JP7577660B2 - Method for producing phosphor particles - Google Patents

Description

The present invention relates to a method for manufacturing phosphor particles.

Various developments have been made on phosphors up to now. For example, the technology described in Patent Document 1 is known as this type of technology. Patent Document 1 describes a manufacturing method for SrLiAl ₃ N ₄ :Eu (SLAN phosphor) (see claim 1, paragraph 0113, etc. of Patent Document 1).

International Publication No. 2013/175336

However, as a result of the inventor's investigations, it was found that there is room for improvement in terms of internal quantum efficiency in the method for manufacturing phosphor particles described in Patent Document 1 above.

The present inventors have conducted research and found that a different phase that occurs during the manufacturing process of phosphor particles can cause a decrease in the luminescence characteristics of the phosphor, such as the internal quantum efficiency.
Based on this knowledge, the inventors conducted further intensive research and discovered that by appropriately selecting the type of flux to be mixed into the raw material mixture of the phosphor particles and performing acid treatment using a mixed liquid containing an acid and an alcohol during the manufacturing process, phosphor particles with excellent internal quantum efficiency can be realized, which led to the completion of the present invention.

Although the detailed mechanism is unclear, it is thought that LiF functions as an appropriate flux, promoting grain growth and improving the optical properties of the phosphor particles, and that acid treatment makes it possible to remove foreign phases that arise when LiF is used.

On the other hand, when _SrF2 is used as the flux, the amount of the heterogeneous phase remaining after the reaction is larger than that of LiF, and even if an acid treatment is performed, it becomes difficult to remove the heterogeneous phase, resulting in a decrease in the internal quantum efficiency.

According to the present invention,
A method for producing phosphor particles having a composition including at least one element M ¹ selected from the group consisting of Sr, Mg, Ca, and Ba, at least one element M ² selected from the group consisting of Li and Na, at least one element M ³ selected from the group consisting of Eu and Ce, and a group consisting of Al and N, comprising:
a mixing step of mixing a raw material mixture containing each element constituting the composition with LiF to obtain a mixture;
A calcination step of calcining the mixture;
A grinding step of grinding the mixture after the firing step to obtain a ground product;
an acid treatment step of subjecting the pulverized material to an acid treatment using a mixed liquid containing an acid and an alcohol;
a hydrofluoric acid treatment step of subjecting the pulverized material after the acid treatment step to a hydrofluoric acid treatment;
a heat treatment step of heating the pulverized material after the hydrofluoric acid treatment step in the atmosphere;
A method for producing phosphor particles having the following structure is provided.

The present invention provides a method for producing phosphor particles having excellent internal quantum efficiency.

A manufacturing method for phosphor particles in this embodiment will be described.

The method for manufacturing phosphor particles is for producing phosphor particles having a composition including at least one element M ¹ selected from the group consisting of Sr, Mg, Ca, and Ba, at least one element M ² selected from the group consisting of Li and Na, at least one element M ³ selected from the group consisting of Eu and Ce, Al, and a group consisting of N.

The method for producing phosphor particles can include a mixing step, a firing step, a pulverizing step, an acid treatment step, a hydrofluoric acid treatment step, and a heat treatment step.
Each step will be described in detail.

(Mixing process)
In the mixing step, a raw material mixture containing each element constituting the composition of the phosphor is mixed with LiF as a flux to obtain a mixture. For example, each raw material may be weighed so as to obtain the desired phosphor particles and mixed to obtain a powdery mixture.

The method for mixing the raw materials is not particularly limited, but may be, for example, a method in which the raw materials are thoroughly mixed using a mixing device such as a mortar, a ball mill, a V-type mixer, or a planetary mill.
Strontium nitride, lithium nitride, and the like, which react violently with moisture and oxygen in the air, should be handled appropriately in a glove box whose interior is replaced with an inert atmosphere, or using a mixing device.

