JP7507150B2 - Surface-coated phosphor particles, method for producing surface-coated phosphor particles, and light-emitting device - Google Patents

Description

The present invention relates to surface-coated phosphor particles, a method for manufacturing surface-coated phosphor particles, and a light-emitting device.

Light-emitting devices formed by combining light-emitting diodes (LEDs) and phosphors are widely used in lighting devices and backlights for liquid crystal display devices. In particular, when using light-emitting devices in liquid crystal display devices, high color reproducibility is required, so the use of phosphors with a narrow full width at half maximum of the fluorescence spectrum (hereinafter simply referred to as "half width") is desirable.

Conventionally used red phosphors with narrow half-widths include nitride phosphors or oxynitride phosphors activated with Eu ²⁺ . Representative pure nitride phosphors include Sr ₂ Si ₅ N ₈ :Eu ²⁺ , CaAlSiN ₃ :Eu ²⁺ (abbreviated as CASN), (Ca,Sr)AlSiN ₃ :Eu ²⁺ (abbreviated as SCASN), etc. CASN phosphors and SCASN phosphors have peak wavelengths in the range of 610 to 680 nm, and their half-widths are relatively narrow, ranging from 75 nm to 90 nm. However, when these phosphors are used as light-emitting devices for liquid crystal displays, a further expansion of the color reproduction range is desired, and phosphors with narrower half-widths are desired.

In recent years, SrLiAl ₃ N ₄ :Eu ²⁺ (abbreviated as SLAN) phosphor has become known as a narrow band red phosphor with a half-width of 70 nm or less, and light emitting devices using this phosphor are expected to have excellent color rendering properties and color reproducibility.

Patent document 1 discloses a SLAN phosphor having a specific composition.

JP 2017-088881 A

SLAN phosphors have the property of easily decomposing when they come into contact with water. This property is the cause of the decrease in luminescence intensity over time. In recent years, there has been a demand for further improvement in the reliability of light-emitting devices that use SLAN phosphors, and there is also a demand for further improvement in the moisture resistance of SLAN phosphors.

As a result of the inventor's investigations, it has been found that, although the detailed mechanism is unclear, in particles containing SLAN phosphors or nitride phosphors having a similar crystal structure, the moisture resistance of the particles can be stably evaluated by using the fluorine element content in the entire particle and the mass increase rate before and after high temperature and high humidity testing as indicators, and that by setting the fluorine element content to a predetermined value or above and the mass increase rate to a predetermined value or below, it is possible to suppress the decrease in fluorescence intensity in a water exposure environment, i.e., to improve moisture resistance.

According to the present invention, there is provided a surface-coated phosphor particle including a particle containing a phosphor and a coating portion coating the surface of the particle, the phosphor having 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 a, b, c, and d are each within the range of 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
The filling,
The content of fluorine element is 15% by mass or more and 30% by mass or less with respect to the entire surface-coated phosphor particles,
The surface-coated phosphor particles are provided with a mass increase rate of 15% or less as measured under the following conditions.
(Conditions for measuring mass increase rate)
The initial mass of the powder made of the surface-coated phosphor particles is W1, the mass of the powder after 50 hours under conditions of a temperature of 60° C. and a humidity of 90% RH is W2, and the mass increase rate is calculated as (W2-W1)/W1×100(%).

According to the present invention, there is also provided a method for producing the above-mentioned surface-coated phosphor particles, comprising: a mixing step of mixing raw materials; a firing step of firing the mixture obtained in the mixing step; and an acid treatment step of mixing the fired product obtained in the firing step with an acidic solution,
The present invention provides surface-coated phosphor particles, characterized in that in the mixing step, the amount of ^M1 charged is 1.10 or more and 1.20 or less when the molar ratio of Al is 3.

The present invention also provides a light-emitting device having the above-mentioned surface-coated phosphor particles and a light-emitting element.

The present invention provides technology relating to nitride phosphor particles with improved moisture resistance.

Below, an embodiment of the present invention is described in detail.

The surface-coated phosphor particles according to the embodiment include a particle containing a phosphor and a coating portion that coats the surface of the particle. Details of the surface-coated phosphor particles are described below.

