Europium activated β-sialon phosphor

Abstract

One aspect of the present disclosure provides a europium-activated β sialon phosphor that has a diffuse reflectance of at least 96% for light of a wavelength of 800 nm. The diffuse reflectance for light of a wavelength of 800 nm, the diffuse reflectance for light of a wavelength of 500 nm, and the chromaticity X of the europium-activated β sialon phosphor satisfy expression (1): ((diffuse reflectance for light of a wavelength of 800 nm)-(diffuse reflectance for light of a wavelength of 500 nm))-(166.67×(chromaticity X)-Y)≤0. In the expression, the value of Y is at least 45.93.

Description

[Technical Field]

[0001] The present disclosure relates to europium-activated β-sialon phosphors. [Background technology]

[0002] Oxynitride phosphors are known to have little decrease in brightness with increasing temperature and excellent durability. Among oxynitride phosphors, europium-activated β-sialon is known as a green phosphor that can be excited by ultraviolet light, visible light, or the like.

[0003] A europium-activated β-sialon phosphor can be obtained by, for example, heating a raw material mixture containing silicon nitride powder, aluminum nitride powder, and europium oxide powder under a nitrogen atmosphere. In the course of studying the practical application of β-sialon phosphors, efforts are also being made to improve their brightness.

[0004] For example, Patent Document 1 describes a method for producing a β-sialon phosphor, which includes a first heat-treatment step of heat-treating a mixture containing an aluminum compound, a first europium compound, and silicon nitride to obtain a first heat-treated product, and a second heat-treatment step of heat-treating the first heat-treated product and a second europium compound in a rare gas atmosphere to obtain a second heat-treated product. Patent Document 2 also proposes a method for producing a β-sialon phosphor, which includes a firing step of firing a raw material mixture of the β-sialon phosphor at a temperature of 1820°C to 2200°C in a nitrogen atmosphere to obtain a fired product, and an annealing step of annealing the fired product at a temperature of 1100°C or higher in a reducing atmosphere. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2017-002278 [Patent Document 2] International Publication No. 2010 / 143590 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present disclosure is to provide a phosphor having excellent internal quantum efficiency. [Means for solving the problem]

[0007] The present disclosure provides the following [1] to [5].

[0008] [1] The diffuse reflectance for light with a wavelength of 800 nm is 96% or more, The diffuse reflectance for light with a wavelength of 800 nm, the diffuse reflectance for light with a wavelength of 500 nm, and the chromaticity X are ([Diffuse reflectance for light with a wavelength of 800 nm] - [Diffuse reflectance for light with a wavelength of 500 nm]) - (166.67 × [Chromaticity X] - Y) ≦ 0 Equation (1) [In the formula (1), Y is a value of 45.93 or more.] Europium-activated β-sialon phosphor that satisfies the above relationship. [2] The europium-activated β-sialon phosphor according to [1], which has a diffuse reflectance of 80.0% or more for light with a wavelength of 500 nm. [3] The europium-activated β-sialon phosphor according to [1] or [2], which has an absorptivity of 7% or less for light with a wavelength of 600 nm. [4] The europium-activated β-sialon phosphor according to any one of [1] to [3], which has an average particle size of 14 μm or more. [5] The europium-activated β-sialon phosphor according to any one of [1] to [4], which contains at least one element selected from the group consisting of strontium, barium, gadolinium, erbium, titanium, yttrium, and hafnium.

[0009] One aspect of the present disclosure provides a europium-activated β-sialon phosphor having a diffuse reflectance of 96% or greater for light with a wavelength of 800 nm, wherein the diffuse reflectance for light with a wavelength of 800 nm, the diffuse reflectance for light with a wavelength of 500 nm, and the chromaticity X satisfy the relationship ([diffuse reflectance for light with a wavelength of 800 nm] - [diffuse reflectance for light with a wavelength of 500 nm]) - (166.67 × [chromaticity X] - Y) ≤ 0, where Y is a value of 45.93 or greater.

[0010] The europium-activated β-sialon phosphor has excellent diffuse reflectance for light with a wavelength of 800 nm, and the diffuse reflectance, the diffuse reflectance for light with a wavelength of 500 nm, and the chromaticity X satisfy the conditions of the predetermined relational expression shown in the above formula (1), and therefore can exhibit excellent internal quantum efficiency.

[0011] The inventors believe that the reason why excellent internal quantum efficiency is achieved by having excellent diffuse reflectance for light with a wavelength of 800 nm and having the diffuse reflectance and chromaticity X for light with a wavelength of 500 nm satisfying the relationship of formula (1) above is due to the following reasons. First, a [diffuse reflectance for light with a wavelength of 800 nm] of 100% is considered to mean that there is no excess absorption that does not contribute to light emission. When the [diffuse reflectance for light with a wavelength of 800 nm] is less than 100%, the value of the difference A: [100% - (diffuse reflectance for light with a wavelength of 800 nm)] can be said to be an indicator corresponding to "absorption due to crystal defects or heterophases in the phosphor." Furthermore, it is believed that the absorption corresponding to the difference A extends to around 500 nm, which is the emission wavelength range of europium-activated β-sialon phosphors. On the other hand, factors that reduce the [diffuse reflectance of light with a wavelength of 500 nm] in the emission wavelength range of europium-activated β-sialon phosphors are thought to include, in addition to the "absorption of crystal defects or heterogeneous phases in the phosphor" that acts as an absorption source for light with a wavelength of 800 nm as mentioned above, "absorption by divalent europium" that is the absorption for emission, and "absorption of crystal defects or heterogeneous phases in the phosphor" that specifically absorb light with a wavelength of 500 nm. In other words, the value of difference B: [100% - (diffuse reflectance of light with a wavelength of 500 nm)] includes the above three elements, so it is not easy to directly detect the influence of only the "crystal defects or heterogeneous phases in the phosphor" that specifically absorb light with a wavelength of 500 nm.

