TWI843841B - Surface-coated phosphor particle, method for producing surface-coated phosphor particle, and light emitting device - Google Patents

Abstract

A surface-coated phosphor particle of the present invention includes a particle containing a phosphor and a coating portion that coats the surface of the particle, wherein the phosphor has a composition represented by the general formula M¹ _a M² _b M³ _c Al₃ N_4-d O_d (wherein M¹ is one or more elements selected from the group consisting of Sr, Mg, Ca, and Ba, M² is one or more elements selected from the group consisting of Li and Na, and M³ is one or more elements selected from the group consisting of Eu and Ce), in which the values for a, b, c, and d satisfy each 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 elemental fluorine content is at least 15% by mass but not more than 30% by mass of the entire surface-coated phosphor particle, and the rate of mass increase obtained by measurement under prescribed conditions is 15% or less.

Description

Surface-coated fluorescent particles, method for manufacturing surface-coated fluorescent particles, and light-emitting device

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

Light-emitting devices formed by combining light-emitting diodes (LEDs) and phosphors have been widely used in lighting devices or backlights of liquid crystal display devices, etc. In particular, when liquid crystal display devices use light-emitting devices, there is a demand for high color reproducibility, so it is desirable to use a phosphor with a small half-value full width (hereinafter referred to as "half-value width") of the fluorescent spectrum.

As red phosphors with narrow half-value widths, nitride phosphors or oxynitride phosphors activated by Eu ²⁺ are known. Representative pure nitride phosphors include Sr ₂ Si ₅ N ₈ :Eu ²⁺ , CaAlSiN ₃ :Eu ²⁺ (CASN for short), (Ca,Sr)AlSiN ₃ :Eu ²⁺ (SCASN for short), etc. CASN phosphors and SCASN phosphors have peak wavelengths in the range of 610 to 680 nm, and their half-value 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, there is a demand for a phosphor with a wider color reproduction range and a narrower half-value width.

In recent years, SrLiAl ₃ N ₄ :Eu ²⁺ (abbreviated as SLAN) phosphors are known as narrow-band red phosphors having a half-value width of 70 nm or less. Light-emitting devices using these phosphors are expected to have excellent color rendering properties or color reproducibility.

Patent document 1 discloses a SLAN phosphor having a specific composition. [Prior art document] [Patent document]

Patent document 1: Japanese Patent Application Publication No. 2017-088881

[The problem that the invention wants to solve]

SLAN phosphors have the property of being easily decomposed when in contact with water. This property is the main reason why the luminous intensity decreases over time. In recent years, the reliability of light-emitting devices using SLAN phosphors needs to be further improved, and the moisture resistance of SLAN phosphors also needs to be further improved. [Means for solving the problem]

The inventors of the present invention have found that, although the detailed mechanism of particles containing SLAN phosphors or nitride phosphors having a crystal structure similar thereto is still unclear, it has been clearly known that by using the content of fluorine element relative to the entire particle and the mass increase rate before and after the high temperature and high humidity test as indicators, the moisture resistance of the particles can be stably evaluated. Furthermore, by setting the content of fluorine element to a predetermined value or more and the mass increase rate to a predetermined value or less, the reduction in fluorescence intensity in a water exposure environment can be suppressed, that is, the moisture resistance can be improved.

According to the present invention, a surface-coated fluorescent particle can be provided, comprising _: a particle containing a fluorescent body, and ^a coating portion covering the surface of the particle; the fluorescent body has a composition represented by the general formula ^{M1aM2bM3cAl3N4} _{-dOd ,} wherein ^M1 is one _or more elements selected from Sr _{, Mg} ^, Ca and Ba, ^M2 is one or more elements selected from Li and Na, and ^M3 is one or more elements selected from Eu and Ce, and a, b, c, and d meet 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 content of fluorine element relative to the entire surface-coated fluorescent particles is 15 mass % or more and 30 mass % or less, and the mass increase rate measured under the following conditions is 15% or less; (Mass increase rate measurement conditions) The initial mass of the powder formed by the surface-coated fluorescent particles is set to W1, the mass of the powder after 50 hours under the conditions of temperature 60°C and humidity 90%RH is set to W2, and the mass increase rate is calculated as (W2-W1)/W1×100(%).

In addition, according to the present invention, a method for producing the surface-coated fluorescent particles can be provided, which is characterized in that it includes the following steps: a mixing step, mixing the raw materials; a calcining step, calcining the mixture obtained by the mixing step; and an acid treatment step, mixing the calcined product obtained by the calcining step and an acidic solution; in the mixing step, when the molar ratio of the Al is set to 3, the input amount of the ^M1 is greater than 1.10 and less than 1.20 in terms of the molar ratio.

In addition, according to the present invention, a light-emitting device can be provided, which has the above-mentioned surface-coated fluorescent particles and a light-emitting element. [Effect of the invention]

According to the present invention, a technology for improving the moisture resistance of nitride fluorescent particles can be provided.

The following is a detailed description of the embodiments of the present invention.

The surface-coated fluorescent particles of the embodiment include: particles containing a fluorescent body, and a coating portion covering the surface of the particles. The following is a detailed description of the surface-coated fluorescent particles.

