Fluorescent substance powder, inkjet ink including same, light-emitting element, light-emitting device, and method for producing fluorescent substance powder

Abstract

Provided are a fluorescent substance powder which has a high luminescent efficiency although being fine, and a method for producing the fluorescent substance powder. This fluorescent substance powder includes at least a Group-2 element (A), sulfur (S), and a luminescence center element (M), has a 90% volume-cumulative diameter (D90) of 10.0 μm or less, and has a lattice strain (σ), as determined by analyzing an X-ray diffraction profile by a WPPF method, of 0.300% or less.

Description

Phosphor powder, inkjet ink using the same, light-emitting element, light-emitting device, and method for producing phosphor powder

[0001] The present invention relates to a phosphor powder, an ink-jet ink using the same, a light-emitting element, a light-emitting device, and a method for producing the phosphor powder.

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

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

[0004] In recent years, advances in display technology have garnered attention in mini (mini) LED displays and micro (μ) LED displays. μLED displays are composed of independent μLEDs for each of the R (red), G (green), and B (blue) subpixels. Each package (cell) corresponding to a subpixel is separated by a partition (package rib), preventing color mixing due to light from adjacent packages. Reflecting the size of the subpixel, the package is extremely small, measuring, for example, less than 1000 μm on a side. An excitation source such as an LED is provided on the bottom of the package, and a phosphor layer is provided on top of it. The phosphor layer is fabricated by filling the package with phosphor powder. Each package is filled with phosphor powder of a different color (red, green, blue) from the adjacent packages.

[0005] Phosphor powders are often synthesized by a dry method (solid-phase method) that utilizes a solid-phase reaction of raw material powders. For example, Patent Document 1 discloses a method of mixing silicon nitride powder, aluminum nitride powder, europium oxide powder, etc., and then firing and crushing the resulting mixed powder at 1950°C to obtain a phosphor (paragraphs

[0077] to

[0083] of Patent Document 1).

[0006] In addition, the use of an inkjet process has been proposed as a method for filling phosphor powder into objects such as display packages. In this process, ink containing phosphor powder (inkjet ink) is sprayed from the nozzle holes of an inkjet head, thereby filling or coating the object. The inkjet process allows for precise filling of phosphor powder into minute areas. It also has the advantage of minimal material waste and excellent total cost. The inkjet process is particularly suitable for the field of μLED display manufacturing, where phosphor powder is filled into minute packages.

[0007] JP 2023-107773 A

[0008] As described above, it has been proposed to synthesize phosphor powder by a dry method and to use an inkjet process to fill the synthesized phosphor powder.

[0009] However, the inventors have found that conventional phosphor powders have problems. Namely, there is a demand for high brightness displays, and the phosphor powders used therefor are required to have high luminous efficiency.

[0010] On the other hand, there is also a demand for higher resolution displays, and as a result, package sizes are becoming ever smaller. To miniaturize the package, the phosphor powder used to fill it must also be made finer. This is because it is difficult to fill a small package with coarse phosphor powder. Even if it were possible to fill it, only an uneven phosphor layer would be obtained, and if the package is thin, the coarse particles could act as foreign matter and impair the surface smoothness.

[0011] In particular, when using the cost-effective inkjet process to fill phosphor powder, the nozzle holes of the inkjet head must be made smaller to accommodate the miniaturization of package sizes, but large particles of phosphor powder cannot pass through the small nozzle holes and may clog the nozzle holes.

[0012] However, the dry method utilizes a solid-state reaction that takes place at high temperatures. As a result, the particles that make up the powder often grow into hard, coarse particles, making the powder unsuitable for use in displays.

[0013] Although it is possible to reduce the size of phosphor powder by pulverization, strong pulverization is required to break down the hard, coarse particles (intragranular fracture). However, even with strong pulverization, there is a limit to how fine the resulting powder can be. Furthermore, strong pulverization causes strong damage during pulverization, which can result in the resulting powder containing a large amount of strain and potentially reduced luminous efficiency. Furthermore, the resulting particles are prone to agglomeration, and even if fine primary particles are obtained, they are prone to forming coarse secondary particles (aggregated particles). Therefore, conventional phosphor powders have difficulty achieving both high luminous efficiency and high fineness, making them insufficient to meet the demand for higher resolution and brightness in displays.

[0014] The present inventors have conducted extensive research in light of these conventional problems. As a result, they have discovered that by employing a novel wet method (liquid-phase method) using a Group 2 element salt, a luminescent center element salt, an alkali metal sulfide, and sulfur as raw materials, and by utilizing a specified wet media-less crushing method, it is possible to obtain a phosphor powder with few coarse particles and small lattice distortion. This phosphor powder is fine yet has high luminous efficiency, and is expected to be particularly suitable for use in high-resolution, high-brightness displays.

[0015] The present invention was completed based on these findings, and an object of the present invention is to provide a fine phosphor powder with high luminous efficiency and a method for producing the same.

[0016] The present invention includes the following aspects (1) to (11). In this specification, the expression "to" includes the numerical values ​​at both ends. In other words, "X to Y" is synonymous with "at least X and at most Y."

[0017] (1) A phosphor powder containing at least a Group 2 element (A), sulfur (S), and a luminescent center element (M), having a volume-based cumulative 90% diameter (D90) of 10.0 μm or less, and having a lattice distortion (σ) of 0.300% or less as determined by analyzing an X-ray diffraction profile using the WPPF method.

[0018] (2) The phosphor powder of (1) above, having a cumulative 50% diameter (D50) on a volume basis of 0.050 μm or more and 10.0 μm or less.

[0019] (3) The phosphor powder of (1) or (2) above, wherein the product (D50×σ) of the cumulative 50% diameter (D50) on a volume basis and the lattice distortion (σ) is 0.40 μm·% or less.

[0020] (4) The phosphor powder has the formula: Ca １－ｘ Sr ｘ A phosphor powder according to any one of (1) to (3) above, having a composition represented by S:M (where M is a luminescent center element, and x is 0≦x≦1).

[0021] (5) The phosphor powder of (4) above, wherein the luminescent center atom M contains europium (Eu).

[0022] (6) The phosphor powder according to any one of (1) to (5) above, which has an internal quantum efficiency of 40% or more.

[0023] (7) An inkjet ink containing the phosphor powder according to any one of (1) to (6) above and a solvent.

[0024] (8) A light-emitting device comprising an excitation source and any one of the phosphor powders (1) to (6) above, wherein the phosphor powder is excited by irradiation with light from the excitation source to emit visible light.

[0025] (9) A light emitting device comprising the light emitting element of (8) above.

[0026] (10) The light-emitting device according to (9) above, which is a display.

