Europium-activated β-type sialon phosphor and light-emitting device

Abstract

To provide a europium activating β-type sialon phosphor with excellent internal quantum efficiency.SOLUTION: In one aspect of the present disclosure, a europium activating β-type sialon phosphor contains at least one element selected from the group consisting of yttrium, titanium, and gadolinium, wherein the total content of the at least one element is more than 0 ppm and less than 1,000 ppm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a europium-activated β-sialon phosphor and a light-emitting device.

Background Art

[0002] Oxynitride phosphors are known as phosphors with little decrease in luminance 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] The β-sialon phosphor can be obtained, for example, by heating a raw material mixture containing silicon nitride powder, aluminum nitride powder, and europium oxide powder in a nitrogen atmosphere. In the study of practical application of the β-sialon phosphor, studies have also been made to further improve the luminous efficiency (for example, Patent Document 1).

[0004] In addition, studies have been made to improve the emission luminance. For example, Patent Document 2 describes a first heat treatment step of obtaining a first heat treatment product by heat-treating a mixture containing an aluminum compound, a first europium compound, and silicon nitride, and a second heat treatment step of obtaining a second heat treatment product by heat-treating the first heat treatment product and a second europium compound in a rare gas atmosphere. Patent Document 3 also proposes a manufacturing method of a β-sialon phosphor including a firing step of firing a raw material mixture of the β-sialon phosphor in a nitrogen atmosphere at a temperature of 1820°C to 2200°C 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

Patent Document

[0006] This disclosure aims to provide a europium-activated β-type sialon phosphor with excellent internal quantum efficiency. [Means for solving the problem]

[0007] One aspect of this disclosure provides a europium-activated β-type sialon phosphor containing at least one element selected from the group consisting of yttrium, titanium, and gadolinium, wherein the total content of the at least one element is greater than 0 ppm and less than 1000 ppm.

[0008] The above-mentioned europium-activated β-type sialon exhibits excellent internal quantum efficiency because it contains the aforementioned elements in predetermined amounts.

[0009] The above-mentioned at least one element may be yttrium, the above-mentioned at least one element may be titanium, or the above-mentioned at least one element may be both yttrium and titanium. The above-mentioned europium-activated β-type sialon phosphor is superior in internal quantum efficiency by containing a predetermined amount of yttrium or titanium.

[0010] The above-mentioned element contains at least one of yttrium and titanium, and the total content of yttrium and titanium may be between 0.1 and 500 ppm. Having the total content of yttrium and titanium within this range allows for a further reduction of crystal defects in the phosphor, resulting in superior internal quantum efficiency.

[0011] The above-mentioned at least one element may contain at least one of yttrium and titanium, and may have an absorption rate of 5% or less for excitation light with a wavelength of 600 nm.

[0012] At least one of the above elements may be gadolinium. The above europium-activated β-type sialon phosphor contains a predetermined amount of gadolinium and therefore exhibits superior internal quantum efficiency.

[0013] The gadolinium content may be between 0.1 and 300 ppm. Having a gadolinium content within this range allows for a greater reduction in crystal defects in the phosphor, resulting in superior internal quantum efficiency.

[0014] Europium-activated β-type sialon phosphors, in which at least one of the above elements is gadolinium, may have an absorption rate of 6% or less for excitation light at a wavelength of 600 nm.

[0015] One aspect of this disclosure is the provision of a europium-activated β-type sialon phosphor containing alkaline earth metal elements, wherein the total content of the alkaline earth metal elements is greater than 0 ppm and less than 1000 ppm.

[0016] The above europium-activated β-type sialon phosphor contains a predetermined amount of alkaline earth metal elements, resulting in excellent internal quantum efficiency.

[0017] The above alkaline earth metal element may be magnesium or strontium. Including magnesium or strontium can further reduce crystal defects in the phosphor, resulting in superior internal quantum efficiency.

[0018] The total content of the above alkaline earth metal elements may be between 0.1 and 500 ppm. Having the alkaline earth metal element content within this range allows for a greater reduction in crystal defects in the phosphor, resulting in superior internal quantum efficiency.

[0019] The europium-activated β-type sialon phosphor containing the above-mentioned alkaline earth metal element may have an absorption rate of 7% or less for excitation light at a wavelength of 600 nm.

[0020] One aspect of the present disclosure is a light-emitting device including a light-emitting element that emits primary light and a wavelength converter that absorbs a part of the primary light and emits secondary light having a wavelength longer than that of the primary light, wherein the wavelength converter includes the above-described europium-activated β-sialon phosphor.

[0021] Since the light-emitting device includes the above-described europium-activated β-sialon phosphor as a wavelength converter, it has excellent luminous efficiency.

Advantages of the Invention

[0022] According to the present disclosure, an europium-activated β-sialon phosphor having excellent internal quantum efficiency can be provided.

Embodiments for Carrying Out the Invention

[0023] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are examples for explaining the present disclosure and are not intended to limit the present disclosure to the following contents.

[0024] Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more. The content of each component in the composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition. The "steps" in this specification may be steps independent of each other or steps performed simultaneously.

[0025] One embodiment of the europium-activated β-sialon phosphor contains at least one element selected from the group consisting of yttrium, titanium, and gadolinium. The europium-activated β-sialon phosphor may contain, for example, one or two elements selected from the group consisting of yttrium, titanium, and gadolinium among the above elements, and may also contain one element selected from the group consisting of yttrium, titanium, and gadolinium. The above at least one element may be, for example, yttrium, titanium, or gadolinium. When the europium-activated β-sialon phosphor contains two of the above elements, the above at least one element may be yttrium and titanium. For example, the europium-activated β-sialon phosphor may be a phosphor containing yttrium, a phosphor containing titanium, or a phosphor containing yttrium and titanium. That is, the europium-activated β-sialon phosphor may contain at least one of yttrium and titanium. The europium-activated β-sialon phosphor may also be a phosphor containing gadolinium.

[0026] The above europium-activated β-sialon phosphor may contain β-sialon as the main crystal or may consist of β-sialon. The europium-activated β-sialon phosphor may contain heterophases 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 :Eu may have a composition represented by the compositional formula. In the above compositional formula, z may be 0.0 < z ≤ 4.2 or 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 when manufacturing the phosphor.

[0027] In the composition of the europium-activated β-type sialon phosphor according to this embodiment, the nitrogen (N) and oxygen (O) content can be quantified using an oxygen-nitrogen analyzer, and the europium (Eu), silicon (Si), aluminum (Al), yttrium (Y), titanium (Ti), and gadolinium (Gd) content can be confirmed by quantitative elemental analysis using an ICP emission spectrometer.

[0028] In the europium-activated β-type sialon phosphor, the total content of at least one of the above elements is greater than 0 ppm and less than 1000 ppm. The total content of at least one of the above elements can be adjusted depending on the type of element contained in the europium-activated β-type sialon phosphor.

[0029] The total content of yttrium and titanium is greater than 0 ppm and less than 1000 ppm, based on the total amount of europium-activated β-type sialon phosphor. The europium-activated β-type sialon phosphor according to this embodiment exhibits superior internal quantum efficiency, and the inventors estimate the reason for this effect as follows: In other words, in the europium-activated β-type sialon phosphor according to this embodiment, defects such as vacancies in the phosphor that occur during the manufacturing of the phosphor are filled with yttrium or titanium ions, thereby reducing defects and resulting in superior internal quantum efficiency.

[0030] The lower limit of the yttrium content may be, for example, 0.1 ppm or more, or 0.2 ppm or more, based on the total amount of europium-activated β-type sialon phosphor. By keeping the lower limit of the yttrium content within the above range, the internal quantum efficiency of the europium-activated β-type sialon phosphor can be further improved. The upper limit of the yttrium content may be, for example, 800 ppm or less, 600 ppm or less, or 500 ppm or less, based on the total amount of europium-activated β-type sialon phosphor. By keeping the upper limit of the yttrium content within the above range, the generation of atypical phases derived from excessively added yttrium can be suppressed, and the generation of non-luminescent components can be suppressed, thereby suppressing a decrease in the luminescence properties of the europium-activated β-type sialon phosphor. The yttrium content may be adjusted within the range described above, and may be, for example, 0.1 to 900 ppm or 0.1 to 500 ppm based on the total amount of europium-activated β-type sialon phosphor.

