JP7594193B2 - Manufacturing method of ceramic composite - Google Patents

Description

The present invention relates to a method for manufacturing a ceramic composite.

Light-emitting devices are known that include a light-emitting diode (LED) or laser diode (LD) and a wavelength conversion member that contains a phosphor that converts the wavelength of light emitted from the LED or LD light-emitting element. Such light-emitting devices are used, for example, as light sources for in-vehicle lighting, general lighting, backlights for liquid crystal display devices, projectors, etc.

For example, Patent Document 1 discloses a ceramic composite that includes a Ce-activated yttrium aluminum garnet phosphor, an inorganic material made of aluminum oxide present between phosphor particles, and additive particles having a particle size smaller than the phosphor particles that are attached so as to cover at least a portion of the surface of the phosphor particles.

JP 2015-149394 A

A ceramic composite containing a phosphor and a light-transmitting inorganic material is required to suppress variation in the color tone of the light emitted from the ceramic composite.
Therefore, an object of one aspect of the present invention is to provide a method for producing a ceramic composite capable of suppressing variation in the color tone of emitted light.

The first aspect of the present invention is a method for producing a ceramic composite, comprising: preparing a raw material mixture containing rare earth aluminate phosphor particles and aluminum oxide particles, the content of particles having a particle size of 25.4 μm or more as measured by a laser diffraction method being 0.5 volume % or less; molding the raw material mixture to obtain a molded body; and firing the molded body to obtain a sintered body.

According to one aspect of the present invention, it is possible to provide a method for manufacturing a ceramic composite that can suppress variation in the color tone of emitted light.

1 is a flowchart showing a first embodiment of a method for manufacturing a ceramic composite. 1 is a schematic plan view of a light emitting device according to one embodiment of the present invention. A schematic cross-sectional view taken along line IIB-IIB' in Figure 2A. FIG. 2 is a graph showing the volume-based particle size distribution of the aluminum oxide particles used in Examples 1 and 2 and the aluminum oxide particles used in Comparative Example 1, measured by a laser diffraction method.

The ceramic composite manufacturing method and ceramic composite are described below based on the embodiments. However, the embodiments shown below are merely examples for embodying the technical concept of the present invention, and the present invention is not limited to the ceramic composite manufacturing method and ceramic composite described below. The relationship between color names and chromaticity coordinates, and the relationship between the wavelength range of light and the color names of monochromatic light, follow JIS Z8110. In addition, in this specification, ceramics refers to any inorganic nonmetallic material at temperatures below 1000°C.

The method for producing a ceramic composite includes preparing a raw material mixture containing rare earth aluminate phosphor particles and aluminum oxide particles in which the content of particles having a particle size of 25.4 μm or more as measured by a laser diffraction method is 0.5 volume % or less, molding the raw material mixture to obtain a molded body, and firing the molded body to obtain a sintered body.

Figure 1 is a flow chart showing a first embodiment of a method for manufacturing a ceramic composite. The steps of the method for manufacturing a ceramic composite will be described with reference to the drawing. As shown in Figure 1, the method for manufacturing a ceramic composite includes preparing a raw material mixture S101, molding the raw material mixture to obtain a molded body S102, and firing the molded body to obtain a sintered body S103.

In preparing the raw material mixture, the raw material mixture contains rare earth aluminate phosphor particles and aluminum oxide particles having a particle size of 25.4 μm or more measured by laser diffraction method of 0.5 vol% or less. If the content of the aluminum oxide particles having a particle size of 25.4 μm or more measured by laser diffraction method is 0.5 vol% or less with respect to the total volume of the aluminum oxide particles of 100 vol%, abnormal growth of aluminum oxide crystals due to firing is suppressed, and a sintered body in which the generation of defective parts is suppressed can be obtained. The content of particles having a particle size of 25.4 μm or more in the aluminum oxide particles contained in the raw material mixture is more preferably 0.4 vol% or less, even more preferably 0.3 vol% or less, even more preferably 0.2 vol% or less, particularly preferably 0.1 vol% or less, and may be 0 vol%. The particle size of the aluminum oxide particles measured by laser diffraction method may be 32.0 μm or less.

When preparing the raw material mixture, the particle size of the aluminum oxide particles can be measured using a laser diffraction particle size measuring device (e.g., Mastersizer 2000, manufactured by Malvern) that uses the laser diffraction method, and the content (volume %) of particles in each particle size range relative to the total volume of aluminum oxide particles (100 volume %) can be measured from the volume-based particle size distribution.

When the molded body obtained by molding the raw material mixture is fired, the crystals generated from the aluminum oxide particles grow abnormally, and the resulting sintered body may have defects called, for example, "agglomerations," "voids," or "dents." If defects such as "agglomerations," "voids," or "dents" are generated in the sintered body, the color tone of the emitted light may vary and the product yield may decrease. In defects that appear in sintered bodies, "agglomerations" are defects that are presumed to be caused by small particles gathering around large particles to form large crystal phases, and are whitish defects. In defects that appear in sintered bodies, "voids" are defects that are presumed to be caused by the presence of large particles that make it difficult for the crystal phase to grow, and the crystal phase remains small, and are blackish defects. In defects that appear in sintered bodies, "dents" are defects that occur when small particles gather around relatively large particles, causing abnormal crystal growth, and the abnormally grown crystals cause the crystal phases to not be in close contact, resulting in a concave surface.

For example, when preparing a raw material mixture, if aluminum oxide particles with a particle size of 25.4 μm or more (measured by laser diffraction) exceed 0.5% by volume, small particles will gather around relatively large particles with a particle size of 25.4 μm or more, causing abnormal crystal growth, resulting in defects in the sintered body such as "agglomerations," "voids," or "depressions," which can cause variations in the color tone of the emitted light and reduce product yields.

In preparing the raw material mixture, the aluminum oxide particles preferably have a particle size of 20.2 μm or more and less than 25.4 μm measured by a laser diffraction method of 1.0 vol.% or less relative to the total volume of the aluminum oxide particles (100 vol.%). If the content of particles having a particle size of 20.2 μm or more and less than 25.4 μm in the aluminum oxide particles contained in the raw material mixture is 1.0 vol.% or less, abnormal growth of aluminum oxide crystals is more suppressed, and a ceramic composite having fewer defective parts and suppressed color variation in light emission can be obtained. The content of particles having a particle size of 20.2 μm or more and less than 25.4 μm in the aluminum oxide particles contained in the raw material mixture is more preferably 0.8 vol.% or less, more preferably 0.7 vol.% or less, even more preferably 0.6 vol.% or less, particularly preferably 0.5 vol.% or less, and may be 0.1 vol.% or more, or may be 0.2 vol.% or more. It is preferable that the aluminum oxide particles do not contain particles with a particle size of 25.4 μm or more as measured by a laser diffraction method, relative to 100% by volume of the total amount of the aluminum oxide particles.