In the mixing step, the amount of M ¹ charged is preferably 1.10 or more in molar ratio when the molar ratio of Al is 3. By setting the amount of M ¹ charged to 1.10 or more in molar ratio, the shortage of M ¹ in the phosphor due to the volatilization of M ¹ during the firing step is suppressed, defects in M ¹ are less likely to occur, and the crystallinity is maintained well. As a result, it is presumed that a narrow band fluorescent spectrum is obtained and the emission intensity can be increased. In addition, in the mixing step, the amount of M ¹ charged is preferably 1.20 or less in molar ratio when the molar ratio of Al is 3. By setting the amount of M ¹ charged to 1.20 or less in molar ratio, the increase of the heterophase containing M ¹ is suppressed, and the heterophase is easily removed by the acid treatment step, and the emission intensity can be increased.

Each raw material used in the mixing step may contain one or more selected from the group consisting of a metal element contained in the composition of the phosphor and a metal compound containing the metal element. Examples of the metal compound include nitrides, hydrides, fluorides, oxides, carbonates, chlorides, etc. Among these, from the viewpoint of improving the luminous intensity of the phosphor, nitrides are preferably used as the metal compound containing ^M1 and ^M2 . Specifically, examples of the metal compound containing ^M1 include _Sr3N2 , _SrN2 , _SrN , etc. Examples of the metal compound containing ^M2 include _Li3N , LiN3 _{, etc.} Examples of the metal compound containing ^M3 include _Eu2O3 , EuN, and _EuF3 . Examples of the metal compound containing _Al include AlN, _AlH3 , _AlF3 , and _LiAlH4 .

In the mixing step, the lower limit of the amount of LiF added is, for example, 1% by mass or more, preferably 2% by mass or more, more preferably 4% by mass or more, based on the total 100% by mass of LiF and the raw material mixture. This allows phosphor particles with excellent internal quantum efficiency to be realized. On the other hand, the upper limit of the amount of LiF added may be, for example, 10% by mass or less, preferably 5% by mass or less, based on the total 100% by mass of LiF and the raw material mixture.
As the flux, LiF may be used alone, or may be used in combination with other fluxes.
The content of LiF in the flux used in the mixing step is, for example, 50 mass % or more, preferably 80 mass % or more, and more preferably 100 mass %.

(Firing process)
In the firing step, the mixture is fired. For example, the mixture may be fired while being filled in a firing vessel.

It is preferable that the firing container has a structure that can enhance airtightness. It is preferable that the firing container is made of a material that is stable under high-temperature atmospheric gas and does not easily react with the mixture of raw materials and their reaction products. For example, it is preferable to use a container made of boron nitride or carbon, or a container made of a high-melting point metal such as molybdenum, tantalum, or tungsten.

It is preferable to fill the inside of the firing vessel with an atmospheric gas of a non-oxidizing gas such as argon, helium, hydrogen, or nitrogen.

[Firing temperature]
The lower limit of the firing temperature in the firing step is preferably 900° C. or higher, more preferably 1000° C. or higher, and even more preferably 1100° C. or higher. On the other hand, the upper limit of the firing temperature is preferably 1500° C. or lower, more preferably 1400° C. or lower, and even more preferably 1300° C. or lower. By setting the firing temperature within the above range, it is possible to reduce the amount of unreacted raw materials after the firing step is completed, and also to suppress decomposition of the main crystal phase.

[Type of firing atmosphere gas]
As the type of the firing atmosphere gas in the firing step, for example, a gas containing nitrogen as an element can be preferably used. Specifically, nitrogen and/or ammonia can be mentioned, and nitrogen is particularly preferable. Similarly, inert gases such as argon and helium can also be preferably used. The firing atmosphere gas may be composed of one type of gas or may be a mixed gas of multiple types of gases.

[Firing atmosphere gas pressure]
The pressure of the firing atmosphere gas is selected depending on the firing temperature, but is usually in a pressurized state in the range of 0.1 MPa·G to 10 MPa·G. The higher the pressure of the firing atmosphere gas, the higher the decomposition temperature of the phosphor becomes, but in consideration of industrial productivity, it is preferably 0.5 MPa·G to 1 MPa·G.

[Baking time]
The firing time in the firing step is selected within a time range that does not cause problems such as a large amount of unreacted material, insufficient growth of phosphor particles, or reduced productivity. The lower limit of the firing time is preferably 0.5 hours or more, more preferably 1 hour or more, and even more preferably 2 hours or more. The upper limit of the firing time is preferably 48 hours or less, more preferably 36 hours or less, and even more preferably 24 hours or less.