[0031] The lower limit of the titanium content may be, for example, 0.1 ppm or more, or 0.2 ppm or more, based on the total amount of europium-activated β-type sialon phosphor. Having the lower limit of the titanium content within the above range can further improve the internal quantum efficiency of the europium-activated β-type sialon phosphor. The upper limit of the titanium content may be, for example, 800 ppm or less, 600 ppm or less, or 500 ppm or less, based on the total amount of europium-activated β-type sialon phosphor. Having the upper limit of the titanium content within the above range can suppress the generation of extraneous phases derived from excessively added titanium and suppress the formation of non-luminescent components, thereby suppressing a decrease in the luminescence properties of the europium-activated β-type sialon phosphor. The titanium content may be adjusted within the above range, for example, 0.1 to 900 ppm, or 0.1 to 500 ppm, based on the total amount of europium-activated β-type sialon phosphor.

[0032] The lower limit of the total yttrium and titanium content may be, for example, 0.1 ppm or more, or 0.2 ppm or more, based on the total amount of europium-activated β-type sialon phosphor. By keeping the lower limit of the total yttrium and titanium content within the above range, the internal quantum efficiency of the europium-activated β-type sialon phosphor can be further improved. The upper limit of the total yttrium and titanium content may be, for example, 800 ppm or less, 600 ppm or less, or 500 ppm or less, based on the total amount of europium-activated β-type sialon phosphor. By keeping the upper limit of the total yttrium and titanium content within the above range, the generation of heterogeneous phases derived from excessively added yttrium and titanium elements can be suppressed, and the generation of non-luminescent components can be suppressed, thereby suppressing a decrease in the luminescence properties of the europium-activated β-type sialon phosphor. The total content of yttrium and titanium may be adjusted within the range described above, for example, 0.1 to 900 ppm or 0.1 to 500 ppm, based on the total amount of europium-activated β-type sialon phosphor.

[0033] The gadolinium content is greater than 0 ppm and less than 1000 ppm, based on the total amount of europium-activated β-type sialon phosphor. The europium-activated β-type sialon phosphor according to this embodiment exhibits superior internal quantum efficiency, and the inventors estimate the reason for this effect as follows: In the europium-activated β-type sialon phosphor according to this embodiment, defects such as vacancies in the phosphor that occur during the manufacturing of the phosphor are filled with gadolinium ions, thereby reducing defects and resulting in superior internal quantum efficiency.

[0034] The lower limit of the gadolinium content may be, for example, 0.1 ppm or more, or 0.2 ppm or more, based on the total amount of the europium-activated β-sialon phosphor. When the lower limit of the gadolinium content is within the above range, the internal quantum efficiency of the europium-activated β-sialon phosphor can be further improved. The upper limit of the gadolinium content may be, for example, 800 ppm or less, 600 ppm or less, 500 ppm or less, or 300 ppm or less, based on the total amount of the europium-activated β-sialon phosphor. When the upper limit of the gadolinium content is within the above range, the generation of heterogeneous phases derived from excessively added gadolinium can be suppressed, and the generation of non-luminescent components can be suppressed, so that the deterioration of the luminescence characteristics of the europium-activated β-sialon phosphor can be suppressed. The gadolinium content may be adjusted within the above range, and may be, for example, 0.1 to 900 ppm, 0.1 to 500 ppm, or 0.1 to 300 ppm, based on the total amount of the europium-activated β-sialon phosphor.

[0035] Another embodiment of the europium-activated β-sialon phosphor contains an alkaline earth metal element. The europium-activated β-sialon phosphor may contain β-sialon as the main crystal, or may consist of 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 is Si 6-Z Al Z O Z N 8-Z :Eu may have a composition represented by the compositional formula. In the above compositional formula, z may be 0.0 < z ≦ 4.2, or may be 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 when manufacturing the phosphor.

[0036] In the composition of the europium-activated β-sialon phosphor according to this embodiment, the content of alkaline earth metal elements such as magnesium (Mg) and strontium (Sr) can be confirmed by performing quantitative analysis of the elements using an ICP emission spectroscopic analyzer.

[0037] Alkaline earth metals may be those known as Group II elements in the periodic table published by IUPAC. The above alkaline earth metal elements may include, for example, at least one selected from the group consisting of magnesium, calcium, strontium, and barium, and preferably magnesium or strontium.

[0038] The total content of the above alkaline earth metal elements is greater than 0 ppm and less than 1000 ppm, based on the total amount of europium-activated β-type sialon phosphor. The europium-activated β-type sialon phosphor according to this embodiment exhibits excellent internal quantum efficiency, and the inventors estimate the reason for this effect as follows: In other words, in the europium-activated β-type sialon phosphor according to this embodiment, defects such as vacancies in the phosphor that occur during the manufacturing of the phosphor are filled with ions of elements belonging to alkaline earth metals, thereby reducing defects and resulting in excellent internal quantum efficiency.

[0039] The lower limit of the total content of alkaline earth metal elements may be, for example, 0.1 ppm or more, or 0.2 ppm or more, based on the total amount of europium-activated β-type sialon phosphor. By keeping the lower limit of the total content of alkaline earth metal elements within the above range, the internal quantum efficiency of the europium-activated β-type sialon phosphor can be further improved. The upper limit of the total content of alkaline earth metal elements may be, for example, 800 ppm or less, 600 ppm or less, 500 ppm or less, or 300 ppm or less, based on the total amount of europium-activated β-type sialon phosphor. By keeping the upper limit of the total content of alkaline earth metal elements within the above range, the generation of different phases derived from excessively added alkaline earth metal elements can be suppressed, and the generation of non-luminescent components can be suppressed, thereby suppressing a decrease in the luminescence properties of the europium-activated β-type sialon phosphor. The total content of the above alkaline earth metal elements may be adjusted within the range described above, and may be, for example, 0.1 to 900 ppm, 0.1 to 500 ppm, or 0.1 to 300 ppm, based on the total amount of europium-activated β-type sialon phosphor.

[0040] The 50% cumulative diameter (D50) in the volume-based cumulative particle size distribution of the europium-activated β-type sialon phosphor according to this disclosure may be adjusted according to the application of the phosphor. The 50% cumulative diameter (D50) in the volume-based cumulative particle size distribution of the europium-activated β-type sialon phosphor may be, for example, 0.1 to 50 μm, 3 to 40 μm, or 6 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.

[0041] In this specification, D50 refers to the particle size at which the cumulative value from the smallest particle size reaches 50% of the total particle size distribution curve measured by laser diffraction and scattering. The particle size distribution curve for phosphors is performed in accordance with the particle size distribution measurement method by laser diffraction and scattering described in JIS R 1629:1997 "Method for Measuring Particle Size Distribution of Fine Ceramics Raw Materials by Laser Diffraction and Scattering". A particle size distribution analyzer can be used for measurement. Specifically, first, 0.1 g of the phosphor to be measured is placed in 100 mL of deionized water, a small amount of sodium hexametaphosphate is added, and the mixture is dispersed using an ultrasonic homogenizer for 3 minutes to obtain the measurement sample. The particle size is then measured using a particle size distribution analyzer, and D50 is determined from the obtained particle size distribution. D50 is also called the median diameter and represents the average particle size of the target particles. As a particle size distribution analyzer, for example, the "Microtrac MT3300EX II" (product name) manufactured by Microtrac-Bell Co., Ltd. can be used. As an ultrasonic homogenizer, for example, the "Ultrasonic Homogenizer US-150E" manufactured by Nippon Seiki Seisakusho Co., Ltd. (product name, tip size: φ20, Amplitude: 100%, oscillation frequency: 19.5KHz, amplitude: approximately 31μm) can be used.

[0042] The europium-activated β-type sialon phosphor according to this disclosure has suppressed absorption for light at a wavelength of 600 nm. The absorption of europium in the phosphor for light at a wavelength of 600 nm is small, and the effect of fluorescence generated from the phosphor is also small at this wavelength. Therefore, if the absorption rate for light at a wavelength of 600 nm is high, it is considered to be absorption due to defects or non-luminescent components of other phases. In the europium-activated β-type sialon phosphor according to this disclosure, for example, the absorption rate for excitation light at a wavelength of 600 nm can be 7% or less, 6.8% or less, 6.0% or less, 5.0% or less, 4.8% or less, 4.5% or less, or 4.0% or less. Because the absorption for excitation light at a wavelength of 600 nm is suppressed in this europium-activated β-type sialon phosphor, and the effect of defects or non-luminescent components of other phases is small, it can have superior internal quantum efficiency.