In preparing the raw material mixture, the aluminum oxide particles preferably have a particle size of 16.0 μm or more and less than 20.2 μm as measured by a laser diffraction method of 1.5 vol% or less relative to the total volume of the aluminum oxide particles (100 vol%). If the content of particles having a particle size of 16.0 μm or more and less than 20.2 μm in the aluminum oxide particles contained in the raw material mixture is 1.5 vol% or less, abnormal growth of aluminum oxide crystals is further suppressed, and a ceramic composite having fewer defective parts and suppressed color variation in light emission can be obtained. The content of particles having a particle size of 16.0 μm or more and less than 20.2 μm in the aluminum oxide particles contained in the raw material mixture is more preferably 1.4 vol% or less, and may be 1.3 vol% or less, 0.1 vol% or more, 0.2 vol% or more, or 0.3 vol% or more.

In preparing the raw material mixture, the aluminum oxide particles preferably have a particle size of 12.7 μm or more and less than 16.0 μm as measured by a laser diffraction method of 2.0 vol. % or less relative to the total volume of the aluminum oxide particles (100 vol. %). If the content of particles having a particle size of 12.7 μm or more and less than 16.0 μm in the aluminum oxide particles contained in the raw material mixture is 2.0 vol. % or less, abnormal growth of aluminum oxide crystals is further suppressed, and a ceramic composite having fewer defective parts and suppressed color variation in light emission can be obtained. The content of particles having a particle size of 12.7 μm or more and less than 16.0 μm in the aluminum oxide particles contained in the raw material mixture is more preferably 1.9 vol. % or less, may be 1.8 vol. % or less, or may be 0.1 vol. % or more.

In preparing the raw material mixture, the aluminum oxide particles preferably have a particle size of 10.1 μm or more and less than 12.7 μm as measured by laser diffraction method of 2.5 vol% or less relative to the total volume of the aluminum oxide particles (100 vol%). If the content of particles with a particle size of 10.1 μm or more and less than 12.7 μm in the aluminum oxide particles contained in the raw material mixture is 2.5 vol% or less, abnormal growth of aluminum oxide crystals is further suppressed, and a ceramic composite with fewer defective parts and suppressed variation in the color tone of emitted light can be obtained. The content of particles with a particle size of 10.1 μm or more and less than 12.7 μm in the aluminum oxide particles contained in the raw material mixture is more preferably 2.2 vol% or less, and may be 0.1 vol% or more.

In preparing the raw material mixture, the aluminum oxide particles preferably have a content of particles having a particle size of 8.0 μm or more and less than 10.1 μm as measured by a laser diffraction method of 1.0 vol. % or less relative to the total volume of the aluminum oxide particles (100 vol. %). If the content of particles having a particle size of 8.0 μm or more and less than 10.1 μm in the aluminum oxide particles contained in the raw material mixture is 1.0 vol. % or less, abnormal growth of aluminum oxide crystals is further suppressed, and a ceramic composite having fewer defective parts and suppressed variation in the color tone of emitted light can be obtained. The content of particles having a particle size of 8.0 μm or more and less than 10.1 μm in the aluminum oxide particles contained in the raw material mixture is more preferably 0.9 vol. % or less, and may be 0.1 vol. % or more.

In preparing the raw material mixture, the aluminum oxide particles preferably have a content of particles having a particle diameter of 1.0 μm or more and less than 8.0 μm as measured by a laser diffraction method of 61 vol% or more, may be 63 vol% or more, may be 65 vol% or more, and may be 85 vol% or less, may be 80 vol% or less, or may be 75 vol% or less, relative to the total volume of the aluminum oxide particles (100 vol%). If the content of particles having a particle diameter of 1.0 μm or more and less than 8.0 μm in the aluminum oxide particles contained in the raw material mixture is within the range of 61 vol% to 85 vol%, a crystal phase containing aluminum oxide that has a small color difference from the light wavelength-converted by the rare earth aluminate phosphor is easily formed by firing, and a ceramic composite with reduced variation in the color tone of the emitted light can be obtained. The aluminum oxide particles may have a content of particles having a particle diameter of 1.0 μm or more and less than 7.9 μm as measured by a laser diffraction method of 61 vol% to 85 vol% relative to the total volume of the aluminum oxide particles.

In preparing the raw material mixture, the aluminum oxide particles may have a particle size ratio of more than 0 μm and less than 1.0 μm measured by a laser diffraction method relative to 100% of the total volume of the aluminum oxide particles, the remainder being particles with a particle size outside the range of more than 0 μm and less than 1.0 μm. The aluminum oxide particles may have a particle size ratio of more than 0 μm and less than 1.0 μm measured by a laser diffraction method relative to 100% of the total volume of the aluminum oxide particles of 26.9 vol% or less, 26.5 vol% or less, 26.0 vol% or less, 25.9 vol% or less, 25 vol% or less, or 0.1 vol% or more.

In preparing the raw material mixture, the volume average particle size at which the cumulative value from the small diameter side in the volume-based particle size distribution of the aluminum oxide particles measured by the laser diffraction method is 50% is preferably in the range of 1.0 μm to 2.0 μm, and may be in the range of 1.2 μm to 1.8 μm, or may be in the range of 1.5 μm to 1.7 μm. If the volume average particle size at which the cumulative value from the small diameter side in the volume-based particle size distribution of the aluminum oxide particles contained in the raw material mixture is 50% is in the range of 1.0 μm to 2.0 μm, a crystal phase containing aluminum oxide that has a small color difference from the light wavelength-converted by the rare earth aluminate phosphor is easily formed by firing, and a ceramic composite with reduced variation in the color tone of the emitted light can be obtained.

In preparing the raw material mixture, the aluminum oxide particles preferably have a VD value expressed by VD = (D ₇₅ -D ₂₅ )/(D ₇₅ +D 25 ), where D ₂₅ and D ₇₅ are the particle sizes at which the cumulative values from the small diameter side in the volume-based particle size distribution measured by a laser diffraction method are 25% and ₇₅ %, respectively. If the VD value in the particle size distribution of the aluminum oxide particles is less than 0.6, the particle size distribution of the aluminum oxide particles becomes narrow and the sizes of the aluminum oxide particles are uniform, so that a crystalline phase containing aluminum oxide of uniform size (a second crystalline phase described later) is formed in the sintered body. The light incident on the ceramic composite made of the sintered body is scattered at the grain boundaries of the second crystalline phase of uniform size, and the color difference between the light wavelength-converted by the rare earth aluminate phosphor contained in the first crystalline phase described later and the light transmitted through the second crystalline phase becomes small, so that the variation in color tone of the light emitted from the ceramic composite can be suppressed. The VD value of the aluminum oxide particles may be 0.599 or less, 0.570 or less, 0.400 or more, or 0.450 or more.