[0012] Therefore, if we first assume the difference between difference B and difference A (difference B - difference A: ([diffuse reflectance for light with a wavelength of 800 nm] - [diffuse reflectance for light with a wavelength of 500 nm])), this can be used as an evaluation index for "absorption by divalent europium" and "absorption by crystal defects or heterogeneous phases in the phosphor" that specifically absorbs light with a wavelength of 500 nm. Next, for "absorption by divalent europium," which is absorption for luminescence, we use the relationship with chromaticity X. When examining the relationship between ([diffuse reflectance for light with a wavelength of 800 nm] - [diffuse reflectance for light with a wavelength of 500 nm]) and chromaticity X, if there is a difference in the value of ([diffuse reflectance for light with a wavelength of 800 nm] - [diffuse reflectance for light with a wavelength of 500 nm]) for phosphors with the same chromaticity X, this can be seen as a difference in "absorption by crystal defects or heterogeneous phases in the phosphor" that specifically absorbs light with a wavelength of 500 nm. In other words, by focusing on this relationship, it is possible to evaluate "crystal defects or heterogeneous phases in the phosphor" that specifically absorb light with a wavelength of 500 nm, which is difficult to detect directly. Satisfying the relationship of the above formula (1) corresponds to suppressing "crystal defects or heterogeneous phases in the phosphor" that specifically absorb light with a wavelength of 500 nm, that is, reducing the proportion of defects and heterogeneous phases in the phosphor, thereby making it possible to obtain a phosphor with excellent internal quantum efficiency.

[0013] The europium-activated β-sialon phosphor may have a diffuse reflectance of 80% or more for light with a wavelength of 500 nm. A diffuse reflectance within this range means that the phosphor has little influence from defects in the crystal structure or from heterogeneous phases that are non-luminescent components, which can result in superior internal quantum efficiency.

[0014] The europium-activated β-sialon phosphor may have an absorptivity of 7% or less for light with a wavelength of 600 nm. The absorptivity in the above range for light with a wavelength of 600 nm means that the crystal structure constituting the phosphor has few defects and few heterophases, which are non-luminescent components, and can exhibit better internal quantum efficiency.

[0015] The europium-activated β-sialon phosphor may have an average particle size of 14 μm or more.

[0016] The europium-activated β-sialon phosphor may contain at least one element selected from the group consisting of strontium, barium, gadolinium, erbium, titanium, yttrium, and hafnium. [Effects of the Invention]

[0017] According to the present disclosure, a phosphor with excellent internal quantum efficiency can be provided. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a graph showing the relationship between the difference in diffuse reflectance and the chromaticity X of the phosphors prepared in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are merely examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following contents.

[0020] Unless otherwise specified, the materials exemplified in this specification can be used singly or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified.

[0021] One embodiment of the europium-activated β-sialon phosphor has a diffuse reflectance of 96% or more with respect to light having a wavelength of 800 nm. Further, the europium-activated β-sialon phosphor satisfies the relationship of the following formula (1) with respect to the diffuse reflectance with respect to light having a wavelength of 800 nm, the diffuse reflectance with respect to light having a wavelength of 500 nm, and chromaticity X. In the following formula (1), Y represents a value of 45.93 or more, and the lower limit value of Y may be, for example, 46.00 or more, 46.20 or more, 46.30 or more, 46.40 or more, or 46.50 or more, and Y may be 46.53. (Diffuse reflectance with respect to light having a wavelength of 800 nm - Diffuse reflectance with respect to light having a wavelength of 500 nm) - (166.67 × [Chromaticity X] - Y) ≤ 0 ··· Formula (1)

[0022] The europium-activated β-sialon phosphor may contain, as a main crystal, a crystal having the same crystal structure as β-sialon, or may be composed of a crystal having the same crystal structure as β-sialon. The europium-activated β-sialon phosphor may contain heterogeneous phases as long as the gist of the present disclosure is not impaired. The europium-activated β-sialon phosphor contains Si 6-Z Al Z O Z N 8-Z It may have a composition represented by the composition formula of :Eu. In the above composition formula, z satisfies 0.0 < z < 6.0, may satisfy 0.0 < z < 4.2, may satisfy 0.0 < z < 2.0, or may satisfy 0.0 < z ≤ 0.5. The composition of the europium-activated β-sialon phosphor can be adjusted by changing the components and composition ratios of the raw material composition.

[0023] In the composition of the europium-activated β-sialon phosphor, the contents of nitrogen atoms (N) and oxygen atoms (O) can be quantified by an oxygen-nitrogen analyzer, and the contents of europium (Eu), silicon (Si), and aluminum (Al) can be confirmed by performing elemental quantitative analysis using an ICP emission spectrometer.

[0024] The europium-activated β-sialon phosphor may contain at least one element selected from the group consisting of strontium, barium, gadolinium, erbium, titanium, yttrium, and hafnium, or may contain at least one element selected from the group consisting of strontium and barium, or may contain at least one element selected from the group consisting of gadolinium, erbium, titanium, yttrium, and hafnium, which are metals with relatively high melting points.

[0025] When the europium-activated β-sialon phosphor contains the above elements, the total content of strontium, barium, gadolinium, erbium, titanium, yttrium, and hafnium may be, for example, 0 to 5000 ppm, 0.5 to 3000 ppm, or 0.5 to 1500 ppm. When the europium-activated β-sialon phosphor contains the above elements, the total content of strontium and barium may be, for example, 0 to 5000 ppm, 3 to 3000 ppm, or 5 to 1500 ppm. When the europium-activated β-sialon phosphor contains the above elements, the total content of gadolinium, erbium, titanium, yttrium, and hafnium may be, for example, 0 to 1000 ppm, 0.5 to 600 ppm, or 0.5 to 500 ppm.

[0026] The europium-activated β-sialon phosphor contains strontium (Sr), barium (Ba), gadolinium (Gd), erbium (Er), titanium (Ti), yttrium (Y), or hafnium (Hf), and the content thereof can be confirmed by quantitative analysis of the elements using an ICP optical emission spectrometer.