The phosphor constituting the particles of this embodiment is represented by the general formula M ¹ _a M ² _b M ³ _c Al ₃ N _4-d O _d , where a, b, c, 4-d, and d represent the molar ratio of each element.

In the above general formula, ^M1 is one or more elements selected from Sr, Mg, Ca and Ba. Preferably, ^M1 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.

In the above general formula, ^M2 is one or more elements selected from Li and Na. Preferably, ^M2 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 b of ^M2 in the above range, the crystal structure stability can be improved.

In the above general formula, ^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.

In the above general formula, the lower limit of the oxygen molar ratio d is preferably 0 or more, more preferably 0.05 or more. On the other hand, the upper limit of the oxygen molar ratio d is preferably 0.40 or less, more preferably 0.35 or less. By setting the oxygen molar ratio 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 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 surface-coated phosphor particles of this embodiment have a mass increase rate of 15% or less, measured under the following conditions.
(Conditions for measuring mass increase rate)
The initial mass of the powder made of surface-coated phosphor particles is W1, and the mass of the powder made of surface-coated phosphor particles after 50 hours under conditions of a temperature of 60° C. and a humidity of 90% RH is W2. The mass increase rate is calculated by the formula (W2-W1)/W1×100(%).
Before the measurement, the surface-coated phosphor particles are preferably stored for a predetermined period of time in an ultra-low humidity dry box with an internal humidity of 1% RH or less.
The mass increase rate can be adjusted by controlling the components of the coating portion formed on the surface of the phosphor particle and the coating form.

The surface-coated phosphor particles of this embodiment have the above-mentioned coating portion, and the mass increase rate before and after the durability test is set to 15% or less, thereby improving the moisture resistance of the phosphor and thereby enabling the emission intensity to be maintained for a long period of time. The mass increase of the surface-coated phosphor particles is thought to be caused by hydrolysis and hydroxylation reactions of the uncoated portions.

In the surface-coated phosphor particles of this embodiment, the mass increase rate before and after the durability test is preferably 12% or less, and more preferably 5% or less. By setting the mass increase rate before and after the durability test within the above range, the moisture resistance of the phosphor can be further improved, and the luminous intensity can be maintained for a longer period of time.

In this embodiment, the content of fluorine element relative to the entire surface-coated phosphor particles is 15 mass% or more and 30 mass% or less. By making the content of fluorine element relative to the entire surface-coated phosphor particles 15 mass% or more, it is possible to improve moisture resistance. By making the content of fluorine element relative to the entire surface-coated phosphor particles 30 mass% or less, it is possible to maintain a sufficient luminous intensity while improving moisture resistance.
The lower limit of the content of the fluorine element relative to the entire surface-coated phosphor particles is more preferably 18% by mass or more, and even more preferably 20% by mass or more. The upper limit of the content of the fluorine element relative to the entire surface-coated phosphor particles is more preferably 27% by mass or less, and even more preferably 25% by mass or less. By setting the lower limit of the content of the fluorine element within the above range, the moisture resistance can be further improved. Furthermore, by setting the upper limit of the content of the fluorine element within the above range, the moisture resistance can be further improved while maintaining a sufficient luminous intensity.
The fluorine element is derived from a fluoride of a metal element used as a raw material, which will be described later, or is added in a fluorine treatment step, which will be described later, and does not constitute the crystal structure of the phosphor.

In this embodiment, the fluorine element content and mass increase rate in the particles can be controlled within a desired range 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 heating process performed after the hydrofluoric acid treatment, etc.

The surface-coated phosphor particles of this embodiment can suppress the fluorescence intensity in a water exposure environment, preferably suppress the decrease in fluorescence intensity in a high humidity environment such as 90% RH or higher, and more preferably suppress the decrease in fluorescence intensity in a high temperature and high humidity environment.