(Crushing process)
In the pulverization step, the raw material mixture (calcined product) after the calcination step is pulverized to obtain a pulverized product.

The state of the fired product obtained by the firing process varies from powder to lump, depending on the raw material composition and firing conditions. The fired product can be made into powder of a specified size by the crushing/grinding process and/or classification operation process.

In the above-mentioned crushing and grinding process, in order to prevent the incorporation of impurities resulting from the process, it is preferable that the components of the equipment that come into contact with the sintered material are made of ceramics such as silicon nitride, alumina, and sialon.

The average particle size of the pulverized material may be adjusted so that the average particle size of the phosphor particles is 5 μm or more and 30 μm or less. This makes the phosphor particles excellent in excitation light absorption efficiency and light emission efficiency, making them suitable for use in LEDs, etc.

(Acid treatment process)
In the acid treatment step, the pulverized material is treated with an acid using a mixed liquid containing an acid and an alcohol.
The acid treatment may be carried out by adding the ground material to a mixed solution containing an acid and an alcohol, or by adding an acid to the ground material in the alcohol. During the acid treatment, the mixed solution may be left to stand, or may be stirred under appropriate conditions.
After the acid treatment, decantation (solid-liquid separation) may be performed using alcohol, if necessary. Decantation may be performed once or twice or more times. This allows the acid to be washed and removed from the pulverized product.
Thereafter, the ground product is filtered and dried.

For example, an inorganic acid may be used as the acid, and specific examples include nitric acid, hydrochloric acid, acetic acid, sulfuric acid, formic acid, and phosphoric acid. Among inorganic acids, it is preferable to use at least one of nitric acid and hydrochloric acid. These may be used alone or in combination of two or more.

The mixture may contain a water solvent.

As the alcohol, for example, an aliphatic alcohol, specifically, MeOH, EtOH, IPA, etc., is used.

The alcohol and acid may be mixed so that the concentration of acid in the mixture is, for example, 0.1% to 5% by mass, preferably 0.5% to 3% by mass.

The acid treatment can dissolve and remove impurity elements contained in the raw materials, impurity elements originating from the firing vessel, foreign phases that arise during the firing process, and impurity elements mixed in during the crushing process. In other words, the acid treatment can wash away foreign matter, etc. This can improve the internal quantum efficiency of the phosphor.

As an example of acid treatment, the crushed material may be dispersed and immersed in a mixed liquid containing acid and alcohol for, for example, 0.5 hours or more and 5 hours or less.

(Hydrofluoric acid treatment process)
In the hydrofluoric acid treatment, the pulverized material after the acid treatment step is subjected to hydrofluoric acid treatment.

For the hydrofluoric acid treatment, an aqueous solution containing hydrogen fluoride as a compound containing elemental fluorine, that is, so-called hydrofluoric acid, is preferably used.
The hydrofluoric acid treatment may be carried out by adding the pulverized material to hydrofluoric acid, for example.
The lower limit of the concentration of hydrogen fluoride (HF) in hydrofluoric acid is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. On the other hand, the upper limit of the concentration of hydrogen fluoride in hydrofluoric acid is preferably 40% by mass or less, more preferably 38% by mass or less, and even more preferably 35% by mass or less.
By setting the hydrogen fluoride concentration to the above-mentioned lower limit or more, a coating portion containing (NH ₄ ) ₃ AlF ₆ can be formed on at least a part of the outermost surface of the phosphor-containing particle. On the other hand, by setting the hydrogen fluoride concentration to the above-mentioned upper limit or less, it is possible to suppress the reaction between the particles and hydrofluoric acid from becoming too vigorous.

The pulverized material and hydrofluoric acid can be mixed by a stirring means such as a stirrer.
The lower limit of the mixing time of the pulverized material and hydrofluoric acid is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 15 minutes or more, while the upper limit of the mixing time of the fired material and hydrofluoric acid is preferably 30 minutes or less, more preferably 25 minutes or less, and even more preferably 20 minutes or less.
By setting the mixing time of the pulverized material and hydrofluoric acid within the above range, a coating portion containing (NH ₄ ) ₃ AlF ₆ can be stably formed on at least a part of the outermost surface of the particle containing the phosphor.