[0043] When the europium-activated β-sialon phosphor contains at least one of yttrium and titanium, the absorption rate for light at a wavelength of 600 nm can be, for example, 5.0% or less, 4.8% or less, 4.5% or less, or 4.0% or less. When the europium-activated β-type sialon phosphor contains gadolinium, the absorption rate for light at a wavelength of 600 nm can be, for example, 6.0% or less, 5.5% or less, or 5% or less.

[0044] When a europium-activated β-type sialon phosphor contains an alkaline earth metal element, the absorption rate for light at a wavelength of 600 nm can be, for example, 7% or less, 6% or less, or 5% or less.

[0045] The europium-activated β-type sialon phosphors relating to this disclosure exhibit excellent internal quantum efficiency, which can be, for example, over 80%, 81% or more, 82% or more, 83% or more, or 84% or more.

[0046] In this specification, light absorption rate and internal quantum efficiency refer to the quantum efficiency obtained when a phosphor is excited using near-ultraviolet light with a wavelength of 455 nm, unless otherwise specified. The internal quantum efficiency is specifically determined by the method described in the examples of this specification.

[0047] The europium-activated β-type sialon phosphor according to this disclosure can be manufactured, for example, by the following method. An example of a method for manufacturing the europium-activated β-type sialon phosphor may be a method comprising: a firing step of obtaining a fired body containing β-type sialon from a raw material composition containing a silicon source, an aluminum source, and a europium source, with at least one of these being included as a nitride, by one or more heat treatments; and an annealing step of obtaining an annealed body from the above-fired body and a mixture containing at least one source of an element selected from the group consisting of noble gases, reducing gases, and inert gases, by one or more annealing treatments in an atmosphere containing at least one selected from the group consisting of noble gases, reducing gases, and inert gases, wherein the mixture contains at least one of an alkaline earth metal element and at least one of an alkaline earth metal element as a constituent element. Examples of sources for at least one element selected from the group consisting of yttrium, titanium, and gadolinium include at least one selected from the group consisting of elemental yttrium, elemental titanium, compounds containing yttrium as a constituent element, and compounds containing titanium as a constituent element, as well as elemental gadolinium or at least one of compounds containing gadolinium as a constituent element. An example of this will be explained below.

[0048] The raw material composition contains a compound having elements that constitute europium-activated β-type sialon, and includes at least a silicon source, an aluminum source, and a europium source. In the raw material composition, at least one of the silicon source, aluminum source, and europium source is a nitride. Since this nitride contains nitrogen, which is a constituent element of europium-activated β-type sialon, it is also a nitrogen source.

[0049] A silicon source refers to a compound or element containing silicon as a constituent element, an aluminum source refers to a compound or element containing aluminum as a constituent element, and a 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 called a silicon compound, a compound containing aluminum as a constituent element is also called an aluminum compound, and a compound containing europium as a constituent element is also called a europium compound.

[0050] The silicon compound, aluminum compound, and europium compound may each be a nitride, oxide, oxynitride, or hydroxide. The raw material composition may also further contain β-type sialon or europium-activated β-type sialon. Here, β-type sialon or europium-activated β-type sialon is an aggregate or core material.

[0051] Examples of silicon compounds include silicon nitride (Si3N4) and silicon oxide (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, 3.0% by mass or less, or 1.3% by mass or less. When the oxygen content of silicon nitride is within the above range, the occurrence of defects in the β-type SiAlON crystal can be suppressed.

[0052] Examples of aluminum compounds include aluminum nitride (AlN), aluminum oxide (Al2O3), and aluminum hydroxide (Al(OH)3).

[0053] Examples of europium compounds include europium oxide, europium nitride, and europium halides. Examples of europium halides include europium fluoride, europium chloride, europium bromide, and europium iodide. Europium compounds preferably contain europium oxide. The valency of europium in europium halides may be divalent or trivalent, and preferably divalent.

[0054] The raw material mixture can be prepared by weighing and mixing each compound. The mixing may be done using either a dry or wet mixing method. A dry mixing method may involve mixing each component using, for example, a V-type mixer. A wet mixing method may involve preparing a solution or slurry by adding a solvent or dispersion medium such as water, mixing the components, and then removing the solvent or dispersion medium.

[0055] The heating temperature in the firing process may be, for example, 1800-2500°C, 1800-2400°C, 1850-2100°C, 1900-2100°C, 1900-2050°C, or 1920-2050°C. By setting the heating temperature in the firing process to 1800°C or higher, the particle growth of β-type sialon can be promoted, and the amount of europium solid solution can be made more sufficient. By setting the heating temperature in the firing process to 2500°C or lower, the decomposition of β-type sialon crystals can be sufficiently suppressed.

[0056] While a longer heating time in the firing process is preferable from the standpoint of promoting the primary particle growth of β-type sialon, excessively long heating times can increase crystal defects. Therefore, the heating time may be, for example, 1 to 30 hours, 3 to 25 hours, or 5 to 20 hours.

[0057] The heating of the raw material mixture in the calcination process may be carried out, for example, under a nitrogen atmosphere. Heating under conditions of high nitrogen partial pressure can suppress the decomposition of silicon nitride at high temperatures. Furthermore, high-temperature processing can promote particle growth. The heating of the raw material mixture in the calcination process may also be carried out, for example, under pressure. The pressure in this case may be, for example, 0.01 to 200 MPaG, 0.02 to 200 MPaG, 0.1 to 200 MPaG, 0.1 to 100 MPaG, 0.1 to 50 MPaG, 0.1 to 15 MPaG, or 0.1 to 5 MPaG.

[0058] The number of heat treatments in the firing process may be one, but may be two or more, for example, two to five times, or two to four times. By performing multiple heat treatments, a europium-activated β-type sialon phosphor with superior luminescence intensity can be obtained.

[0059] In the firing process, one or more heat treatments are performed. When multiple heat treatments are performed, they are sequentially referred to as the first heat treatment, the second heat treatment, etc., and each heat treatment process is sequentially referred to as the first firing process, the second firing process, etc. For example, if the above-described manufacturing method involves two heat treatments in the firing process, the firing process may also be said to include a process of first heat treatment of a raw material composition containing nitride to obtain a first heat-treated body, and a second firing process of second heat treatment of the first heat-treated body to obtain a second heat-treated body. In this case, the second heat-treated body corresponds to a firing body containing β-type sialon. Before performing multiple heat treatments, a silicon source, an aluminum source, and a europium source may be further mixed and then heat-treated.

[0060] If the firing process involves two or more heat treatments, the heating temperature, heating time, atmosphere during heating, and heating pressure for the first firing process can be the same as those for the heating processes described above. The heating temperature, heating time, atmosphere during heating, and heating pressure for the second and subsequent firing processes may be the same as or different from those for the first firing process. However, even if the heating temperature, heating time, atmosphere during heating, and heating pressure for the second and subsequent firing processes differ from those for the first firing process, they must remain within the range of the conditions described above for the heating processes.

[0061] The calcined body obtained in the calcination process has β-type sialon crystals and is a solid solution in which elements that act as luminescence centers are solidly dissolved in a portion of the crystals, and is capable of emitting fluorescence itself. The calcined body obtained in the calcination process may be in the form of lumps, and the particle size may be adjusted by crushing or other means prior to the annealing process.

[0062] Next, an annealing step is performed. In the manufacturing method of this example, the annealing step means a step of obtaining an annealed body from a mixture containing the calcined body obtained in the calcination step described above and a source of at least one element selected from the group consisting of yttrium, titanium, and gadolinium, or at least one of an alkaline earth metal element and a compound having an alkaline earth metal element as a constituent element. The above step may be, for example, a step of annealing a mixture containing the calcined body obtained in the calcination step described above and at least one selected from the group consisting of yttrium element, titanium element, a compound having yttrium as a constituent element, and a compound having titanium as a constituent element, or a step of annealing a mixture containing the calcined body obtained in the calcination step described above and at least one of gadolinium element or a compound having gadolinium as a constituent element, or a step of annealing a mixture containing the calcined body obtained in the calcination step described above and at least one of an alkaline earth metal element and a compound having an alkaline earth metal element as a constituent element. In the annealing process, an annealed body is obtained from the mixture by one or more heat treatments.

