Therefore, it is possible to manufacture light-emitting devices with a high EQE. Furthermore, because the particle size is small and can be highly dispersible, uniform filling into a micro package is possible.

[0033] In contrast, phosphor powder with a particle gauge evaluation value of more than 50 μm contains coarse primary particles and secondary particles (aggregated particles, agglomerated particles). Therefore, the paste (phosphor-containing composition) containing this phosphor powder has poor filling properties, making it difficult to uniformly fill the package ribs. From the viewpoint of filling the package ribs, a particle gauge evaluation value of 45 μm or less is preferable, and 40 μm or less is more preferable. On the other hand, if the particle gauge evaluation value is less than 10 μm, the particle diameter of the phosphor powder becomes small, resulting in a decrease in the EQE of the phosphor and a decrease in the luminous efficiency of the element. From the viewpoint of luminous efficiency, a particle gauge evaluation value of 15 μm or more is preferable.

[0034] In this regard, conventional phosphor powders are not specifically designed for μLED applications. Therefore, even when attempting to fill a paste containing conventional phosphor powder into micro-package ribs, uniform filling is difficult. Specifically, phosphor powders are generally produced by a solid-state reaction method in which raw materials are fired. To fully promote the reaction and fully develop the fluorescent properties, firing at a relatively high temperature is necessary. Therefore, conventional phosphor powders contain large primary particles or secondary particles (aggregated particles, aggregated particles) formed by the solidification or aggregation of primary particles. The presence of such coarse particles (primary particles, secondary particles) in the paste disrupts the flow of the paste during filling, resulting in uneven filling of the package ribs.

[0035] On the other hand, there are known techniques for producing a paste in which fine phosphor powder is uniformly dispersed, by strongly crushing the phosphor powder or strongly dispersing the phosphor paste, with the aim of uniformly filling the package ribs. For example, in Patent Documents 1 and 2, phosphor paste is produced by dispersing and kneading phosphor powder, binder resin, and organic solvent using a triple roll, homogenizer, kneader, or other means, and the resulting paste is said to be homogeneous and have excellent dispersibility (see

[0027] of Patent Document 1 and

[0012] of Patent Document 2).

[0036] However, although phosphor pastes made with strong crushing and dispersion are effective in filling package ribs uniformly, the luminous efficiency of light-emitting devices made using them is not high. The reason for this is thought to be that the phosphor particles in the phosphor paste are severely damaged by the strong crushing and dispersion, which causes defects in the crystal structure of the phosphor particles and reduces the EQE.

[0037] In other words, the phosphor powder of this embodiment has a small particle size. Furthermore, this phosphor powder can be dispersed sufficiently even with a gentle method using a revolution-rotation type agitator / deaerator, enabling uniform filling of the fine package ribs with minimal damage. This clearly differs from conventional powders, which require powerful dispersion methods such as a homogenizer.

[0038] Assuming that the phosphor powder satisfies the above-mentioned conditions regarding D80, the cumulative 10% diameter (D10) is preferably 10 μm or less, more preferably 5.0 μm or less. The cumulative 50% diameter (D50) is preferably 25 μm or less, more preferably 20 μm or less. Furthermore, the cumulative 90% diameter (D90) is preferably 50 μm or less, more preferably 30 μm or less. If D10, D50, and D90 are within the above-mentioned ranges, the external quantum efficiency and internal quantum efficiency can be further improved without causing a decrease in the absorptivity of the phosphor. Note that D10, D50, and D90 are values ​​in the volumetric particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method.

[0039] The phosphor powder of this embodiment is not limited in its material composition as long as it exhibits fluorescent properties. Fluorescent materials are composed of a host crystal and a luminescent center (activator), and many of them have the luminescent center dissolved in an appropriate host crystal at a concentration of several percent. Known fluorescent materials include oxide-based, sulfide-based, oxysulfide-based, nitride-based, and oxynitride-based materials, and any of these may be used.