[0027] (11) A method for producing a phosphor powder, the method comprising the following steps: preparing a first solution containing a first solvent and a salt of a Group 2 element (A) and a salt of a luminescent center element (M) dissolved or dispersed in the first solvent; preparing a second solution containing a second solvent, sulfur (S), and an alkali metal sulfide dissolved in the second solvent; mixing and stirring the first solution and the second solution to obtain a third solution in which a sulfide containing a Group 2 element and a luminescent center element is dissolved and a precipitate containing an alkali metal salt is deposited; subjecting the third solution to a solid-liquid separation process to remove the precipitate; drying the third solution from which the precipitate has been removed to obtain a phosphor precursor made of a polysulfide containing a Group 2 element and a luminescent center element; calcining the phosphor precursor to obtain a fired phosphor product; and crushing the fired phosphor product by a pressurized spray-type wet media-less crushing method or a rocking wet media-less crushing method to obtain a crushed phosphor product.

[0028] According to the present invention, there are provided fine phosphor powders with high luminous efficiency and a method for producing the same.

[0029] 1 shows SEM images of phosphors synthesized by a wet method (liquid phase method), and 2 shows SEM images of phosphors synthesized by a dry method (solid phase method).

[0030] Specific embodiments of the present invention (hereinafter referred to as "present embodiments") are described below. However, the present invention is not limited to the following embodiments, and various modifications are possible within the scope of the present invention. Furthermore, in this specification, any combination of preferred aspects can be adopted as long as technical consistency can be achieved. For example, one preferred numerical range and another preferred numerical range can be combined arbitrarily.

[0031] <<1. Phosphor Powder>> The phosphor powder of this embodiment contains at least a Group 2 element (A), sulfur (S), and a luminescent center element (M). The phosphor powder is composed of a host crystal and the luminescent center element that is ionized and doped into the host crystal. In this embodiment, the Group 2 element and sulfur form a sulfide host crystal, which is doped with the ionized luminescent center element. The phosphor powder may be composed only of a Group 2 element, sulfur, and the luminescent center element, or may contain other elements.

[0032] The Group 2 elements (A) are elements belonging to Group 2 of the periodic table, and are a collective term for beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). The Group 2 elements, together with sulfur, constitute a sulfide, which is the host crystal. The phosphor powder may contain one type of Group 2 element, or may contain a combination of multiple types of Group 2 elements. As the Group 2 element, at least one selected from the group consisting of Ca, Sr, and Ba is preferred, at least one selected from the group consisting of Ca and Sr is more preferred, and Ca is particularly preferred.

[0033] The luminescent center element (M) is an element that becomes a luminescent ion in a phosphor. When excitation light is irradiated onto a phosphor, the luminescent ion absorbs the excitation light, and electrons in the ground level are excited to an excited level. When these excited electrons return to the ground level, the difference energy is emitted as fluorescence. Examples of luminescent center elements include rare earth elements and transition elements. Among these, it is preferable to include at least one selected from the group consisting of europium (Eu), cerium (Ce), samarium (Sm), magnesium (Mg), lanthanum (La), pselaodium (Pr), neodymium (Nd), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), copper (Cu), silver (Ag), gold (Au), nickel (Ni), zirconium (Zr), manganese (Mn), gallium (Ga), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), and bismuth (Bi), and it is particularly preferable to include europium (Eu).

[0034] According to a preferred embodiment, the phosphor powder includes a host crystal containing at least one Group 2 element (A) selected from the group consisting of strontium (Sr) and calcium (Ca) and sulfur (S), and a luminescent center element (M). More preferably, the phosphor powder is represented by the general formula: Ca １－ｘ Sr ｘ The phosphor powder has a composition represented by S:M (where M is a luminescent center element, and x is 0≦x≦1). The phosphor powder may contain only one of Sr and Ca. However, it is preferable to contain both Sr and Ca. Specifically, the phosphor powder has a composition represented by the above-mentioned general formula (Ca １－ｘ Sr ｘ In the ratio of XA to XM, it is preferable that the molar amount XA of the Group 2 element A (Ca, Sr, etc.) and the molar amount XM of the luminescent center element M satisfy the condition 0.050≦x≦0.98. Furthermore, the ratio of XM to the sum of XA, XM / (XA+XM) of the Group 2 element A (Ca, Sr, etc.) and XM, XM, is preferably 0.0010 or more and 0.10 or less. A phosphor powder having such a composition and containing Eu as the luminescent center element emits red light when irradiated with excitation light having a wavelength of 450 nm.

[0035] According to another preferred embodiment, the phosphor powder includes a host crystal containing at least one Group 2 element (A) selected from the group consisting of barium (Ba), strontium (Sr), and calcium (Ca), gallium (Ga), and sulfur (S), and a luminescent center element (M). More preferably, the phosphor powder is represented by the general formula: AGa ２ S ４ The phosphor powder contains a crystal represented by the formula: XA:M (where A is at least one Group 2 element selected from the group consisting of Ba, Sr, and Ca, and M is a luminescent center element). In this case, the ratio of XA to the sum of the molar amount XA of the Group 2 element A (Ba, Sr, Ca, etc.) and the molar amount XM of the luminescent center element M (XM / (XA+XM)) is preferably 0.0010 or more and 0.30 or less. A phosphor powder having such a composition and containing Eu as the luminescent center element emits green light when irradiated with excitation light having a wavelength of 450 nm.

[0036] The phosphor powder of this embodiment is not limited to those having the above-mentioned composition, and is applicable to this embodiment as long as it contains a Group 2 element, a luminescent center element, and sulfur and exhibits fluorescent properties.

[0037] The phosphor powder of this embodiment has a cumulative 90% diameter (D90) on a volume basis of 10.0 μm or less. D90 is an index of the size and amount of coarse particles contained in the powder. Powders with a large D90 contain many large coarse particles. In this embodiment, by keeping D90 within the above-mentioned range, the phosphor powder can be refined. In contrast, phosphor powders with a D90 greater than 10.0 μm contain many coarse particles, making uniform filling into micro-packages, particularly uniform filling using an inkjet process, difficult. From this perspective, D90 is preferably 5.0 μm or less, more preferably 2.0 μm or less. On the other hand, from the perspective of easily maintaining even higher luminous efficiency, D90 is preferably 0.10 μm or more, more preferably 0.30 μm or more, and even more preferably 0.50 μm or more. Furthermore, from the viewpoint of promoting miniaturization while maintaining high luminous efficiency, D90 is preferably 0.10 μm or more and 10.0 μm or less, more preferably 0.30 μm or more and 5.0 μm or less, and even more preferably 0.50 μm or more and 2.0 μm or less. D90 is measured using a laser diffraction particle size distribution analyzer. Specifically, it is determined by the method described in the examples below or a method similar thereto.

[0038] The phosphor powder of this embodiment has a lattice distortion (σ) of 0.300% or less, as determined by analyzing the X-ray diffraction profile using the Whole Powder Pattern Fitting (WPPF) method. The WPPF (Whole Powder Pattern Fitting) method is a technique for fitting a relatively wide angular range of the XRD profile based on lattice constant information. The WPPF method has advantages such as a high ability to resolve overlapping diffraction lines.