[0063] Compounds containing yttrium as a constituent element and compounds containing titanium as a constituent element may be, for example, oxides, nitrides, and hydroxides, but oxides are preferred. Compounds containing yttrium as a constituent element and compounds containing titanium as a constituent element may be, for example, yttrium oxide (Y2O3) and titanium oxide (Ti2O3).

[0064] The total amount of elemental yttrium, elemental titanium, compounds containing yttrium as a constituent element, and compounds containing titanium as a constituent element may be, for example, 0.01 to 4% by mass, 0.05 to 3% by mass, or 0.1 to 3% by mass, relative to the total amount of the above mixture. By setting the above amount to 0.01% by mass or more, at least one of yttrium and titanium can be easily introduced by the phosphor, and the internal quantum efficiency of the resulting europium-activated β-type sialon phosphor can be further improved. By setting the above amount to 4% by mass or less, the decrease in the luminescence properties of the resulting europium-activated β-type sialon phosphor can be suppressed.

[0065] Compounds containing gadolinium as a constituent element may be, for example, oxides, nitrides, and hydroxides, but oxides are preferred. Compounds containing gadolinium as a constituent element may be, for example, gadolinium oxide (Gd2O3).

[0066] The total amount of elemental gadolinium and compounds containing gadolinium as a constituent element may be, for example, 0.01 to 4% by mass, 0.05 to 3% by mass, or 0.1 to 3% by mass, relative to the total amount of the above mixture. By setting the total amount of elemental gadolinium and compounds containing gadolinium as a constituent element to 0.01% by mass or more, it becomes easier to introduce gadolinium into the phosphor, and the internal quantum efficiency of the resulting europium-activated β-type sialon phosphor can be further improved. By setting the total amount of elemental gadolinium and compounds containing gadolinium as a constituent element to 4% by mass or less, the extraneous phase derived from excess added gadolinium can be suppressed, and the decrease in the luminescence properties of the resulting europium-activated β-type sialon phosphor can be suppressed.

[0067] Compounds containing alkaline earth metal elements as constituent elements may be, for example, oxides, carbonates, nitrides, and hydroxides, but oxides or carbonates are preferred. The alkaline earth metal elements may be the alkaline earth metal elements exemplified as constituent components of europium-activated β-type sialon phosphors. Compounds containing alkaline earth metal elements as constituent elements may be, for example, magnesium oxide (MgO), strontium carbonate (SrCO3), strontium nitride (Sr2N3), and strontium oxide (SrO).

[0068] The total amount of alkaline earth metal elements and compounds containing alkaline earth metal elements as constituent elements may be, for example, 0.01 to 4% by mass, 0.05 to 3% by mass, 0.1 to 3% by mass, or 0.1 to 1.5% by mass relative to the total amount of the above mixture. By setting the total amount of alkaline earth metal elements and compounds containing alkaline earth metal elements as constituent elements to 0.01% by mass or more, it becomes easier to introduce alkaline earth metal elements into the phosphor, and the internal quantum efficiency of the resulting europium-activated β-type sialon phosphor can be further improved. By setting the total amount of alkaline earth metal elements and compounds containing alkaline earth metal elements as constituent elements to 4% by mass or less, the extraphase derived from excessively added alkaline earth metal elements can be suppressed, and the decrease in the luminescence properties of the resulting europium-activated β-type sialon phosphor can be suppressed.

[0069] The annealing process is carried out in an atmosphere containing at least one gas selected from the group consisting of noble gases, reducing gases, and inert gases. By performing the annealing process in an atmosphere containing noble gases, reducing gases, or inert gases, the proportion of divalent europium in the europium solid solution can be increased.

[0070] The above noble gas may contain, for example, argon and helium, or may contain argon, or consist of argon. The above reducing gas may contain, for example, ammonia, hydrocarbons, carbon monoxide, and hydrogen, or may contain hydrogen, or consist of hydrogen. The inert gas may contain, for example, nitrogen, or consist of nitrogen. The atmosphere of the annealing process may be a mixture of two or more of the above noble gases, reducing gases, and inert gases. When the atmosphere of the annealing process is the above mixed gas, the content of the reducing gas may be, for example, 1 to 50 volume percent or 4 to 20 volume percent based on the total volume of the mixed gas. The content of the inert gas may be, for example, 1 to 50 volume percent or 4 to 20 volume percent based on the total volume of the mixed gas.

[0071] The pressure used during the annealing process may be the same as the pressure used in the firing process, but preferably it is lower than the pressure conditions used in the firing process, and more preferably it is atmospheric pressure.

[0072] The annealing temperature must be set lower than the heating temperature in the firing process. The upper limit of the annealing temperature may be, for example, 1700°C or less, or 1680°C or less. By setting the upper limit of the annealing temperature within the above range, further particle growth in the fired body, aggregation between solid solutions, formation of secondary particles, etc., which would cause the particles to coarseen can be suppressed. 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. By setting the lower limit of the annealing temperature within the above range, the crystal defect density of β-type sialon contained in the annealed body can be reduced, and the internal quantum efficiency can be further improved. The annealing temperature can be adjusted within the above range, for example, 1000 to 1700°C, or 1100 to 1680°C.

[0073] The heating time in the annealing process may be, for example, 1 to 30 hours, 2 to 25 hours, or 3 to 20 hours, from the viewpoint of further reducing crystal defects in the phosphor contained in the annealed body.

[0074] In the annealing process, one or more annealing treatments are performed. When multiple annealing treatments are performed, they are sequentially referred to as the first annealing treatment, the second annealing treatment, etc., and each annealing treatment step can also be sequentially referred to as the first annealing step, the second annealing step, etc. For example, if the above-described manufacturing method involves two annealing treatments in the annealing process, the annealing process can also be said to include a step of performing a first annealing treatment on the fired body to obtain a first annealed body, and a second annealing treatment step of performing a second annealing treatment on the first annealed body to obtain a second annealed body. In this case, the second annealed body corresponds to the above-described annealed body.

[0075] If the annealing process involves two or more annealing treatments, the temperature, heating time, and heating pressure for the first annealing treatment can be the same as those specified for the annealing treatments in the preceding annealing treatments. The temperature, heating time, and heating pressure for the second and subsequent annealing treatments may be the same as or different from those for the first annealing treatment. However, even if the temperature, heating time, and heating pressure for the second and subsequent annealing treatments differ from those for the first annealing treatment, they must remain within the range of the conditions specified for the annealing treatments described above.

[0076] The number of annealing treatments in the annealing process may be one, but may also be two or more, for example, two to five times, or two to four times. By performing multiple annealing treatments, the crystal defect density of β-type sialon contained in the annealed material can be reduced, and a europium-activated β-type sialon phosphor with superior internal quantum efficiency can be obtained.

[0077] When annealing is performed multiple times in the annealing process, a source of at least one element selected from the group consisting of yttrium, titanium, and gadolinium (for example, elemental yttrium, elemental titanium, compounds containing yttrium as a constituent element, and compounds containing titanium as a constituent element, or elemental gadolinium and compounds containing gadolinium as a constituent element, etc.), or at least one of elemental alkaline earth metals and compounds containing alkaline earth metal elements as constituent elements may be blended all at once in the first annealing process, or they may be blended in separate steps in multiple annealing processes, but it is preferable to blend them all at once in the first annealing process. When these compounds are divided and blended, the explanation regarding the total blending amount of at least one element selected from the group consisting of yttrium, titanium, and gadolinium, or at least one of alkaline earth metal elements and compounds having alkaline earth metal elements as constituent elements, shall be interpreted and applied as the total amount of at least one of the elements selected from the group consisting of yttrium, titanium, and gadolinium, or at least one of alkaline earth metal elements and compounds having alkaline earth metal elements as constituent elements, blended in multiple annealing processes.

[0078] A method for producing europium-activated β-type sialon phosphor may include other steps in addition to the calcination and annealing steps. Other steps may include, for example, a step of treating the annealed body obtained in the annealing step with at least one of an acid and an alkali, or a classification step of adjusting the particle size of the annealed body or the annealed body after acid treatment. The step of treating the annealed body with acid is called the acid treatment step, and the step of treating the annealed body with alkali is called the alkali treatment step.