[0040] For example, oxide-based fluorescent materials include (Y, Gd, Lu)3(Al, Ga)5O 12 :Ce 3+, (Ba,Sr,Ca)2SiO4:Eu 2+ , (Ba,Sr,Ca)3MgSi2O8:Eu 2+ , CaAl 12 O 19 :Mn 4+ , Ca3Sc2Si3O 12 :Ce 3+ , CaSc2O4:Ce 3+ , (Ba,Sr)3SiO5:Eu 2+ , Li2SrSiO4:Eu 2+ , Ba9Sc2Si6O 24 :EU 2+ , Ca3Si2O7:Eu 2+ , LiSrPO4:Eu 2+ , CaLa4Si3O 13 :EU 3+ , Ba2Gd3Li3Mo8O 32 :EU 3+ and BaMgAl 10 O 17 :EU 2+ ,Mn 2+ Examples include:

[0041] (Ba,Sr,Ca)Ga2S4:Eu as a sulfide-based fluorescent material 2+ , (Ba,Sr,Ca)Ga2S4:Ce 3+ , (Sr,Ca)S:Eu 2+ , SrCdS:Eu 2+ and ZnS:Cu.

[0042] (La,Y)2O2S:Eu as an oxysulfide fluorescent material 3+ and La(Ca,Sr)Ga3S6O:Eu 2+ Examples include:

[0043] (Ba,Sr,Ca)2Si5N8:Eu as a nitride-based fluorescent material 2+ , (Ba,Ca,Sr)AlSiN3:Eu 2+ , La3Si6N 11 :Ce 3+ , (Ba,Sr,Ca)LiAl3N4:Eu 2+ , Sr(Mg3SiN4):Eu 2+and (Ba,Sr)2Si5N8:Eu 2+ Examples include:

[0044] Oxynitride fluorescent materials include Eu-containing α-type sialon, Eu-containing β-type sialon, and Ba9Sc3Si6O 21 N3:Eu 2+ , Ba3Si6O 12 N2:Eu 2+ , BaSi2O2N2:Eu 2+ and (Ba,Sr,Ca)AlSi(ON)3:Eu 2+ Examples include:

[0045] Other fluorescent materials include Sr 10 (PO4)6C 12 :EU 2+ and K2(Si,Ge,Ti)F6:Mn 4+ Examples include:

[0046] According to a preferred embodiment, the phosphor powder includes a host crystal containing at least one metal element selected from the group consisting of barium (Ba), strontium (Sr), and calcium (Ca), gallium (Ga), and sulfur (S), as well as a luminescent center, as in the composition listed above for the sulfide-based fluorescent material. The luminescent center preferably contains at least one element selected from the group consisting of europium (Eu), cerium (Ce), manganese (Mn), and samarium (Sm). From the viewpoint of increasing the internal quantum efficiency (IQE) upon excitation with blue light emitted from an LED, the luminescent center preferably contains Eu, and preferably contains a divalent ion of Eu (Eu 2+ ), and more preferably Eu 2+ More preferably, the phosphor powder contains only the general formula: MGa2S4:Eu 2+ (wherein M is at least one element selected from the group consisting of Ba, Sr, and Ca). Phosphor powder having such a composition emits green light when excited by excitation light in the near-ultraviolet to blue region (approximately 300 nm to 510 nm).

[0047] According to another preferred embodiment, the phosphor powder includes a host crystal containing sulfur (S) and at least one metal element selected from the group consisting of strontium (Sr) and calcium (Ca), as well as a luminescent center, as in the composition listed above for the sulfide-based fluorescent material. The luminescent center preferably contains at least one element selected from the group consisting of europium (Eu), cerium (Ce), manganese (Mn), and samarium (Sm). More preferably, the phosphor powder has a general formula: MS:Eu 2+ (wherein M is at least one element selected from the group consisting of Sr and Ca). Phosphor powder having such a composition emits red light when excited by excitation light having a wavelength in the ultraviolet to visible light range (approximately 250 nm to 610 nm).

