Method for producing phosphor powder and light-emitting device

Abstract

To provide a method for producing a phosphor powder which hardly deteriorates and has high reliability and can suppress the aggregation of particles even when particle diameter is small.SOLUTION: There is provide a method for producing a phosphor powder containing phosphor particles represented by the general formula, (Ca1-x-ySrxEuy)AlSiN3 in which 0≤x<1, 0<y<1, 1-x-y>0, which comprises: a mixing step of mixing a raw material powder to obtain a mixed powder; a calcination step of calcining the mixed powder to obtain a calcined product; and an acid treatment step of heat-treating the calcined product in an acid solution having an acid concentration of less than 0.500 mol / L. When in the cumulative distribution of particle diameter based on volume measured by laser diffraction / scattering after ultrasonic homogenization treatment of a dispersion of the phosphor powder (1), the particle diameter at which the cumulative value from small particle diameters reaches 50% of the total is defined as Dy50, Dy50 is less than 1.7 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing phosphor powder and a light emitting device. [Background technology]

[0002] Phosphor particles with reduced particle size are used as color conversion materials in micro LED displays that achieve high-brightness, high-definition light emission, etc. Patent Document 1 discloses phosphor particles in which phosphor powder is pulverized and decanted under appropriate conditions to reduce the particle size while suppressing particle aggregation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2022 / 118600 Summary of the Invention [Problem to be solved by the invention]

[0004] If phosphor powder with a small particle size aggregates, the dispersibility of the phosphor powder decreases, which may lead to a decrease in the uniformity of the coated surface. On the other hand, if aggregation of the phosphor powder can be suppressed, the dispersibility of the phosphor powder improves, enabling highly uniform coating.

[0005] The tendency of powder particles to agglomerate, i.e., the tendency of particles to adhere to each other, is expressed by the magnitude of the relative adhesive force, which is the ratio of the cohesive force acting on the powder, such as van der Waals force, to the separating force, such as gravity (≒ van der Waals force / gravity). Here, van der Waals force is proportional to particle size, and gravity is proportional to the cube of particle size, so the relative adhesive force is inversely proportional to the square of particle size. Therefore, generally, the smaller the particle size, the greater the relative adhesive force, and the more likely the particles are to agglomerate. Furthermore, phosphor powders are required to maintain their performance even in various environments.

[0006] The present disclosure provides a method for producing a phosphor powder that is highly reliable and resistant to deterioration, by suppressing particle aggregation even when the particle size is small, and also provides a light-emitting device that includes a phosphor powder that is highly reliable and resistant to deterioration, by suppressing particle aggregation even when the particle size is small. [Means for solving the problem]

[0007] One aspect of the present disclosure provides the following method for producing a phosphor powder.

[0008] [1] General formula (Ca 1-x-y Sr x EU y )AlSiN3, 0≦x<1, 0 <y<1、1-x-y> 0, the method for producing a phosphor powder containing phosphor particles, the method comprising: a mixing step of mixing raw material powders to obtain a mixed powder; and a firing step of firing the mixed powder to obtain a fired product. and an acid treatment step of heat-treating the fired product in an acid solution having an acid concentration of less than 0.500 mol / L, wherein, in a cumulative distribution (1) of volumetric particle diameters measured by a laser diffraction / scattering method after subjecting a dispersion of the phosphor powder to ultrasonic homogenization, Dy50 is defined as the particle diameter when the integrated value from small particle diameters reaches 50% of the total, and Dy50 is less than 1.7 μm.

[0009] In the method for producing phosphor powder described above in [1], the fired product is heat-treated in an acid solution with an acid concentration of less than 0.500 mol / L in the acid treatment step. By performing the acid treatment step, an oxide film is formed on the surface of the phosphor powder, suppressing degradation of the phosphor powder under high temperature and humidity conditions and improving reliability. Furthermore, by using a dilute acid solution with an acid concentration of less than 0.500 mol / L in the acid treatment step, an oxide film can be formed on the particle surface while suppressing hydrolysis of the phosphor crystals. This allows for the production of phosphor powder in which the generation of ultrafine powder, which causes aggregation, is sufficiently suppressed. The phosphor powder obtained by the above production method contains little ultrafine powder, thereby suppressing aggregation. Furthermore, by having Dy50 of less than 1.7 μm, the particle diameter can be reduced.

[0010] The method for producing the phosphor powder in [1] above may be the following methods [2] to [8].

[0011] [2] The method for producing a phosphor powder according to [1], wherein, in the cumulative distribution (2) of volumetric particle diameters measured by a laser diffraction / scattering method without subjecting the dispersion to ultrasonic homogenization treatment, Dx97 is the particle diameter at which the integrated value from small particle diameters reaches 97% of the total, and Dy97 is the particle diameter at which the integrated value from small particle diameters reaches 97% of the total in the cumulative distribution (1), Dx97 / Dy97 is 5.0 or less.

[0012] The phosphor powder obtained by the manufacturing method [2] above has a Dx97 / Dy97 ratio of 5.0 or less. Dy represents the particle size obtained from the cumulative particle size distribution (1) after ultrasonic homogenization under specified conditions, and Dx represents the particle size obtained from the cumulative particle size distribution (2) before ultrasonic homogenization. By performing ultrasonic homogenization, it is possible to measure the particle size of agglomerated particles in a state where the agglomerated particles are deaggregated due to physical bonding. Therefore, the smaller the Dx97 / Dy97 value, the smaller the difference in particle size between agglomerated particles and deaggregated particles, and the more agglomerated the phosphor powder is. Therefore, the phosphor powder obtained by the manufacturing method [2] above has higher reliability while further suppressing the aggregation of particles with small particle sizes. Furthermore, phosphor powders with reduced ultrafine particles can suppress light scattering due to excessive surface area of the phosphor powder. Therefore, such phosphor powders have high light absorptivity.

[0013] [3] A method for producing a phosphor powder according to [1] or [2], wherein, in a cumulative distribution (2) of volumetric particle diameters measured by a laser diffraction / scattering method without subjecting the dispersion to ultrasonic homogenization treatment, Dx90 is the particle diameter at which the integrated value from small particle diameters reaches 90% of the total, and Dy90 is the particle diameter at which the integrated value from small particle diameters reaches 90% of the total in the cumulative distribution (1), Dx90 / Dy90 is 2.0 or less.