In preparing the raw material mixture, the aluminum oxide particles preferably have a purity of 99.0% by mass or more, more preferably 99.5% by mass or more. When the purity of the aluminum oxide of the aluminum oxide particles is 99.0% by mass or more, impurities are few, the generation of defective parts is suppressed, and a sintered body capable of emitting light with high brightness can be manufactured. The purity of the aluminum oxide of the aluminum oxide particles may refer to the purity stated in the catalog. However, since impurities may adhere to the aluminum oxide particles during distribution, the purity of the aluminum oxide of the aluminum oxide particles can also be determined by measurement. The purity can be determined by measuring the mass of the aluminum oxide particles, then calcining the aluminum oxide particles at 800°C for 1 hour in an air atmosphere to remove organic matter and moisture attached or adsorbed to the aluminum oxide particles, measuring the mass of the aluminum oxide particles after calcination, and dividing the mass of the aluminum oxide particles after calcination by the mass of the aluminum oxide particles before calcination to determine the purity of the aluminum oxide particles.

In preparing the raw material mixture, the rare earth aluminate phosphor particles preferably have a composition contained in the composition formula represented by the following formula (I): The rare earth element contained in the rare earth aluminate phosphor particles is also referred to as a first rare earth element.
( Ln ¹ _1-a Ce _a ) ₃ (Al _c G a _b ) ₅ O ₁₂ (I)
(In the formula (I), Ln ¹ is at least one selected from the group consisting of Y, Gd, Lu and Tb, and a, b and c satisfy 0<a≦0.22, 0≦b≦0.4, 0<c≦1.1, 0.9≦b+c≦1.1.)

The first rare earth element Ln ¹ contained in the rare earth aluminate phosphor particles may contain two or more elements selected from the group consisting of Y, Lu, Gd and Tb. The first rare earth element Ln ¹ may be at least one selected from the group consisting of Y, Lu and Gd. The first rare earth element Ln ¹ may be Y and Gd, or Y and Lu. When the rare earth aluminate phosphor particles contain two or more first rare earth elements Ln ¹ and the first rare earth element Ln ¹ is Y and Gd, the molar ratio of Y and Gd (Y:Gd) in the composition of the first rare earth aluminate phosphor is preferably in the range of 99.5:0.5 to 70:30, may be in the range of 99:1 to 80:20, or may be in the range of 99:1 to 90:10.

In the formula (1), a may be 0.0003≦a≦0.20, 0.001≦a≦0.150, 0.002≦a≦0.100, 0.004≦a≦0.090, or 0.005≦a≦0.080.

In the formula (1), b may be 0.02≦b≦0.3, or 0.04≦b≦0.24. In the formula (1), c may be 0.6≦c≦1.0, or 0.7≦c≦1.0. In the formula (1), the sum of b and c may be 1 (b+c=1).

In preparing the raw material mixture, the rare earth aluminate phosphor particles preferably have an average particle size measured by a Fisher Sub-Sieve Sizer (hereinafter also referred to as "FSSS") method in the range of 10 μm to 20 μm, and may be in the range of 12 μm to 18 μm. The FSSS method is a type of air permeability method, which uses the flow resistance of air to measure the specific surface area and mainly determines the particle size of primary particles. The average particle size measured by the FSSS method is the Fisher Sub-Sieve Sizer's Number. If the average particle size of the rare earth aluminate phosphor particles measured by the FSSS method is within the range of 10 μm to 20 μm, when sintered together with aluminum oxide particles in which the content of particles with a particle size of 25.4 μm or more is 0.5 volume % or less, the color difference between the light wavelength-converted by the rare earth aluminate phosphor and the light emitted from the aluminum oxide crystal phase formed by firing becomes small, and a ceramic composite containing a sintered body with reduced variation in the color tone of the emitted light can be obtained.

In preparing the raw material mixture, the raw material mixture may contain rare earth oxide particles. The rare earth oxide particles have a composition different from that of the rare earth aluminate phosphor. The rare earth oxide particles do not contain an activator element in their composition. If the raw material mixture contains rare earth oxide particles, the rare earth oxide particles and aluminum oxide particles are more likely to react when the molded body described below is fired, abnormal growth of aluminum oxide crystals is suppressed, and a sintered body containing a crystal phase with a uniform crystal size can be obtained.

Specifically, the rare earth oxide particles are preferably at least one selected from the group consisting of Y ₂ O ₃ , La ₂ O ₃ , Pr ₇ O ₁₁ , Nd ₂ O ₃ , Gd ₂ O ₃ , Tb ₄ O ₇ , Yb ₂ O ₃ , and Lu ₂ O _3. The rare earth oxide particles are more preferably at least one selected from the group consisting of Y ₂ O ₃ , La ₂ O ₃ , Nd ₂ O ₃ , Gd ₂ O ₃ , Tb ₄ O ₇ , Yb ₂ O ₃ , and Lu ₂ O ₃ , and even more preferably at least one selected from the group consisting of Y ₂ O ₃ , Gd ₂ O ₃ , Tb ₄ O ₇ , and Lu ₂ O ₃ . The rare earth oxide particles may be used alone or in combination of two or more kinds. The rare earth element contained in the rare earth oxide particles is also called the second rare earth element. The second rare earth element is at least one selected from the group consisting of Sc, Y, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

The average particle size of the rare earth oxide particles measured by the FSSS method is preferably in the range of 0.05 μm or more and less than 5 μm, and more preferably in the range of 0.1 μm or more and 4 μm or less. If the average particle size of the rare earth oxide particles is in the range of 0.05 μm or more and less than 5 μm, the rare earth oxide particles and the aluminum oxide particles are more likely to react when the molded body described below is fired, and abnormal growth of the aluminum oxide crystals is more likely to be suppressed.

The content of rare earth aluminate phosphor particles in the raw material mixture is preferably in the range of 5% by mass to 40% by mass, may be in the range of 6% by mass to 38% by mass, or may be in the range of 7% by mass to 35% by mass. When the raw material mixture is composed of rare earth aluminate phosphor particles and aluminum oxide particles, the aluminum oxide particles in the raw material mixture are the remainder obtained by subtracting the content of rare earth aluminate phosphor particles from the raw material mixture. When the raw material mixture is composed of rare earth aluminate phosphor particles, aluminum oxide particles, and rare earth oxide particles, the total amount of aluminum oxide particles and rare earth oxide particles is the remainder obtained by subtracting the rare earth aluminate phosphor particles from the raw material mixture.