The coating preferably constitutes at least a part of the surface of the particle containing the phosphor. Furthermore, the coating preferably contains a fluorine compound containing elemental fluorine, and more preferably contains a fluorine-containing compound containing elemental fluorine and elemental aluminum.
In the fluorine-containing compound, it is preferable that fluorine and 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. Note that the fluorine-containing compound may be composed of a single compound containing fluorine element and aluminum element.
The coating portion constitutes at least a part of the outermost surface of the phosphor-containing particle, and thus 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, but it is sufficient that the coating portion is configured to cover at least a portion of the particle surface, and may be configured to cover the entire particle surface. 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 particle containing the phosphor, and a form in which the fluorine-containing compound continuously coats the surface of the particle containing the phosphor.

In the surface-coated phosphor particles of this embodiment, the diffuse reflectance with respect to light irradiation with a wavelength of 300 nm is, for example, 56% or more, more preferably 58% or more, and more preferably 60% or more.
Furthermore, the surface-coated phosphor particles have a diffuse reflectance of, for example, 85% or more, and preferably 86% or more, with respect to light irradiation at the peak wavelength of the fluorescent spectrum. By providing such characteristics, the luminous efficiency is further increased, and the luminous intensity is improved.

An example of the surface-coated phosphor particles of this embodiment preferably has a peak wavelength in the range of 640 nm to 670 nm and a half-width of 45 nm to 60 nm when excited with blue light having a wavelength of 455 nm. By having such characteristics, excellent color rendering and color reproducibility can be expected.

When an example of the surface-coated phosphor particles of this embodiment is excited with blue light having a wavelength of 455 nm, it is preferable that the color purity of the emitted color satisfies the x value of 0.680≦x<0.735 in the CIE-xy chromaticity diagram. By having 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 an x value of 0.735 or more exceeds the maximum value in the CIE-xy chromaticity diagram, so it is preferable that the above range is satisfied.

(Method for producing surface-coated phosphor particles)
The surface-coated phosphor particles of this embodiment can be manufactured by a mixing process for mixing the raw materials, a firing process for firing the mixture obtained by the mixing process, and an acid treatment process for mixing the fired product obtained by the firing process with an acidic solution. In addition to the above processes, it is preferable to add a fluorine treatment process for mixing the fired product that has been subjected to the acid treatment process with a compound containing fluorine element, and a heating process for applying a heat treatment to the result obtained by the fluorine treatment process.

(Mixing process)
The mixing step is a step of obtaining a powdered raw material mixture by mixing the raw materials weighed so as to obtain the desired surface-coated phosphor particles. The method of mixing the raw materials is not particularly limited, but for example, a method of thoroughly mixing the raw materials using a mixing device such as a mortar, a ball mill, a V-type mixer, or a planetary mill is available. Note that strontium nitride, lithium nitride, etc., which react violently with moisture and oxygen in the air, are appropriately handled in a glove box whose inside 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 of the crystal structure is well maintained. 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 M ¹ and M ^2. Specifically, examples of the metal compound containing M ¹ include Sr ₃ N ₂ , SrN ₂ , SrN, etc. Examples of the metal compound containing M ² include Li ₃ N, LiN ₃ , etc. Examples of the metal compound containing M ³ include Eu ₂ O ₃ , EuN, and EuF _3. Examples of the metal compound containing Al include AlN, AlH ₃ , AlF ₃ , and LiAlH _4. In addition, a flux may be added as necessary. Examples of the flux include LiF, _SrF2 , _BaF2 , and _AlF3 .

(Firing process)
In the firing step, the mixture of the raw materials is filled in a firing container and fired. The firing container is preferably provided with a structure that can enhance airtightness, and the inside of the firing container is preferably filled with an atmosphere gas of a non-oxidizing gas such as argon, helium, hydrogen, or nitrogen. The firing container is preferably made of a material that is stable under a high-temperature atmosphere gas and does not easily react with the mixture of the raw materials and its 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.

[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. However, in consideration of industrial productivity, it is preferable to set the pressure to 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. In the method for producing surface-coated phosphor particles according to the embodiment, 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.