[0014] The phosphor powder obtained by the manufacturing method [3] above has a Dx90 / D90 ratio of 2.0 or less. The phosphor powder obtained by the manufacturing method [3] above has higher reliability while further suppressing aggregation of particles with small particle diameters. In addition, it has a higher light absorption rate.

[0015] [4] The method for producing a phosphor powder according to any one of [1] to [3], wherein, in the cumulative distribution (1), when the particle diameter when the integrated value from small particle diameters reaches 10% of the whole is defined as Dy10, Dy10 is 0.4 μm or more.

[0016] The phosphor powder obtained by the manufacturing method [4] above has a further reduction in ultrafine particles with small particle diameters that cause aggregation. Such phosphor powder can further reduce aggregation. In addition, light scattering can be further suppressed, resulting in a higher light absorption rate.

[0017] [5] The method for producing a phosphor powder according to any one of [1] to [4], wherein A is the oxygen content of the phosphor powder obtained by the heat treatment in the acid treatment step, and B is the oxygen content of the phosphor powder after storing the phosphor powder in an environment at a temperature of 85°C and a humidity of 85% for 250 hours, and B / A is 3.00 or less.

[0018] The phosphor powder obtained by the manufacturing method [5] above can suppress an increase in oxygen content after storage for 250 hours in an environment at a temperature of 85°C and a humidity of 85%. Such phosphor powder can suppress performance degradation even in harsh environments. Therefore, the phosphor powder of [5] above has even higher reliability.

[0019] [6] The method for producing a phosphor powder according to any one of [1] to [5], wherein the acid solution contains hydrochloric acid.

[0020] In the manufacturing method [6] above, the acid solution contains hydrochloric acid. By oxidizing with hydrochloric acid, a sufficient oxide film can be formed on the surface of the phosphor powder, resulting in a highly reliable phosphor powder. In addition, hydrolysis of the phosphor is suppressed, ultrafine powder is reduced, and aggregation is further suppressed, resulting in a phosphor powder with even higher light absorption.

[0021] [7] The method for producing a phosphor powder according to any one of [1] to [6], wherein in the acid treatment step, the fired product is heat-treated in the acid solution at a temperature of 25 to 90°C. [8] The method for producing a phosphor powder according to any one of [1] to [7], wherein in the acid treatment step, the fired product is heat-treated in the acid solution for 5 minutes to 10 hours.

[0022] In the method for producing phosphor powder described above in [7], the temperature at which the fired product is heat-treated in the acid solution is 25 to 90°C. By performing the heat treatment at such a temperature, the acid treatment of the phosphor powder can be carried out sufficiently, and a highly reliable phosphor powder can be obtained. Furthermore, a phosphor powder with a higher light absorption rate can be obtained while further suppressing aggregation. In the method for producing phosphor powder described above in [8], the time at which the fired product is heat-treated in the acid solution is 5 minutes to 10 hours. By performing the heat treatment for the above period of time, a highly reliable phosphor powder can be obtained. Furthermore, the acid treatment of the phosphor powder can be carried out sufficiently, and a phosphor powder with a higher light absorption rate can be obtained while further suppressing aggregation.

[0023] One aspect of the present disclosure provides the following light-emitting device [9] or

[10] .

[0024] [9] 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, wherein the wavelength converter contains a phosphor powder obtained by the manufacturing method described in any one of [1] to [8].

[10] The light emitting device according to [9], wherein the light emitting element includes at least one selected from the group consisting of a mini LED and a micro LED.

[0025] The light emitting device of [9] above contains, as a wavelength converter, a phosphor powder obtained by the manufacturing methods of [1] to [8] above. Therefore, it is possible to exhibit excellent color rendering properties. Furthermore, the light emitting device of

[10] above contains, as a light emitting element, at least one selected from the group consisting of a mini LED and a micro LED. Therefore, it is possible to provide a light emitting device that can achieve high brightness and high definition. [Effects of the Invention]

[0026] According to the present disclosure, there is provided a method for producing a phosphor powder that is highly reliable and resistant to deterioration, and capable of suppressing particle aggregation even when the particle size is small, and there is also provided a light-emitting device that includes a phosphor powder that is highly reliable and resistant to deterioration, and capable of suppressing particle aggregation even when the particle size is small. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram showing a light emitting device. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. The upper or lower limit of a numerical range specified in the present disclosure may be replaced with any value shown in the examples. Furthermore, the upper and lower limit values individually described may be arbitrarily combined. Unless otherwise specified, the materials or components exemplified in the present disclosure may be used alone or in combination of two or more.

[0029] <Method of manufacturing phosphor powder> A method for producing a phosphor powder according to one embodiment of the present invention is to prepare a phosphor powder containing a compound of the general formula (Ca 1-x-y Sr x EU y)AlSiN3, 0≦x<1, 0 <y<1、1-x-y> A method for producing a phosphor powder containing phosphor particles having a Dy50 of 0.0 comprises a mixing step of mixing raw material powders to obtain a mixed powder, a firing step of firing the mixed powder to obtain a fired product, and an acid treatment step of heat-treating the resulting fired product in an acid solution having an acid concentration of less than 0.500 mol / L, wherein, in a cumulative distribution (1) of volumetric particle sizes measured by laser diffraction / scattering method after ultrasonic homogenization of a phosphor powder dispersion, Dy50 is defined as the particle size at which the cumulative value from small particle sizes reaches 50% of the total, and Dy50 is less than 1.7 μm. The phosphor powder obtained by the above production method has a small particle size and is highly reliable because it is inhibited from deteriorating under high temperature and high humidity conditions, and can inhibit aggregation of phosphor particles.