[0048] Regarding the ratio of luminescence centers in the phosphor powder, from the viewpoint of improving luminescence intensity, the ratio (XA / (XM+XA)) of the molar amount XA of element A, which is a luminescent element, to the sum (XM+XA) of the molar amount XM of element M contained in the phosphor powder and the molar amount XA of element A, is preferably 0.05 or more, more preferably 0.07 or more, and even 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 even more preferably 0.20 or less.

[0049] The phosphor powder may or may not have a coating layer. However, providing a coating layer can improve durability, such as moisture resistance. From the viewpoint of improving durability while maintaining the good luminescence properties of the phosphor, the coating layer is preferably made of one or more inorganic compounds, such as oxides containing silicon dioxide (SiO), zinc oxide (ZnO), aluminum oxide (AlO), titanium oxide (TiO), and / or boron (B), or metal sulfates such as barium sulfate (BaSO).

[0050] The phosphor powder may contain components other than the fluorescent material, such as a flux component such as a sintering aid that is added during the synthesis of the phosphor powder.

[0051] <<2. Phosphor Powder Manufacturing Method>> The phosphor powder of this embodiment can be produced by any method as long as it satisfies the above-mentioned requirements. However, phosphor powders synthesized by a solid-state reaction method are preferred. Specifically, a phosphor coarse powder is synthesized from raw materials by a solid-state reaction method, and this phosphor coarse powder is then subjected to particle size adjustment processes such as crushing and classification. A preferred production method is described below using a phosphor powder containing a host crystal containing at least one metal element selected from the group consisting of barium (Ba), strontium (Sr), and calcium (Ca), gallium (Ga), and sulfur (S), and containing europium (Eu) as the luminescent center, as an example.

[0052] First, a raw material mixture is obtained by weighing and mixing at least one of a strontium (Sr) raw material, a barium (Ba) raw material, and a calcium (Ca) raw material, a gallium (Ga) raw material, a sulfur (S) raw material, and a europium (Eu) raw material. The strontium (Sr) raw material, the barium (Ba) raw material, and the calcium (Ca) raw material may be oxides, double oxides, and / or carbonates of the respective elements. The gallium (Ga) raw material may be oxides (Ga2O3, GaO). The sulfur (S) raw material may be strontium sulfide (SrS), barium sulfide (BaS), calcium sulfide (CaS), sulfur (S), silicon sulfide (SiS2), cerium sulfide (Ce2S3), hydrogen sulfide (HS) gas, or the like. As the europium (Eu) raw material, europium compounds such as europium fluoride (EuF3), europium oxide (Eu2O3), and europium chloride (EuCl3) can be used.

[0053] In order to adjust the emission wavelength of the phosphor powder and improve the EQE, rare earth elements such as praseodymium (Pr) and samarium (Sm) may be added to the raw materials. Furthermore, in order to improve the excitation efficiency, at least one element selected from rare earth elements such as scandium (Sc), lanthanum (La), gadolinium (Gd), and lutetium (Lu) may be added to the raw materials as a sensitizer. However, it is preferable that the amount of each of these elements be 5 mol % or less relative to strontium (Sr). By keeping the content of these elements at 5 mol % or less, it is possible to prevent the precipitation of a large amount of heterophases and a significant decrease in brightness. Furthermore, alkali metal elements and silver ions (Ag + Monovalent cationic metals such as Cr, Ni, and Cr, and halogen ions such as chlorine (Cl), fluorine (F), and iodine (I) may be added to the raw materials as charge compensation agents. In terms of charge compensation effect and brightness, the amount of the added agent is preferably approximately equal to the content of the aluminum group or rare earth element.

[0054] The method for mixing the raw materials is not limited. Either a dry method or a wet method may be used. In the case of dry mixing, for example, zirconia balls are used as media and the raw material mixture is mixed in a mixer such as a paint shaker or a ball mill, and dried as necessary. In the case of wet mixing, a solvent such as water is added to the raw materials to form a suspension, and the mixture is mixed in a mixer such as a paint shaker or a ball mill using zirconia balls as media. The media is then separated using a sieve or the like, and the solvent is removed from the suspension by a drying method such as reduced pressure drying or vacuum drying.