[0027] The europium-activated β-sialon phosphor has a diffuse reflectance of 96.0% or more for light with a wavelength of 800 nm, and may have a diffuse reflectance of 96.5% or more, 97.0% or more, 97.5% or more, or 98.0% or more. The europium-activated β-sialon phosphor has reduced absorption of light with a wavelength of 800 nm and is less affected by defects and heterogeneous phases that are non-luminescent components, and therefore may have a superior internal quantum efficiency. The upper limit of the diffuse reflectance of the europium-activated β-sialon phosphor for light with a wavelength of 800 nm may be adjusted to satisfy the relationship of formula (1) above, and may be, for example, 99.0% or less or 98.5% or less. The diffuse reflectance of the europium-activated β-sialon phosphor for light with a wavelength of 800 nm may be adjusted to satisfy the relationship of formula (1) above, and may be, for example, 96.0 to 99.0%.

[0028] The europium-activated β-sialon phosphor may have a diffuse reflectance of 80.0% or more, 82.0% or more, 83.0% or more, or 83.5% or more for light with a wavelength of 500 nm. A diffuse reflectance within the above range for light with a wavelength of 500 nm means that the phosphor is less affected by defects in the crystal structure or by heterogeneous phases that are non-luminescent components, resulting in a more excellent internal quantum efficiency. The upper limit of the diffuse reflectance of the europium-activated β-sialon phosphor for light with a wavelength of 500 nm may be adjusted to satisfy the relationship of formula (1) above, and may be, for example, 84.5% or less, or 84.0% or less. The europium-activated β-sialon phosphor may have a diffuse reflectance of 80.0% to 84.5% for light with a wavelength of 500 nm for light with a wavelength of 500 nm.

[0029] The term "diffuse reflectance" as used herein refers to a value determined from the diffuse reflectance spectrum of a europium-activated β-sialon phosphor measured using a UV-visible spectrophotometer. The diffuse reflectance is determined by the procedure described in the Examples of this specification. The UV-visible spectrophotometer may be, for example, a "V-550" (product name) manufactured by JASCO Corporation.

[0030] The europium-activated β-sialon phosphor also has a low absorptance for light with a wavelength of 600 nm. The absorptance of the phosphor for light with a wavelength of 600 nm may be, for example, 7% or less, 6% or less, 5% or less, 4% or less, or 3% or less. A 600 nm absorptance within the above range means that the phosphor has few defects in its crystalline structure and few heterophases, which are non-luminescent components, and can exhibit better internal quantum efficiency. The lower limit of the absorptance of the phosphor for light with a wavelength of 600 nm is not particularly limited, but is generally greater than 0%, 1% or more, or 2% or more. The absorptance of the phosphor for light with a wavelength of 600 nm may be adjusted within the above range, and may be, for example, 1 to 7% or 2 to 7%.

[0031] The europium-activated β-sialon phosphor has excellent internal quantum efficiency, and the internal quantum efficiency of the europium-activated β-sialon phosphor can be, for example, more than 82%, 83% or more, 84% or more, 85% or more, 86% or more, or 87% or more.

[0032] The internal quantum efficiency in this specification refers to the quantum efficiency obtained when a phosphor is excited with light having a wavelength of 455 nm. Specifically, the internal quantum efficiency is determined by measuring it using the method described in the examples of this specification.

[0033] The 50% cumulative diameter (D50, average particle diameter) in the volume-based cumulative particle size distribution of the europium-activated β-sialon phosphor may be adjusted depending on the application of the phosphor. The 50% cumulative diameter (D50) in the volume-based cumulative particle size distribution of the europium-activated β-sialon phosphor may be, for example, 14 μm or more, and may be 14 to 50 μm, 16 to 40 μm, or 18 to 30 μm. D50 can be controlled, for example, by adjusting conditions such as heating temperature and heating time during phosphor production, as well as by classification.

[0034] In this specification, D50 refers to the particle size at which the cumulative value from the smallest particle size reaches 50% of the total in the volume-based particle size distribution curve measured by laser diffraction / scattering. The particle size distribution curve for phosphors is measured in accordance with the particle size distribution measurement method using laser diffraction / scattering described in JIS R 1629:1997, "Method for Measuring Particle Size Distribution of Fine Ceramics Raw Materials by Laser Diffraction / Scattering." A particle size distribution analyzer can be used for the measurement. Specifically, 0.1 g of the phosphor to be measured is first placed in 100 mL of ion-exchanged water, a small amount of sodium hexametaphosphate is added, and the sample is dispersed using an ultrasonic homogenizer for 3 minutes. The particle size is measured using a particle size distribution analyzer, and D50 is determined from the resulting particle size distribution. D50, also known as the median diameter, refers to the average particle size of the target particles. An example of a particle size distribution analyzer is the "Microtrac MT3300EX II" (product name) manufactured by Microtrac Bell Corporation. As the ultrasonic homogenizer, for example, "Ultrasonic Homogenizer US-150E" (product name, tip size: φ20, Amplitude: 100%, oscillation frequency: 19.5 KHz, amplitude: approximately 31 μm) manufactured by Nippon Seiki Seisakusho Co., Ltd. can be used.

[0035] The europium-activated β-sialon phosphor can be produced, for example, by the following method: One example of a europium-activated β-sialon phosphor is a method for producing a europium-activated β-sialon phosphor, comprising: a firing step of obtaining a fired body from a raw material composition containing a silicon source, an aluminum source, and a europium source, at least one of which is present as a nitride, by one or more heat treatments; and an annealing step of obtaining an annealed body from a mixture containing the fired body and a halogen compound containing at least one of strontium (Sr) and barium (Ba) as a constituent element, or a compound containing at least one element selected from the group consisting of gadolinium, erbium, titanium, yttrium, and hafnium, by one or more annealing treatments in an atmosphere containing at least one element selected from the group consisting of a rare gas, a reducing gas, and an inert gas.