[0039] The higher the crystallinity of the powder, the smaller the lattice strain. By keeping the lattice strain within the above-mentioned range, it is possible to increase the luminous efficiency of the phosphor powder. In contrast, phosphor powder with a lattice strain of more than 0.300% has low crystallinity and it is difficult to obtain high luminous efficiency. From the viewpoint of improving luminous efficiency, the lattice strain is preferably 0.150% or less, more preferably 0.100% or less, even more preferably 0.050% or less, even more preferably 0.010% or less, particularly preferably 0.005% or less, and most preferably 0.001% or less. The lower limit of the lattice strain is not specified. It is sufficient that it is 0% or more, and it may be 0.0001% or more. The lattice strain is determined by the method performed in the examples described below or a method equivalent thereto.

[0040] The crystallite size of the phosphor powder is preferably 50 nm (500 Å) or more, and more preferably 100 nm (1000 Å) or more. The higher the crystallinity of the powder, the larger the crystallite size. Therefore, by increasing the crystallite size, it is possible to further increase the luminous efficiency of the phosphor powder. There is no upper limit to the crystallite size, provided that it is equal to or less than the particle diameter. However, it is typically 500 nm (5000 Å) or less. The crystallite size can be determined by the method described in the Examples below or a method similar thereto.

[0041] The cumulative 50% diameter (D50) of the phosphor powder on a volume basis is preferably 0.050 μm or more and 10.0 μm or less, more preferably 0.10 μm or more and 5.0 μm or less, and even more preferably 0.20 μm or more and 2.0 μm or less, provided that it is smaller than D90. The phosphor powder of this embodiment not only has fewer coarse particles, but also allows the average particle diameter itself to be reduced. By reducing D50, it becomes possible to more effectively promote uniform filling into micro-packages. Note that D50 is measured using a laser diffraction particle size distribution analyzer. Specifically, it is determined by the method described in the examples below or a method similar thereto.

[0042] The cumulative 10% diameter (D10) of the phosphor powder on a volume basis is preferably 0.30 μm or more, more preferably 0.50 μm or more, and even more preferably 1.00 μm or more, provided that it is smaller than D90 and D50. D10 is an indicator of the size and amount of ultrafine particles contained in the powder. By appropriately increasing D10, the proportion of ultrafine particles is reduced, thereby further improving the luminescence characteristics of the phosphor powder. The following mechanism is believed to be the reason for this. Specifically, the fired product is crushed during phosphor powder production to obtain the phosphor powder. The finer the particles, the more difficult they are to crush, so stronger crushing energy is required for crushing. When strong crushing energy is applied so that a large amount of ultrafine particles are produced, the strain in the ultrafine particles increases, which is thought to degrade the luminescence characteristics of the resulting phosphor powder. In other words, phosphor powder with a low proportion of ultrafine particles is thought to have high luminescence characteristics due to the small strain in the ultrafine particles.

[0043] The product (D50 x σ) of the cumulative 50% diameter (D50) and lattice strain (σ) on a volume basis of the phosphor powder is preferably 0.40 μm·% or less, more preferably 0.20 μm·% or less, even more preferably 0.030 μm·% or less, particularly preferably 0.010 μm·% or less, and most preferably 0.007 μm·% or less. By using D50 x σ as an index and reducing this index, it is possible to achieve both finer grains and high luminous efficiency at a higher level. The lower limit of D50 x σ is not specified. It may be 0 μm·% or more, and may be 0.001 μm·% or more.

[0044] The internal quantum efficiency (IQE) of the phosphor powder is preferably 40% or more, more preferably 50% or more, and most preferably 60% or more. The internal quantum efficiency is the efficiency with which the light absorbed by the phosphor is converted into another light, and is a measure of the luminous efficiency. By using a phosphor powder with a high internal quantum efficiency, it becomes possible to increase the brightness when applied to applications such as displays. There is no specified upper limit for the internal quantum efficiency. However, it is usually 100% or less.

[0045] The external quantum efficiency (EQE) of the phosphor powder is preferably 20% or more, and more preferably 30% or more. The external quantum efficiency is the efficiency with which the incident light irradiated on the phosphor is converted into another light. There is no specified upper limit for the external quantum efficiency. However, it is usually 100% or less.

[0046] The absorptivity (Abs) of the phosphor powder is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. The absorptivity is the proportion of incident light irradiated onto the phosphor that is absorbed by the phosphor. There is no specified upper limit for the absorptivity. However, it is usually 100% or less. The internal quantum efficiency, external quantum efficiency, and absorptivity can be determined by the method described in the Examples below or a method similar thereto.

[0047] <<2. Inkjet Ink>> The inkjet ink of this embodiment contains the above-described phosphor powder and a solvent. The phosphor powder of this embodiment is fine, and the content of coarse particles is reduced. Therefore, it is suitable for phosphor powder filling using an inkjet process. The inkjet ink of this embodiment has little risk of clogging even if the nozzle diameter of the inkjet head is small. Therefore, it is suitable for filling into micro-packages for displays.

[0048] The ink contains a solvent in addition to the phosphor powder. The solvent may be water, alcohol, ketone, ester, ether, aromatic hydrocarbon solvent, aliphatic hydrocarbon solvent, or the like, either alone or in combination. The ink may also contain additives such as a binder resin, such as polyvinyl alcohol or acrylic resin, a dispersant, or a surfactant.

[0049] <<3. Light-Emitting Element>> The light-emitting element of this embodiment includes an excitation source (light source) and the above-described phosphor powder. In this light-emitting element, the phosphor powder is excited by light irradiation from the excitation source and emits visible light. A blue-emitting LED with a wavelength of 420 nm or more and 500 nm or less is suitable as the excitation source (light source). As long as light from the excitation source is incident on the phosphor powder, the arrangement of the phosphor powder and the excitation source is not limited. For example, when the light-emitting element is applied to a μLED display, an LED serving as an excitation source is arranged at the bottom within each package, and a phosphor is filled and arranged above it. However, the light-emitting element of this embodiment is not limited to an element for a μLED display.

[0050] The light-emitting element may contain the phosphor powder in a powder state alone, or may contain the phosphor powder in a mixture with a resin, such as one or more resins selected from the group consisting of thermoplastic resins, thermosetting resins, ionizing radiation curable resins, and two-component curable resins.

[0051] <<4. Light-Emitting Device>> The light-emitting device of this embodiment includes the above-described light-emitting element. Examples of light-emitting devices include, but are not limited to, well-known applications such as illumination, backlights for mobile terminals, and displays (display devices). Among these, displays are preferred, μLED displays or mini-LED displays are more preferred, and μLED displays are particularly preferred.