When the raw material mixture contains rare earth aluminate phosphor particles, aluminum oxide particles, and rare earth oxide particles, the content of the rare earth oxide particles is preferably in the range of 0.01% by mass to 3% by mass. When the raw material mixture is composed of rare earth aluminate phosphor particles, aluminum oxide particles, and rare earth oxide particles, the content of the aluminum oxide particles is the remainder obtained by subtracting the total amount of the rare earth aluminate phosphor particles and the rare earth oxide particles from the total amount. When the raw material mixture contains rare earth oxide particles in an amount within the above range, it is possible to suppress the abnormal growth of aluminum oxide crystals caused by the reaction between the rare earth oxide particles and the aluminum oxide particles when firing the molded body described below. When the abnormal growth of aluminum oxide crystals is suppressed, a sintered body containing a crystal phase containing aluminum oxide with a narrow grain size distribution and uniform crystal size can be obtained. The resulting sintered body has a narrow particle size distribution in the crystal phase formed from the aluminum oxide base material, and the crystals have a uniform crystal diameter. Light incident on the ceramic composite is wavelength converted by the rare earth aluminate phosphor and scattered by the crystal phase containing aluminum oxide, suppressing variation in the color tone of the light emitted from the ceramic composite containing the sintered body.

Preparing the raw material mixture may include sieving the aluminum oxide particles and mixing the sieved aluminum oxide particles with rare earth aluminate phosphor particles. The mixing may include mixing the sieved aluminum oxide particles with the rare earth aluminate phosphor particles and, if necessary, rare earth oxide particles.

When preparing the raw material mixture, the aluminum oxide particles are sieved to obtain aluminum oxide particles having a particle size of 25.4 μm or more, as measured by laser diffraction, of 0.5 volume % or less.

In preparing the raw material mixture, the sieving of the aluminum oxide particles is preferably performed by sieving the aluminum oxide particles with a mesh size of 308 μm or less. The aluminum oxide particles are preferably sieved with a mesh size of 308 μm or less, and the aluminum oxide particles that have passed through the sieve are used. By sieving the aluminum oxide particles with a mesh size of 308 μm or less, the aluminum oxide particles that have passed through the sieve have a content of particles with a particle size of 25.4 μm or more measured by a laser diffraction method of 0.5 vol. % or less relative to the total volume 100 vol. % of the aluminum oxide particles. By using the aluminum oxide particles that have passed through the sieve and firing them with rare earth aluminate phosphor particles, it is possible to obtain a sintered body that suppresses abnormal growth of the aluminum oxide crystals and suppresses the generation of defective parts such as "aggregation," "voids," or "depressions." The sieve may be a nylon #50 mesh with a mesh size of 308 μm and a wire diameter of 200 μm. For example, a sieve with 308 μm mesh size can be used, such as NB50 (manufactured by NBC Meshtec Co., Ltd.).

The aluminum oxide particles are preferably sieved through a sieve with an opening of 160 μm or more. The aluminum oxide particles are preferably sieved through a sieve with an opening of 160 μm or more, and the aluminum oxide particles that have passed through the sieve are used. By sieving the aluminum oxide particles through a sieve with an opening of 160 μm or more, the aluminum oxide particles that have passed through the sieve have a content of particles with a particle size of 25.4 μm or more measured by a laser diffraction method of 0.5 vol. % or less relative to the total volume of the aluminum oxide particles (100 vol. %). By using the aluminum oxide particles that have passed through the sieve and firing them with rare earth aluminate phosphor particles, it is possible to obtain a sintered body that suppresses abnormal growth of aluminum oxide crystals and suppresses the generation of defective parts such as "aggregation," "voids," or "depressions." The sieve may be a nylon #110 mesh with an opening of 160 μm and a wire diameter of 71 μm. For example, a sieve with 160 μm mesh size, such as N-No. 110S (manufactured by NBC Meshtec Co., Ltd.), can be used. Sieving is preferably performed at least once, but may be performed two or more times.

In preparing the raw material mixture, the aluminum oxide particles, the rare earth aluminate phosphor particles, and, if necessary, the rare earth oxide particles may be mixed by dry mixing or wet mixing.

Dry mixing may be carried out using a mixer that is commonly used industrially. Examples of mixers include a ball mill, a vibration mill, a roll mill, and a jet mill.

In the wet mixing, aluminum oxide particles, rare earth aluminate phosphor, and, if necessary, rare earth oxide particles are dispersed in a liquid medium to obtain a slurry, and then the aluminum oxide particles and rare earth aluminate phosphor particles dispersed in the slurry are dried in an air atmosphere at a temperature of 80°C to 105°C for 15 hours to 48 hours to obtain a raw material mixture. The liquid medium may be deionized water, an alcohol having a linear or branched alkyl group having 1 to 4 carbon atoms, or a mixture thereof.

Preparing the raw material mixture may include sieving the aluminum oxide particles, mixing the sieved aluminum oxide particles with rare earth aluminate phosphor particles and, if necessary, rare earth oxide particles, and sieving the resulting mixture.

In preparing the raw material mixture, the rare earth aluminate phosphor, aluminum oxide particles, and, if necessary, rare earth oxide particles are mixed, and the resulting raw material mixture is sieved to suppress aggregation of the raw material mixture. The raw material mixture may be sieved using a sieve with an opening of 308 μm or less. The raw material mixture may be sieved using a sieve with an opening of 160 μm or more. The sieve with an opening of 308 μm or 160 μm may be a sieve used to sieve aluminum oxide particles. The raw material mixture may be sieved at least once, and may be sieved two or more times.

In forming the raw material mixture to obtain a molded body, a known method such as press molding can be used as a method for forming the raw material mixture. Examples of press molding methods include die press molding and cold isostatic pressing (CIP), the terminology of which is defined in JIS Z2500:2000, No. 2109. In addition, the raw material mixture may be compressed uniaxially to form it. As a method for forming the raw material mixture, two types of methods may be adopted to adjust the shape of the resulting molded body. For example, the raw material mixture may be molded by die press and then CIP may be performed. The raw material mixture may be compressed uniaxially by the roller bench method and then CIP may be performed. It is preferable that the CIP is performed by pressing the raw material mixture to form it using cold isostatic pressing with water as a medium.

The pressure during die press molding or uniaxial compression molding is preferably in the range of 5 MPa to 50 MPa, more preferably in the range of 5 MPa to 30 MPa. If the pressure during die press molding or uniaxial compression molding is in the above range, the molded body can be shaped into the desired shape.

The pressure in the CIP is preferably in the range of 50 MPa to 200 MPa, more preferably in the range of 50 MPa to 180 MPa. When the pressure in the CIP is in the range of 50 MPa to 200 MPa, a molded body can be formed that can be fired at 1550°C to 1800°C, as described below, to obtain a ceramic composite with a relative density of 95% or more.

In the case where the molded body is fired to obtain a sintered body, the firing temperature is preferably in the range of 1550°C to 1800°C, more preferably in the range of 1600°C to 1750°C, and even more preferably in the range of 1650°C to 1700°C. In the case where the molded body is fired to obtain a sintered body, if the firing temperature is in the range of 1550°C to 1800°C, a sintered body containing a first crystal phase containing the rare earth aluminate phosphor, a second crystal phase containing aluminum oxide, and optionally a third crystal phase generated by crystal growth of the rare earth oxide can be obtained without dissolving the rare earth aluminate phosphor, and a ceramic composite consisting of the sintered body can be obtained.