[0079] The acid treatment or alkali treatment process can, for example, further reduce the crystal defect density in the phosphors contained in the annealed body, remove silicon present on the solid solution surface generated by the thermal decomposition of β-type Sialon, and remove AlN polytypoids, which are pseudopolymorphs of aluminum nitride (AlN) produced as by-products during the preparation of the first calcined body. The acid may include, for example, hydrofluoric acid and nitric acid. The acid may be a mixed acid of hydrofluoric acid and nitric acid. The alkali may include, for example, sodium hydroxide.

[0080] The classification process may be carried out by either a wet classification method or a dry classification method. Examples of wet classification include elutriation classification, in which the annealed material is added to a mixed solvent containing deionized water and a dispersant (e.g., sodium hexametaphosphate), or to a mixed solvent containing deionized water and ammonia water, stirred, and then allowed to stand to remove particles with a small particle size.

[0081] The europium-activated β-type sialon phosphor according to this disclosure may be used alone or in combination with other phosphors. Because the europium-activated β-type sialon phosphor according to this disclosure exhibits excellent internal quantum efficiency, it is suitably used in light-emitting devices such as LEDs. The phosphor may also be dispersed in a curing resin. The curing resin is not particularly limited, and for example, resins used as sealing resins for light-emitting devices can be used.

[0082] One embodiment of the light-emitting device comprises a light-emitting element that emits primary light, and a wavelength converter that absorbs a portion of the primary light and emits secondary light having a wavelength longer than the wavelength of the primary light. The wavelength converter contains the europium-activated β-type sialon phosphor described above. The light-emitting element that emits primary light may be, for example, an InGaN blue LED. The light-emitting element and the wavelength converter may be dispersed in a encapsulating resin or the like.

[0083] Although several embodiments have been described above, this disclosure is not limited in any way to the embodiments described above. Furthermore, the descriptions of the embodiments described above are applicable to each other. [Examples]

[0084] The contents of this disclosure will be described in more detail below with reference to examples and comparative examples. However, this disclosure is not limited to the examples described below.

[0085] (Comparative example I-1) [Preparation of Europium-Activated β-Type Sialon Phosphor] Each raw material was measured out into a container so that it amounted to 96.0% by mass of silicon nitride (Si3N4), 2.8% by mass of aluminum nitride (AlN), 0.5% by mass of aluminum oxide (Al2O3), and 0.7% by mass of europium oxide (Eu2O3). These were then mixed using a V-type mixer (manufactured by Tsutsui Chemical Machinery Co., Ltd.) to obtain a mixture. The resulting mixture was passed through a sieve with a mesh size of 250 μm to remove aggregates, thereby obtaining the raw material composition. Aggregates that did not pass through the sieve were crushed and their particle size was adjusted to allow them to pass through the sieve.

[0086] 200 g of the raw material composition prepared as described above was weighed into a cylindrical boron nitride container with a lid (manufactured by Denka Co., Ltd., a molded product mainly composed of boron nitride (product name: Denka Boron Nitride N-1), inner diameter: 10 cm, height: 10 cm). Then, this container was placed in an electric furnace equipped with a carbon heater and heated to 2020°C under a nitrogen gas atmosphere (pressure: 0.90 MPaG), and heated at a heating temperature of 2020°C for 8 hours (calcination process). After heating, the loosely aggregated mass of the sample in the container was taken into a mortar and crushed. After crushing, it was passed through a sieve with a mesh size of 250 μm to obtain a powdered first calcined body.

[0087] Next, the first calcined body was filled into a cylindrical boron nitride container, and this container was placed in an electric furnace equipped with a carbon heater. The temperature was raised to 1450°C under an argon gas atmosphere (pressure: 0.025 MPaG), and heating was carried out at a heating temperature of 1450°C for 3 hours (annealing process). After heating, the loosely aggregated mass of particles in the container was crushed in a mortar and pestle, and a powder was obtained by passing it through a 250 μm sieve.

[0088] 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 carried out for 30 minutes while stirring at a temperature of 75°C. After the acid treatment, stirring was stopped and the powder was allowed to settle, and the supernatant and the fine powder purified by the acid treatment were removed. Then, distilled water was added and stirred again. Stirring was stopped and the powder was allowed to settle, and the supernatant and fine powder were removed. This operation was repeated until the pH of the aqueous solution was 8 or less and the supernatant was clear, and the obtained precipitate was filtered and dried to obtain europium-activated β-type sialon phosphor.

[0089] (Comparative example I-2) Europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example I-1, except that the atmosphere in the annealing process was changed from an argon gas atmosphere to a hydrogen gas atmosphere, and the processing temperature in the annealing process was changed to 1650°C in an electric furnace equipped with a metal heater.

[0090] (Example I-1) In the annealing process, the mixture was prepared so that the amount of yttrium oxide was 0.1% by mass relative to the total amount of the first calcined body and yttrium oxide (100% by mass), and then heated under a hydrogen gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example I-2.

[0091] (Example I-2) Europium-activated β-type sialon phosphor was obtained in the same manner as in Example I-1, except that the amount of yttrium oxide was changed to 0.5% by mass.

[0092] (Example I-3) Europium-activated β-type sialon phosphor was obtained in the same manner as in Example I-1, except that the amount of yttrium oxide was changed to 1% by mass.

[0093] (Comparative example I-3) Europium-activated β-type sialon phosphor was obtained in the same manner as in Example I-1, except that the amount of yttrium oxide was changed to 5% by mass.

[0094] (Example I-4) In the annealing process, the mixture was prepared so that the amount of yttrium oxide was 0.5% by mass relative to the total amount of the first calcined body and yttrium oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example I-1.

[0095] (Example I-5) In the annealing process, the mixture was prepared so that the amount of titanium dioxide was 0.1% by mass relative to the total amount of the first calcined body and titanium dioxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example I-1.

[0096] (Example I-6) Europium-activated β-type sialon phosphor was obtained in the same manner as in Example I-5, except that the amount of titanium dioxide was changed to 0.5% by mass.

[0097] (Example I-7) Europium-activated β-type sialon phosphor was obtained in the same manner as in Example I-5, except that the amount of titanium dioxide was changed to 1% by mass.

[0098] (Comparative example I-4) Europium-activated β-type sialon phosphor was obtained in the same manner as in Example I-5, except that the amount of titanium dioxide was changed to 5% by mass.

[0099] (Comparative example I-5) In the annealing process, the mixture was prepared so that the amount of zirconium oxide was 0.1% by mass relative to the total amount of the first calcined body and zirconium oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example I-1.

[0100] (Comparative Example I-6) Europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example I-5, except that the amount of zirconium oxide was changed to 0.5% by mass.

[0101] (Comparative example I-7) In the annealing process, the mixture was prepared so that the amount of zinc oxide was 0.1% by mass relative to the total amount of the first calcined body and zinc oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example I-1.

[0102] (Comparative example I-8) Europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example I-7, except that the amount of zinc oxide was changed to 0.5% by mass.

[0103] (Comparative Example I-9) A standard sample of β-type Sialon phosphor (manufactured by Sialon Co., Ltd., NIMS Standard Green lot No. NSG1301) was used as the phosphor for Comparative Example I-9.

[0104] <Measurement of the respective content of yttrium, titanium, zirconium, and zinc> The content of yttrium, titanium, zirconium, and zinc in each europium-activated β-type sialon phosphor prepared in Examples I-1 to I-7 and Comparative Examples I-1 to I-8 was measured as follows. The results are shown in Table 1.

[0105] <Content of yttrium, titanium, zirconium, and zinc> The content of yttrium, titanium, zirconium, and zinc in europium-activated β-type sialon phosphor was measured using the following procedure. The phosphor was dissolved by pressurized acid decomposition to prepare a sample solution. The obtained sample solution was subjected to quantitative elemental analysis using an ICP emission spectrometer (manufactured by Rigaku Corporation, product name: CIROS-120). The detection limits for yttrium (Y), titanium (Ti), zirconium (Zr), and zinc (Zn) were 100 ppb each.