[0052] <<5. Method for Producing Phosphor Powder>> The method for producing phosphor powder of this embodiment includes the following steps: a step of preparing a first solution containing a first solvent and a salt of a Group 2 element (A) and a salt of a luminescent center element (M) dissolved or dispersed in the first solvent (first solution preparation step); a step of preparing a second solution containing a second solvent, sulfur (S), and an alkali metal sulfide dissolved in the second solvent (second solution preparation step); and a step of mixing and stirring the first solution and the second solution to dissolve the sulfide containing the Group 2 element and the luminescent center element and precipitate a precipitate containing the alkali metal salt. The method includes a step of obtaining a third solution by subjecting the obtained third solution to solid-liquid separation to remove precipitates (solid-liquid separation step), a step of drying the third solution from which the precipitates have been removed to obtain a phosphor precursor composed of a polysulfide containing a Group 2 element and a luminescent center element (drying step), a step of calcining the obtained phosphor precursor to obtain a calcined phosphor product (calcining step), and a step of crushing the obtained calcined phosphor product by a pressurized jet-type wet media-less crushing method or a shaking-type wet media-less crushing method to obtain a crushed phosphor product (crushing step). If necessary, a step of washing the crushed phosphor product (washing step) may be provided. Details of each step are described below.

[0053] <First solution preparation step> In the first solution preparation step, a first solution containing a first solvent and a salt of a Group 2 element (A) and a salt of a luminescent center element (M) dissolved or dispersed in the first solvent is prepared.

[0054] The first solvent contains a salt of a Group 2 element and a salt of a luminescent center element dissolved or dispersed therein, and functions to form a reaction field in the subsequent reaction step. The first solvent is preferably an organic solvent. Furthermore, from the viewpoint of efficiently obtaining a sulfide with high purity, the first solvent preferably has a boiling point of 110°C or less. Specifically, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and t-butyl alcohol are preferred, with ethanol being particularly preferred. One or a mixture of two or more of the above-mentioned solvents may also be used. Furthermore, the amount of the first solvent is preferably an amount that can sufficiently dissolve or disperse the salt of a Group 2 element and the salt of a luminescent center element.

[0055] The salt of the Group 2 element (A) is a raw material of the Group 2 element, which is the main component of the phosphor powder. Therefore, the type can be determined depending on the composition of the target phosphor powder. Although not limited, the salt of the Group 2 element is preferably a salt containing at least one element selected from calcium (Ca), strontium (Sr), and barium (Ba), more preferably a salt containing at least one element selected from Ca and Sr, and particularly preferably a salt of Ca. Furthermore, the salt is preferably at least one selected from nitrates, chlorides, sulfates, and carbonates, and particularly preferably chlorides.

[0056] The amount of the salt of the Group 2 element is preferably 1.0 to 10.0 times the amount of the alkali metal sulfide added to the second solution in terms of molar ratio.

[0057] The salt of the luminescent center element (M) is a raw material of the luminescent center element, which is the main component of the phosphor powder. Therefore, the type can be determined depending on the composition of the target phosphor powder. Although not limited thereto, the salt of the luminescent center element is preferably a salt containing at least one element selected from the group consisting of europium (Eu), cerium (Ce), magnesium (Mg), lanthanum (La), pselaodium (Pr), neodymium (Nd), samarium (Sm), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), copper (Cu), silver (Ag), gold (Au), nickel (Ni), zirconium (Zr), manganese (Mn), gallium (Ga), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), and bismuth (Bi), and a salt of Eu is particularly preferred. The salt is preferably at least one selected from nitrates, chlorides, sulfates, and carbonates, with chlorides being particularly preferred.

[0058] The amount of the salt of the luminescent center element may be determined depending on the composition of the desired phosphor powder.

[0059] The first solution may be prepared by any method as long as it contains a salt of a Group 2 element and a salt of a luminescent center element dissolved or dispersed in the first solvent. For example, the first solution may be prepared by adding a salt of a Group 2 element and a salt of a luminescent center element to the first solvent and stirring the mixture. The first solvent may or may not be heated during stirring. Furthermore, if the target phosphor powder contains elements other than the Group 2 element, the luminescent center element, and sulfur, a salt of the other element may be added to the first solution.

[0060] <Second Solution Preparing Step> In the second solution preparing step, a second solution containing a second solvent, sulfur (S), and an alkali metal sulfide dissolved in the second solvent is prepared.

[0061] The second solvent contains an alkali metal sulfide and functions to form a reaction field in the subsequent reaction step. The second solvent is preferably an organic solvent. Furthermore, from the viewpoint of efficiently obtaining a sulfide with high purity, the second solvent preferably has a boiling point of 110°C or less. Specifically, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and t-butyl alcohol are preferred, with ethanol being particularly preferred. One or a mixture of two or more of the above-mentioned solvents may also be used. The type of the second solvent may be the same as or different from the first solvent. Furthermore, the amount of the second solvent is preferably an amount that can sufficiently dissolve the alkali metal sulfide.

[0062] Sulfur (S) is a raw material for sulfur, which is the main component of phosphor powder. In other words, sulfide phosphor powder can be obtained by using sulfur as a raw material. In particular, by using a large amount of sulfur, polysulfides that can be easily crushed can be obtained, making it possible to efficiently produce fine phosphor powder with high luminous efficiency. From the viewpoint of suppressing the residue of raw materials that inhibit luminescence, the amount of sulfur blended is preferably 1.0 to 10.0 times the amount of alkali metal sulfide in molar ratio. Note that, from the viewpoint of increasing reactivity, it is preferable that the sulfur be in powder form.

[0063] The alkali metal sulfide reacts with the anion component of the salt contained in the first solution to form a by-product that is easy to remove. In other words, by using the alkali metal sulfide, the anion component can be removed in the form of an alkali metal salt. The alkali metal sulfide is also a raw material for sulfur, which is the main component of the phosphor powder. As the alkali metal sulfide, a sulfide of at least one alkali metal selected from the group consisting of lithium (Li), sodium (Na), potassium (K), and hydrates thereof is preferred, and sodium sulfide (Na ２ S) is particularly preferred.

[0064] The second solution may be prepared by any method as long as it contains sulfur and an alkali metal sulfide dissolved in the second solvent. For example, the second solution may be prepared by adding sulfur and an alkali metal sulfide to the second solvent and stirring the mixture. The second solvent may or may not be heated during stirring. The second solution is a suspension (slurry).

[0065] Incidentally, when preparing the first solution, a salt of a Group 2 element and a salt of a luminescent center element are dissolved or dispersed in a first solvent. Preferably, the salt of a Group 2 element and the salt of a luminescent center element are dissolved in the first solvent. From this viewpoint, it is desirable that the first solvent be a solvent that has high solubility for the salt of a Group 2 element and the salt of a luminescent center element. Similarly, it is desirable that the second solvent be a solvent that has high solubility for an alkali metal sulfide.

[0066] Meanwhile, in the subsequent reaction step, an ion exchange reaction occurs between the salt of the Group 2 element, the salt of the luminescent center element, the alkali metal sulfide, and sulfur, producing a phosphor precursor, which is a polysulfide containing the Group 2 element and the luminescent center element, and also producing an alkali metal salt as a by-product. While the polysulfide (phosphor precursor) dissolves in the solvent (a mixed solvent of the first and second solvents), the alkali metal salt (by-product) is barely soluble and forms a precipitate. The by-product can be removed by subjecting the solution after the reaction step to solid-liquid separation. Therefore, from the perspective of removing as many by-products as possible and obtaining a high-purity phosphor powder, it is desirable that the first and second solvents have low solubility for the alkali metal salt (by-product).