When the molded body is fired to obtain a sintered body, the firing can be carried out in an oxygen-containing atmosphere. The oxygen content in the oxygen-containing atmosphere is preferably 5% by volume or more, more preferably 10% by volume or more, and even more preferably 15% by volume or more. The molded body may be fired in an air atmosphere (oxygen content of 20% by volume or more). When the molded body is fired to obtain a sintered body, the firing can be carried out in an atmospheric pressure (0.101 MPa) atmosphere.

In sintering the molded body to obtain a sintered body, the sintering time is preferably from 2 to 20 hours, and may be from 4 to 10 hours. After sintering, the method may include cooling the first sintered body to a temperature of from 20°C to 200°C in an air atmosphere for from 1 to 100 hours.

The process of sintering a molded body to obtain a sintered body may include a first sintering of the molded body to obtain a first sintered body, and a second sintering of the obtained first sintered body to obtain a second sintered body.

In sintering the molded body to obtain a sintered body, it is preferable that the temperature, atmosphere, and time for the primary sintering of the molded body and the cooling of the resulting first sintered body are similar to the temperature, atmosphere, time, and cooling for sintering the molded body in sintering the aforementioned molded body to obtain a sintered body.

In the case of sintering a molded body to obtain a sintered body, the molded body is preferably sintered at a temperature of 1500°C to 1800°C by hot isostatic pressing (HIP), as defined in JIS Z2500:2000, No. 2112. The second sintered body obtained by sintering the first sintered body has a higher relative density. The temperature of the secondary sintering is preferably in the range of 1550°C to 1800°C, more preferably in the range of 1600°C to 1750°C, and even more preferably in the range of 1650°C to 1700°C. The secondary sintering can be performed in an argon or nitrogen atmosphere.

In the secondary firing, the pressure in the HIP is preferably in the range of 50 MPa to 300 MPa, and more preferably in the range of 80 MPa to 200 MPa. When the pressure in the HIP is in the range of 50 MPa to 300 MPa, the entire second sintered body can be made uniform and have a higher density without damaging the crystal structure of the first crystal phase containing the rare earth aluminate phosphor.

The secondary firing by HIP is preferably carried out for, for example, 0.5 to 20 hours, and may be carried out for 1 to 10 hours. After the secondary firing, the second sintered body may be cooled to 20°C to 200°C in an argon or nitrogen atmosphere for 1 to 10 hours.

The method for producing a ceramic composite may include at least one of annealing, processing, and surface treatment, or may include two or more of them, or may include three of them. The annealing, processing, or surface treatment is preferably performed after firing the molded body to obtain a sintered body. When the method for firing the molded body to obtain a sintered body includes a first firing of the molded body to obtain a first sintered body and a second firing of the first sintered body to obtain a second sintered body, the annealing, processing, or surface treatment is preferably performed after the second firing of the first sintered body to obtain the second sintered body.

The annealing treatment is a heat treatment in a reducing atmosphere at a temperature lower than the firing temperature in the case where the molded body is fired to obtain a sintered body. When the firing of the molded body to obtain a sintered body includes a first firing of the molded body to obtain a first sintered body and a second firing of the first sintered body to obtain a second sintered body, the heat treatment is performed at a temperature lower than the first firing temperature and the second firing temperature. By annealing the sintered body in a reducing atmosphere, the oxidized activation element contained in the first crystal phase containing the rare earth aluminate phosphor can be reduced, and the decrease in wavelength conversion efficiency and the decrease in brightness due to the oxidation of the activation element that is the luminescence center can be suppressed. The reducing atmosphere may be an atmosphere containing at least one rare gas selected from the group consisting of helium, neon, and argon, or nitrogen gas, and hydrogen gas or carbon monoxide gas, and it is more preferable that the atmosphere contains at least argon or nitrogen gas, and hydrogen gas or carbon monoxide gas. The annealing treatment may be performed on the sintered body or the first sintered body, or on the second sintered body, or on either the first sintered body or the second sintered body.

The temperature of the annealing treatment is lower than the firing temperature, and is preferably in the range of 1000°C to 1500°C. The temperature of the annealing treatment is more preferably in the range of 1000°C to 1400°C, and even more preferably in the range of 1100°C to 1350°C. If the annealing treatment temperature is lower than the firing temperature, the primary firing temperature, or the secondary firing temperature, and is in the range of 1000°C to 1500°C, the oxidized activator element contained in the first crystal phase containing the rare earth aluminate phosphor in the ceramic composite can be reduced, and the decrease in wavelength conversion efficiency and the decrease in brightness can be suppressed.

Processing may involve cutting the obtained sintered body to a desired size or thickness. The thickness of the sintered body is preferably processed to a range of 100 μm to 400 μm. If the thickness of the sintered body is within the range of 100 μm to 400 μm, the color variation between the light wavelength-converted by the rare earth aluminate phosphor contained in the first crystal phase constituting the sintered body and the light transmitted through the third crystal phase when the second crystal phase and the third crystal phase are included is small, and light with small color variation can be emitted from the ceramic composite. Processing can be performed using a known cutting method, for example, a method using at least one method selected from blade dicing, laser dicing, and wire saw. Of these, a wire saw is preferred because it can further reduce unevenness on the cut surface.

Surface treatment is a process of surface-treating the surface of the cut piece obtained by cutting the obtained sintered body. By surface treatment, the surface of the ceramic composite containing the sintered body can be made into an appropriate state in order to improve the luminescence characteristics of the ceramic composite. By the above-mentioned processing and surface treatment, a ceramic composite containing a sintered body of a desired shape, size, or thickness can be obtained. Surface treatment may be performed before or after processing the sintered body. Examples of the surface treatment method include at least one method selected from a sandblasting method, a mechanical grinding method, and a chemical etching method.

The ceramic composite made of the above-mentioned sintered body can be used as a component constituting the wavelength conversion member of a light-emitting device in combination with a light source. An example of a light-emitting device using a ceramic composite will be described below.