The state of the fired product obtained by the firing process varies from powder to lumps depending on the raw material composition and firing conditions. In preparation for actual use as surface-coated phosphor particles, a crushing/grinding process and/or a classification process for powdering the fired product to a predetermined size may be provided. In addition, in order to obtain the absorption efficiency of excitation light and sufficient luminous efficiency, it is preferable that the average particle diameter of the surface-coated phosphor particles is adjusted to 5 μm or more and 30 μm or less when used as surface-coated phosphor particles for LEDs. In addition, in the above-mentioned crushing/grinding process, in order to prevent the inclusion of impurities derived from the process, it is preferable that the components of the equipment that come into contact with the fired product are made of high-toughness ceramics such as silicon nitride, alumina, and sialon.

(Acid treatment process)
The acidic solution used in the acid treatment step is preferably an aqueous solution, and the contact with the acidic solution is generally performed by dispersing the fired product in an acidic aqueous solution containing one or more of nitric acid, hydrochloric acid, acetic acid, sulfuric acid, formic acid, and phosphoric acid, followed by stirring for several minutes to several hours.
Specifically, the above-mentioned fired product can be dispersed in a mixed solution of an organic solvent and an acidic solution, stirred for several minutes to several hours, and then washed with an organic solvent. The acid treatment can dissolve and remove impurity elements contained in the raw materials, impurity elements originating from the firing vessel, foreign phases generated during the firing process, and impurity elements mixed in during the crushing process. At the same time, it is possible to remove fine powder, which suppresses light scattering and improves the light absorption rate of the phosphor.
The organic solvent may be an alcohol such as methanol, ethanol, or 2-propanol, or a ketone such as acetone. The acid solution may be one or more of nitric acid, hydrochloric acid, acetic acid, sulfuric acid, formic acid, and phosphoric acid. The mixing ratio of these solutions is adjusted so that the concentration of the acid solution relative to the organic solvent is, for example, 0.1% by volume to 3% by volume.

(Fluorine treatment process)
In the fluorine treatment process, a hydrofluoric acid solution is preferably used as a compound containing fluorine element to be mixed with the fired product that has been subjected to the acid treatment process. The lower limit of the concentration of the hydrofluoric acid solution is preferably 25% or more, more preferably 27% or more, and even more preferably 30% or more. On the other hand, the upper limit of the concentration of the hydrofluoric acid solution is preferably 38% or less, more preferably 36% or less, and even more preferably 34% or less. By making the concentration of the hydrofluoric acid solution 25% 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 particles containing phosphor. On the other hand, by making the concentration of the hydrofluoric acid solution 38% or less, the reaction between the particles and hydrofluoric acid can be suppressed from becoming too intense.
The mixture of the calcined product having undergone the acid treatment process and the hydrofluoric acid aqueous solution can be carried out by a stirring means such as a stirrer. The lower limit of the mixing time of the calcined product and the hydrofluoric acid aqueous solution is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 15 minutes or more. On the other hand, the upper limit of the mixing time of the calcined product and the hydrofluoric acid aqueous solution 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 calcined product and the hydrofluoric acid aqueous solution 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 particles containing phosphor.

(Heating process)
When the resultant product obtained by the fluorine treatment contains (NH ₄ ) ₃ AlF ₆ as the coating portion, a heating step may be performed after the above steps. The lower limit of the heating temperature in the heating step is preferably 220° C. or more, and more preferably 250° C. or more. On the other hand, the upper limit of the heating temperature is preferably 500° C. or less, more preferably 450° C. or less, and even more preferably 400° C. or less.
By setting the heating temperature to 220° C. or higher, the following reaction formula (1) proceeds, whereby (NH ₄ ) ₃ AlF ₆ can be converted to AlF ₃ .
( _NH4 ) _3AlF6 → _AlF3 + _3NH3 +3HF... ( ₁ )
On the other hand, by setting the heating temperature to 500° C. or less, the crystal structure of the phosphor can be well maintained and the emission 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.
The heating step is preferably carried out in air or a nitrogen atmosphere, so that the substance in the heating atmosphere itself does not inhibit the above reaction formula (1) and the target substance can be produced.