In this embodiment, by appropriately adjusting the type of acid and solvent in the acid treatment process, the acid concentration, the hydrofluoric acid concentration in the hydrofluoric acid treatment process, the hydrofluoric acid treatment time, the heating temperature and heating time in the heat treatment process performed after the hydrofluoric acid treatment, etc., a coating portion that covers the surface of the particles containing phosphor can be formed.

(Heat treatment process)
In the heat treatment, the pulverized material after the hydrofluoric acid treatment is heated in the atmosphere.

When the resultant product obtained by the hydrofluoric acid treatment contains (NH ₄ ) ₃ AlF ₆ as a coating portion, a part or all of the (NH ₄ ) ₃ AlF ₆ can be converted to AlF ₃ by carrying out a heat treatment process.

The lower limit of the heating temperature in the heat treatment process is preferably 220°C or higher, and more preferably 250°C or higher. On the other hand, the upper limit of the heating temperature is preferably 380°C or lower, more preferably 350°C or lower, and even more preferably 330°C or lower.

By setting the heating temperature to the above lower limit or higher, the following reaction formula (1) proceeds, whereby (NH ₄ ) ₃ AlF ₆ can be converted to AlF ₃ .
(NH ₄ ) ₃ AlF ₆ → AlF ₃ +3NH ₃ +3HF...(1)

On the other hand, by keeping the heating temperature below the upper limit, the crystal structure of the phosphor can be well maintained and the luminescence intensity can be increased.

The lower limit of the heating time is preferably 1 hour or more, more preferably 1.5 hours or more, and even more preferably 2 hours or more. On the other hand, the upper limit of the heating time is preferably 6 hours or less, more preferably 5.5 hours or less, and even more preferably 5 hours or less. By setting the heating time within the above range, (NH ₄ ) ₃ AlF ₆ can be reliably converted into AlF ₃ having higher moisture resistance.

It is preferable to carry out the heat treatment process in air or in a nitrogen atmosphere. This allows the target substance to be produced without the substance in the heating atmosphere itself interfering with the above reaction formula (1).

The phosphor particles of this embodiment are described below.

The phosphor particles of this embodiment may be composed of surface-coated phosphor particles including a particle containing a phosphor and a coating portion that coats the surface of the particle.

The phosphor contained in the phosphor particles has a composition represented by the general formula M ¹ _a M ² _b M ³ _c Al ₃ N _4-d O _d . In the general formula, M ¹ is one or more elements selected from Sr, Mg, Ca, and Ba, M ² is one or more elements selected from Li and Na, and M ³ is one or more elements selected from Eu and Ce. In the general formula, a, b, c, 4-d, and d represent the molar ratios of each element.

In the general formula, a, b, c, and d satisfy the following formulas.
0.850≦a≦1.150
0.850≦b≦1.150
0.001≦c≦0.015
0≦d≦0.40
0≦d/(a+d)<0.30

^M1 is one or more elements selected from Sr, Mg, Ca and Ba, and preferably contains at least Sr. The lower limit of the molar ratio a of ^M1 is preferably 0.850 or more, more preferably 0.950 or more. On the other hand, the upper limit of the molar ratio a of ^M1 is preferably 1.150 or less, more preferably 1.100 or less, and even more preferably 1.050 or less. By setting the molar ratio a of ^M1 in the above range, the crystal structure stability can be improved.

^M2 is one or more elements selected from Li and Na, and preferably contains at least Li. The lower limit of the molar ratio b of ^M2 is preferably 0.850 or more, more preferably 0.950 or more. On the other hand, the upper limit of the molar ratio b of ^M2 is preferably 1.150 or less, more preferably 1.100 or less, and even more preferably 1.050 or less. By setting the molar ratio a of ^M2 in the above range, the crystal structure stability can be improved.

^M3 is an activator added to the host crystal, i.e., an element constituting the luminescent center ion of the phosphor, and is one or more elements selected from Eu and Ce. ^M3 can be selected depending on the desired emission wavelength, and preferably contains at least Eu.
The lower limit of the molar ratio c of ^M3 is preferably 0.001 or more, more preferably 0.005 or more. On the other hand, the upper limit of the molar ratio c of ^M3 is preferably 0.015 or less, more preferably 0.010 or less. By setting the lower limit of the molar ratio c of ^M3 within the above range, sufficient luminescence intensity can be obtained. In addition, by setting the upper limit of the molar ratio c of ^M3 within the above range, concentration quenching can be suppressed and the luminescence intensity can be maintained at a sufficient value.