[0036] The raw material composition contains compounds having elements that are constituent elements of europium-activated β-sialon, and contains at least a silicon source, an aluminum source, and a europium source. In the raw material composition, at least one of the silicon source, the aluminum source, and the europium source is a nitride. The nitride contains nitrogen, which is a constituent element of europium-activated β-sialon, and therefore also serves as a nitrogen source. The silicon source refers to a compound or element containing silicon as a constituent element, the aluminum source refers to a compound or element containing aluminum as a constituent element, and the europium source refers to a compound or element containing europium as a constituent element. In this specification, a compound containing silicon as a constituent element is also referred to as a silicon compound, a compound containing aluminum as a constituent element is also referred to as an aluminum compound, and a compound containing europium as a constituent element is also referred to as a europium compound. The silicon compound, the aluminum compound, and the europium compound may each be any of a nitride, an oxide, an oxynitride, and a hydroxide. The raw material composition may further contain β-sialon or europium-activated β-sialon, where the β-sialon or europium-activated β-sialon is an aggregate or core material.

[0037] Examples of silicon compounds include silicon nitride (Si3N4) and silicon dioxide (SiO2). It is preferable to use silicon nitride with a high α fraction. The α fraction of silicon nitride may be, for example, 80% by mass or more, 90% by mass or more, or 95% by mass or more. When the α fraction of silicon nitride is within the above range, primary particle growth can be promoted. It is preferable to use silicon nitride with a low oxygen content. The oxygen content of silicon nitride may be, for example, 3% by mass or less, 2% by mass or less, 1.5% by mass or less, or 1.3% by mass or less. When the oxygen content of silicon nitride is within the above range, it is possible to suppress the occurrence of defects in the β-sialon crystal and the main crystalline phase of the europium-activated β-sialon phosphor.

[0038] Examples of aluminum compounds include aluminum nitride (AlN), aluminum oxide (Al2O3), and aluminum hydroxide (Al(OH)3).

[0039] Examples of europium compounds include europium oxide (europium oxide), europium nitride (europium nitride), and europium halides. Examples of europium halides include europium fluoride, europium chloride, europium bromide, and europium iodide. The europium compound preferably includes europium oxide. The valence of europium in the europium compound may be divalent or trivalent, and preferably includes divalent.

[0040] The raw material mixture can be prepared by weighing and mixing each compound. Mixing can be performed by a dry mixing method or a wet mixing method. The dry mixing method can be, for example, a method in which each component is mixed using a V-type mixer or the like. The wet mixing method can be, for example, a method in which a solvent or dispersion medium such as water is added to prepare a solution or slurry, the components are mixed, and then the solvent or dispersion medium is removed.

[0041] The heating temperature in the firing step may be, for example, 1800 to 2500°C, 1800 to 2400°C, 1850 to 2100°C, 1900 to 2100°C, 1900 to 2050°C, or 1920 to 2050°C. By setting the heating temperature in the firing step to 1800°C or higher, grain growth of the main crystalline phase of the β-sialon and europium-activated β-sialon phosphor can be promoted, and the amount of europium dissolved in the solid solution can be made more sufficient. By setting the heating temperature in the firing step to 2500°C or lower, decomposition of the β-sialon crystal and the main crystalline phase of the europium-activated β-sialon phosphor can be sufficiently suppressed.

[0042] The heating time in the firing step is preferably long from the viewpoint of promoting primary particle growth of the main crystalline phase of the β-sialon and europium-activated β-sialon phosphor, but if the heating time is too long, crystal defects may increase, so the heating time may be, for example, 1 to 30 hours, 3 to 25 hours, or 5 to 20 hours.

[0043] The raw material mixture may be heated in a nitrogen atmosphere in the firing step. Heating under conditions of a high nitrogen partial pressure can suppress decomposition of silicon nitride at high temperatures. Furthermore, treatment at high temperatures can promote particle growth. The raw material mixture may be heated under pressure in the firing step. The pressure may be, for example, 0.01 to 200 MPaG, 0.02 to 200 MPaG, 0.05 to 200 MPaG, 0.1 to 100 MPaG, 0.5 to 100 MPaG, 0.5 to 50 MPaG, 0.5 to 15 MPaG, or 0.5 to 5 MPaG.

[0044] The fired body obtained in the firing step may be a solid solution having β-sialon crystals, with a luminescence center element dissolved in a portion of the crystals, and may itself be capable of emitting fluorescence. That is, the fired body may contain a europium-activated β-sialon phosphor. The fired body obtained in the firing step may be in the form of a mass, and the particle size may be adjusted by crushing or the like prior to the annealing step.

[0045] Next, an annealing step is performed. In this specification, the annealing step refers to a step of obtaining an annealed body from a mixture containing the fired body obtained in the firing step described above and a halogen compound containing at least one element selected from the group consisting of Sr (strontium) and Ba (barium) as a constituent element, or a compound containing at least one element selected from the group consisting of Gd (gadolinium), Er (erbium), Ti (titanium), Y (yttrium), and Hf (hafnium). In the annealing step, the annealed body is obtained from the mixture by one or more heat treatments. The internal quantum efficiency of the europium-activated β-sialon phosphor that may be contained in the fired body can also be further improved by undergoing the annealing step.

[0046] The halogen compound containing at least one of strontium and barium as a constituent element may be used in combination with a plurality of elements or may be used alone, but is preferably used alone because it is easy to control the reaction system during the annealing treatment.Halogen elements constituting the halogen compound include, for example, F (fluorine) and Cl (chlorine).The halogen element constituting the halogen compound is preferably Cl, from the viewpoint of further reducing the melting point of the halogen compound and further improving the internal quantum efficiency.