[0055] The resulting raw material mixture is then fired to produce a fired product. Before firing, the raw material mixture may or may not be subjected to pulverization, classification, and / or drying, as necessary.

[0056] Firing is preferably carried out at a temperature of 1000°C or higher. At 1000°C or higher, sufficient and uniform firing can be achieved. The upper limit of the firing temperature cannot be determined in general because it is determined by the endurance temperature of the firing furnace and the production temperature. However, firing at a temperature of 1000°C or higher and 1200°C or lower is preferable. The firing time is determined in relation to the firing temperature. However, a temperature of 2 hours or higher and 24 hours or lower is preferable.

[0057] The firing atmosphere may be an inert gas or a reducing gas, etc. Examples include an argon atmosphere, a nitrogen atmosphere, a sulfur atmosphere, an argon atmosphere containing hydrogen gas, a nitrogen atmosphere containing hydrogen gas, a hydrogen sulfide atmosphere, etc. Among these, firing in a hydrogen sulfide atmosphere is preferred.

[0058] When the raw material mixture contains a sulfur (S) raw material, it can be calcined under an atmosphere of hydrogen sulfide, carbon disulfide, or an inert gas. When hydrogen sulfide or carbon disulfide is used, it becomes a sulfur compound during calcination, which has the effect of suppressing decomposition of the product. On the other hand, when the raw material does not contain a sulfur raw material, it is preferable to calcinate under a sulfur-containing atmosphere such as hydrogen sulfide or carbon disulfide.

[0059] The fired product is then crushed into powder. Crushing may be performed by either a dry method or a wet method. In the case of the wet method, ethanol, water, or the like can be used as a dispersion medium. Crushing may be performed using a known crusher such as a ball mill, stamp mill, jet mill, crusher, and / or paint shaker. However, in order to reduce damage to the resulting phosphor powder, it is preferable to crush the fired product using a means such as a ball mill, which places less strain on the fired product. If necessary, the crushed product obtained by crushing may be subjected to a classification process.

[0060] The classification is preferably performed using an ultrasonic sieve. Using an ultrasonic sieve makes it possible to classify fine particles without clogging. It is also preferable to repeatedly crush and classify the fired material. Repeated crushing and classification makes it possible to obtain phosphor powder with a small particle gauge evaluation value. Specifically, it is preferable to crush the fired material and then classify it using a sieve, and then repeat the crushing and sieving operations on the fired material remaining on the sieve. In this way, the phosphor powder of this embodiment can be obtained.

[0061] <<3. Phosphor-containing composition>> The phosphor-containing composition of this embodiment contains the above-described phosphor powder and a resin. The phosphor-containing composition is a phosphor paste that is a precursor of the phosphor. That is, the phosphor is produced by applying or molding the phosphor-containing composition.

[0062] The resin may be, for example, one or more selected from thermoplastic resins, thermosetting resins, ionizing radiation curable resins, and two-component curable resins. Examples of thermoplastic resins include polyolefin resins such as polyethylene and polypropylene; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate resins; polyacrylic acid resins such as polyacrylic acid or its esters, polymethacrylic acid or its esters; polyvinyl resins such as polystyrene and polyvinyl chloride; cellulose resins such as triacetyl cellulose; and urethane 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 curable resins include acrylic resins, urethane resins, vinyl ester resins, and polyester alkyd resins. These resins may be used not only as polymers but also as oligomers or monomers. Examples of two-component curable resins include epoxy resins.

[0063] The amount of phosphor powder contained in the phosphor-containing composition is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, per 100 parts by mass of resin, from the viewpoint of ensuring absorption and facilitating the attainment of a sufficient EQE, while the amount is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, from the viewpoint of favorable filling into the package ribs.

[0064] The phosphor-containing composition may contain an organic solvent, an additive, and the like. The viscosity of the phosphor-containing composition (paste) can be adjusted by adding an organic solvent. Any known organic solvent that dissolves resins may be used. As the additive, an inorganic filler such as glass particles or metal oxide particles, or a flow adjuster made of an organic component may be used.