[0106] [Evaluation of Europium-Activated β-Type Sialon Phosphor] For each europium-activated β-type sialon phosphor prepared in Examples I-1 to I-7 and Comparative Examples I-1 to I-9, the absorption rate, internal quantum efficiency, external quantum efficiency, chromaticity X, and absorption rate when irradiated with excitation light at a wavelength of 455 nm were evaluated using the method described later. The results are shown in Table 1.

[0107] <Absorptivity, internal quantum efficiency, and external quantum efficiency> The absorptivity (excitation light absorptivity), internal quantum efficiency, and external quantum efficiency of a phosphor when irradiated with excitation light at a wavelength of 455 nm were calculated using the following procedure. First, the phosphor to be measured was packed into a concave cell so that its surface was smooth, and attached to the opening of an integrating sphere. Monochromatic light spectrally separated to a wavelength of 455 nm from a Xe lamp, which is the light source, was introduced into the integrating sphere as excitation light for the phosphor using an optical fiber. 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.

[0108] The emission intensity of the phosphor was determined from the obtained fluorescence spectrum data. The number of excitation photons (Qref) and fluorescence photons (Qem) were also calculated from the obtained fluorescence spectrum data. The number of excitation photons was calculated in the same wavelength range as the number of excitation photons, while the number of fluorescence photons was calculated in the range of 465 to 800 nm. Using the same apparatus, a standard reflector with 99% reflectivity (Labsphere, Spectralon®) was attached to the aperture of the integrating sphere, and the spectrum of excitation light at a wavelength of 455 nm was measured. The number of excitation photons (Qex) was then calculated from the spectrum in the wavelength range of 450 to 465 nm.

[0109] Based on the calculation results described above, the absorption rate, internal quantum efficiency, and external quantum efficiency of the phosphor being measured were determined using the following formulas for excitation light at 455 nm. Absorption rate of excitation light at 455 nm = ((Qex - Qref) / Qex) × 100 Internal quantum efficiency = (Qem / (Qex-Qref)) × 100 External quantum efficiency = (Qem / Qex) × 100 Furthermore, the relationship between the external quantum efficiency, the absorption rate of excitation light at 455 nm, and the internal quantum efficiency can be expressed as follows from the above equation. External quantum efficiency = 455nm light absorption rate × internal quantum efficiency

[0110] <Chromaticity X> Chromaticity X was determined by calculating the CIE chromaticity coordinate x value (chromaticity X) in the XYZ color system defined in JIS Z8781-3:2016, according to JIS Z8724:2015, from spectral data in the wavelength range of 465 to 780 nm of the fluorescence spectrum.

[0111] <600nm light absorption rate> A standard reflector with a reflectivity of 99% (Spectralon®, manufactured by Labsphere) was placed in the side opening of the integrating sphere. Monochromatic light, spectrally separated to a wavelength of 600 nm from a light source (Xe lamp), was introduced into this integrating sphere via an optical fiber, and the reflected light spectrum was measured using a spectrophotometer (MCPD-7000, manufactured by Otsuka Electronics Co., Ltd.). The number of incident photons (Qex(600)) was calculated from the spectrum in the wavelength range of 590-610 nm.

[0112] Next, a concave cell was filled with β-type Sialon phosphor so that its surface was smooth, and then set into the opening of the integrating sphere. Monochromatic light with a wavelength of 600 nm was then irradiated onto the cell, and the incident reflected light spectrum was measured using a spectrophotometer. The incident reflected light photon number (Qref(600)) was calculated from the obtained spectral data. The incident reflected light photon number (Qref(600)) was calculated in the same wavelength range as the incident light photon number (Qex(600)). From the two obtained photon numbers, the 600 nm light absorption rate was calculated based on the following formula. 600nm light absorption rate = ((Qex(600)-Qref(600)) / Qex(600))×100

[0113] The measured values ​​for the phosphor's absorptivity, internal quantum efficiency, external quantum efficiency, and chromaticity X may fluctuate if the manufacturer of the measuring device, the manufacturing lot number, etc., changes. Therefore, the values ​​measured by the measurement method described herein should be adopted as the various measured values. However, if the manufacturer of the measuring device, the manufacturing lot number, etc., are changed, the measured values ​​can also be corrected using the measured values ​​from the standard sample of β-type sialon phosphor mentioned above as a reference value. The standard sample of β-type sialon phosphor listed as Comparative Example I-9 above can be used as the standard sample to obtain the reference value.

[0114] [Table 1]

[0115] (Comparative Example II-1) [Preparation of Europium-Activated β-Type Sialon Phosphor] Each raw material was measured out into a container so that it amounted to 96.0% by mass of silicon nitride (Si3N4), 2.8% by mass of aluminum nitride (AlN), 0.5% by mass of aluminum oxide (Al2O3), and 0.7% by mass of europium oxide (Eu2O3). These were then mixed using a V-type mixer (manufactured by Tsutsui Chemical Machinery Co., Ltd.) to obtain a mixture. The resulting mixture was passed through a sieve with a mesh size of 250 μm to remove aggregates, thereby obtaining the raw material composition. Aggregates that did not pass through the sieve were crushed and their particle size was adjusted to allow them to pass through the sieve.

[0116] 200 g of the raw material composition prepared as described above was weighed into a cylindrical boron nitride container with a lid (manufactured by Denka Co., Ltd., a molded product mainly composed of boron nitride (product name: Denka Boron Nitride N-1), inner diameter: 10 cm, height: 10 cm). Then, this container was placed in an electric furnace equipped with a carbon heater and heated to 2020°C under a nitrogen gas atmosphere (pressure: 0.90 MPaG), and heated at a heating temperature of 2020°C for 8 hours (calcination process). After heating, the loosely aggregated mass of the sample in the container was taken into a mortar and crushed. After crushing, it was passed through a sieve with a mesh size of 250 μm to obtain a powdered first calcined body.

[0117] Next, the first calcined body was filled into a cylindrical boron nitride container, and this container was placed in an electric furnace equipped with a carbon heater. The temperature was raised to 1450°C under an argon gas atmosphere (pressure: 0.025 MPaG), and heating was carried out at a heating temperature of 1450°C for 3 hours (annealing process). After heating, the loosely aggregated mass of particles in the container was crushed in a mortar and pestle, and a powder was obtained by passing it through a 250 μm sieve.

[0118] 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 carried out for 30 minutes while stirring at a temperature of 75°C. After the acid treatment, stirring was stopped and the powder was allowed to settle, and the supernatant and the fine powder purified by the acid treatment were removed. Then, distilled water was added and stirred again. Stirring was stopped and the powder was allowed to settle, and the supernatant and fine powder were removed. This operation was repeated until the pH of the aqueous solution was 8 or less and the supernatant was clear, and the obtained precipitate was filtered and dried to obtain europium-activated β-type sialon phosphor.

[0119] (Comparative Example II-2) In the annealing process, the mixture was prepared so that the amount of cerium oxide was 0.1% by mass relative to the total amount of the first calcined body and cerium oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example II-1.

[0120] (Comparative Example II-3) In the annealing process, the mixture was prepared so that the amount of cerium oxide was 0.5% by mass relative to the total amount of the first calcined body and cerium oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example II-1.

[0121] (Comparative Example II-4) In the annealing process, the mixture was prepared so that the amount of lanthanum oxide was 0.1% by mass relative to the total amount of the first calcined body and lanthanum oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example II-1.

[0122] (Comparative Example II-5) In the annealing process, the mixture was prepared so that the amount of lanthanum oxide was 0.5% by mass relative to the total amount of the first calcined body and lanthanum oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example II-1.

[0123] (Example II-1) In the annealing process, the mixture was prepared so that the amount of gadolinium oxide was 0.1% by mass relative to the total amount of the first calcined body and gadolinium oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example II-1.

[0124] (Example II-2) In the annealing process, the mixture was prepared so that the amount of gadolinium oxide was 0.5% by mass relative to the total amount of the first calcined body and gadolinium oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example II-1.

[0125] (Example II-3) In the annealing process, the mixture was prepared so that the amount of gadolinium oxide was 1% by mass relative to the total amount of the first calcined body and gadolinium oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example II-1.

[0126] (Comparative Example II-6) In the annealing process, the mixture was prepared so that the amount of gadolinium oxide was 5% by mass relative to the total amount of the first calcined body and gadolinium oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example II-1.