[0030] General formula (Ca 1-x-y Sr x EU y )AlSiN3, 0≦x<1, 0 <y<1、1-x-y> The phosphor particles having a crystal structure of CaAlSiN3 may include at least one phosphor particle selected from the group consisting of CASN and SCASN. Generally, CASN has a crystal structure in which the main crystal phase is the same as CaAlSiN3. On the other hand, a crystal structure in which the main crystal phase is the same as CaAlSiN3 and contains Sr is called SCASN. CASN or SCASN is mainly CaAlSiN3. 2+ A part of Eu acts as a luminescence center 2+ By being substituted with , they function as red-emitting phosphors. Therefore, CASN and SCASN are used as phosphors that convert low-wavelength light such as blue light into high-wavelength light such as red light. The phosphor powder in this disclosure refers to an aggregate containing a plurality of such phosphor particles.

[0031] In the mixing step, raw material powders are mixed to form a mixed powder. Examples of raw material powders include europium compounds, strontium compounds such as strontium nitride, calcium compounds such as calcium nitride, silicon nitrides such as α-type silicon nitride, and aluminum nitride. Each of the raw material powders is preferably in the form of a powder.

[0032] Examples of europium compounds include oxides containing europium, hydroxides containing europium, nitrides containing europium, oxynitrides containing europium, and halides containing europium. These can be used alone or in combination of two or more. Among these, it is preferable to use europium oxide, europium nitride, and europium fluoride alone, and it is more preferable to use europium oxide alone.

[0033] In the firing process described below, europium is divided into three types: one that dissolves in the CASN or SCASN crystals, one that volatilizes, and one that remains as a heterophase component. The heterophase component must be removed in the acid treatment process described below to reduce light absorption.

[0034] In the mixing step, the mixed powder can be obtained, for example, by dry-mixing the raw material powders, or by wet-mixing the raw material powders in an inert solvent that does not substantially react with the raw material powders, followed by removing the solvent. Examples of mixing devices that can be used include a small mill mixer, a V-type mixer, a rocking mixer, a ball mill, and a vibration mill. After mixing using the device, agglomerates can be removed using a sieve, if necessary, to obtain the mixed powder.

[0035] In order to prevent deterioration of the raw material powder and unintended incorporation of oxygen, the mixing step is preferably carried out in a nitrogen atmosphere and in an environment with as little moisture (humidity) as possible.

[0036] In the firing step, the mixed powder obtained in the mixing step is fired to obtain a fired product. The firing temperature in the firing step is not particularly limited, but is preferably 1800°C or higher and 2100°C or lower, and more preferably 1900°C or higher and 2000°C or lower. When the firing temperature is above the lower limit, grain growth of the phosphor particles proceeds more effectively. Therefore, the light absorption rate can be improved while further suppressing aggregation of the phosphor powder. When the firing temperature is below the upper limit, the decomposition of the phosphor particles can be further suppressed. Therefore, the light absorption rate can be improved while further suppressing aggregation of the phosphor powder.

[0037] Other conditions in the firing step, such as the temperature rise time, temperature rise rate, heating retention time, and pressure, are not particularly limited and may be adjusted as appropriate depending on the raw materials used. The heating retention time is preferably 3 hours or more and 30 hours or less, and the pressure is preferably 0.6 MPa or more and 10 MPa or less. From the viewpoint of controlling the oxygen concentration, the firing step is preferably carried out in a nitrogen gas atmosphere. That is, the firing step is preferably carried out in a nitrogen gas atmosphere with a pressure of 0.6 MPa or more and 10 MPa or less.

[0038] In the firing step, the method of firing the mixed powder can be, for example, a method in which the mixed powder is filled into a container made of a material (such as tungsten) that does not react with the mixed powder during firing, and heated in a nitrogen atmosphere.

[0039] The firing step may include an annealing step in which the fired product is further heated at a temperature lower than the firing temperature. The annealing step is preferably performed in an atmosphere containing at least one gas selected from the group consisting of a rare gas and an inert gas. The rare gas may contain, for example, argon, helium, or the like, or may contain argon or consist of argon. The inert gas may contain, for example, nitrogen, or the like, or may consist of nitrogen.

[0040] The annealing step may be performed under atmospheric pressure or under pressure. When the annealing step is performed under a pressure environment, the pressure in the annealing step may be, for example, 0.10 MPa or more, or 0.12 MPa or more. The pressure in the annealing step may be, for example, 0.95 MPa or less, 0.70 MPa or less, 0.50 MPa or less, or 0.30 MPa or less. The pressure in the annealing step may be, for example, 0.10 to 0.95 MPa. Pressure in the present disclosure refers to absolute pressure.

[0041] In the annealing step, the mixture of the fired product obtained in the above step and other additives may be heat-treated. The method for preparing the mixture may be the same as that in the above mixing step.

[0042] The annealing temperature in the annealing step may be, for example, 1350° C. or higher, 1400° C. or higher, 1450° C. or higher, 1500° C. or higher, or 1550° C. or higher. The annealing temperature in the annealing step may be, for example, 1850° C. or lower, 1830° C. or lower, 1820° C. or lower, 1800° C. or lower, or lower than 1800° C. The annealing temperature in the annealing step may be, for example, 1350 to 1850° C. or 1400 to 1850° C.

[0043] The heating time in the annealing step may be, for example, 0.5 hours or more, 1.0 hour or more, 1.5 hours or more, 3.0 hours or more, or 4.0 hours or more. The heating time in the annealing step may be, for example, 30.0 hours or less, 20.0 hours or less, 10.0 hours or less, 8.0 hours or less, or 5.0 hours or less. The heating time in the annealing step may be, for example, 0.5 to 30.0 hours, 1.5 to 10.0 hours, or 4.0 to 8.0 hours.

[0044] The fired product obtained through the firing step, or the firing step and the annealing step, is a granular or lumpy fired product. The fired product may be made into a powder by using the crushing step, the pulverizing step, and the classification step, either alone or in combination, as described below.

[0045] The crushing step is a step of crushing the sintered product obtained in the firing step or the firing step and the annealing step when the sintered product is in a lumpy state. For example, a mortar or a general crusher may be used for crushing.