[0065] The phosphor-containing composition is produced by mixing and kneading phosphor powder, resin, and, if necessary, organic solvents and additives. Mixing and kneading can be performed by known methods. However, it is preferable to avoid placing an excessively large load on the phosphor powder. Applying a large load can cause damage to the phosphor powder, such as crystal defects, which can reduce the luminous efficiency of the resulting light-emitting device.

[0066] The mixing and kneading are preferably carried out using, for example, a revolutionary-rotation type agitator / deaerator and / or a planetary mixer. Among these, it is preferable to use a revolutionary-rotation type agitator / deaerator to agitate, deaerate, and disperse the slurry. The revolutionary-rotation type agitator / deaerator allows for gentle dispersion, and by using this, it is possible to obtain a phosphor-containing composition without damaging the phosphor powder.

[0067] When using a revolution-rotation type agitation / deaerating device, the revolution speed is preferably 200 rpm or more and 2000 rpm or less. The rotation speed is preferably set to follow the revolution speed at 3% or more and 40% or less. The operation time is preferably 1 minute or more and 30 minutes or less. The obtained phosphor-containing composition can be used as a phosphor paste for producing a phosphor.

[0068] In contrast, conventional dispersion devices such as homogenizers and sand mills use forced agitation, such as high-speed rotating agitator blades or media, to perform dispersion. While this allows for high dispersion, particles collide with the agitator during dispersion, easily generating crystal defects. Furthermore, kneaders and other kneading dispersion devices use agitator blades to perform agitation under pressure. This applies strong compressive and shear forces to the particles, making them prone to defects. Roll-type dispersion devices such as three-roll mills also apply strong compressive and shear forces to the particles, making them prone to defects. Therefore, these methods are prone to damaging the phosphor powder, adversely affecting the luminescence intensity when used in light-emitting devices.

[0069] <<4. Phosphor>> The phosphor of this embodiment is made of the phosphor-containing composition described above. That is, the phosphor-containing composition (phosphor paste) is applied or molded, and then dried and / or cured as necessary to produce the phosphor. The phosphor has phosphor powder (particles) dispersed in a resin matrix. The phosphor can be used as a phosphor layer in a μLED display.

[0070] <<5. Light-emitting element>> The light-emitting element of this embodiment includes the above-described phosphor and excitation source. The excitation source functions to emit light toward the phosphor to excite it. A blue-emitting LED with a wavelength of 250 nm or more and 510 nm or less is suitable as the excitation source. The arrangement of the phosphor and excitation source is not limited as long as light from the excitation source is incident on the phosphor. However, it is preferable to arrange the phosphor directly above the excitation source. This allows the phosphor to absorb all of the light emitted from the excitation source and perform color conversion. For example, when the light-emitting element is applied to a μLED display, it is preferable to arrange the LED as the excitation source below and the phosphor above it within each package rib.

[0071] In a preferred embodiment, the phosphor and excitation source are filled into the internal gap of the frame-shaped package rib. The diameter of the internal gap of the package rib is preferably 1000 μm or less, but may be 100 μm or less, or even 30 μm or less. The phosphor powder of this embodiment can be uniformly filled into such a small package, and it is possible to fabricate a light-emitting device with high luminous efficiency. The lower limit of the diameter of the internal gap of the package rib may be such that a minimum size large enough to fill with the phosphor powder is ensured.

[0072] <<6. Light-emitting device>> The light-emitting device of this embodiment includes the light-emitting element described above. A μLED display is suitable as the light-emitting device. In a μLED display, the subpixels of the display (R (red), G (green), and B (blue)) are each composed of an independent LED, and the size of the subpixels is as small as 1000 μm or less. A μLED including the light-emitting element of this embodiment has high luminous efficiency at each pixel, despite the subpixels being small. Therefore, it has the characteristics of high luminous intensity and small luminous intensity variations and color unevenness. [Example]

[0073] The present invention will be described in more detail using the following examples, but the present invention is not limited to the following examples.