In this embodiment, by appropriately adjusting the type of acid and solvent in the acid treatment step, the acid concentration, the concentration of hydrofluoric acid in the fluorine treatment step, the fluorine treatment time, the heating temperature and heating time in the heating step performed after the fluorine treatment, etc., a coating portion that covers the surface of the particles containing phosphor can be formed, and surface-coated phosphor particles can be obtained in which the fluorine element content is 15 mass% or more and 30 mass% or less with respect to the entire surface-coated phosphor particles, and the mass increase rate measured under the above-mentioned conditions is 15% or less.
According to the method for producing surface-coated phosphor particles described above, it is possible to produce nitride phosphor particles having improved moisture resistance and capable of maintaining luminous intensity for a long period of time.

(Light emitting device)
The light emitting device according to the embodiment includes the surface-coated phosphor particles according to the above-described embodiment and a light emitting element.
The light emitting element may be an ultraviolet LED, a blue LED, a fluorescent lamp, or a combination of these. The light emitting element is preferably one that emits light with a wavelength of 250 nm or more and 550 nm or less, and more preferably a blue LED light emitting element that emits light with a wavelength of 420 nm or more and 500 nm or less.

As the phosphor particles used in the light emitting device, in addition to the surface-coated phosphor particles of the above-mentioned embodiment, phosphor particles having other luminous colors can be used in combination. Phosphor particles having other luminous colors include blue-emitting phosphor particles, green-emitting phosphor particles, yellow-emitting phosphor particles, orange-emitting phosphor particles, and red phosphors, such as Ca ₃ Sc ₂ Si ₃ O ₁₂ : Ce, CaSc ₂ O ₄ : Ce, β-SiAlON: Eu, Y ₃ Al ₅ O ₁₂ : Ce, Tb ₃ Al ₅ O ₁₂ : Ce, (Sr, Ca, Ba) ₂ SiO ₄ : Eu, La ₃ Si ₆ N ₁₁ : Ce, α-SiAlON: Eu, Sr ₂ Si ₅ N ₈ : Eu, etc. Phosphor particles that can be used in combination with the surface-coated phosphor particles of the above-described embodiment are not particularly limited and can be appropriately selected according to the brightness, color rendering, etc. required for the light-emitting device. By mixing the surface-coated phosphor particles of the above-described embodiment with phosphor particles of other luminous colors, it is possible to realize white colors of various color temperatures, such as daylight white and warm white.
Light-emitting devices include lighting devices, backlight devices, image display devices, and signal devices.

By adopting the surface-coated phosphor particles of the above-mentioned embodiment, the light-emitting device of this embodiment can achieve high light-emitting intensity while improving reliability.

The above describes embodiments of the present invention, but these are merely examples of the present invention and various configurations other than those described above can also be adopted.

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

Example 1
The phosphor has a composition represented by M ¹ _a M ² _b M ³ _c Al ₃ N _4-d O _d , and in order to obtain a phosphor that satisfies M ¹ = Sr, M ² = Li, and M ³ = Eu, Sr ₃ N ₂ (manufactured by Taiheiyo Cement Corporation), Li ₃ N (manufactured by Materion Co., Ltd.), AlN (manufactured by Tokuyama Corporation), and Eu ₂ O ₃ (manufactured by Shin-Etsu Chemical Co., Ltd.) were used as raw materials, and LiF (manufactured by Wako Pure Chemical Industries Co., Ltd.) was used as a flux. When the molar ratio of Al was 3, the amount of Sr charged was set to 1.15 in molar ratio, and the amount of Eu charged was set to 0.0115 in molar ratio. 5% by mass of LiF was added to the total amount of the raw material mixture and the flux, 100% by mass. As described above, the amount of Eu charged was set to 0.0115 in molar ratio when the molar ratio of Al was 3.
The method for producing the surface-coated phosphor particles of Example 1 will be specifically described below.
AlN, Eu ₂ O ₃ and LiF were weighed and mixed in the air, and then agglomerations 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 maintained an inert atmosphere with moisture of 1 ppm or less and oxygen of 1 ppm or less. After that, the above-mentioned Sr ₃ N ₂ and Li 3 N were 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 then the aggregates were broken down using a nylon sieve with an opening of 150 μm to obtain a raw material mixture of the phosphor. Since Sr and Li are easily scattered during firing, they were mixed in amounts larger than the theoretical values.
Next, the raw material mixture was filled 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 inside of the electric furnace was degassed to a vacuum state, and then firing was started under a pressurized nitrogen atmosphere of 0.8 MPa·G from room temperature. After the temperature in the electric furnace reached 1100°C, firing was continued while maintaining the temperature for 8 hours, and then cooled to room temperature. The obtained fired product was crushed in a mortar, classified with a nylon sieve with an opening of 75 μm, and collected.
In the acid treatment step, the fired powder was added to a mixed solution of MeOH (99%) (Kokusan Chemical Co., Ltd.) and HNO ₃ (60%) (Wako Pure Chemical Industries, Ltd.), stirred for 3 hours, and then classified to obtain a phosphor powder.
The obtained phosphor powder was added to a 30% hydrofluoric acid aqueous solution and stirred for 15 minutes to carry out a fluorine treatment process. After the fluorine treatment process, the solution was washed by decantation with MeOH until it became neutral, and solid-liquid separation was performed by filtration. The solid content was dried and passed through a sieve with 45 μm openings to break up the agglomerates, and the surface-coated phosphor particles of Example 1 were obtained.