[0046] The pulverization process is a process in which the obtained fired product is pulverized to adjust the particle size. A general pulverizer can be used in the pulverization process. Examples of general pulverizers and disintegrators include a ball mill, a jet mill, and a Henschel mixer. From the viewpoint of suppressing the occurrence of scratches, cracks, etc. on the surface of the fired product, it is desirable to perform the pulverization under gentle conditions. From the viewpoint of pulverization under gentle conditions, for example, it is desirable to perform the pulverization process by wet ball mill pulverization in the presence of a medium such as ion-exchanged water. Furthermore, zirconia balls can be used in the ball mill. The particle size of the phosphor powder can be controlled by adjusting the pulverization time in the pulverization process.

[0047] The method for producing phosphor powder may include a classification step. By including the classification step, the optical properties of the resulting phosphor powder can be further improved. The classification step may be performed, for example, by decantation. The classification step is performed by adding the material to be treated (e.g., a fired product that has been subjected to a pulverization step) to a dispersion medium, preparing a dispersion and stirring the mixture, then precipitating the fired product in the dispersion and removing the supernatant. After removing the supernatant, the precipitate is collected by filtration and dried to obtain a powdered fired product from which fine particles have been removed. In the classification step, the preparation of the dispersion and the removal of the supernatant may be repeated. Examples of dispersion media include distilled water and an aqueous solution of sodium hexametaphosphate. The particle size of the phosphor powder can be controlled by adjusting the classification point in the classification step.

[0048] In the acid treatment step, the fired product obtained through the above steps is heat-treated in an acid solution with an acid concentration of less than 0.500 mol / L. This allows for the formation of an oxide film on the particle surface while suppressing hydrolysis of the phosphor crystals. This allows for the formation of an oxide film to suppress degradation of the phosphor powder, sufficiently increasing reliability, and sufficiently suppressing the generation of ultrafine powder and preventing aggregation, resulting in a phosphor powder. Furthermore, at least a portion of impurities that do not contribute to light emission can be removed, improving light absorption.

[0049] The acid solution can be an aqueous solution containing at least one acid selected from hydrofluoric acid, sulfuric acid, phosphoric acid, hydrochloric acid, and nitric acid. The acid solution preferably contains hydrochloric acid. By using an acid solution containing hydrochloric acid, an oxide film can be sufficiently formed on the surface of the phosphor particles, improving the reliability of the phosphor powder. Furthermore, excessive acid can prevent the generation of ultrafine powder, further suppressing aggregation.

[0050] The acid concentration of the acid solution is less than 0.500 mol / L, and may be 0.400 mol / L or less, or 0.300 mol / L or less. By ensuring that the acid concentration of the acid solution is within this range, an oxide film is formed on the surface of the phosphor particles, suppressing degradation and improving reliability, while preventing the generation of ultrafine powder due to hydrolysis caused by excessive acid. The phosphor powder obtained by such an acid treatment process can be sufficiently prevented from agglomerating. Furthermore, by reducing the ultrafine powder, light scattering due to excessive surface area can be suppressed, resulting in a phosphor powder with high light absorptivity. The acid concentration of the acid solution may be 0.0100 mol / L or more. For example, the acid concentration of the acid solution may be in the range of 0.0100 mol / L or more and less than 0.500 mol / L.

[0051] The acid treatment can be carried out by dispersing the fired product in the acid solution described above. The temperature during stirring may be, for example, 25 to 90°C, 40 to 90°C, or 50 to 70°C. By performing the heat treatment at such a temperature, the acid treatment of the phosphor powder can be sufficiently carried out, and a highly reliable phosphor powder can be obtained. In addition, a phosphor powder with a higher light absorptance can be obtained while further suppressing aggregation.

[0052] The stirring time may be, for example, 5 minutes to 10 hours, or 30 minutes to 3 hours. By carrying out the heat treatment for the above time, a highly reliable phosphor powder can be obtained. In addition, the acid treatment of the phosphor powder can be carried out sufficiently, and a phosphor powder with a higher light absorption rate can be obtained while further suppressing aggregation.

[0053] After the acid treatment step, substances other than the phosphor particles may be separated by filtration, and substances adhering to the phosphor particles may be washed with water. Also, a crushing step and a classification step may be performed before or after the acid treatment step to adjust the particle size of the phosphor powder.

[0054] Phosphor powder can be manufactured through the above steps. However, the above manufacturing method is merely an example and is not limited thereto. The phosphor powder obtained by the phosphor powder manufacturing method of this embodiment can suppress particle aggregation even when the particle diameter is small, and is resistant to deterioration and highly reliable. It also has high light absorption. Therefore, such phosphor powder can be suitably used in light-emitting devices equipped with mini LEDs, micro LEDs, etc.

[0055] The reliability of the phosphor powder in the present disclosure can be evaluated by whether it maintains its performance after being exposed to harsh conditions in an exposure test. The exposure test in the present disclosure is performed by storing the powder for 250 hours in an environment at a temperature of 85°C and a humidity of 85%. Furthermore, the performance can be evaluated by the oxygen content and the light absorbance at 455 nm. Therefore, if the changes in the oxygen content and light absorbance before and after the exposure test are small, it can be said that the powder has high reliability.

[0056] When the oxygen content of the phosphor powder before the exposure test is A and the oxygen content after storing the phosphor powder for 250 hours in an environment at a temperature of 85°C and humidity of 85% is B, B / A may be 3.00 or less, 2.00 or less, or 1.70 or less. The oxygen content (oxygen content A, B) in the present disclosure refers to the oxygen content as the total amount of oxygen. The oxygen content can be measured using a commercially available oxygen / nitrogen analyzer. Such phosphor powders do not increase in oxygen content even when stored in harsh environments, and can suppress a decrease in light absorptance. Therefore, they have even higher reliability. B / A may be 1.00 or more. The range of B / A may be, for example, 1.00 to 3.00.

[0057] The oxygen content A in the phosphor powder before the exposure test may be 6.10% by mass or less, or may be 6.05% by mass or less. When the oxygen content A is in this range, the oxygen content in the phosphor powder is sufficiently reduced. Such phosphor powder has a sufficiently reduced amount of impurities. Therefore, it has a higher light intensity. The oxygen content A may be 3.00% by mass or more, or may be 3.20% by mass or more. The range of the oxygen content A may be, for example, 3.00 to 6.10% by mass.