[0074] (1) Preparation of phosphor powder and phosphor [Example 1] Barium sulfide (BaS), strontium sulfide (SrS), europium sulfide (EuS), and gallium sulfide (GaS) were prepared and weighed out to a molar ratio of Ba 0.22, Sr 0.65, Eu 0.13, and Ga 2.00. The weighed materials were then mixed in a paint shaker with 3 mm diameter zirconia balls for 100 minutes to obtain a raw material composition. The resulting raw material composition was then fired in a hydrogen sulfide (HS) atmosphere at a heating rate of 5°C / min, a firing temperature of 1100°C, and a firing time of 6 hours to obtain a fired product.

[0075] The resulting fired material and solvent were placed in a pot with balls (media) and processed in a ball mill. The resulting slurry was filtered from the balls and then dried overnight at 80°C. The dried material was then crushed using a mortar and pestle for 15 minutes, and then sieved using an ultrasonic sieve with 25 μm openings for 30 minutes. The crushed material on the sieve was subjected to the ball milling, drying, crushing, and sieving procedures repeatedly until the crushed material on the sieve accounted for 10% or less of the total. The crushed material on the sieve was then collected and evaluated as phosphor powder. The ball milling was performed under the following conditions.

[0076] - Ball: 3mm diameter zirconia beads -Baking amount: 50g - Solvent: Ethanol, 50g -Ball weight: 96g - Pot size: 300cc - Rotation speed: 100 rpm - Processing time: 1 hour

[0077] [Example 2] A fired product was prepared using the same procedure as in Example 1. The fired product and solvent were placed in a pot together with balls (media) and processed in a ball mill. The resulting slurry was filtered from the balls and then dried overnight at 80°C. The dried product was then crushed using a mortar and pestle for 15 minutes, and then sieved using an ultrasonic sieve with 25 μm openings for 30 minutes. The crushed material on the sieve was subjected to the ball milling, drying, crushing, and sieving procedures repeatedly until the crushed material on the sieve accounted for 10% or less of the total. The crushed material on the sieve was then collected and evaluated as phosphor powder. The ball milling was performed under the following conditions.

[0078] - Ball: 7mm diameter zirconia beads -Baking amount: 50g - Solvent: Ethanol, 50g -Ball weight: 96g - Pot size: 300cc - Rotation speed: 100 rpm - Processing time: 30 minutes

[0079] [Example 3] A fired product was prepared using the same procedure as in Example 1. The fired product and solvent were placed in a pot together with balls (media) and processed in a ball mill. The resulting slurry was filtered from the balls and then dried overnight at 80°C. The dried product was then crushed using a mortar and pestle for 15 minutes, and then sieved using an ultrasonic sieve with 32 μm openings for 30 minutes. The crushed material on the sieve was subjected to the ball milling, drying, crushing, and sieving procedures repeatedly until the crushed material on the sieve accounted for 10% or less of the total. The crushed material on the sieve was then collected and evaluated as phosphor powder. The ball milling was performed under the following conditions.

[0080] - Ball: φ10mm zirconia beads -Baking amount: 50g - Solvent: Ethanol, 50g -Ball weight: 96g - Pot size: 300cc - Rotation speed: 100 rpm - Processing time: 30 minutes

[0081] [Comparative Example 1] A fired product was prepared using the same procedure as in Example 1. The fired product and solvent were placed in a pot together with balls (media) and processed in a ball mill. The resulting slurry was filtered from the balls and then dried at 80°C for 24 hours. The dried product was then crushed for 15 minutes using a mortar and pestle, and the crushed dried product was evaluated as a phosphor powder. The ball milling was carried out under the following conditions:

[0082] - Ball: 3mm diameter zirconia beads -Baking amount: 50g - Solvent: Ethanol, 50g -Ball weight: 96g - Pot size: 300cc - Rotation speed: 100 rpm - Processing time: 3 hours

[0083] Comparative Example 2 A fired product was produced using the same procedure as in Example 1. The fired product and solvent were placed in a pot together with balls (media) and processed in a ball mill. The resulting slurry was filtered from the balls and then dried at 80°C for a day and night. The dried product was then crushed using a mortar and pestle for 15 minutes, and then sieved using an ultrasonic sieve with 25 μm openings for 30 minutes. The crushed material that fell through the sieve was collected and evaluated as phosphor powder. The ball milling was performed under the following conditions.