The light emitting device preferably comprises a wavelength conversion member containing a ceramic composite and an excitation light source.
FIG. 2A shows an example of a light emitting device, and is a schematic plan view of the light emitting device 100, and FIG. 2B is a schematic cross-sectional view of the light emitting device 100 along the line IIB-IIB' shown in FIG. 2A. The light emitting device 100 includes a light emitting element 20 made of an LED or LD, and a wavelength conversion member 30 made of a ceramic composite excited by light from the light emitting element 20 to emit light. The light emitting element 20 is flip-chip mounted on the mounting substrate 10 via bumps that are conductive members 60. The light emitting element 20 is an excitation light source for the light emitting device 100, and the wavelength conversion member 30 is bonded to the light emitting surface of the light emitting element 20. The light emitting element 20 and the wavelength conversion member 30 may be bonded via an adhesive layer 40. The light emitting element 20 and the wavelength conversion member 30 have their sides covered by a covering member 50 that reflects light. The light emitting element 20 can receive power from the outside of the light emitting device 100 via wiring and the conductive member 60 formed on the mounting substrate 10, causing the light emitting device 100 to emit light. The light emitting device 100 may include a semiconductor element 70 such as a protective element for protecting the light emitting element 20 from destruction due to application of an excessive voltage. The covering member 50 is provided, for example, so as to cover the semiconductor element 70. The covering member 50 may include a resin 51 and at least one additive material 52 selected from the group consisting of a colorant, a phosphor, and a filler. Each member used in the light emitting device will be described below. For details, the disclosure of JP 2014-112635 A may be referenced.

The light-emitting element may be, for example, an LED chip or an LD chip, which is a semiconductor light-emitting element using a nitride-based semiconductor. The light-emitting element preferably has an emission peak wavelength in the range of 380 nm to 500 nm, more preferably has an emission peak wavelength in the range of 390 nm to 495 nm, even more preferably has an emission peak wavelength in the range of 400 nm to 490 nm, and particularly preferably has an emission peak wavelength in the range of 420 nm to 490 nm. The light-emitting element is provided with a p-electrode and an n-electrode. The p-electrode and n-electrode of the light-emitting element may be formed on the same side of the light-emitting element, or may be provided on different sides. The light-emitting element may be flip-chip mounted.

The wavelength conversion member may be the ceramic composite described above. The size of the ceramic composite used as the wavelength conversion member may be large enough to cover the entire light extraction surface of the light emitting element. An adhesive layer may be interposed between the light emitting element and the wavelength conversion member, and the light emitting element and the wavelength conversion member may be fixed to each other by the adhesive layer. The wavelength conversion member may be a member including the ceramic composite described above and another member, such as a light-transmitting member.

An example of a method for manufacturing a light emitting device will be described. For details, refer to the disclosures of, for example, Japanese Patent Application Laid-Open No. 2014-112635 or Japanese Patent Application Laid-Open No. 2017-117912. The method for manufacturing a light emitting device preferably includes a step of arranging a light emitting element, a step of arranging a semiconductor element as necessary, a step of forming a wavelength conversion member including a ceramic composite, a step of bonding the light emitting element and the wavelength conversion member, and a step of forming a coating member.
In the step of arranging the light emitting element, the light emitting element is arranged on a mounting substrate and mounted thereon. The light emitting element and the semiconductor element are, for example, flip-chip mounted on the mounting substrate.
In the step of adhering the light emitting element and the wavelength conversion member, the wavelength conversion member is opposed to the light emitting surface of the light emitting element, and the wavelength conversion member is bonded onto the light emitting element by an adhesive layer.
In the step of forming the covering member, the side surfaces of the light emitting element and the wavelength conversion member except for the light emitting surface are covered with the composition for the covering member, and a covering member is formed on the side surfaces of the light emitting element and the wavelength conversion member except for the light emitting surface. This covering member is for reflecting light emitted from the light emitting element, and is formed so as to cover the side surfaces without covering the light emitting surface of the wavelength conversion member and to embed the semiconductor element.
In this manner, the light emitting device shown in FIGS. 2A and 2B can be manufactured.

The present invention will be described in detail below with reference to examples. The present invention is not limited to these examples.

Example 1
In preparing the raw material mixture, this embodiment includes sieving aluminum oxide particles, and mixing the sieved aluminum oxide particles, rare earth aluminate phosphor particles, and rare earth oxide particles.
The aluminum oxide particles used were aluminum oxide (Al ₂ O ₃ ) particles with a purity of 99% by mass. The purity of the aluminum oxide was determined by calcining the aluminum oxide particles at 800° C. for 1 hour in an air atmosphere and measuring the mass of the aluminum oxide before and after calcination.
In preparing the raw material mixture, the aluminum oxide particles were sieved using N-No. 110S (manufactured by NBC Meshtec Co., Ltd.) with a mesh size of 160 μm, a wire diameter of 71 μm, and a nylon #110 mesh. Sieving was performed once. The aluminum oxide particles that were sieved had a particle size of 20.2 μm or more and less than 25.4 μm and a particle size of 25.4 μm or more, both of which were 0% by volume, as measured by a laser diffraction method described later.
Rare _{earth aluminate phosphor particles were prepared which contained Ce as an activator element, and Y and Gd as first rare earth elements, and had a composition represented by (Y0.806Gd0.16Ce0.034)3Al5O12, which is included in the} composition formula represented by formula (I) above. The average particle size of the rare earth aluminate phosphor particles measured by the FSSS method described below was 15 μm.
Yttrium oxide (Y ₂ O ₃ ) particles were prepared as rare earth oxide particles containing Y as the second rare earth element. The average particle size of the yttrium oxide particles measured by the FSSS method described below was 0.1 μm.
In preparing the raw material mixture, the sieved aluminum oxide particles, the rare earth aluminate phosphor particles, and the rare earth oxide particles were mixed by weighing 11 g of the rare earth aluminate phosphor particles, 88.9 g of the aluminum oxide particles, and 0.1 g of the yttrium oxide particles, and mixing them in a dry ball mill, and the balls serving as the mixing medium were removed to prepare the raw material mixture (corresponding to S101 of preparing the raw material mixture in FIG. 1). With respect to 100% by mass of the raw material mixture consisting of the rare earth aluminate phosphor particles, the aluminum oxide particles, and the yttrium oxide particles in total, the content of the rare earth aluminate phosphor particles was 11.0% by mass, the content of the aluminum oxide particles was 88.9% by mass, and the content of the yttrium oxide particles was 0.1% by mass.

In molding the raw material mixture to obtain a molded body, the raw material mixture was filled into a mold and formed into a cylindrical molded body with a diameter of 100 mm and a thickness of 12 mm at a pressure of 10 MPa (102 kgf/ ^cm2 ). The obtained molded body was placed in a packaging container and vacuum-packed, and subjected to CIP at 176 MPa using a cold isostatic pressing device (manufactured by Kobe Steel, Ltd. (KOBELCO)) to mold the raw material mixture to obtain a molded body (corresponding to S102 of molding the raw material mixture to obtain a molded body in FIG. 1).