[0047] The melting point of the halogen compound may be, for example, 800 to 1500 ° C., 800 to 1450 ° C., 800 to 1400 ° C., 800 to 1350 ° C., 800 to 1300 ° C., 800 to 1250 ° C., 800 to 1200 ° C., 800 to 1150 ° C., 800 to 1000 ° C., or 900 to 1000 ° C. By using a compound with a relatively low melting point as the halogen compound, the annealing temperature can be lowered, and a liquid phase can be formed at a relatively low temperature. Therefore, impurities such as carbon and europium-derived heterophases in the europium-activated β-sialon phosphor in the fired product can be more easily extracted. Therefore, when an acid treatment step described later is performed, the internal quantum efficiency of the resulting europium-activated β-sialon phosphor can be further improved.

[0048] The boiling point of the halide may be, for example, 1200 to 2500° C., 1200 to 2400° C., 1200 to 2300° C., or 1300 to 2300° C. By using a compound having a boiling point within the above range as the halide, it is possible to more sufficiently prevent the halide from being removed from the system during the annealing treatment.

[0049] The total amount of the halogen compounds may be, for example, 0.001 to 15% by mass, based on the total amount of the mixture. The lower limit of the total amount of the halogen compounds may be, for example, 0.01% by mass or more, 0.05% by mass or more, 0.1% by mass or more, 0.15% by mass or more, or 0.3% by mass or more, based on the total amount of the mixture. When the lower limit of the total amount of the halogen compounds is within the above range, the internal quantum efficiency of the resulting europium-activated β-sialon phosphor can be further improved. The upper limit of the total amount of the halogen compounds may be, for example, 13% by mass or less, 12% by mass or less, or 10% by mass or less, based on the total amount of the mixture. When the upper limit of the total amount of the halogen compounds is within the above range, deterioration of the optical properties of the europium-activated β-sialon phosphor due to a large amount of residual halogen or the like can be more sufficiently suppressed.

[0050] Compounds containing at least one element selected from the group consisting of gadolinium, erbium, titanium, yttrium, and hafnium as a constituent element may be used in combination or alone, but are preferably used alone because the reaction system during annealing can be easily controlled. Oxides are preferred as compounds containing at least one element selected from the group consisting of gadolinium, erbium, titanium, yttrium, and hafnium as a constituent element. The use of these oxides makes it easier to extract impurities such as carbon and europium-derived heterophases contained in the europium-activated β-sialon phosphor. Therefore, when the acid treatment step described below is performed, heterophases other than the europium-activated β-sialon phosphor can be more sufficiently reduced, and the internal quantum efficiency of the resulting europium-activated β-sialon phosphor can be further improved.

[0051] When oxides are used as compounds containing at least one element selected from the group consisting of gadolinium, erbium, titanium, yttrium, and hafnium as a constituent element, the total amount of the oxides may be, for example, 0.001 to 5 mass% based on the total amount of the mixture. The lower limit of the total amount of the oxides may be, for example, 0.01 mass% or more, 0.05 mass% or more, or 0.1 mass% or more based on the total amount of the mixture. When the lower limit of the total amount of the oxides is within the above range, the internal quantum efficiency of the resulting europium-activated β-sialon phosphor can be further improved. The upper limit of the total amount of the oxides may be, for example, 4 mass% or less, 3 mass% or less, or 2 mass% or less based on the total amount of the mixture. When the upper limit of the total amount of the oxides is within the above range, when an acid treatment step described below is performed, the oxides containing heterophases or the like can be sufficiently reduced by the acid treatment step, and deterioration of the optical properties of the resulting europium-activated β-sialon phosphor can be more sufficiently suppressed.

[0052] The annealing treatment is carried out in an atmosphere containing at least one gas selected from the group consisting of a rare gas, a reducing gas, and an inert gas, and by carrying out the annealing treatment in an atmosphere containing a rare gas, a reducing gas, or an inert gas, the proportion of divalent europium in the europium in the solid solution can be increased.

[0053] The rare gas may contain, for example, argon, helium, etc., or may contain argon or may consist of argon. The reducing gas may contain, for example, ammonia, hydrocarbon, carbon monoxide, hydrogen, etc., or may contain hydrogen or may consist of hydrogen. The inert gas may contain, for example, nitrogen, etc., or may consist of nitrogen. The atmosphere for the annealing step may be a mixed gas of two or more of the rare gas, the reducing gas, and an inert gas. When the mixed gas is used as the atmosphere for the annealing step, the content of the reducing gas may be, for example, 1 to 50 vol% or 4 to 20 vol% based on the total volume of the mixed gas at standard conditions. The content of the inert gas may be, for example, 1 to 50 vol% or 4 to 20 vol% based on the total volume of the mixed gas at standard conditions.

[0054] The pressure during the annealing treatment may be the same as that during the firing step, but is preferably lower than the pressure conditions during the firing step, and more preferably atmospheric pressure.Specifically, the pressure during this treatment may be, for example, 0.01 to 100 MPaG, 0.02 to 100 MPaG, 0.02 to 50 MPaG, 0.02 to 30 MPaG, 0.02 to 15 MPaG, 0.02 to 10 MPaG, or 0.02 to 5 MPaG.

[0055] The annealing temperature must be set lower than the heating temperature in the sintering step. The upper limit of the annealing temperature may be, for example, 1700°C or lower, 1650°C or lower, 1600°C or lower, 1550°C or lower, or 1500°C or lower. Setting the upper limit of the annealing temperature within the above range prevents the halide compound from being removed from the system and prevents further grain growth in the sintered body from causing aggregation between solid solutions, secondary particle formation, and other particle coarsening. The lower limit of the annealing temperature may be, for example, 1000°C or higher, 1100°C or higher, 1200°C or higher, 1300°C or higher, or 1400°C or higher. Setting the lower limit of the annealing temperature within the above range melts the halide compound to form a liquid phase, thereby enabling more efficient extraction of impurities in a mixture containing the sintered body into the liquid phase. Furthermore, the reaction between the oxide and heterophases and impurities can be promoted. Setting the lower limit of the annealing temperature within the above range also reduces the density of crystal defects in the annealed body. This can further improve the internal quantum efficiency of the resulting europium-activated β-sialon phosphor.The annealing temperature can be adjusted within the above-mentioned range, and may be, for example, 1000 to 1700°C, or 1100 to 1680°C.