[0058] The oxygen content B after storing the phosphor powder for 250 hours in an environment at a temperature of 85°C and a humidity of 85% may be 10.0% by mass or less, or may be 9.0% by mass or less. By keeping the oxygen content within this range, the oxygen content does not increase even when stored in a harsh environment, and a decrease in light absorptance can be suppressed. The oxygen content B may be 5.00% by mass or more. An example of the range of the oxygen content B may be 5.00 to 10.0% by mass.

[0059] When the light absorptance of the phosphor powder at a wavelength of 455 nm is C and the light absorptance of the phosphor powder at a wavelength of 455 nm after storing the phosphor powder for 250 hours in an environment at a temperature of 85°C and a humidity of 85% is D, D / C may be 0.95 to 1.00 or 0.98 to 1.00. When D / C is in this range, a decrease in light absorptance can be suppressed and performance can be maintained even when stored in a harsh environment. Therefore, such a phosphor powder has even higher reliability.

[0060] The light absorptance C at a wavelength of 455 nm of the phosphor powder before the exposure test may be 80.5% or more, or even 81.0% or more. When the light absorptance C at a wavelength of 455 nm is within this range, blue light is not unnecessarily transmitted and the light absorptance is sufficiently high, making it suitable for use as a wavelength converter in light-emitting elements such as mini-LEDs and micro-LEDs. The light absorptance at a wavelength of 455 nm can be measured, for example, using an MCPD-7000 manufactured by Otsuka Electronics Co., Ltd.

[0061] The phosphor powder obtained by the manufacturing method of this embodiment has a volume-based particle size cumulative distribution (1) measured by laser diffraction / scattering after ultrasonic homogenization of a phosphor powder dispersion. When the cumulative particle size Dy50 is defined as the particle size at which the cumulative value from the smallest particle size reaches 50% of the total, the Dy50 is less than 1.7 μm. The Dy50 of the phosphor powder may be 1.6 μm or less, 1.3 μm or less, or 1.0 μm or less. Since such phosphor powders can have sufficiently small particle sizes, they are suitable for use as wavelength converters in small-sized light-emitting devices such as mini-LEDs and micro-LEDs. The Dy50 may be 0.6 μm or more. The Dy50 range may be, for example, 0.6 μm or more but less than 1.7 μm.

[0062] Ultrasonic homogenization of a phosphor powder dispersion is a process for breaking down aggregations between particles in the phosphor powder. In this disclosure, aggregated particles are sometimes referred to as secondary particles, and unagglomerated particles are sometimes referred to as primary particles. Homogenization breaks down the physical bonds between the secondary particles of the phosphor powder, converting them into primary particles. Therefore, by comparing the particle diameters at a predetermined integrated value in the cumulative volume-based particle diameter distribution of the phosphor powder, which can be measured by laser diffraction / scattering, before and after ultrasonic homogenization, it is possible to determine whether the primary particles of the phosphor powder are agglomerated.

[0063] Ultrasonic homogenization can be performed, for example, by the following method. A dispersion of 30 mg of phosphor powder dispersed in 100 mL of a 0.2% by mass aqueous solution of sodium hexametaphosphate is placed in a cylindrical container with a bottom inner diameter of 5.5 cm. Next, the transducer (a cylindrical tip with an outer diameter of 20 mm) of an ultrasonic homogenizer is inserted from above the dispersion, and with the transducer immersed to a depth of 1.0 cm, ultrasonic waves are irradiated onto the dispersion for 3 minutes at a frequency of 19.5 kHz and an output of 150 W. Ultrasonic homogenization of phosphor powder can be performed using the method described above.

[0064] The laser diffraction / scattering method can be used in accordance with the method described in JIS Z 8825:2013, "Particle size analysis - Laser diffraction / scattering method." A laser diffraction / scattering particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name: LS-13 320) or the like can be used for the measurement. In the present disclosure, the cumulative distribution of volumetric particle sizes measured by the laser diffraction / scattering method after subjecting a phosphor powder dispersion to ultrasonic homogenization is referred to as cumulative distribution (1). Furthermore, the cumulative distribution of volumetric particle sizes measured by the laser diffraction / scattering method before subjecting the dispersion to ultrasonic homogenization is referred to as cumulative distribution (2).

[0065] In cumulative distribution (1), Dy97 is the particle diameter at which the cumulative value from the small particle diameter reaches 97% of the total, and in cumulative distribution (2), Dx97 is the particle diameter at which the cumulative value from the small particle diameter reaches 97% of the total. The Dx97 / Dy97 ratio of the phosphor powder may be 5.0 or less. Such phosphor powder contains less ultrafine particles and suppresses aggregation. Furthermore, the reduction in ultrafine particles prevents light scattering due to excessively high surface area of the phosphor powder, resulting in a higher light absorptivity. Dx97 / Dy97 may be 4.0 or less, 3.0 or less, 2.0 or less, or 1.5 or less. A phosphor powder having a Dx97 / Dy97 ratio within this range has a sufficient reduction in ultrafine particles, further suppresses aggregation, and thus has a higher light absorptivity. Dx97 / Dy97 may be 1.0 or more. The Dx97 / Dy97 ratio may be, for example, in the range of 1.0 to 5.0.

[0066] Dx97 may be 20.0 μm or less, 10.0 μm or less, or 5.0 μm or less. When Dx97 is in this range, aggregation of the phosphor powder is further suppressed, and the particle size can be further reduced. Dx97 may be 2.5 μm or more, or 3.0 μm or more. When Dx97 is in this range, ultrafine powder in the phosphor powder can be reduced, light scattering can be suppressed, and light absorptance can be further increased. The range of Dx97 may be, for example, 2.5 to 20.0 μm.

[0067] Dy97 may be 10.0 μm or less, 5.0 μm or less, 3.0 μm or less, or 2.0 μm or less. By having Dy97 in this range, the particle size of the phosphor can be further reduced. Dy97 may be 1.5 μm or more, or 2.0 μm or more. By having Dy97 in this range, it is possible to reduce ultrafine powder in the phosphor powder, suppress light scattering, and further increase light absorptance. The range of Dy97 may be, for example, 1.5 to 10.0 μm.