In the case of firing a molded body to obtain a sintered body, this embodiment includes a primary firing of the molded body to obtain a first sintered body, and a secondary firing of the obtained first sintered body to obtain a second sintered body.
In the process of sintering the molded body to obtain a sintered body, the obtained molded body was subjected to primary sintering at a temperature of 1650°C in an air atmosphere (0.101 MPa, oxygen concentration 20% by volume) using a sintering furnace (manufactured by Marusho Denki Co., Ltd.) to obtain a first sintered body. The primary sintering time was 6 hours. After the primary sintering, the first sintered body was cooled to 150°C in 12 hours.
In the process of sintering the molded body to obtain a sintered body, the obtained first sintered body was subjected to secondary sintering by hot isostatic pressing (HIP) using a hot isostatic pressing (HIP) device (manufactured by Kobe Steel, Ltd. (KOBELCO)) in a nitrogen gas atmosphere (99.99% by volume or more) using nitrogen gas as a pressure medium at a temperature of 1650°C and a pressure of 195 MPa for 2 hours to obtain a second sintered body. The secondary sintering time was 2 hours. After the secondary sintering, the second sintered body was cooled to 150°C in 5 hours.
In this embodiment, after firing the molded body to obtain a sintered body, specifically, in firing the molded body to obtain a sintered body, the obtained first sintered body is subjected to a second firing to obtain a second sintered body, and then processing is performed.
The second sintered body was cut into a predetermined shape and size using a wire saw to obtain a processed second sintered body (corresponding to S103 in FIG. 1, where the molded body is fired to obtain a sintered body).
In this embodiment, after the compact is fired to obtain a sintered body, specifically, after the first sintered body obtained in the firing of the compact to obtain a sintered body is fired secondarily to obtain a second sintered body, surface treatment is performed. The surface treatment is performed after the above-mentioned processing.
The cut surface of the processed second sintered body was polished by a surface grinder to obtain a ceramic composite of Example 1 consisting of a plate-like second sintered body having a thickness of 180 μm.

Example 2
In this example, a ceramic composite of Example 2 consisting of a plate-like sintered body having a thickness of 180 μm was obtained in the same manner as in Example 1, except that in preparing the raw material mixture, the aluminum oxide particles were sieved as follows.
In preparing the raw material, the aluminum oxide particles were sieved using NB50 (manufactured by NBC Meshtec Co., Ltd.) with a mesh size of 308 μm, a wire diameter of 200 μm, and a nylon #50 mesh. Sieving was performed once. The sieved aluminum oxide particles had a particle size of 25.4 μm or more, as measured by a laser diffraction method described below, of 0% by volume.

Comparative Example 1
In this comparative example, a ceramic composite of Comparative Example 2 consisting of a plate-like sintered body having a thickness of 180 μm was obtained in the same manner as in Example 1, except that the aluminum oxide particles were not sieved in preparing the raw material mixture.
The aluminum oxide particles not subjected to sieving had a particle content of 1.1% by volume having a particle size of 25.4 μm or more as measured by a laser diffraction method described below. The purity of the aluminum oxide particles was determined in the same manner as in Example 1.

The volumetric particle size distribution of each aluminum oxide particle used in Examples 1 and 2 and Comparative Example 1 was measured using a laser diffraction particle size measuring device (Mastersizer 2000, manufactured by Malvern) to determine the content ratio of particles of each particle size relative to the total amount of aluminum oxide particles. In addition, the volume average particle size at which the cumulative value from the small diameter side in the volumetric particle size distribution is 50% was determined, and the results are shown in Table 1. Figure 3 shows the volumetric particle size distribution of each aluminum oxide particle. As shown in Table 1 described later, in the volumetric particle size distribution of the aluminum oxide particles used in Comparative Example 1, the content ratio near 25.4 μm was 1.1 vol.%. In addition, it can be confirmed from Figure 3 that the aluminum oxide particles used in Comparative Example 1, which were not sieved, contained a large number of coarse particles.

The average particle size of the rare earth aluminate phosphor particles and the yttrium oxide particles, which are rare earth oxide particles, was measured by the FSSS method as follows.
Using a Fisher Sub-Sieve Sizer Model 95 (manufactured by Fisher Scientific), 1 ^cm3 of sample material for each particle was measured out in an environment of 25°C temperature and 70% relative humidity, packed in a dedicated tubular container, and then dry air at a constant pressure was allowed to flow, the specific surface area was read from the pressure difference, and the particle size was calculated by the FSSS method. The results are as described above.

For each of the obtained ceramic composites of the examples and comparative examples, the light emitting device 100 shown in Figures 2A and 2B was fabricated as follows. The light emitting element 20 and the semiconductor element 70 were placed on the mounting substrate 10. Specifically, the light emitting element 20 was formed by stacking nitride semiconductors on a sapphire substrate, had a thickness of about 0.11 mm, a planar shape of a substantially square of about 1.0 mm square, and had a dominant wavelength of 450 nm. The light emitting element 20 and the semiconductor element 70 were arranged in a line so that the sapphire substrate side, which is a semiconductor growth substrate, became the light emitting surface, and were flip-chip mounted on the conductive pattern formed on the mounting substrate 10 using the conductive member 60 made of Au.
Next, silicone resin was placed as adhesive 40 on the upper surface of the light-emitting element 20 to bond the wavelength conversion member 30 formed from each of the ceramic composites of the examples and comparative examples into a plate shape to the upper surface of the sapphire substrate of the light-emitting element 20.
Next, the covering member 50 was disposed around the light emitting element 20, the wavelength conversion member 30, and the semiconductor element 70. The covering member 50 was disposed along the side surfaces of the light emitting element 20 and the wavelength conversion member 30, and the semiconductor element 70 was completely buried in the covering member 50. Dimethyl silicone resin was used as the resin 51 contained in the covering member 50, and titanium oxide particles having an average particle size of 0.28 μm were contained as the light reflective material 52 in an amount of 60 mass % relative to the resin 51. Through these steps, the light emitting device 100 shown in FIG. 2A and FIG. 2B was fabricated.
The light emitting devices using the ceramic composites of the Examples and Comparative Examples were evaluated as follows. The results are shown in Table 1.

Forty light-emitting devices using each of the ceramic composites of the examples and comparative examples were produced, and the chromaticity coordinates (x, y) in the chromaticity coordinate system of the CIE (International Commission on Illumination) 1931 chromaticity diagram were determined using an imaging colorimeter (ProMetric I8, manufactured by Radiant Vision Systems). The average value of the chromaticity coordinates (x, y) of the 40 light-emitting devices using each of the ceramic composites of the examples and comparative examples was taken as the chromaticity coordinates (x, y) of the ceramic composites of the examples and comparative examples. In addition, the standard deviation (1σ) of the chromaticity coordinates (x, y) of the 40 light-emitting devices using each of the ceramic composites of the examples and comparative examples was determined as an index for evaluating the variation in color tone. The results are shown in Table 1.

The ceramic composites made of the sintered bodies of Examples 1 and 2 were manufactured using a raw material mixture containing aluminum oxide particles in which the content of particles with a particle size of 25.4 μm or more, as measured by laser diffraction, was 0.5 volume % or less. This suppressed abnormal growth of aluminum oxide crystals during firing, and no defects such as "aggregates," "voids," or "depressions" were identified when examining the surface of the resulting sintered body in SEM images taken with a scanning electron microscope.