The lower limit of the molar ratio d of oxygen (O) is preferably 0 or more, more preferably 0.05 or more. On the other hand, the upper limit of the molar ratio d of oxygen is preferably 0.40 or less, more preferably 0.35 or less. By setting the molar ratio d of oxygen in the above range, the crystal state of the phosphor can be stabilized and the luminous intensity can be maintained at a sufficient value.
The content of oxygen element in the phosphor is preferably less than 2 mass%, more preferably 1.8 mass% or less. By making the content of oxygen element less than 2 mass%, the crystal state of the phosphor can be stabilized and the emission intensity can be maintained at a sufficient value.

The lower limit of the value of d/(a+d) calculated from the molar ratio of ^M1 and oxygen, i.e., a and d, is preferably 0 or more, and more preferably 0.05 or more. On the other hand, the upper limit of the value of d/(a+d) is preferably less than 0.30, and more preferably 0.25 or less. By setting d/(a+d) in the above range, the crystal state of the phosphor can be stabilized and the emission intensity can be maintained at a sufficient value.

The coating portion constitutes at least a portion of the outermost surface of the particle containing the phosphor described above. The coating portion includes a fluorine-containing compound that contains a fluorine element and an aluminum element.

In the fluorine-containing compound, it is preferable that the fluorine element and the aluminum element are directly covalently bonded, and more specifically, it is preferable that the fluorine-containing compound contains either or both of (NH ₄ ) ₃ AlF ₆ and AlF _3. The fluorine-containing compound may be composed of a single compound containing the fluorine element and the aluminum element.

The coating portion containing a fluorine-containing compound constitutes at least a part of the outermost surface of the particle containing the phosphor, so that the moisture resistance of the phosphor constituting the particle can be improved. From the viewpoint of further improving the moisture resistance of the phosphor, it is more preferable that the coating portion contains _AlF3 .

The form of the coating portion is not particularly limited. Examples of the coating portion include a form in which a large number of particulate fluorine-containing compounds are distributed on the surface of the particles containing the phosphor, and a form in which the fluorine-containing compound continuously coats the surface of the particles containing the phosphor. The coating portion may be configured to cover a part or the entirety of the particle surface.

The characteristics of the phosphor particles are explained below.

The phosphor particles have a diffuse reflectance with respect to irradiation with light having a wavelength of 300 nm of, for example, 56% or more, preferably 65% or more, and more preferably 70% or more.
Furthermore, the phosphor particles have a diffuse reflectance with respect to light irradiation at the peak wavelength of the fluorescence spectrum of, for example, 80% or more, preferably 83% or more, and more preferably 85% or more.
By providing such a diffuse reflectance, the luminous efficiency is further increased, and the luminous intensity is improved.

When excited with blue light having a wavelength of 455 nm, the phosphor particles may be configured so that the peak wavelength is, for example, in the range of 640 nm to 670 nm, and the half-width is, for example, 45 nm to 60 nm. By having such characteristics, excellent color rendering and color reproducibility can be expected.

When excited with blue light having a wavelength of 455 nm, the phosphor particles may be configured such that the x value in the CIE-xy chromaticity diagram satisfies, for example, 0.680≦x<0.735.
With such characteristics, excellent color rendering and color reproducibility can be expected. If the x value is 0.680 or more, red light emission with good color purity can be expected, and since an x value of 0.735 or more exceeds the maximum value in the CIE-xy chromaticity diagram, it is preferable that the above range is satisfied.

The light emitting device according to this embodiment will be described below.
The light emitting device according to this embodiment includes phosphor particles and a light emitting element.

As the light-emitting element, an ultraviolet LED, a blue LED, a fluorescent lamp, or a combination of these can be used. The light-emitting element is preferably one that emits light with a wavelength of 250 nm or more and 550 nm or less, and in particular, a blue LED light-emitting element that emits light with a wavelength of 420 nm or more and 500 nm or less is preferable.