[0068] In cumulative distribution (2), when the particle diameter at which the integrated value from the small particle diameter reaches 90% of the total is defined as Dx90, and when the particle diameter at which the integrated value from the small particle diameter reaches 90% of the total is defined as Dy90, in cumulative distribution (1), the ratio Dx90 / Dy90 may be 2.0 or less, 1.5 or less, 1.2 or less, or 1.1 or less. Such phosphor powder has a higher light absorptance because aggregation is further suppressed. Dx90 / Dy90 may be 1.0 or more. The range of Dx90 / Dy90 may be, for example, 1.0 to 2.0.

[0069] Dx90 may be 10.0 μm or less, 5.0 μm or less, 3.0 μm or less, or 2.5 μm or less. When Dx90 is in this range, secondary particles formed by aggregation of the phosphor powder can be reduced, and the particle size can be further reduced. Dx90 may be 1.0 μm or more, or 1.5 μm or more. When Dx90 is in this range, ultrafine particles of the phosphor powder can be reduced, light scattering can be suppressed, and light absorptance can be further increased. The range of Dx90 may be, for example, 1.0 to 10.0 μm.

[0070] Dy90 may be 3.5 μm or less, 3.0 μm or less, 2.5 μm or less, or 2.0 μm or less. By having Dy90 in this range, the particle size of the phosphor can be further reduced. Dy90 may be 1.0 μm or more, or 1.5 μm or more. By having Dy90 in this range, it is possible to reduce ultrafine powder in the phosphor powder, suppress light scattering, and further increase the light absorptance. The range of Dy90 may be, for example, 1.0 to 3.5 μm.

[0071] In the cumulative distribution (2), when the particle diameter when the integrated value from the small particle diameter reaches 10% of the total is defined as Dy10, Dy10 may be 0.4 μm or more, or may be 0.5 μm or more. Phosphor powder with Dy10 in this range has a sufficiently reduced amount of ultrafine powder. Because the amount of ultrafine powder is sufficiently reduced, light scattering caused by an excessively large surface area of the phosphor powder can be suppressed. Therefore, such phosphor powder has a higher light absorption rate. Dy10 may be 1.0 μm or less. An example of the range of Dy10 is 0.4 to 1.0 μm.

[0072] <Light-emitting device> FIG. 1 is a diagram showing a light emitting device 10. The light emitting device 10 includes a light emitting element 20 that emits primary light and a wavelength converter 30 that absorbs part of the primary light and emits secondary light having a wavelength longer than that of the primary light. The wavelength converter 30 contains the above-mentioned phosphor powder. The wavelength converter 30 may be provided in contact with an upper portion of the light emitting element 20.

[0073] The light emitting element 20 emits excitation light and may be a blue LED. A terminal 40 is connected to the bottom of the light emitting element 20. When the terminal 40 is connected to a power source, the light emitting element 20 can emit light.

[0074] The excitation light emitted from the light-emitting element 20 may be wavelength-converted by the wavelength converter 30. When the excitation light is blue light, the blue light is wavelength-converted to red light by the wavelength converter 30 including CASN and / or SCASN.

[0075] The wavelength converter 30 may be composed of the above-mentioned phosphor particles and a sealant that seals the phosphor particles. Various curable resins can be used as the sealant. Any curable resin can be used as long as it is sufficiently transparent and can obtain the optical properties required for the display. An example of the sealant is a silicone resin. Silicone resin is preferably used from the viewpoints of transparency and heat resistance.

[0076] The light-emitting element 20 includes at least one selected from the group consisting of a mini LED and a micro LED. The size of the mini LED may be 100 to 2000 μm, 200 to 1000 μm, or 300 to 800 μm. On the other hand, the size of the micro LED may be 1 μm or more and less than 100 μm, 10 to 80 μm, or 30 to 60 μm. By ensuring that the size of the mini LED or micro LED is within this range, high-brightness, high-precision light emission can be achieved in displays and the like incorporating the light-emitting device 10.

[0077] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. [Example]

[0078] The present disclosure will be described in more detail below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0079] Example 1 The following raw material powders were prepared in a glove box maintained in an atmosphere such as nitrogen with a moisture content of 1 mass ppm or less and an oxygen content of 1 mass ppm or less.

[0080] Alpha-type silicon nitride powder (Si3N4, SN-E10 grade, manufactured by UBE Corporation) Calcium nitride powder (Ca3N2, manufactured by Taiheiyo Cement Corporation) Aluminum nitride powder (AlN, E grade, manufactured by Tokuyama Corporation) Strontium nitride powder (SrN, manufactured by Materion) Europium oxide powder (Eu2O3, manufactured by Nippon Yttrium Co., Ltd.)

[0081] The raw material powders were mixed using a small mill mixer to obtain a mixture of 25.65 mass% Si3N4, 2.98 mass% Ca3N2, 22.49 mass% AlN, 43.09 mass% Sr2N, and 5.79 mass% Eu2O3. After mixing, the mixture was sieved using a 150 μm mesh sieve to remove aggregates, and the powder that remained under the sieve was used as a mixed powder. The mixed powder was then filled into a tungsten container with a lid.

[0082] The container filled with the mixed powder was removed from the glove box and quickly placed in an electric furnace equipped with a carbon heater. The furnace was thoroughly evacuated to a pressure of 0.1 Pa or less. Heating was initiated while continuing the evacuation. After reaching 850°C, nitrogen gas was introduced into the furnace, maintaining the furnace atmosphere at a constant pressure of 0.8 MPaG. The temperature continued to rise to 1950°C even after the introduction of nitrogen gas. After sintering at this temperature (1950°C) for 4 hours, heating was stopped and the mixture was cooled. After cooling to room temperature, the red lumps recovered from the container were crushed in a mortar (crushing process) and passed through a sieve with 250 μm openings to obtain a powder (sintered product). The resulting powder was then placed in a ball mill and subjected to wet crushing to prepare a crushed product (crushing process). The crushed product was removed and precipitated in distilled water. Further distilled water was added and stirred. After stirring, the crushed product was allowed to settle, and the supernatant and fine powder were removed. This process of adding distilled water, stirring, and removing the supernatant and fine powder was repeated until the supernatant became transparent (classification process). The resulting precipitate was filtered and then dried in the air. During the classification process, the pH of the distilled water added to the ground material was maintained at 8 or less.