[0127] (Comparative Example II-7) A standard sample of β-type Sialon phosphor (manufactured by Sialon Co., Ltd., NIMS Standard Green lot No. NSG1301) was used as the phosphor for Comparative Example II-7.

[0128] <Measurement of the respective contents of gadolinium, cerium, and lanthanum> The gadolinium, cerium, and lanthanum content of each europium-activated β-type sialon phosphor prepared in Examples II-1 to II-3 and Comparative Examples II-1 to II-7 was measured by the following method. The results are shown in Table 2.

[0129] <Gadolinium, Cerium, and Lanthanum Content> The gadolinium, cerium, and lanthanum content in europium-activated β-type sialon phosphor was measured using the following procedure. The phosphor was dissolved by pressurized acid decomposition to prepare a sample solution. The resulting sample solution was subjected to quantitative elemental analysis using an ICP emission spectrometer (Rigaku Corporation, product name: CIROS-120). The detection limits for gadolinium (Gd), cerium (Ce), and lanthanum (La) were 100 ppb each.

[0130] [Evaluation of Europium-Activated β-Type Sialon Phosphor] For each europium-activated β-type sialon phosphor prepared in Examples II-1 to II-3 and Comparative Examples II-1 to II-7, the absorption rate, internal quantum efficiency, external quantum efficiency, chromaticity X, chromaticity Y, and absorption rate when irradiated with excitation light at a wavelength of 455 nm were evaluated using the method described later. The results are shown in Table 2.

[0131] <Absorptivity, internal quantum efficiency, and external quantum efficiency> The absorptivity (excitation light absorptivity), internal quantum efficiency, and external quantum efficiency of a phosphor when irradiated with excitation light at a wavelength of 455 nm were calculated using the following procedure. First, the phosphor to be measured was packed into a concave cell so that its surface was smooth, and attached to the opening of an integrating sphere. Monochromatic light spectrally separated to a wavelength of 455 nm from a Xe lamp, which is the light source, was introduced into the integrating sphere as excitation light for the phosphor using an optical fiber. 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.

[0132] The emission intensity of the phosphor was determined from the obtained fluorescence spectrum data. The number of excitation photons (Qref) and fluorescence photons (Qem) were also calculated from the obtained fluorescence spectrum data. The number of excitation photons was calculated in the same wavelength range as the number of excitation photons, while the number of fluorescence photons was calculated in the range of 465 to 800 nm. Using the same apparatus, a standard reflector with 99% reflectivity (Labsphere, Spectralon®) was attached to the aperture of the integrating sphere, and the spectrum of excitation light at a wavelength of 455 nm was measured. The number of excitation photons (Qex) was then calculated from the spectrum in the wavelength range of 450 to 465 nm.

[0133] Based on the calculation results described above, the absorption rate, internal quantum efficiency, and external quantum efficiency of the phosphor being measured were determined using the following formulas for excitation light at 455 nm. Absorption rate of excitation light at 455 nm = ((Qex - Qref) / Qex) × 100 Internal quantum efficiency = (Qem / (Qex-Qref)) × 100 External quantum efficiency = (Qem / Qex) × 100 Furthermore, the relationship between the external quantum efficiency, the absorption rate of excitation light at 455 nm, and the internal quantum efficiency can be expressed as follows from the above equation. External quantum efficiency = 455nm light absorption rate × internal quantum efficiency

[0134] <Chromaticity X and Y> Chromaticity X and Y were determined from spectral data in the wavelength range of 465 to 780 nm of the fluorescence spectrum by calculating the x-value (chromaticity X) and y-value (chromaticity Y) of the CIE chromaticity coordinate in the XYZ color system specified in JIS Z8781-3:2016, in accordance with JIS Z8724:2015.

[0135] <600nm light absorption rate> A standard reflector with a reflectivity of 99% (Spectralon®, manufactured by Labsphere) was placed in the side opening of the integrating sphere. Monochromatic light, spectrally separated to a wavelength of 600 nm from a light source (Xe lamp), was introduced into this integrating sphere via an optical fiber, and the reflected light spectrum was measured using a spectrophotometer (MCPD-7000, manufactured by Otsuka Electronics Co., Ltd.). The number of incident photons (Qex(600)) was calculated from the spectrum in the wavelength range of 590-610 nm.

[0136] Next, a concave cell was filled with β-type Sialon phosphor so that its surface was smooth, and then set into the opening of the integrating sphere. Monochromatic light with a wavelength of 600 nm was then irradiated onto the cell, and the incident reflected light spectrum was measured using a spectrophotometer. The incident reflected light photon number (Qref(600)) was calculated from the obtained spectral data. The incident reflected light photon number (Qref(600)) was calculated in the same wavelength range as the incident light photon number (Qex(600)). From the two obtained photon numbers, the 600 nm light absorption rate was calculated based on the following formula. 600nm light absorption rate = ((Qex(600)-Qref(600)) / Qex(600))×100

[0137] The measured values ​​for the phosphor's absorption rate, internal quantum efficiency, external quantum efficiency, chromaticity X, and chromaticity Y may fluctuate if the manufacturer of the measuring device, the manufacturing lot number, etc., changes. Therefore, the values ​​measured by the measurement method described herein should be adopted as the various measured values. However, if the manufacturer of the measuring device, the manufacturing lot number, etc., are changed, the measured values ​​can also be corrected using the measured values ​​from the standard sample of β-type sialon phosphor mentioned above as a reference value. The standard sample of β-type sialon phosphor listed as Comparative Example II-7 above can be used as the standard sample to obtain the reference value.

[0138] [Table 2]

[0139] (Comparative Example III-1) [Preparation of Europium-Activated β-Type Sialon Phosphor] Each raw material was measured out into a container so that it amounted to 96.0% by mass of silicon nitride (Si3N4), 2.8% by mass of aluminum nitride (AlN), 0.5% by mass of aluminum oxide (Al2O3), and 0.7% by mass of europium oxide (Eu2O3). These were then mixed using a V-type mixer (manufactured by Tsutsui Chemical Machinery Co., Ltd.) to obtain a mixture. The resulting mixture was passed through a sieve with a mesh size of 250 μm to remove aggregates, thereby obtaining the raw material composition. Aggregates that did not pass through the sieve were crushed and their particle size was adjusted to allow them to pass through the sieve.

[0140] 200 g of the raw material composition prepared as described above was weighed into a cylindrical boron nitride container with a lid (manufactured by Denka Co., Ltd., a molded product mainly composed of boron nitride (product name: Denka Boron Nitride N-1), inner diameter: 10 cm, height: 10 cm). Then, this container was placed in an electric furnace equipped with a carbon heater and heated to 2020°C under a nitrogen gas atmosphere (pressure: 0.90 MPaG), and heated at a heating temperature of 2020°C for 8 hours (calcination process). After heating, the loosely aggregated mass of the sample in the container was taken into a mortar and crushed. After crushing, it was passed through a sieve with a mesh size of 250 μm to obtain a powdered first calcined body.

[0141] Next, the first calcined body was filled into a cylindrical boron nitride container, and this container was placed in an electric furnace equipped with a carbon heater. The temperature was raised to 1450°C under an argon gas atmosphere (pressure: 0.025 MPaG), and heating was carried out at a heating temperature of 1450°C for 3 hours (annealing process). After heating, the loosely aggregated mass of particles in the container was crushed in a mortar and pestle, and a powder was obtained by passing it through a 250 μm sieve.

[0142] 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 carried out for 30 minutes while stirring at a temperature of 75°C. After the acid treatment, stirring was stopped and the powder was allowed to settle, and the supernatant and the fine powder purified by the acid treatment were removed. Then, distilled water was added and stirred again. Stirring was stopped and the powder was allowed to settle, and the supernatant and fine powder were removed. This operation was repeated until the pH of the aqueous solution was 8 or less and the supernatant was clear, and the obtained precipitate was filtered and dried to obtain europium-activated β-type sialon phosphor.

[0143] (Example III-1) In the annealing process, the mixture was prepared so that the amount of magnesium oxide was 0.1% by mass relative to the total amount of the first calcined body and magnesium oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example III-1.

[0144] (Example III-2) In the annealing process, the mixture was prepared so that the amount of magnesium oxide was 0.5% by mass relative to the total amount of the first calcined body and magnesium oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example III-1.