As the phosphor particles, in addition to the phosphor particles, phosphor particles emitting other luminescent colors may be used in combination.
Phosphor particles of other luminescent colors include blue-emitting phosphor particles, green-emitting phosphor particles, _yellow -emitting phosphor particles, orange-emitting phosphor particles, and red phosphors, for example, _Ca3Sc2Si3O12 : _Ce , _CaSc2O4 :Ce, β- _SiAlON :Eu _{, Y3Al5O12} :Ce, _{Tb3Al5O12 :} Ce, ( _Sr ,Ca, _Ba ) _2SiO4 : _{Eu , La3Si6N11} :Ce _, α _- SiAlON _: Eu, _Sr2Si5N8 : _Eu , and the like.

The other phosphor particles are not particularly limited and can be selected appropriately depending on the brightness, color rendering, etc. required for the light-emitting device. By mixing phosphor particles with phosphor particles of other luminescent colors, it is possible to realize white light of various color temperatures, such as daylight white and incandescent white.

Specific examples of light-emitting devices include lighting devices, backlight devices, image display devices, and signal devices.

By incorporating phosphor particles, the light-emitting device can achieve high luminous intensity while improving reliability.

Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than those described above can be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications, improvements, etc. that can achieve the object of the present invention are included in the present invention.

The present invention will now be described in detail with reference to examples, but the present invention is in no way limited to the description of these examples.

<Preparation of phosphor particles>
(Comparative Example 1)
[Mixing process]
AlN (Tokuyama Corp.), Eu ₂ O ₃ (Shin-Etsu Chemical Co., Ltd.) and LiF (Wako Pure Chemical Industries, Ltd.) were weighed and mixed in air, and then agglomerates were broken down using a nylon sieve with 150 μm openings to obtain a pre-mixture.
The premix was moved into a glove box that held a nitrogen atmosphere with moisture of 1 ppm or less and oxygen of 1 ppm or less. Sr ₃ N ₂ (manufactured by Taiheiyo Cement Corporation) and Li 3 N (manufactured by Materion Corporation) were then weighed out and mixed so that the value of a was 15% excess and the value of b was ₂₀ % excess in the stoichiometric ratio (a=1, b=1), and the mixture was crushed with a nylon sieve with a mesh size of 150 μm to obtain a raw material mixture of phosphor. Sr and Li were mixed in amounts larger than the theoretical values because they tend to scatter during firing.
Here, the amount of Sr charged was 1.15 in molar ratio when the molar ratio of Al was 3, and the amount of Eu charged was 0.01 in molar ratio. 5 mass% of LiF was added as a flux to the total amount of the raw material mixture and flux of 100 mass%. Note that, as described above, the amount of Eu charged was 0.01 in molar ratio when the molar ratio of Al was 3.

[Firing process]
Next, the raw material mixture was charged into a cylindrical BN container with a lid (manufactured by Denka Co., Ltd.).
Next, the container filled with the mixture of phosphor raw materials was taken out of the glove box, and then placed in an electric furnace (manufactured by Fuji Dempa Kogyo Co., Ltd.) equipped with a graphite heat insulator and a carbon heater, where a firing step was carried out.
At the start of the firing process, the electric furnace was degassed to a vacuum state, and then firing was started from room temperature under a pressurized nitrogen atmosphere of 0.8 MPa·G. After the temperature in the electric furnace reached 1100° C., firing was continued for 8 hours while maintaining the temperature, and then the material was cooled to room temperature.

[Crushing process]
The obtained fired product was pulverized in a mortar and then classified using a nylon sieve with 75 μm openings, to obtain a phosphor powder of Comparative Example 1.