[0067] From the above viewpoints, it is preferable to select a combination of the first solvent, the second solvent, the salt of the Group 2 element, the salt of the luminescent center element, and the alkali metal sulfide. Although not limited thereto, the first solvent and the second solvent are preferably ethanol, the salt of the Group 2 element and the salt of the luminescent center element are preferably chlorides, and the alkali metal sulfide is preferably sodium sulfide (Na ２ S) is preferred.

[0068] Furthermore, the order of the first solution step and the second solution step is not limited as long as the first solution and the second solution are prepared.

[0069] <Reaction Step> In the reaction step, the first solution and the second solution are mixed and stirred to obtain a third solution in which a sulfide containing a Group 2 element and a luminescent center element is dissolved and a precipitate containing an alkali metal salt is deposited. When the first solution and the second solution are mixed and stirred, an ion exchange reaction occurs between the salt of the Group 2 element, the salt of the luminescent center element, the alkali metal sulfide, and sulfur contained therein, producing a phosphor precursor that is a polysulfide containing a Group 2 element and a luminescent center element, and also producing an alkali metal salt as a by-product. While the polysulfide (phosphor precursor) dissolves in the third solution, the alkali metal salt (by-product) is barely dissolved and forms a precipitate.

[0070] For example, calcium chloride (CaCl) is a salt of a Group 2 element. ２ ) as a salt of the luminescent center element, europium chloride (EuCl ３ ) as an alkali metal sulfide, sodium sulfide (Na ２ When ethanol is used as both the first and second solvents, the reaction shown in the following formula (1) proceeds to the right, producing polysulfides containing calcium and europium ((Ca,Eu)S ｘ ) and sodium chloride (NaCl) are produced in ethanol.

[0071] CaCl ２ +EuCl ３ +Na ２ S+S → (Ca, Eu)S ｘ +NaCl↓ (1)

[0072] (Ca,Eu)S ｘhas a high solubility in ethanol, whereas NaCl has a low solubility. Therefore, NaCl hardly dissolves and forms a precipitate.

[0073] The method for mixing the first solution and the second solution is not particularly limited. The second solution may be added to the first solution, the first solution may be added to the second solution, or the first solution and the second solution may be added and mixed simultaneously. The mixing and the resulting reaction can be carried out at room temperature and atmospheric pressure. Specifically, the mixing can be carried out at a temperature of 0°C or higher and 40°C or lower under atmospheric pressure.

[0074] <Solid-Liquid Separation Step> In the solid-liquid separation step, the obtained third solution is subjected to a solid-liquid separation treatment to remove precipitates. As described above, the polysulfide (phosphor precursor) containing a Group 2 element and a luminescent center element dissolves in the third solution, whereas the alkali metal salt (by-product) is barely soluble and forms a precipitate. Therefore, the by-product can be separated and removed by the solid-liquid separation treatment. The solid-liquid separation can be performed by a known method, such as filtration, centrifugation, or decantation. The method is not limited as long as it can remove the precipitate.

[0075] <Drying Step> In the drying step, the third solution from which the precipitate has been removed is dried to obtain a phosphor precursor composed of a polysulfide containing a Group 2 element and a luminescent center element. Drying can be performed by a known method, such as heat drying or vacuum drying. Drying conditions vary depending on the type of solvent (first solvent, second solvent) used, and therefore cannot be determined in general. When ethanol is used, for example, the drying conditions include maintaining the solution at 40°C or higher and 70°C or lower for 1 hour to 72 hours.

[0076] <Firing step> In the firing step, the obtained phosphor precursor is fired to obtain a fired phosphor. The phosphor precursor contains polysulfides. When this phosphor precursor is fired, the polysulfides undergo a thermal decomposition reaction and are converted into a fired phosphor. For example, when the group 2 element is calcium (Ca) and the luminescent center element is europium (Eu), the fired phosphor is obtained as (Ca, Eu)S. ｘ The polysulfide having the composition is thermally decomposed to produce a fired phosphor having the composition CaS:Eu.

[0077] Firing is carried out under conditions that allow a fired phosphor of the desired composition to be obtained. In order to fully promote the thermal decomposition reaction, it is preferable to carry out firing for a long period of time at a relatively high temperature. On the other hand, if the firing time is excessively high or excessively long, the resulting fired phosphor may be sintered and become coarse. Therefore, it is preferable to carry out firing under conditions that allow the thermal decomposition reaction to fully proceed while preventing the phosphor from becoming coarse. The optimal firing temperature and holding time vary depending on the phosphor composition, and it is difficult to determine them in general. For example, firing is carried out under conditions that allow the temperature to be between 500°C and 1200°C and to be held for between 0.50 hours and 12 hours. In addition, firing is carried out under conditions that allow the temperature to be between 500°C and 1200°C and to be held for between 0.50 hours and 12 hours. ２ It is preferable to carry out the baking in an inert gas atmosphere such as argon (Ar) or argon (Ar). The baking may be carried out continuously with the preceding drying treatment or as an independent treatment.

[0078] In the manufacturing method of this embodiment, the precursor used for firing is a polysulfide, which allows for the production of a fired product that can be easily crushed in subsequent processes. That is, when the polysulfide is thermally decomposed, fine phosphor particles are formed in the fired product. These phosphor particles are loosely bonded to each other. Therefore, the fired product can be easily crushed into fine particles.

[0079] In addition, since the precursor is a polysulfide, hydrogen sulfide (H ) is corrosive, toxic, and flammable. ２ There is no need to introduce a sulfur-containing gas such as sulfur dioxide (S) into the firing atmosphere. This allows the phosphor powder to be produced safely. Another advantage is that firing can be carried out at room temperature and atmospheric pressure. However, the production method of this embodiment is not limited to methods that do not involve the introduction of a sulfur-containing gas. It goes without saying that a sulfur-containing gas may be introduced when the amount of sulfur contained in the precursor is insufficient.

[0080] <Crushing step> In the crushing step, the obtained phosphor fired product is crushed by a pressurized jet type wet media-less crushing method or a rocking type wet media-less crushing method to obtain a crushed phosphor product. In the fired product after the firing step, fine phosphor particles are loosely bonded to each other. By performing the crushing treatment, the bonds between the phosphor particles are loosened, and a powder is obtained.

[0081] The manufacturing method of this embodiment is characterized by the use of a pressurized injection wet media-less crushing method or a vibration wet media-less crushing method. The pressurized injection wet media-less crushing method is a technique in which high pressure is applied to a suspension (slurry) containing the material to be treated and sprayed from a micro-nozzle. The material to be treated is sprayed at high speed and crushed by shear force upon impact with the solid object, or by the effects of cavitation, turbulence, etc. Pressurized injection wet media-less crushing is distinguished from media-agitation-type pulverization such as attritors, paint shakers, ball mills, and bead mills in that it does not use media such as balls or beads. It also differs from ultrasonic homogenizers and high-pressure homogenizers in that it crushes the pressurized injected material to be treated by the effects of shear force, cavitation, and / or turbulence, etc.