Example 2
After the fluorine treatment, the phosphor powder was passed through a sieve with 45 μm mesh to deflocculate the agglomerates. The surface-coated phosphor particles of Example 2 were obtained using the same amounts of raw materials and using the same procedures as in Example 1, except that the phosphor powder was heated at 300° C. for 4 hours in an air atmosphere.

Example 3
After the fluorine treatment, the phosphor powder was passed through a sieve with 45 μm mesh to deflocculate the agglomerates. The surface-coated phosphor particles of Example 3 were obtained using the same amounts of raw materials and using the same procedures as in Example 1, except that the phosphor powder was heated at 400° C. for 4 hours in an air atmosphere.

(Comparative Example 1)
Phosphor particles of Comparative Example 1 were obtained using the same amounts of raw materials and following the same procedures as in Example 1, except that a 20% aqueous hydrofluoric acid solution was used in the fluorine treatment.

(Comparative Example 2)
The phosphor particles of Comparative Example 2 were obtained using the same amounts of raw materials and using the same procedures as in Example 1, except that the phosphor powder was fluorine-treated using a 20% aqueous hydrofluoric acid solution, and then passed through a sieve with 45 μm openings to deflocculate the agglomerates, and then heated at 400° C. for 4 hours in an air atmosphere.

For the surface-coated phosphor particles of each Example and each Comparative Example, the subscripts a to d of each element in the chemical composition (that is, general formula: M ¹ _a M ² _b M ³ _c Al ₃ N _4-d O _d ) of all crystal phases were determined.
The above subscripts a to d were obtained by analyzing the obtained phosphor particles by the following method. That is, Sr, Li, Al, and Eu were calculated using the analysis results obtained by an ICP optical emission spectrometer (SPECTRO, CIROS-120), and O and N were calculated using the analysis results obtained by an oxygen/nitrogen analyzer (HORIBA, EMGA-920). The numerical values of a to d for the phosphors of the examples and comparative examples are shown in Table 1.

(Fluorine content)
The fluorine element content relative to the entire surface-coated phosphor particles of each Example and the fluorine element content relative to the entire phosphor particles of each Comparative Example were calculated using the analysis results obtained using a sample combustion device (Mitsubishi Chemical Analytech Co., Ltd., AQF-2100H) and an ion chromatograph (Nippon Dionex Co., Ltd., ICS1500).