Example 1
5 g of the phosphor powder obtained in the same manner as in Comparative Example 1 was added to a mixed solution of 500 ml of MeOH (purity 99%) (manufactured by Kokusan Chemical Co., Ltd.) and 10 ml of nitric acid ( _HNO3 concentration 60%) (manufactured by Wako Pure Chemical Industries, Ltd.), and the mixture was stirred for 3 hours. The mixture was neutralized by decantation with MeOH, filtered, and dried to obtain a phosphor powder.
[Hydrofluoric acid treatment process]
The obtained phosphor powder was added to hydrofluoric acid having a hydrogen fluoride concentration of 30% and stirred for 15 minutes to carry out a hydrofluoric acid treatment process. After the hydrofluoric acid treatment process, the phosphor powder was passed through a sieve with a mesh size of 45 μm to break up agglomerates.
[Heat treatment]
The phosphor powder from which the agglomerations had been deflocculated was subjected to a heat treatment at 300° C. for 4 hours in an air atmosphere, thereby obtaining the phosphor powder of Example 1.

Example 2
The phosphor powder of Example ₂ was obtained using the same amounts of raw materials and in the same procedure as in Example 1, except that the phosphor powder obtained in the same manner as in Comparative Example 1 was added to a mixed solution of EtOH and nitric acid (HNO3 concentration 60%) (manufactured by Wako Pure Chemical Industries, Ltd.) and stirred for 3 hours.

Example 3
The phosphor powder of Example ₃ was obtained using the same amounts of raw materials and in the same procedure as in Example 1, except that the phosphor powder obtained in the same manner as in Comparative Example 1 was added to a mixed solution of IPA and nitric acid (HNO3 concentration 60%) (manufactured by Wako Pure Chemical Industries, Ltd.) and stirred for 3 hours.

(Comparative Example 2)
A phosphor powder of Comparative Example 2 was obtained using the same amounts of raw materials and in the same procedure as in Example 1, except that SrF2 was used as the _flux instead of LiF.

The crystal phases of the phosphor powders obtained in Examples 1 to 3 and Comparative Example 1 were examined by powder X-ray diffraction measurement (XRD measurement) using Cu-Kα rays, and it was confirmed that the crystal phases were all phosphors having a composition represented by Sr _a Li _b Eu _c Al ₃ N _4-d O _d .

For the obtained phosphor particles, the subscripts a to d of each element of Sr _a Li _b Eu _c Al ₃ N _4-d O _d were obtained. Specifically, the subscripts a to d were calculated using the analysis results of Sr, Li, Al, and Eu using an ICP optical emission spectrometer (SPECTRO, CIROS-120) and O and N using an oxygen/nitrogen analyzer (HORIBA, EMGA-920).
The numerical values a to d of each phosphor particle are shown in Table 1.

The obtained phosphor particles were evaluated based on the following criteria:

(Internal quantum efficiency, peak wavelength, half width, chromaticity x)
A standard reflector (Spectralon, manufactured by Labsphere) with a reflectance of 99% was set at the side opening (φ10 mm) of an integrating sphere (φ60 mm). Monochromatic light dispersed at a wavelength of 455 nm from a Xe lamp as a light source was introduced into this integrating sphere through an optical fiber, and the spectrum of the reflected light was measured with a spectrophotometer (MCPD-7000, manufactured by Otsuka Electronics Co., Ltd.). At that time, the number of excitation light photons (Qex) was calculated from the spectrum in the wavelength range of 450 to 465 nm. Next, a concave cell filled with a phosphor so that the surface was smooth was set at the opening of the integrating sphere, and monochromatic light with a wavelength of 455 nm was irradiated, and the spectrum of the reflected light and fluorescence of the excitation was measured with a spectrophotometer. The number of excitation reflected light photons (Qref) and the number of fluorescence photons (Qem) were calculated from the obtained spectral data. The number of reflected excited light photons was calculated in the same wavelength range as the number of excited light photons, and the number of fluorescent photons was calculated in the range of 465 to 800 nm. The internal quantum efficiency = Qem/(Qex-Qref) x 100 was calculated from the obtained three types of photon counts.
From the fluorescence spectrum obtained by this measurement, the peak wavelength, half width, and chromaticity x value were determined. The chromaticity was calculated according to a method in accordance with JIS Z 8724 (Method of measuring color-light source color-), and the chromaticity coordinates (x, y) were calculated by the calculation method in the XYZ color system specified in JIS Z 8701. However, the wavelength range used for calculating the chromaticity coordinates was 550 to 780 nm.