[0082] Pressurized injection wet media-less crushing does not use crushing media, so damage during crushing is minimal, and crushed material with little distortion can be obtained. Another advantage is that there is little risk of impurities being mixed in. In contrast, methods that use media cause significant damage to the processed material, making it difficult to suppress the reduction in distortion. Furthermore, there is a risk of impurities being mixed in from the media. Therefore, phosphor powder with little lattice distortion can be obtained, despite the fact that there are few coarse particles.

[0083] In the crushing process, the phosphor burned material is added to a crushing solvent to form a slurry, and the resulting slurry is introduced into a pressurized injection-type wet media-less crushing device. Examples of crushing solvents include alcohols such as methanol, ethanol, and propanol, as well as water. During the crushing process, the pressurized slurry is sprayed from a micro-nozzle. The crushing process is preferably performed under conditions that sufficiently crush the coarse particles while minimizing lattice strain within the particles. It is also desirable to perform the process under conditions that suppress the generation of ultrafine particles. For example, from the viewpoint of promoting the crushing of coarse particles, the pressure (discharge pressure) applied to the slurry is preferably 1 MPa or more, more preferably 10 MPa or more. On the other hand, excessively high pressure can increase lattice strain and result in excessively large amounts of ultrafine particles. From the viewpoint of suppressing the increase in lattice strain and the generation of ultrafine particles, the pressure (discharge pressure) may be 300 MPa or less, 200 MPa or less, or even 100 MPa or less. The number of passes during crushing can be set to obtain the desired phosphor powder. The number of passes may be one, two, three, or more.

[0084] The crushing may be performed by a rocking wet media-less crushing method. The rocking wet media-less crushing method is a technique in which a container (crushing container) filled with a suspension (slurry) containing the material to be processed is rocked to apply a collision pressure to the material to be processed, thereby crushing it. Specifically, it can be performed using a high-speed rocking crushing device such as a rocking mill. Rocking wet media-less crushing has the advantage that it does not use crushing media and can produce crushed material with little lattice distortion and ultrafine particles without the risk of impurity contamination.

[0085] <Washing Step> If necessary, a step of washing the obtained crushed phosphor material (washing step) may be provided. Although the amount may be small, the crushed phosphor may contain residual alkali metal sources as by-products. Furthermore, excess Group 2 elements, luminescent center elements, and / or sulfur components may remain. By carrying out the washing process, these by-products and excess components can be reduced, and a highly pure phosphor powder can be obtained.

[0086] The washing method is not limited as long as it reduces by-products and excess components. For example, the crushed phosphor material may be washed with a washing liquid such as water. For example, the crushed material may be placed in a washing liquid, and a series of operations of stirring, leaving the material to stand, and removing the supernatant liquid may be repeated once or multiple times. When washing with a washing liquid, a step of drying the washed crushed material under heat and / or reduced pressure may be added.

[0087] The phosphor powder of this embodiment can be obtained in this manner. The phosphor powder obtained by this method is characterized by its high luminous efficiency despite its fine size. Specifically, unlike the dry (solid-phase) method, this method uses a wet (liquid-phase) synthesis method in which crystals are grown in liquid, enabling the synthesis of phosphor particles with small primary particle diameters and high crystallinity. Furthermore, in the manufacturing method of this embodiment, by-products are generated in the solution in the form of solid precipitates, and the solid by-products (precipitates) are removed by solid-liquid separation. This effectively minimizes by-product contamination. Furthermore, the specified wet media-less crushing method minimizes damage during crushing and minimizes impurity contamination. Therefore, the resulting phosphor powder has minimal distortion and high purity. Furthermore, this method is characterized by its high luminous efficiency despite its fine size.

[0088] In contrast, it is difficult to obtain fine phosphor powder using the dry method. Although a method of pulverizing the powder by strong crushing is known, it causes significant damage to the phosphor powder and introduces impurities, making it difficult to obtain phosphor powder with low distortion and high luminous efficiency.

[0089] The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples.

[0090] (1) Preparation of Phosphor Powder [Example 1] In Example 1, a phosphor fired product was synthesized by a wet method, and the resulting phosphor fired product was subjected to pressurized injection type wet media-less crushing. Specifically, the phosphor powder was prepared according to the following procedure.

[0091] <Synthesis of fired phosphor> Calcium chloride (CaCl) was used as a starting material. ２ ) powder, sulfur (S) powder, europium chloride (EuCl３ ) powder, sodium sulfide (Na ２ S) powder was prepared. Ethanol was also prepared as a solvent. Next, CaCl ２ The powder is Na ２ 1.3 times the molar amount of S powder, EuCl ３ The powder is Na ２ The amount of S powder was 0.01 times (1 at%), and the amount of S powder was Na ２ The amount was weighed out so that the molar ratio was 2.5 times that of the S powder.

[0092] Weighed CaCl ２ Powder and EuCl ３ The powder was stirred in ethanol to dissolve completely, and the first solution was prepared. ２ S powder and S powder were stirred in ethanol to obtain Na ２ The S powder was dissolved in the third solution to prepare a second solution. The first and second solutions were then mixed and stirred at room temperature and pressure to prepare a third solution. During this process, a reaction occurred in the third solution, resulting in the formation of a precipitate consisting of sodium chloride (NaCl). The precipitate was removed from the third solution, and the supernatant was recovered. The recovered supernatant was then subjected to solid-liquid separation using a centrifuge.

[0093] The solution obtained after the solid-liquid separation treatment was then vacuum dried at 60°C for 12 hours to obtain a phosphor precursor. The obtained phosphor precursor was placed in a firing furnace and fired at 800°C for 2 hours in a nitrogen atmosphere to obtain a fired phosphor. During firing, nitrogen was flowed into the firing furnace at a flow rate of 1 L / min.

[0094] A scanning electron microscope (SEM) image of the obtained fired phosphor is shown in Figure 1. The particle size was as fine as about 1 µm.

[0095] <Crushing of the fired phosphor product> Next, the obtained fired phosphor product was placed in ethanol to prepare a slurry with a concentration of 5% by mass. The obtained slurry was then subjected to pre-crushing using an ultrasonic cleaner (US-10PS, SND Corporation) at an output of 100 W for 3 minutes. The pre-crushed slurry was then introduced into a liquid-injection wet media-less crusher (Starburst Mini, Sugino Machine Corporation) and subjected to crushing treatment. The discharge pressure was 200 MPa, and the number of passes was one. In this manner, a phosphor powder was prepared.

[0096] Example 2 A phosphor powder was prepared in the same manner as in Example 1, except that the number of passes during the crushing treatment using the pressurized injection type wet media-less crusher was changed to 2.

[0097] Example 3 A phosphor powder was prepared in the same manner as in Example 1, except that the number of passes during the crushing treatment using the pressurized injection type wet media-less crusher was changed to 3.