[0084] - Ball: 3mm diameter zirconia beads -Baking amount: 50g - Solvent: Ethanol, 50g -Ball weight: 96g - Pot size: 300cc - Rotation speed: 100 rpm - Processing time: 20 hours

[0085] (2) Evaluation The phosphor powders prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were evaluated for various properties as follows.

[0086] <Particle size distribution> The particle size distribution of the phosphor powder was measured using a laser diffraction particle size analyzer (Microtrac-Bell Corporation, MT3300EXII). First, the circulation system of the device was filled with a 99.5% ethanol solution, and the sample (phosphor powder) was added so that the transmittance was 95-60%. Upon addition, the sample was subjected to ultrasonic dispersion (40 W, 180 seconds). Next, the particle size was measured while circulating the particles in the solvent in the measurement cell. From this measurement, a cumulative particle size distribution curve on a volume basis was obtained, from which the cumulative 90% diameter (D90), 80% diameter (D80), 50% diameter (D50), and 10% diameter (D10) were calculated. The particle size measurement was performed under the following conditions.

[0087] -Flow rate: 80% - Ultrasound: 40W, 180 seconds - SetZero time: 10 seconds - Measurement time: 30 seconds - Number of measurements: 1 -Transparency:Transparent - Particle refractive index: 2.46 -Particle shape: non-spherical - Solvent refractive index: 1.36

[0088] <Grain gauge evaluation> A slurry for particle gauge evaluation was prepared from the phosphor powder, and the resulting slurry was used to evaluate particle gauge. Specifically, the phosphor powder was added to 100 parts by mass of silicone resin (TSJ3150, manufactured by Momentive Performance Materials) at a ratio of 40 parts by mass, and then mixed. The mixture was then dispersed using a revolution-type stirring and degassing device to prepare a slurry. The dispersion was carried out under the following conditions:

[0089] - Rotating type agitation and degassing device: Photo Chemical Co., Ltd., Kakuhunter SK-300SII - Operation mode: Stirring mode - Revolution speed: 1000 rpm - Rotation speed: 40% of revolution - Driving time: 2 minutes

[0090] The obtained evaluation slurry was then coated on a particle gauge and evaluated in accordance with JIS K5600-2-5: 1999. Specifically, the coated slurry was observed for a location where 5 to 10 spots appeared across the grooves in a width of 3 mm, and the groove depth at that location was determined.

[0091] <Fluorescence properties> The fluorescent properties of the phosphor powder and the phosphor were evaluated using the samples. The phosphor was prepared as follows: 40 parts by mass of phosphor powder was added to 100 parts by mass of silicone resin and mixed, and the mixture was kneaded and dispersed using the above-mentioned revolution-type stirring and degassing device to prepare a phosphor-containing composition (phosphor paste). The dispersion conditions were the same as those described above. A 100 μm-thick coating film was then prepared from the obtained phosphor-containing composition to serve as the phosphor.

[0092] Next, one side of the sample was irradiated with 460 nm LED light, and the light emitted from the other side was measured using a spectrometer (Ocean Insight, USB4000). Based on the obtained measurement data, the external quantum efficiency (EQE) was calculated using the following procedure.

[0093] The formula for calculating the EQE of a sample when the excitation light is 460 nm is shown below.

[0094] P1(λ) was the LED light spectrum at 460 nm, and P2(λ) was the sample spectrum. The area L1, where spectrum P1(λ) is enclosed by the excitation wavelength range of 440 nm to 488 nm, was calculated according to the following formula (i), and the obtained value was used as the excitation intensity. The area L2, where spectrum P2(λ) is enclosed by the excitation wavelength range of 440 nm to 488 nm, was calculated according to the following formula (ii), and the obtained value was used as the sample scattering intensity. The area E2, where spectrum P2(λ) is enclosed by the excitation wavelength range of 489 nm to 630 nm, was calculated according to the following formula (iii), and the obtained value was used as the sample fluorescence intensity.