(Analysis by X-ray diffraction method)
The crystal structure of the surface-coated phosphor particles of each Example and the phosphor particles of each Comparative Example was confirmed by powder X-ray diffraction pattern using CuKα radiation using an X-ray diffractometer (Ultima IV manufactured by Rigaku Corporation). For Example 1, a peak corresponding to (NH ₄ ) ₃ AlF ₆ was confirmed in the range of 2θ from 16.5° to 17.5°. For Examples 2 and 3, a peak corresponding to AlF ₃ was confirmed in the range of 2θ from 14° to 15°.
In Comparative Example 1, a small peak corresponding to ( _NH4 ) _3AlF6 was observed, but it was weaker than in Example 1, and it is believed that the amount produced was significantly smaller. In Comparative Example ₂ , a peak corresponding to _AlF3 was observed, but it was weaker than in Examples 2 and 3, and it is believed that the amount produced was significantly smaller.

(Surface analysis by XPS)
The surface-coated phosphor particles of each Example and the phosphor particles of each Comparative Example were subjected to surface analysis by XPS. It was confirmed that Al and F exist on the outermost surface of the phosphor particles of each Example, and that Al and F are covalently bonded. From the surface analysis results by XPS and the analysis by X-ray diffraction method, it can be said that in the surface-coated phosphor particles of Example 1, at least a part of the outermost surface of the phosphor particles is composed of (NH ₄ ) ₃ AlF ₆ , and in the surface-coated phosphor particles of Examples 2 and 3, at least a part of the outermost surface of the phosphor particles is composed of AlF ₃ .

(Diffuse Reflectance)
The diffuse reflectance was measured by attaching an integrating sphere device (ISV-469) to a UV-visible spectrophotometer (V-550) manufactured by JASCO Corp. Baseline correction was performed using a standard reflector (Spectralon), and a solid sample holder filled with the surface-coated phosphor particles of each Example or the phosphor particles of each Comparative Example was attached to measure the diffuse reflectance for light with a wavelength of 300 nm and the diffuse reflectance for light with a peak wavelength.

(Light Emitting Characteristics)
The chromaticity x was measured using a spectrophotometer (MCPD-7000 manufactured by Otsuka Electronics Co., Ltd.) and calculated according to the following procedure.
The surface-coated phosphor particles of each Example or the phosphor particles of each Comparative Example were filled into a concave cell so that the surface was smooth, and an integrating sphere was attached. Blue monochromatic light, which was split into a wavelength of 455 nm from a light emission source (Xe lamp), was introduced into the integrating sphere using an optical fiber. The blue monochromatic light was used as an excitation source to irradiate a phosphor sample, and the fluorescence spectrum of the sample was measured.
From the obtained fluorescence spectrum data, the peak wavelength and the half-width of the peak were determined.
In addition, the chromaticity x was calculated based on the wavelength range data of the fluorescence spectrum data in the range of 465 nm to 780 nm in accordance with JIS Z 8724:2015, and was expressed as the CIE chromaticity coordinate x value (chromaticity x) in the XYZ color system defined in JIS Z 8781-3:2016.

(Mass increase rate measurement)
The powders made of the surface-coated phosphor particles of each Example were stored in an ultra-low humidity dry box with an internal humidity of 1% RH or less, which does not cause deterioration of the powder. 1 g of the powder made of the surface-coated phosphor particles of each Example was collected and uniformly spread in a 40 mmφ petri dish. The mass of the petri dish on which the powder was placed was measured, and the initial mass W1 of the powder in the petri dish was measured by subtracting the previously measured mass of the petri dish from the measured mass.
Next, a high temperature and humidity test was carried out by holding the petri dish for 50 hours under conditions of a temperature of 60° C. and a humidity of 90% RH using a thermo-hygrostat (IW-222, manufactured by Yamato Scientific Co., Ltd.). After that, the petri dish was removed from the thermo-hygrostat, and the mass of the dish with the powder placed thereon was measured within 10 minutes. The initial mass W2 of the powder in the petri dish was measured by subtracting the previously measured mass of the petri dish from the measured mass.
Using the obtained W1 and W2, the mass increase rate was calculated by the formula (W2-W1)/W1x100(%). The mass increase rate of the phosphor particles of the comparative example was also calculated in the same manner as above. The obtained results are shown in Table 1.