[0098] Example 4 (Comparative Example) A fired phosphor material was synthesized in the same manner as in Example 1. Thereafter, the fired phosphor material was crushed in the following manner to prepare a phosphor powder.

[0099] <Crushing of the fired phosphor material> The fired phosphor material was placed in ethanol to prepare a slurry with a concentration of 5% by mass. The resulting slurry was then subjected to a crushing treatment using an ultrasonic homogenizer (Mitsui Electric Seiki Co., Ltd., UX-300) for 30 minutes. The output of the ultrasonic homogenizer was set to 50% (150 W).

[0100] Example 5 (Comparative Example) A phosphor powder was prepared in the same manner as in Example 4, except that the powder was subjected to a crushing treatment using an ultrasonic homogenizer for 60 minutes.

[0101] Example 6 (Comparative Example) A fired phosphor material was synthesized in the same manner as in Example 1. Thereafter, the fired phosphor material was crushed in the following manner to prepare a phosphor powder.

[0102] <Crushing of the fired phosphor product> 5 g of the fired phosphor product was placed in ethanol and crushed in a ball mill for 30 minutes. 45 g of zirconia balls were used as media during the ball mill treatment. The ball mill pot was rotated at 300 rpm.

[0103] [Example 7 (Comparative Example)] In Example 7, a fired phosphor material was synthesized by a dry method (solid-phase method), and the resulting fired phosphor material was crushed by a ball mill. Specifically, a phosphor powder was produced according to the following procedure.

[0104] <Synthesis of fired phosphor> Calcium carbonate (CaCO ３ ) to hydrogen sulfide (H ２ The mixture was fired at 850°C for 4 hours in a europium oxide (Eu) atmosphere to obtain calcium sulfide (CaS). ２ O ３ ) was mixed in an amount of 0.3 atomic %, and the resulting mixture was fired in an argon (Ar) atmosphere at 1000°C for 4 hours to obtain a fired product. The argon (Ar) flow rate during firing was 1.0 L / min. The fired product was pulverized and classified using a jet mill (manufactured by Dec Corporation) under a fluid pressure of 12 MPa to obtain a phosphor with a CaS:Eu composition.

[0105] An SEM image of the obtained phosphor is shown in Figure 2. The obtained phosphor had a coarse particle size of about 5 µm.

[0106] <Crushing of the fired phosphor> 50 g of the obtained phosphor was placed in ethanol and crushed in a ball mill for 20 hours. 450 g of zirconia balls were used as media during the ball milling process. The ball mill pot was rotated at 300 rpm.

[0107] [Example 8] In Example 8, a fired phosphor material was synthesized by a wet method, and the resulting fired phosphor material was crushed using a rocking mill. Specifically, a phosphor powder was produced according to the following procedure.

[0108] <Synthesis of fired phosphor> Calcium chloride (CaCl) was used as a starting material. ２ ) powder, strontium chloride (SrCl ２) powder, sulfur (S) powder, europium chloride (EuCl ３ ) powder, and sodium sulfide (Na ２ S) powder was prepared. Methanol and ethanol were also prepared as solvents. Next, CaCl ２ The powder was dissolved in SrCl ２ 0.6 times the amount of powder in molar ratio (Ca / Ca+Sr) = 0.06), Na ２ S powder, CaCl ２ powder and SrCl ２ 0.9 times the molar ratio of the total powder (Na ２ S / (CaCl ２ + SrCl ２ )=0.9), EuCl ３ The powder was ２ S powder was added in an amount of 0.003 times (0.3 at%) of S powder. ２ The amount was weighed out so that the molar ratio was 3.0 times that of the S powder.

[0109] Weighed CaCl ２ powder, SrCl ２ Powder and EuCl ３ The powder was stirred in a mixed solvent of methanol and ethanol to dissolve it completely, and a first solution was prepared. At this time, the mixing ratio of methanol and ethanol in the first solvent was adjusted so that the volume ratio of ethanol to methanol was 4.3 times. ２ S powder and S powder were stirred in ethanol to obtain Na ２ The S powder was dissolved in the third solution to prepare a second solution. The first and second solutions were then mixed and stirred at room temperature and pressure to prepare a third solution. During this process, a reaction occurred in the third solution, resulting in the formation of a precipitate consisting of sodium chloride (NaCl). The precipitate was removed from the third solution, and the supernatant was recovered. The recovered supernatant was then subjected to solid-liquid separation using a centrifuge.

[0110] The solution obtained after the solid-liquid separation was then vacuum dried at 60°C for 12 hours to obtain a phosphor precursor. The obtained phosphor precursor was placed in a firing furnace and fired at 700°C for 2 hours in a nitrogen atmosphere to obtain a fired phosphor. During firing, nitrogen was flowed into the firing furnace at a flow rate of 4 L / min. In this way, the charged composition was adjusted to Sr ０．９４ Ca ０．０６ S: EU ０．００３ A fired phosphor was obtained.

[0111] <Crushing of the fired phosphor product> The obtained fired phosphor product was placed in methanol to prepare a slurry with a concentration of 17% by mass. Next, the obtained slurry was crushed using a rocking mill (Seiwa Giken Co., Ltd., RM-05). The crushing treatment was performed under the conditions of 60 Hz and 30 minutes. In this way, a phosphor powder was prepared.

[0112] Example 9 A fired phosphor material was synthesized in the same manner as in Example 8. Thereafter, the fired phosphor material was crushed in the following manner to prepare a phosphor powder.

[0113] <Crushing of the fired phosphor product> The obtained fired phosphor product was placed in ethanol to prepare a slurry with a concentration of 1.3% by mass. The obtained slurry was then introduced into a wet media-less apparatus (Yoshida Kikai Kogyo Co., Ltd., NVL-AS200) and subjected to a crushing treatment. The discharge pressure was 75 MPa and the number of passes was 5. In this manner, a phosphor powder was prepared.

[0114]

[0115] (2) Evaluation of Phosphor Powder Using the phosphor powders obtained in the examples and comparative examples as samples, various properties were evaluated as follows.

[0116] <Luminescence efficiency (absorbance, external quantum efficiency, internal quantum efficiency)> Using a fluorescence spectrophotometer (JASCO, FP-8500DS), the absorbance (Abs), external quantum efficiency (EQE), and internal quantum efficiency (IQE) of the sample were determined according to a quantum efficiency calculation program. The respective calculation formulas are shown below.

[0117] P1(λ) was the LED light spectrum at 450 nm, and P2(λ) was the sample spectrum. The area L1 enclosed by the spectrum P1(λ) in the excitation wavelength range of 430 nm to 500 nm was calculated according to the following formula (i), and the obtained value was used as the excitation intensity. The area L2 enclosed by the spectrum P2(λ) in the excitation wavelength range of 430 nm to 500 nm was calculated according to the following formula (ii), and the obtained value was used as the sample scattering intensity. The area E2 enclosed by the spectrum P2(λ) in the excitation wavelength range of 500 nm to 850 nm was calculated according to the following formula (iii), and the obtained value was used as the sample fluorescence intensity.