(Absorption rate at 700 nm)
The same measurement was carried out as above, except that monochromatic light having a wavelength of 700 nm was used as the light source from a Xe lamp. For the reflection spectra of the standard reflector and the phosphor, Qex and Qref were calculated from the spectra in the wavelength range of 695 to 710 nm, respectively, and the absorptance = (Qex - Qref) / Qex x 100 was calculated.

(Diffuse Reflectance)
The diffuse reflectance was measured using an integrating sphere (ISV-469) attached to an ultraviolet-visible spectrophotometer (JASCO Corporation, V-550). Baseline correction was performed using a standard reflector (Spectralon), and a solid sample holder filled with the obtained phosphor particles was attached to measure the diffuse reflectance for light of 300 nm and peak wavelength.

The results showed that the powdered phosphor particles of Examples 1 to 3 had improved internal quantum efficiency compared to Comparative Examples 1 and 2.

This application claims priority based on Japanese Patent Application No. 2019-134712, filed on July 22, 2019, the disclosure of which is incorporated herein in its entirety.

Claims (10)

A method for producing phosphor particles having a composition including at least one element M ¹ selected from the group consisting of Sr, Mg, Ca, and Ba, at least one element M ² selected from the group consisting of Li and Na, at least one element M ³ selected from the group consisting of Eu and Ce, and a group consisting of Al and N, comprising:
The phosphor contained in the phosphor particles has a composition represented by the general formula M ¹ _a M ² _b M ³ _c Al ₃ N _4-d O _d (wherein M ¹ is one or more elements selected from Sr, Mg, Ca, and Ba, M ² is one or more elements selected from Li and Na, and M ³ is one or more elements selected from Eu and Ce), and the a, b, c, and d satisfy the following formulas:
0.850≦a≦1.150
0.850≦b≦1.150
0.001≦c≦0.015
0≦d≦0.40
0≦d/(a+d)<0.30
a mixing step of mixing a raw material mixture containing each element constituting the composition with LiF to obtain a mixture;
A calcination step of calcining the mixture;
A grinding step of grinding the mixture after the firing step to obtain a ground product;
an acid treatment step of subjecting the pulverized material to an acid treatment using a mixed liquid containing an acid and an alcohol;
a hydrofluoric acid treatment step of subjecting the pulverized material after the acid treatment step to a hydrofluoric acid treatment;
a heat treatment step of heating the pulverized material after the hydrofluoric acid treatment step in the atmosphere;
A method for producing phosphor particles having the above structure. A method for producing phosphor particles according to claim 1, comprising the steps of:
The method for producing phosphor particles, wherein in the mixing step, an amount of the LiF added is 1 mass % or more with respect to a total of 100 mass % of the LiF and the raw material mixture. A method for producing phosphor particles according to claim 1 or 2, comprising the steps of:
The method for producing phosphor particles, wherein the alcohol includes at least one selected from the group consisting of MeOH, EtOH, and IPA. A method for producing phosphor particles according to any one of claims 1 to 3, comprising the steps of:
The method for producing phosphor particles, wherein in the acid treatment step, the acid includes an inorganic acid. A method for producing phosphor particles according to claim 4, comprising the steps of:
The method for producing phosphor particles, wherein the inorganic acid includes nitric acid. A method for producing phosphor particles according to any one of claims 1 to 5, comprising the steps of:
In the acid treatment step, the pulverized material is placed in the mixed solution for 0.5 hours or more and 5 hours or less. A method for producing phosphor particles according to any one of claims 1 to 6, comprising the steps of:
In the hydrofluoric acid treatment step, the pulverized material is treated with hydrofluoric acid having a hydrogen fluoride concentration of 20% by mass or more and 40% by mass or less. A method for producing phosphor particles according to any one of claims 1 to 7 , comprising the steps of:
A method for producing phosphor particles, wherein ^M1 contains at least Sr, ^M2 contains at least Li, and ^M3 contains at least Eu. A method for producing phosphor particles according to any one of claims 1 to 8 , comprising the steps of:
In the firing step, the heating time is kept at a constant temperature in the range of 900° C. to 1300° C. for 1 hour to 10 hours. A method for producing phosphor particles according to any one of claims 1 to 9 , comprising the steps of:
The method for producing phosphor particles, wherein the heating temperature in the heat treatment step is 220° C. or higher and 380° C. or lower.