(Emission intensity ratio)
The emission intensity _I0 was measured for the surface-coated phosphor particles of each Example and the phosphor particles of each Comparative Example before the start of the high temperature and high humidity test. Then, the emission intensity I was measured after the high temperature and high humidity test in which the particles were placed in an environment of 60° C. and 90% RH for 50 hours. The emission intensity ratio I/ _I0 (%) was calculated from the obtained measured values. The results obtained regarding the emission intensity ratio I/ _I0 are shown in Table 1.
The emission intensity was measured using a spectrofluorophotometer (Hitachi High-Technologies Corporation, F-7000) calibrated with rhodamine B and a secondary standard light source. That is, a solid sample holder attached to the spectrophotometer was used to measure the fluorescence spectrum at an excitation wavelength of 455 nm.
The peak wavelength of the fluorescence spectrum of the surface-coated phosphor particles of each Example and the phosphor particles of each Comparative Example was 656 nm. The intensity value at the peak wavelength of the fluorescence spectrum was taken as the emission intensity of the surface-coated phosphor particles or phosphor particles.

As shown in Table 1, it was confirmed that the surface-coated phosphor particles of Examples 1 to 3, in which the mass increase rate is kept to 15% or less, exhibit less decrease in luminescence intensity after high temperature and high humidity testing than Comparative Examples 1 and 2. In Examples 1 to 3, it is believed that by providing a coating portion that keeps the mass increase rate to 15% or less, moisture resistance is improved, and thus the luminescence intensity can be maintained for a long period of time. In contrast, the phosphor particles of Comparative Examples 1 and 2 have a mass increase rate of more than 15%, and it was confirmed that the luminescence intensity after the high temperature and high humidity testing decreases significantly.

This application claims priority based on Japanese Patent Application No. 2019-074460, filed on April 9, 2019, the disclosure of which is incorporated herein in its entirety.

Claims (7)

Particles containing a phosphor;
A coating portion that coats the surface of the particle;
A surface-coated phosphor particle comprising:
The phosphor is
The composition is 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 a, b, c and d are each represented by 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
The filling,
The content of fluorine element is 15% by mass or more and 30% by mass or less with respect to the entire surface-coated phosphor particles,
The mass increase rate measured under the following conditions is 15% or less,
the coating portion constitutes at least a part of the outermost surface of the particle, and contains a fluorine compound containing elemental fluorine and elemental aluminum,
The surface-coated phosphor particles, wherein M1 contains at least Sr, M2 ^contains at least Li, and M3 ^{contains at} least Eu .
(Conditions for measuring mass increase rate)
The initial mass of the powder made of the surface-coated phosphor particles is W1, the mass of the powder after 50 hours under conditions of a temperature of 60° C. and a humidity of 90% RH is W2, and the mass increase rate is calculated as (W2-W1)/W1×100(%). 2. The surface-coated phosphor particle according to claim 1 , which has a diffuse reflectance of 56% or more for light irradiation with a wavelength of 300 nm and a diffuse reflectance of 85% or more for light irradiation at the peak wavelength of the fluorescent spectrum. 3. The surface-coated phosphor particle according to claim 1 , wherein when excited with blue light having a wavelength of 455 nm, the peak wavelength is in the range of 640 nm to 670 nm and the half-value width is 45 nm to 60 nm. 4. The surface-coated phosphor particle according to claim 1, wherein when excited with blue light having a wavelength of 455 nm, the color purity of the emitted color satisfies the x value of 0.680≦x<0.735 in the CIE-xy chromaticity diagram. A method for producing surface-coated phosphor particles according to any one of claims 1 to 4 , comprising the steps of:
A mixing step of mixing the raw materials;
a firing step of firing the mixture obtained by the mixing step;
an acid treatment step of mixing the fired product obtained by the firing step with an acidic solution;
Including,
a molar ratio of Al being 3 in the mixing step, and a molar ratio of ^M1 being 1.10 or more and 1.20 or less in the mixing step. The method for producing surface-coated phosphor particles according to claim 5 , wherein the acid solution used in the acid treatment step is an aqueous hydrofluoric acid solution having a fluorine concentration of 25% or more. A light emitting device comprising the surface-coated phosphor particle according to claim 1 and a light emitting element.