[0118]

[0119] The absorptance (Abs) is the ratio of the excitation light attenuated by the sample to the incident light, and was calculated according to the following formula (iv): ｅｍ is the number of photons of the excitation light irradiated on the sample, N ｅｘ The internal quantum efficiency (IQE) is the value obtained by dividing the number of photons of fluorescence emitted from the sample, N ｅｍ is the number of photons of the excitation light absorbed by the sample, N ａｂｓ The value was calculated according to the following formula (vi):

[0120]

[0121] <Particle Size Distribution> The particle size distribution of the sample was measured using a laser diffraction particle size distribution analyzer (Microtrac Bell, 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 a dispersion treatment such as ultrasonic dispersion (40 W, 180 seconds). Next, the particle size was measured while circulating the particles in the solvent in the measurement cell. From the measurements, a frequency particle size distribution curve and a cumulative particle size distribution curve on a volume basis were obtained, and the cumulative 50% diameter (D50) and cumulative 90% diameter (D90) were calculated from these. The particle size measurement was performed under the following conditions.

[0122] - Flow rate: 80% - Ultrasonic: 40W, 180 seconds - Set Zero time: 10 seconds - Measurement time: 30 seconds - Number of measurements: 1 - Transmittance: Transmitted - Particle refractive index: 2.46 - Particle shape: Aspherical - Solvent refractive index: 1.36

[0123] <XRD Analysis (Lattice Distortion, Crystallite Size)> The sample (phosphor powder) was analyzed by X-ray diffraction (XRD) to obtain an XRD profile. The XRD analysis was performed under the following conditions.

[0124] - X-ray diffraction equipment: fully automatic multipurpose X-ray diffraction equipment (Rigaku Corporation, SmartLab) - Radiation source: CuKα - Detector: D / teX Ultra 250HE (Rigaku Corporation) - Tube current: 200mA - Tube voltage: 45kV - Scanning conditions: focusing method - Scanning axis: 2θ / θ - Scanning range: 10 to 140° - Step width: 0.005° - Scanning speed: 1° / min

[0125] The obtained XRD profile was then analyzed by the WPPF method to determine the lattice strain (σ) and crystallite size. Specifically, the procedure was carried out using integrated powder X-ray analysis software (PDXL2, Rigaku Corporation) as follows.

[0126] First, identification (CaS) was performed using the software's automatic search function. Next, analysis was performed using the WPPF method. At this time, a line standard data file (SRM660a), which is a file of XRD data obtained by measuring LaB6, was selected for line correction. In addition, the peak width was corrected using an external standard sample (SRM66:LaB6). The "split-type Pearson VII function" was used as the peak shape model function.

[0127] Next, on the software operation screen, from the "Basic" tab, select "Refinement parameters" - "Method" and select "Intensity decomposition." Next, refinement was performed. During refinement, various parameters were adjusted until sufficient convergence was achieved.

[0128] <SEM Observation> The sample was observed with a scanning electron microscope (SEM).

[0129] (3) Evaluation Results The evaluation results obtained for the samples of the Examples and Comparative Examples are summarized in Table 2 below.

[0130] The phosphor calcined material was synthesized by a wet method and crushed by a pressurized injection type wet media-less crushing method. All of the example samples (Examples 1 to 3) had a D90 of 10.0 μm or less, a lattice distortion σ of 0.010% or less (0.300% or less), and a relatively high internal quantum efficiency IQE of 54% or more.

[0131] In addition, even in the example samples (Examples 8 and 9) in which the feed composition was changed and the crushing was performed using a rocking wet media-less crushing method (rocking mill) or a pressurized injection wet media-less crushing method, the D90 was 10.0 μm or less, the lattice distortion σ was 0.300% or less, and the internal quantum efficiency IQE was relatively high at 40% or more.

[0132] In contrast, in Examples 4 and 5, where the crushing treatment was performed using an ultrasonic homogenizer, the D90 exceeded 10.0 μm. In addition, in Example 6, where the crushing treatment was performed using a ball mill for 30 minutes, the D90 also exceeded 10.0 μm.

[0133] In Example 7, in which the phosphor fired product was synthesized by a dry method (solid-phase method) and crushed for a long time (20 hours) using a ball mill, the D90 was 10.0 μm or less, but the lattice distortion σ was large at 0.303%, and therefore the internal quantum efficiency IQE was very low at 7.7%.

[0134] In addition, the amount of sodium (Na) in each of the examples and comparative samples was 0.04 mass %.

[0135]

[0136] From the above results, it can be seen that the present embodiment provides a fine phosphor powder with high luminous efficiency and a method for producing the same.

Claims

1. A phosphor powder containing at least a Group 2 element (A), sulfur (S), and a luminescent center element (M), having a volume-based cumulative 90% diameter (D90) of 10.0 μm or less, and having a lattice distortion (σ) of 0.300% or less as determined by analyzing the X-ray diffraction profile using the WPPF method.

2. The phosphor powder according to claim 1, wherein the cumulative 50% diameter (D50) on a volume basis is 0.050 μm or more and 10.0 μm or less.

3. The phosphor powder according to claim 1 or 2, wherein the product (D50 x σ) of the cumulative 50% diameter (D50) on a volume basis and the lattice distortion (σ) is 0.40 μm·% or less.

4. The phosphor powder has the formula: Ca １－ｘ Sr ｘ 3. The phosphor powder according to claim 1, having a composition represented by S:M (where M is a luminescent center element, and x is 0≦x≦1).

5. The phosphor powder according to claim 4, wherein the luminescent center atom M includes europium (Eu).

6. The phosphor powder according to claim 1 or 2, having an internal quantum efficiency of 40% or more.

7. An inkjet ink comprising the phosphor powder according to claim 1 or 2 and a solvent.

8. A light-emitting device comprising an excitation source and the phosphor powder according to claim 1 or 2, wherein the phosphor powder is excited by irradiation with light from the excitation source and emits visible light.

9. A light emitting device comprising the light emitting element according to claim 8.

10. The light emitting device of claim 9, wherein the light emitting device is a display.

11. A method for producing a phosphor powder, comprising the following steps: preparing a first solution containing a first solvent and a salt of a Group 2 element (A) and a salt of a luminescent center element (M) dissolved or dispersed in the first solvent; preparing a second solution containing a second solvent, sulfur (S), and an alkali metal sulfide dissolved in the second solvent; mixing and stirring the first solution and the second solution to obtain a third solution in which a sulfide containing a Group 2 element and a luminescent center element is dissolved and a precipitate containing an alkali metal salt is deposited; subjecting the third solution to solid-liquid separation to remove the precipitate; drying the third solution from which the precipitate has been removed to obtain a phosphor precursor composed of a polysulfide containing a Group 2 element and a luminescent center element; calcining the phosphor precursor to obtain a fired phosphor product; and crushing the fired phosphor product by a pressurized jet-type wet media-less crushing method or a shaking wet media-less crushing method to obtain a crushed phosphor product.

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