[0083] An acid treatment step was further carried out to remove impurities that may have been generated during firing. Specifically, the fired product obtained through the above classification step was immersed in hydrochloric acid with a molar concentration of 0.052 mol / L so that the powder concentration was 26.7 mass%, and then subjected to acid treatment by stirring for 1 hour while heating. The powder and hydrochloric acid solution were then separated by filtration at a room temperature of approximately 25°C, and the powder was washed with pure water. The powder washed with pure water was then dried for 12 hours in a dryer at a temperature of 100°C to 120°C. The phosphor powder of Example 1 was obtained through the above procedure.

[0084] Example 2 A phosphor powder was prepared in the same manner as in Example 1, except that hydrochloric acid with an acid molar concentration of 0.286 mol / L was used for the acid treatment.

[0085] Example 3 A phosphor powder was produced in the same manner as in Example 2, except that the processing conditions for crushing, pulverizing, classifying, etc. of the fired product obtained through the firing step were adjusted.

[0086] Example 4 A phosphor powder was prepared in the same manner as in Example 1, except that hydrochloric acid with an acid molar concentration of 0.403 mol / L was used for the acid treatment.

[0087] (Comparative Example 1) A phosphor powder was prepared in the same manner as in Example 1, except that hydrochloric acid with an acid molar concentration of 0.520 mol / L was used for the acid treatment.

[0088] (Comparative Example 2) A phosphor powder was prepared in the same manner as in Example 1, except that hydrochloric acid with an acid molar concentration of 0.693 mol / L was used for the acid treatment.

[0089] (Comparative Example 3) A phosphor powder was prepared in the same manner as in Example 1, except that hydrochloric acid with an acid molar concentration of 0.867 mol / L was used for the acid treatment.

[0090] Comparative Example 4 A phosphor powder was prepared in the same manner as in Example 1, except that hydrochloric acid with an acid molar concentration of 1.04 mol / L was used for the acid treatment.

[0091] (Comparative Example 5) A phosphor powder was prepared in the same manner as in Example 1, except that hydrochloric acid with an acid molar concentration of 1.56 mol / L was used for the acid treatment.

[0092] (Comparative Example 6) A phosphor powder was prepared in the same manner as in Example 3, except that hydrochloric acid with an acid molar concentration of 1.56 mol / L was used for the acid treatment.

[0093] (Comparative Example 7) Except for using water instead of hydrochloric acid, a phosphor powder was produced in the same manner as in Example 1. That is, the phosphor powder of Comparative Example 7 was not subjected to the acid treatment step.

[0094] (Comparative Example 8) Except for using water instead of hydrochloric acid, a phosphor powder was produced in the same manner as in Example 3. That is, the phosphor powder of Comparative Example 8 was not subjected to the acid treatment step.

[0095] <Confirmation of crystal structure> The powder X-ray diffraction patterns of the phosphor particles of each Example and Comparative Example were measured using an X-ray diffractometer (manufactured by Rigaku Corporation, product name: UItimal V) with Cu-Kα radiation. The crystal structure was confirmed from the powder X-ray diffraction patterns, and the powder X-ray diffraction patterns of the phosphor particles of each Example and Comparative Example were consistent with the diffraction pattern of CaAlSiN crystals.

[0096] <Particle size distribution measurement> In each example and comparative example, the particle size distribution of the phosphor particles before the following treatments was measured using a Microtrac MT3300EXII (Microtrac Bell Corporation), a particle size measurement device that uses laser diffraction and scattering. From the obtained particle size distribution, the particle sizes Dx90 and Dx97, which correspond to the cumulative 90% and 97% from the small particle size in the volume-based cumulative distribution (2), were calculated. The results are shown in Table 1.

[0097] (Treatment) 30 mg of phosphor powder was dispersed in 100 mL of 0.2% by mass aqueous sodium hexametaphosphate solution, and the resulting dispersion was placed in a cylindrical container with a bottom inner diameter of 5.5 cm. Next, the transducer (cylindrical tip with an outer diameter of 20 mm) of an ultrasonic homogenizer was inserted from above the dispersion, and with the transducer immersed to a depth of 1.0 cm, the dispersion was irradiated with ultrasonic waves at a frequency of 19.5 kHz and an output of 150 W for 3 minutes.

[0098] Next, the particle size distribution of the phosphor powder subjected to the above treatment was measured, and from the obtained particle size distribution, the particle sizes Dy10, Dy50, Dy90, and Dy97, which corresponded to the cumulative 10th, 50th, 90th, and 97th percentiles from the smallest particle size in the volume-based cumulative distribution (1), were calculated. The ultrasonic homogenizer used was a "US-150E" (manufactured by Nippon Seiki Seisakusho Co., Ltd.). From the measurement results, Dx90 / Dy90 and Dx97 / Dy97 were calculated. The results are shown in Table 1.

[0099] <Measurement of oxygen content A> The oxygen content A of the phosphor powder was determined as the total amount of oxygen. The oxygen content A was measured using an oxygen / nitrogen analyzer (manufactured by Horiba, Ltd., device name: EMGA-920). Specifically, the phosphor powder was heated from 20°C to 2000°C at a temperature increase rate of 8°C / sec in a helium atmosphere, and the amount of oxygen released was quantified to determine the oxygen content A (mass%) of the entire phosphor powder. The measurement results for each example and comparative example are shown in Table 2.

[0100] <Measurement of light absorption rate C at 455 nm> The phosphor powder was filled into a concave cell so that the surface was smooth. The concave cell filled with the phosphor powder was attached to the opening of an integrating sphere. Monochromatic light with a wavelength of 455 nm, split from a light source (Xe lamp), was introduced into the integrating sphere using an optical fiber as excitation light for the phosphor. This monochromatic light was irradiated onto the phosphor sample, and the fluorescence spectrum of the phosphor powder was measured using a spectrophotometer (MCPD-7000, manufactured by Otsuka Electronics Co., Ltd.).