[0056] The heating time in the annealing treatment may be, for example, 1 to 30 hours, 2 to 25 hours, or 3 to 20 hours, from the viewpoint of more sufficiently extracting impurities in the mixture and further reducing crystal defects in the phosphor contained in the annealed body.

[0057] The method for producing a europium-activated β-sialon phosphor may include other steps in addition to the firing step and the annealing step. Examples of such other steps include a step of treating the annealed body obtained in the annealing step with at least one of an acid and an alkali, and a classification step of adjusting the particle size of the annealed body or the annealed body that has been subjected to an acid treatment or the like. The step of treating the annealed body with an acid is called the acid treatment step, and the step of treating the annealed body with an alkali is called the alkali treatment step.

[0058] The acid treatment step or alkali treatment step can, for example, reduce the crystal defect density in the phosphor contained in the annealed body, remove silicon present on the surface of the solid solution formed by thermal decomposition of β-sialon, remove AlN polytypoid, a pseudo-polymorph of aluminum nitride (AlN) produced as a by-product during preparation of the fired body, and remove heterogeneous phases other than the europium-activated β-sialon phosphor derived from compounds added in the annealing step. The acid may include, for example, hydrofluoric acid, nitric acid, hydrochloric acid, etc. The acid may be a mixed acid of hydrofluoric acid and nitric acid. The alkali may include, for example, sodium hydroxide, etc.

[0059] The classification step may be performed by, for example, either a wet classification method or a dry classification method. Examples of wet classification include elutriation classification, in which the annealed body is added to a mixed solvent containing ion-exchanged water and a dispersant (e.g., sodium hexametaphosphate) or a mixed solvent containing ion-exchanged water and aqueous ammonia, stirred, and then allowed to stand to remove particles with a small particle size.

[0060] Although several embodiments have been described above, the present disclosure is not limited to the above embodiments. Furthermore, the descriptions of the above embodiments can be applied to each other. [Example]

[0061] The present disclosure will be described in more detail below with reference to examples and comparative examples, although the present disclosure is not limited to the following examples.

[0062] Example 1 [Preparation of europium-activated β-sialon phosphor] The raw materials were weighed into a container so that the silicon nitride (Si3N4) was 95.9% by mass, aluminum nitride (AlN) was 2.8% by mass, aluminum oxide (Al2O3) was 0.5% by mass, and europium oxide (Eu2O3) was 0.8% by mass, and mixed using a V-type mixer (manufactured by Tsutsui Scientific Machinery Co., Ltd.) to obtain a mixture. The obtained mixture was passed through a sieve with 250 μm openings to remove aggregates, thereby obtaining a raw material composition. The aggregates that did not pass through the sieve were crushed and the particle size was adjusted so that they would pass through the sieve.

[0063] 200 g of the raw material composition prepared as described above was weighed into a cylindrical boron nitride container with a lid (a molded product made by Denka Co., Ltd., primarily composed of boron nitride (trade name: Denka Boron Nitride N-1), inner diameter: 10 cm, height: 10 cm). The container was then placed in an electric furnace equipped with a carbon heater, heated to 2020°C under a nitrogen gas atmosphere (pressure: 0.90 MPaG), and heated at 2020°C for 8 hours (sintering step). After heating, the sample that had become loosely agglomerated lumps in the container was placed in a mortar and crushed. After crushing, the sample was passed through a sieve with 250 μm openings to obtain a powdered sintered product.

[0064] Next, barium fluoride (BaF2) was blended with the fired body to prepare a mixture. The blending amount of barium fluoride was adjusted to 0.1 mass% based on the total amount of the mixture. The resulting mixture was filled into a cylindrical boron nitride container, and the container was placed in an electric furnace equipped with a carbon heater. The temperature was raised to 1450°C in an argon gas atmosphere (pressure: 0.025 MPaG), and heating was carried out at the heating temperature of 1450°C for 3 hours (annealing step). After heating, the loosely agglomerated particles in the container were crushed in a mortar and passed through a 250 μm sieve to obtain powder.

[0065] Next, the obtained powder was added to a mixed acid of hydrofluoric acid (concentration: 50% by mass) and nitric acid (concentration: 70% by mass) (a mixture of hydrofluoric acid and nitric acid in a volume ratio of 1:1), and acid treatment was performed for 30 minutes while stirring at a temperature of 75°C. After the acid treatment, the stirring was stopped, the powder was allowed to settle, and the supernatant and fine powder refined by the acid treatment were removed. Thereafter, more distilled water was added and the mixture was stirred again. The stirring was stopped, the powder was allowed to settle, and the supernatant and fine powder were removed. This procedure was repeated until the pH of the aqueous solution was 8 or less and the supernatant was transparent, and the resulting precipitate was filtered and dried to obtain a europium-activated β-sialon phosphor.

[0066] Example 2 A europium-activated β-sialon phosphor was obtained in the same manner as in Example 1, except that the amount of barium fluoride added was changed as shown in Table 1.

[0067] Examples 3 to 5 A europium-activated β-sialon phosphor was obtained in the same manner as in Example 1, except that anhydrous barium chloride (BaCl2) was used instead of barium fluoride and the amount of barium chloride added was changed as shown in Table 1.

[0068] (Examples 6 and 7) A europium-activated β-sialon phosphor was obtained in the same manner as in Example 1, except that strontium fluoride (SrF2) was used instead of barium fluoride and the blending amount of strontium fluoride was changed as shown in Table 1.