In the ceramic composites made of the sintered bodies according to Examples 1 and 2, the VD value of aluminum oxide is less than 0.6, the particle size distribution of aluminum oxide particles is narrow, and a second crystal phase containing aluminum oxide particles of uniform size is formed. The light incident on the ceramic composite is scattered at the grain boundaries of the second crystal phase of uniform size, and the color difference between the light wavelength-converted by the rare earth aluminate phosphor contained in the first crystal phase and the light transmitted through the second crystal phase is reduced, and the color variation of the light emitted from the ceramic composite is suppressed.

The light emitting devices using the ceramic composites of Examples 1 and 2 had a smaller standard deviation (xσ, yσ) of the chromaticity coordinates (x, y) of the emitted light than the standard deviation (xσ, yσ) of the chromaticity coordinates (x, y) of the light emitted from the light emitting device using the ceramic composite of Comparative Example 1, suppressing the variation in color tone.

The ceramic composite obtained by the ceramic composite manufacturing method of one embodiment of the present invention can be used in combination with an LED or LD excitation light source as a wavelength conversion member for in-vehicle light sources, lighting devices for general lighting, backlights for liquid crystal display devices, and light sources for projectors.

10: mounting substrate, 20: light emitting element, 30: wavelength conversion member, 40: adhesive layer, 50: coating member, 60: conductive member, 70: semiconductor element, 100: light emitting device.

Claims (15)

preparing a raw material mixture including rare earth aluminate phosphor particles, aluminum oxide particles having a content ratio of particles having a particle size of 25.4 μm or more as measured by a laser diffraction method of 0.5 volume % or less, and rare earth oxide particles having a composition different from that of the rare earth aluminate phosphor particles ;
Molding the raw material mixture to obtain a molded body;
Sintering the molded body to obtain a sintered body;
The aluminum oxide particles have a particle size of 20.2 μm or more and less than 25.4 μm of 1.0 vol % or less, a particle size of 16.0 μm or more and less than 20.2 μm of 1.5 vol % or less, a particle size of 12.7 μm or more and less than 16.0 μm of 2.0 vol % or less, a particle size of 10.1 μm or more and less than 12.7 μm of 2.5 vol % or less, and a particle size of 8.0 μm or more and less than 10.1 μm of 1.0 vol % or less, relative to 100 vol % of the total amount of the aluminum oxide particles, and when the particle sizes at which the integrated values from the small diameter side in the volume-based particle size distribution curve measured by the laser diffraction method are 25% and 75% are expressed as D ₂₅ and D ₇₅ , respectively, VD=(D ₇₅ -D ₂₅ )/(D ₇₅ +D ₂₅ ) is less than 0.6, and the purity of the aluminum oxide is 99% or more,
The method for producing a ceramic composite , wherein the sintering of the compact to obtain a sintered body is performed at a sintering temperature within the range of 1550° C. to 1800° C. in an oxygen-containing atmosphere . 2. The method for producing a ceramic composite according to claim 1, wherein in preparing the raw material mixture, the aluminum oxide particles have a content of particles having a particle size of 1.0 μm or more and less than 8.0 μm as measured by a laser diffraction method of 61 vol% or more relative to 100 vol% of a total amount of the aluminum oxide particles. 3. The method for producing a ceramic composite according to claim 1, wherein in preparing the raw material mixture, the aluminum oxide particles have a content of particles having a particle size of more than 0 μm and less than 1.0 μm as measured by a laser diffraction method of 26.9 vol % or less relative to 100 vol% of a total amount of the aluminum oxide particles. 4. The method for producing a ceramic composite according to claim 1, wherein, in preparing the raw material mixture, the aluminum oxide particles have a volume average particle size, at 50% of the integrated value from the small diameter side in a volume-based particle size distribution measured by a laser diffraction method, in the range of 1.0 μm or more and 2.0 μm or less . 5. The method for producing a ceramic composite according to claim 1, further comprising the steps of: sieving the aluminum oxide particles through a sieve having an opening of 308 μm or less; and preparing the raw material mixture containing the aluminum oxide particles that have passed through the sieve. 6. The method for producing a ceramic composite according to claim 1, further comprising the steps of: sieving the aluminum oxide particles through a sieve having an opening of 160 μm or more; and preparing the raw material mixture containing the aluminum oxide particles that have passed through the sieve. 7. The method for producing a ceramic composite according to claim 1, wherein in preparing the raw material mixture, the rare earth aluminate phosphor, the aluminum oxide particles , and the rare earth oxide particles are dry-mixed. 8. The method for producing a ceramic composite according to claim 1 , wherein, in preparing the raw material mixture, the rare earth aluminate phosphor particles have a composition included in a composition formula represented by the following formula (I):
(Ln ¹ _1-a Ce _a ) ₃ (Al _c Ga _b ) ₅ O ₁₂ (I)
(In the formula (I), Ln ¹ is at least one selected from the group consisting of Y, Gd, Lu, and Tb, and a, b, and c satisfy 0<a≦0.22, 0≦b≦0.4, 0<c≦1.1, and 0.9≦b+c≦1.1.) 9. The method for producing a ceramic composite according to claim 1, wherein in preparing the raw material mixture, the rare earth aluminate phosphor particles have an average particle size measured by a Fischer Subsieve Sizer method in the range of 10 μm to 20 μm. 10. The method for producing a ceramic composite according to claim 1, wherein in preparing the raw material mixture, a content of rare earth aluminate phosphor particles in the raw material mixture is within a range of 5 mass % or more and 40 mass % or less . 11. The method for producing a ceramic composite according to claim 1, wherein in preparing the raw material mixture, the rare earth oxide particles have an average particle size measured by a Fisher Subsieve Sizer method in the range of 0.05 μm or more and less than 5 μm. 12. The method for producing a ceramic composite according to claim 1 , wherein in preparing the raw material mixture, a content of the rare earth oxide particles in the raw material mixture is within a range of 0.01 mass % or more and 3 mass % or less . In the step of sintering the molded body to obtain a sintered body, the molded body is primarily sintered to obtain a first sintered body;
The method for producing a ceramic composite according to claim 1 , further comprising: subjecting the first sintered body to a second firing to obtain a second sintered body. 14. The method for producing a ceramic composite according to claim 13, comprising: performing secondary firing by hot isostatic pressing at a pressure in the range of 50 MPa or more and 300 MPa or less and at a pressure in the range of 1500° C. or more and 1800° C. or less in the second firing to obtain a second sintered body. The method for producing a ceramic composite according to any one of claims 1 to 14, comprising processing the sintered body to a thickness in the range of 100 μm to 400 μm.