[0101] The number of reflected excitation light photons (Qref) and the number of fluorescent photons (Qem) were calculated from the obtained spectral data. The number of reflected excitation light photons was calculated in the same wavelength range as the number of excitation light photons, and the number of fluorescent photons was calculated in the range of 465 to 800 nm.

[0102] Furthermore, using the same device, a standard reflector with a reflectance of 99% (Spectralon (registered trademark) manufactured by Labsphere) was attached to the opening of the integrating sphere to measure the spectrum of excitation light with a wavelength of 455 nm. At this time, the number of excitation light photons (Qex) was calculated from the spectrum in the wavelength range of 450 to 465 nm.

[0103] The light absorptance C at 455 nm of each of the phosphor powders in the Examples and Comparative Examples was calculated using the following formula: The results are shown in Table 2. 455 nm light absorption rate C (%) = {(Qex - Qref) / Qex} × 100

[0104] <Measurement of oxygen content B after exposure test> The phosphor powder was stored for 250 hours in an environment of 85°C temperature and 85% humidity using a constant temperature and humidity dryer (IW222 (trade name), manufactured by Yamato Scientific Co., Ltd.). After storage, the oxygen content B of the phosphor powder was measured. The measurement was performed using the same procedure as for measuring the oxygen content A. B / A was calculated from the oxygen content A and the oxygen content B. The results are shown in Table 2.

[0105] <Measurement of 455 nm light absorbance D after exposure test> The phosphor powder was stored for 250 hours in an environment of 85°C temperature and 85% humidity using a constant temperature and humidity dryer (IW222 (trade name), manufactured by Yamato Scientific Co., Ltd.). After storage, the light absorptance D of the phosphor powder at 455 nm was measured. The measurement was performed using the same procedure as for measuring the light absorptance C. D / C was calculated from the light absorptance C and the light absorptance D. The results are shown in Table 2.

[0106] [Table 1]

[0107] [Table 2]

[0108] As shown in Tables 1 and 2, Examples 1 to 4, which underwent acid treatment using an acid solution with an acid concentration of less than 0.5 mol / L, had lower Dx97 / Dy97 and suppressed aggregation compared to Comparative Examples 1 to 6, which had higher acid concentrations. Furthermore, Comparative Examples 7 and 8, which had an acid concentration of 0, showed large changes in oxygen content and light absorption rate before and after the exposure test, indicating low reliability. Therefore, it was demonstrated that phosphor powders that underwent acid treatment using an acid solution with an acid concentration of less than 0.50 mol / L can suppress aggregation even when the particle size is small, and also have high reliability. [Industrial Applicability]

[0109] According to the present disclosure, it is possible to provide a method for producing a phosphor powder that is highly reliable and resistant to deterioration, by suppressing particle aggregation even when the particle size is small. It is also possible to provide a light-emitting device that includes a phosphor powder that is highly reliable and resistant to deterioration, by suppressing particle aggregation even when the particle size is small. [Explanation of symbols]

[0110] 10...light emitting device, 20...light emitting element, 30...wavelength converter, 40...terminal.

Claims

1. General formula (Ca １－ｘ－ｙ Sr ｘ EU ｙ ) AlSiN ３ A method for producing a phosphor powder containing phosphor particles represented by the formula: a mixing step of mixing the raw material powders to obtain a mixed powder; a firing step of firing the mixed powder to obtain a fired product; an acid treatment step of heat-treating the fired product in an acid solution having an acid concentration of less than 0.500 mol / L; In the cumulative distribution (1) of particle diameters on a volume basis measured by a laser diffraction / scattering method after subjecting the dispersion of the phosphor powder to ultrasonic homogenization, the particle diameter at which the cumulative value from small particle diameters reaches 50% of the total is defined as Dy50. A method for producing a phosphor powder, wherein Dy50 is less than 1.7 μm.

2. In the cumulative distribution (2) of particle diameters on a volume basis measured by a laser diffraction / scattering method without subjecting the dispersion to ultrasonic homogenization treatment, the particle diameter when the cumulative value from small particle diameters reaches 97% of the total is defined as Dx97, In the cumulative distribution (1), when the particle diameter at which the integrated value from small particle diameters reaches 97% of the total is defined as Dy97, 2. The method for producing a phosphor powder according to claim 1, wherein Dx97 / Dy97 is 5.0 or less.

3. In the cumulative distribution (2) of particle diameters on a volume basis measured by a laser diffraction / scattering method without subjecting the dispersion to ultrasonic homogenization treatment, the particle diameter when the cumulative value from small particle diameters reaches 90% of the total is defined as Dx90, In the cumulative distribution (1), when the particle diameter at which the integrated value from small particle diameters reaches 90% of the total is defined as Dy90, 3. The method for producing a phosphor powder according to claim 1, wherein Dx90 / Dy90 is 2.0 or less.

4. In the cumulative distribution (1), when the particle diameter when the integrated value from small particle diameters reaches 10% of the total is defined as Dy10, 3. The method for producing a phosphor powder according to claim 1, wherein Dy10 is 0.4 μm or more.

5. The oxygen content of the phosphor powder obtained by the heat treatment in the acid treatment step is defined as A, When the oxygen content of the phosphor powder after storing it in an environment of a temperature of 85°C and a humidity of 85% for 250 hours is B, 3. The method for producing a phosphor powder according to claim 1, wherein B / A is 3.00 or less.

6. The method for producing a phosphor powder according to claim 1 or 2, wherein the acid solution contains hydrochloric acid.

7. 3. The method for producing a phosphor powder according to claim 1, wherein the temperature when the fired product is heat-treated in the acid solution in the acid treatment step is 25 to 90°C.

8. 3. The method for producing a phosphor powder according to claim 1, wherein in the acid treatment step, the fired product is heat-treated in the acid solution for a period of 5 minutes to 10 hours.

9. A light emitting device comprising: 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 the wavelength of the primary light, A light-emitting device, wherein the wavelength converter comprises a phosphor powder obtained by the method according to claim 1 or 2.

10. 10. The light emitting device according to claim 9, wherein the light emitting element comprises at least one selected from the group consisting of a mini LED and a micro LED.

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