[0069] (Examples 8 to 10) A europium-activated β-sialon phosphor was obtained in the same manner as in Example 1, except that anhydrous strontium chloride (SrCl2) was used instead of barium fluoride and the blending amount of strontium chloride was changed as shown in Table 1.

[0070] Example 11 A europium-activated β-sialon phosphor was obtained in the same manner as in Example 1, except that gadolinium oxide (Gd2O3) was used instead of barium fluoride and the amount of gadolinium oxide added was changed as shown in Table 1.

[0071] Example 12 A europium-activated β-sialon phosphor was obtained in the same manner as in Example 1, except that erbium oxide (Er2O3) was used instead of barium fluoride and the amount of erbium oxide blended was changed as shown in Table 1.

[0072] Example 13 A europium-activated β-sialon phosphor was obtained in the same manner as in Example 1, except that titanium oxide (TiO2) was used instead of barium fluoride and the amount of titanium oxide blended was changed as shown in Table 1.

[0073] Example 14 A europium-activated β-sialon phosphor was obtained in the same manner as in Example 1, except that yttrium oxide (Y2O3) was used instead of barium fluoride and the blending amount of yttrium oxide was changed as shown in Table 1.

[0074] Example 15 A europium-activated β-sialon phosphor was obtained in the same manner as in Example 1, except that hafnium oxide (HfO2) was used instead of barium fluoride and the amount of hafnium oxide blended was changed as shown in Table 1.

[0075] (Comparative Example 1) A europium-activated β-sialon phosphor was obtained in the same manner as in Example 1, except that barium fluoride was not added in the annealing step and only the fired body was annealed.

[0076] (Comparative Example 2) A europium-activated β-sialon phosphor was obtained in the same manner as in Example 1, except that europium oxide (Eu2O3) was used instead of barium fluoride and the amount of europium oxide added was changed as shown in Table 2.

[0077] (Comparative Example 3) A europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example 1, except that the raw material ratio was changed to 94.5 mass% silicon nitride (Si3N4), 3.2 mass% aluminum nitride (AlN), 1.4 mass% aluminum oxide (Al2O3), and 0.9 mass% europium oxide (Eu2O3).

[0078] Comparative Example 4 A europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example 1, except that the raw material ratio was changed to 95.4 mass% silicon nitride (Si3N4), 2.7 mass% aluminum nitride (AlN), 1.1 mass% aluminum oxide (Al2O3), and 0.8 mass% europium oxide (Eu2O3).

[0079] <Diffuse reflectance for light with wavelengths of 800 nm and 500 nm> The diffuse reflectance of the europium-activated β-sialon was measured using an integrating sphere (product name: ISV-469) attached to an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name: V-550). After baseline correction using a standard reflector (Spectralon (registered trademark)), a solid sample holder filled with the phosphor powder to be measured was attached to the spectrophotometer, and the diffuse reflectance was measured in the wavelength range of 500 to 850 nm. Of the measurement results, the diffuse reflectance values ​​at 800 nm and 500 nm were particularly used. The results are shown in Table 1.

[0080] <Chromaticity X> Chromaticity X was determined by measuring and calculating the CIE chromaticity coordinate x value (chromaticity X) in the XYZ color system defined in JIS Z 8781-3:2016 "Colorimetry - Part 3: CIE tristimulus values" from spectral data in the wavelength range of 465 to 780 nm of the fluorescence spectrum, in accordance with the method described in JIS Z 8724:2015 "Methods for measuring color - Light source color."

[0081] <Absorption rate for light with a wavelength of 600 nm> The light absorptance of the europium-activated β-sialon phosphor when irradiated with light having a wavelength of 600 nm was calculated using the following procedure. The results are shown in Table 1.

[0082] First, a standard reflector (Spectralon® manufactured by Labsphere) with a reflectance of 99% was set in the side opening of the integrating sphere. Monochromatic light separated into 600 nm wavelengths from a light source (Xe lamp) was introduced into this integrating sphere using an optical fiber as incident light to the phosphor, and the reflected light spectrum was measured using a spectrophotometer (manufactured by Otsuka Electronics Co., Ltd., product name: MCPD-7000). The number of photons of the incident light (Qex(600)) was calculated from the spectrum in the wavelength range of 590 to 610 nm.

[0083] Next, the concave cell was filled with phosphor to create a smooth surface, and then placed in the opening of the integrating sphere. Monochromatic light with a wavelength of 600 nm was irradiated, and the incident and reflected light spectrum was measured using a spectrophotometer. The incident reflected light photon count (Qref(600)) was calculated from the obtained spectral data. The incident reflected light photon count (Qref(600)) was calculated over the same wavelength range as the incident light photon count (Qex(600)). The 600 nm light absorptance was calculated from the obtained two types of photon counts using the following formula. 600 nm light absorption rate = ((Qex(600) - Qref(600)) / Qex(600)) × 100

[0084] For a standard sample of β-SiAlON phosphor (manufactured by SiAlON Corporation, NIMS Standard Green lot No. NSG1301), the absorptance of 455 nm excitation light, internal quantum efficiency, absorptance of 600 nm excitation light, diffuse reflectance for light with a wavelength of 800 nm, diffuse reflectance for light with a wavelength of 500 nm, and chromaticity X were measured in accordance with the above-mentioned measurement methods. The results were as follows: absorptance of 455 nm excitation light was 74.4%, internal quantum efficiency was 74.8%, absorptance of 600 nm excitation light was 7.6%, diffuse reflectance for light with a wavelength of 800 nm was 95.7%, diffuse reflectance for light with a wavelength of 500 nm was 80.4%, and chromaticity X was 0.356.

[0085] The measured values ​​of the absorptance of 455 nm excitation light, the internal quantum efficiency, the absorptance of 600 nm excitation light, the diffuse reflectance for light with a wavelength of 800 nm, the diffuse reflectance for light with a wavelength of 500 nm, and the chromaticity X may vary if the manufacturer, production lot number, etc. of the measurement device changes. Therefore, the values ​​measured by the measurement method described in this specification are used as the various measured values. However, if the manufacturer, production lot number, etc. of the measurement device are changed, the measured values ​​of the standard sample of the β-sialon phosphor described above can be used as the reference value, and each measured value can be corrected.