[0145] (Example III-3) In the annealing process, the mixture was prepared so that the amount of magnesium oxide was 1% by mass relative to the total amount of the first calcined body and magnesium oxide (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example III-1.

[0146] (Comparative Example III-2) Europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example III-1, except that in the annealing process, the mixture was prepared so that the amount of magnesium oxide was 5% by mass relative to the total amount of the first calcined body and magnesium oxide (100% by mass), and then heated under an argon gas atmosphere.

[0147] (Example III-4) In the annealing process, the mixture was prepared so that the amount of strontium carbonate was 0.1% by mass relative to the total amount of the first calcined body and strontium carbonate (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example III-1.

[0148] (Example III-5) In the annealing process, the mixture was prepared so that the amount of strontium carbonate was 0.5% by mass relative to the total amount of the first calcined body and strontium carbonate (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example III-1.

[0149] (Example III-6) In the annealing process, the mixture was prepared so that the amount of strontium carbonate was 1% by mass relative to the total amount of the first calcined body and strontium carbonate (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example III-1.

[0150] (Example III-7) In the annealing process, the mixture was prepared so that the amount of strontium carbonate was 1.5% by mass relative to the total amount of the first calcined body and strontium carbonate (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example III-1.

[0151] (Comparative Example III-3) In the annealing process, the mixture was prepared so that the amount of strontium carbonate was 5% by mass relative to the total amount of the first calcined body and strontium carbonate (100% by mass), and then heated under an argon gas atmosphere. Otherwise, a europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example III-1.

[0152] (Comparative Example III-4) Europium-activated β-type sialon phosphor was obtained in the same manner as in Comparative Example III-1, except that in the annealing process, the mixture was prepared so that the amount of lithium carbonate was 0.5% by mass relative to the total amount of the first calcined body and lithium carbonate (100% by mass), and then heated under an argon gas atmosphere.

[0153] (Comparative Example III-5) A standard sample of β-type Sialon phosphor (manufactured by Sialon Co., Ltd., NIMS Standard Green lot No. NSG1301) was used as the phosphor for Comparative Example III-5.

[0154] <Measurement of the content of alkaline earth metal elements (magnesium, strontium, and lithium)> The content of alkaline earth metal elements (magnesium, strontium, and lithium) in each europium-activated β-type sialon phosphor prepared in Examples III-1 to III-7 and Comparative Examples III-1 to III-5 was measured by the following method. The results are shown in Table 3.

[0155] <Magnesium, Strontium, and Lithium Content> The magnesium, strontium, and lithium content in europium-activated β-type sialon phosphor was measured using the following procedure. The phosphor was dissolved by pressurized acid decomposition to prepare a sample solution. The resulting sample solution was then subjected to quantitative elemental analysis using an ICP emission spectrometer (Rigaku Corporation, product name: CIROS-120). The detection limits for magnesium (Mg), strontium (Sr), and lithium (Li) were 100 ppb each.

[0156] [Evaluation of Europium-Activated β-Type Sialon Phosphor] For each europium-activated β-type sialon phosphor prepared in Examples III-1 to III-7 and Comparative Examples III-1 to III-5, the absorption rate, internal quantum efficiency, chromaticity X, chromaticity Y, and absorption rate when irradiated with excitation light at a wavelength of 455 nm were evaluated using the method described later. The results are shown in Table 3.

[0157] <Absorption rate and internal quantum efficiency> The absorption rate (excitation light absorption rate) and internal quantum efficiency of a phosphor when irradiated with excitation light at a wavelength of 455 nm were calculated using the following procedure. First, the phosphor to be measured was packed into a concave cell so that its surface was smooth, and attached to the opening of an integrating sphere. Monochromatic light spectrally separated to a wavelength of 455 nm from a Xe lamp, which is the light source, was introduced into the integrating sphere as excitation light for the phosphor using an optical fiber. 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.

[0158] The emission intensity of the phosphor was determined from the obtained fluorescence spectrum data. The number of excitation photons (Qref) and fluorescence photons (Qem) were also calculated from the obtained fluorescence spectrum data. The number of excitation photons was calculated in the same wavelength range as the number of excitation photons, while the number of fluorescence photons was calculated in the range of 465 to 800 nm. Using the same apparatus, a standard reflector with 99% reflectivity (Labsphere, Spectralon®) was attached to the aperture of the integrating sphere, and the spectrum of excitation light at a wavelength of 455 nm was measured. The number of excitation photons (Qex) was then calculated from the spectrum in the wavelength range of 450 to 465 nm.

[0159] Based on the calculation results described above, the absorption rate, internal quantum efficiency, and external quantum efficiency of the phosphor being measured were determined using the following formulas for excitation light at 455 nm. Absorption rate of excitation light at 455 nm = ((Qex - Qref) / Qex) × 100 Internal quantum efficiency = (Qem / (Qex-Qref)) × 100 External quantum efficiency = (Qem / Qex) × 100 Furthermore, the relationship between the external quantum efficiency, the absorption rate of excitation light at 455 nm, and the internal quantum efficiency can be expressed as follows from the above equation. External quantum efficiency = 455nm light absorption rate × internal quantum efficiency

[0160] <Chromaticity X and Y> Chromaticity X and Y were determined from spectral data in the wavelength range of 465 to 780 nm of the fluorescence spectrum by calculating the x-value (chromaticity X) and y-value (chromaticity Y) of the CIE chromaticity coordinate in the XYZ color system specified in JIS Z8781-3:2016, in accordance with JIS Z8724:2015.

[0161] <600nm light absorption rate> A standard reflector with a reflectivity of 99% (Spectralon®, manufactured by Labsphere) was placed in the side opening of the integrating sphere. Monochromatic light, spectrally separated to a wavelength of 600 nm from a light source (Xe lamp), was introduced into this integrating sphere via an optical fiber, and the reflected light spectrum was measured using a spectrophotometer (MCPD-7000, manufactured by Otsuka Electronics Co., Ltd.). The number of incident photons (Qex(600)) was calculated from the spectrum in the wavelength range of 590-610 nm.

[0162] Next, a concave cell was filled with β-type Sialon phosphor so that its surface was smooth, and then set into the opening of the integrating sphere. Monochromatic light with a wavelength of 600 nm was then irradiated onto the cell, and the incident reflected light spectrum was measured using a spectrophotometer. The incident reflected light photon number (Qref(600)) was calculated from the obtained spectral data. The incident reflected light photon number (Qref(600)) was calculated in the same wavelength range as the incident light photon number (Qex(600)). From the two obtained photon numbers, the 600 nm light absorption rate was calculated based on the following formula. 600nm light absorption rate = ((Qex(600)-Qref(600)) / Qex(600))×100

[0163] The measured values ​​for the phosphor's absorptivity, internal quantum efficiency, external quantum efficiency, peak wavelength and full width at half maximum of fluorescence, chromaticity X, and chromaticity Y may fluctuate if the manufacturer of the measuring device, the manufacturing lot number, etc., changes. Therefore, the values ​​measured by the measurement method described herein should be adopted as the various measured values. However, if the manufacturer of the measuring device, the manufacturing lot number, etc., are changed, the measured values ​​can also be corrected using the measured values ​​from the standard sample of β-type sialon phosphor described above as a reference value. The standard sample of β-type sialon phosphor listed as Comparative Example III-5 above can be used as the standard sample to obtain the reference value.

[0164] [Table 3] [Industrial applicability]

[0165] According to this disclosure, a europium-activated β-type sialon phosphor with excellent internal quantum efficiency can be provided.

Claims

1. A material containing at least one element selected from the group consisting of magnesium and strontium, wherein the total content of magnesium and strontium is greater than 0 ppm and 6.2 ppm or less. A europium-activated β-type sialon phosphor with an absorption rate of 7% or less for excitation light at a wavelength of 600 nm.

2. The europium-activated β-type sialon phosphor according to claim 1, wherein the total content of magnesium and strontium is 0.1 to 6.2 ppm.

3. A light-emitting device comprising a light-emitting element that emits primary light, and a wavelength converter that absorbs a portion of the primary light and emits secondary light having a wavelength longer than the wavelength of the primary light, A light-emitting device wherein the wavelength converter includes the europium-activated β-type sialon phosphor described in claim 1 or 2.

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