[0095]

number

[0096] EQE is the number of photons of fluorescence emitted from the sample, N em is the number of photons of the excitation light irradiated on the sample, N ex The value was calculated according to the following formula (vi).

[0097]

number

[0098] <Filling into package ribs> The coating films prepared during the above-described evaluation of fluorescent properties were visually observed, and their ability to fill package ribs was evaluated based on the following criteria. That is, when the surface of the coating film was visually observed, if no phosphor particles were present and no coating unevenness was observed, the coating film was judged to have excellent ability to fill package ribs with internal voids of 1000 μm or less across, and was rated "A" in Table 1. On the other hand, when the surface of the coating film was visually observed and multiple phosphor particles were present on the surface or if coating unevenness was observed, the coating film was judged to have poor ability to fill package ribs with internal voids of 1000 μm or less across, and was rated "B" in Table 1.

[0099] (3) Evaluation results The evaluation results obtained for Examples 1 to 3 and Comparative Examples 1 and 2 are summarized in Table 1. Note that ">50" in the particle gauge evaluation value column indicates that the particle gauge evaluation value exceeded 50 μm, which is the upper limit of detection for the particle gauge evaluation value.

[0100] The phosphor powders of Examples 1 to 3 had a cumulative 80% diameter (D80) in the volume particle size distribution and a particle cage evaluation value that satisfied the ranges specified in this embodiment (D80: 30 μm or less, particle cage evaluation value: 10 μm or more and 50 μm or less). The phosphor powders of Examples 1 to 3 had good packing properties. In addition, the EQE of the coating film was high at 45% or more. In particular, the phosphor powders of Examples 2 and 3 had good packing properties and a high EQE of the coating film at 48%.

[0101] In contrast, the phosphor powder of Comparative Example 1 had a large grain gauge evaluation value of over 50 μm, indicating poor packing properties. The phosphor powder of Comparative Example 2 also had a large grain gauge evaluation value of over 50 μm, indicating poor packing properties. The EQE was also low.

[0102] [Table 1]

[0103] From the above results, it is understood that the phosphor powder of this embodiment can be uniformly filled even in minute package ribs, and that it is possible to fabricate a light-emitting device having a high EQE.

Claims

1. A phosphor powder comprising a plurality of phosphor particles, the phosphor powder has a cumulative 80% diameter (D80) of 30 μm or less in a volume particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method; The phosphor powder is added in a ratio of 40 parts by mass to 100 parts by mass of silicone resin, and then mixed using a revolution-type stirring and degassing device to obtain a slurry, which has a particle cage evaluation value of 10 μm or more and 50 μm or less when measured in accordance with JIS K5600-2-5:1999.

2. 2. The phosphor powder according to claim 1, wherein the phosphor powder comprises a host crystal containing at least one metal element selected from the group consisting of barium (Ba), strontium (Sr), and calcium (Ca), gallium (Ga), and sulfur (S), and a host crystal containing at least one metal element selected from the group consisting of strontium (Sr) and calcium (Ca), and sulfur (S), and a luminescent center.

3. 3. A phosphor-containing composition comprising the phosphor powder according to claim 1 or 2 and a resin, wherein the content of the phosphor powder relative to 100 parts by mass of the resin is 5 parts by mass or more and 70 parts by mass or less.

4. A phosphor comprising the phosphor-containing composition according to claim 3.

5. A light-emitting device comprising the phosphor according to claim 4 and an excitation source.

6. 6. The light-emitting device according to claim 5, wherein the phosphor and the excitation source are filled in an internal gap of a frame-shaped package rib, and the internal gap of the package rib has a diameter of 1000 [mu]m or less.

7. A light emitting device comprising the light emitting element according to claim 5 .

8. 8. The light emitting device according to claim 7, which is a μLED display.

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