[0086] <Average particle diameter (D50)> The average particle size of europium-activated β-sialon was measured using the laser diffraction / scattering method described in JIS R 1629:1997, "Method for measuring particle size distribution of fine ceramic raw materials by laser diffraction / scattering." Specifically, 0.1 g of the target phosphor was placed in 100 mL of ion-exchanged water, a small amount of sodium hexametaphosphate was added, and the sample was dispersed using an ultrasonic homogenizer for 3 minutes. The particle size was measured using a particle size distribution analyzer, and the D50 was determined from the resulting particle size distribution. The particle size distribution analyzer used was a Microtrac MT3300EX II (product name) manufactured by Microtrac-Bell Corporation, and the ultrasonic homogenizer used was an Ultrasonic Homogenizer US-150E (product name, tip size: φ20, amplitude: 100%, oscillation frequency: 19.5 kHz, amplitude: approximately 31 μm) manufactured by Nippon Seiki Seisakusho Co., Ltd.

[0087] <Content of specific metal elements> The total content of strontium, barium, gadolinium, erbium, titanium, yttrium, and hafnium (specific metal elements) in the europium-activated β-sialon was measured using an ICP emission spectrometer. The results are shown in Tables 1 and 2.

[0088] [Table 1]

[0089] [Table 2]

[0090] <Absorption rate, internal quantum efficiency> The light absorptance (excitation light absorptance) and internal quantum efficiency of the europium-activated β-sialon phosphor obtained as described above when irradiated with excitation light having a wavelength of 455 nm were calculated by the following procedure. The results are shown in Table 3.

[0091] First, the phosphor to be measured was filled into a concave cell so that the surface was smooth, and the cell was attached to the opening of the integrating sphere. Monochromatic light with a wavelength of 455 nm was split from a Xe lamp, which served as a light source, and introduced into the integrating sphere using an optical fiber as excitation light for the phosphor. This monochromatic excitation light was irradiated onto the phosphor to be measured, and the fluorescence spectrum was measured. A spectrophotometer (manufactured by Otsuka Electronics Co., Ltd., product name: MCPD-7000) was used for the measurement.

[0092] The number of reflected excitation light photons (Qref) and the number of fluorescent photons (Qem) were calculated from the obtained fluorescence spectrum data. The number of reflected excitation light photons was calculated in the same wavelength range as the number of excitation light photons, and the number of fluorescent photons was calculated in the range of 465 to 800 nm. Using the same device, a standard reflector with a reflectance of 99% (Spectralon (registered trademark), manufactured by Labsphere) was attached to the opening of the integrating sphere to measure the spectrum of excitation light with a wavelength of 455 nm. The number of excitation light photons (Qex) was calculated from the spectrum in the wavelength range of 450 to 465 nm.

[0093] From the above calculation results, the absorptance of the 455 nm excitation light and the internal quantum efficiency of the phosphor to be measured were calculated based on the following formulas. Absorbance of 455 nm excitation light = ((Qex-Qref) / Qex) x 100 Internal quantum efficiency = (Qem / (Qex-Qref)) x 100 External quantum efficiency = (Qem / Qex) x 100 From the above formula, the relationship between the external quantum efficiency, the absorptance of 455 nm excitation light, and the internal quantum efficiency can be expressed as follows: External quantum efficiency = 455nm light absorption rate × internal quantum efficiency

[0094] [Table 3]

[0095] The relationship between the difference in diffuse reflectance for light with a wavelength of 800 nm and the diffuse reflectance for light with a wavelength of 500 nm, obtained from the above results, and chromaticity X is shown in Figure 1. The graph also shows a line (the line at the bottom of the graph) where ([diffuse reflectance for light with a wavelength of 800 nm] - [diffuse reflectance for light with a wavelength of 500 nm]) = 166.67 × [chromaticity X] - 46.53, and a line (the line at the top of the graph) where ([diffuse reflectance for light with a wavelength of 800 nm] - [diffuse reflectance for light with a wavelength of 500 nm]) = 166.67 × [chromaticity X] - 45.93. The area below these lines is the area that satisfies the relationship of Equation (1) when 45.93 is used as the Y value. From this graph, it was confirmed that the above-mentioned example satisfies the relationship of Equation (1) and has excellent internal quantum efficiency.

[0096] For reference, the melting points and boiling points of the halogen compounds used in the examples and comparative examples are shown in Table 4.

[0097] [Table 4] [Industrial Applicability]

[0098] According to the present disclosure, a phosphor with excellent internal quantum efficiency can be provided.

Claims

1. The diffuse reflectance for light with a wavelength of 800 nm is 96% or more, The diffuse reflectance for light with a wavelength of 800 nm, the diffuse reflectance for light with a wavelength of 500 nm, and the chromaticity X are ([Diffuse reflectance for light with a wavelength of 800 nm]−[Diffuse reflectance for light with a wavelength of 500 nm])−(166.67×[Chromaticity X]−Y)≦0 Equation (1) [In the formula (1), Y is a value of 45.93 or more.] Europium-activated β-sialon phosphor that satisfies the above relationship.

2. 2. The europium-activated β-sialon phosphor according to claim 1, which has a diffuse reflectance of 80.0% or more for light with a wavelength of 500 nm.

3. 3. The europium-activated β-sialon phosphor according to claim 1, which has an absorptivity of 7% or less for light having a wavelength of 600 nm.

4. 3. The europium-activated β-sialon phosphor according to claim 1, wherein the average particle size is 14 μm or more.

5. 3. The europium-activated β-sialon phosphor according to claim 1, which contains at least one element selected from the group consisting of strontium, barium, gadolinium, erbium, titanium, yttrium, and hafnium.

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