The phosphor composed of particles of this ^embodiment is represented by the _general formula ^{M1aM2bM3cAl3N4} _{-dOd ,} ^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. It is more desirable that ^M1 contains at least Sr. The lower limit of the molar ratio a of ^M1 is preferably 0.850 or more, and 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 making the molar ratio a of ^M1 fall within the above range, the stability of the crystal structure can be improved.

In the above general formula, ^M2 is one or more elements selected from Li and Na. It is more desirable that ^M2 contains at least Li. The lower limit of the molar ratio b of ^M2 is preferably 0.850 or more, and 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 making the molar ratio b of ^M2 fall within the above range, the stability of the crystal structure can be improved.

In the above general formula, ^M3 is an activator added to the matrix crystal, that is, an element constituting the luminescent center ion of the phosphor, and is selected from one or more elements of Eu and Ce. ^M3 can be selected according to the required luminescent wavelength, and it is ideal to contain at least Eu. The lower limit of the molar ratio c of ^M3 is preferably 0.001 or more, and 0.005 or more is more ideal. On the other hand, the upper limit of the molar ratio c of ^M3 is preferably 0.015 or less, and 0.010 or less is more ideal. By making the lower limit of the molar ratio c of ^M3 fall within the above range, sufficient luminescence intensity can be obtained. In addition, by making the upper limit of the molar ratio c of ^M3 fall within the above range, concentration extinction can be suppressed and the luminescence intensity can be maintained at a sufficient value.

In the above general formula, the lower limit of the molar ratio d of oxygen is preferably 0 or more, and 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, and more preferably 0.35 or less. By making the molar ratio d of oxygen fall within the above range, the crystal state of the phosphor can be stabilized and the luminescence intensity can be maintained at a sufficient value. In addition, the content of oxygen in the phosphor is preferably less than 2 mass%, and more preferably less than 1.8 mass%. If the content of oxygen is less than 2 mass%, the crystal state of the phosphor can be stabilized and the luminescence intensity can be maintained at a sufficient value.

The molar ratio of ^M1 and oxygen, that is, the lower limit of the value of d/(a+d) calculated from a and d is preferably 0 or more, 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, more preferably 0.25 or less. By making d/(a+d) fall within the above range, the crystal state of the phosphor can be stabilized and the luminescence intensity can be maintained at a sufficient value.

The mass increase rate of the surface-coated fluorescent particles of this embodiment measured under the following conditions is less than 15%. (Measurement conditions of mass increase rate) The initial mass of the powder formed by the surface-coated fluorescent particles is set as W1, and the mass of the powder formed by the surface-coated fluorescent particles after 50 hours under the conditions of temperature 60°C and humidity 90%RH is set as W2. The mass increase rate is calculated by the formula (W2-W1)/W1×100(%). In addition, the surface-coated fluorescent particles before measurement are preferably stored in an ultra-low humidity drying oven with an internal humidity of less than 1%RH for a predetermined time. The mass increase rate can be adjusted by controlling the composition or coating morphology of the coating formed on the surface of the fluorescent particles.

The surface-coated fluorescent particles of this embodiment have the above-mentioned coating part and the mass increase rate before and after the durability test is set to 15% or less, thereby improving the moisture resistance of the fluorescent body and maintaining the luminous intensity for a long time. In addition, the mass increase of the surface-coated fluorescent particles can be considered to be caused by the hydrolysis and hydrogenation reaction of the uncoated part.

The surface-coated fluorescent particles of this embodiment preferably have a mass increase rate of 12% or less before and after the durability test, and more preferably, 5% or less. By making the mass increase rate before and after the durability test fall within the above range, the moisture resistance of the fluorescent body can be further improved, and the luminous intensity can be maintained for a longer time.

The content of fluorine element in this embodiment relative to the entire surface-coated fluorescent particles is 15 mass % or more and 30 mass % or less. By making the content of fluorine element relative to the entire surface-coated fluorescent particles 15 mass % or more, moisture resistance can be improved. By making the content of fluorine element relative to the entire surface-coated fluorescent particles 30 mass % or less, moisture resistance can be improved and the luminescence intensity can be maintained at a sufficient value. The lower limit of the content of fluorine element relative to the entire surface-coated fluorescent particles is preferably 18 mass % or more, and 20 mass % or more is more ideal. In addition, the upper limit of the content of fluorine element relative to the entire surface-coated fluorescent particles is preferably 27 mass % or less, and 25 mass % or less is more ideal. By making the lower limit of the content of fluorine element fall within the above range, moisture resistance can be further improved. Furthermore, by making the upper limit of the fluorine element content fall within the above range, the moisture resistance can be further improved and the luminescence intensity can be maintained at a sufficient value. In addition, the fluorine element is derived from the fluoride of the metal element used as the raw material described later, and is added in the fluorine treatment step described later, and does not constitute the crystal structure of the phosphor.

In this embodiment, the content rate and mass increase rate of the fluorine element in the particles can be controlled within a predetermined range by appropriately adjusting the types of acid and solvent in the acid treatment step, the acid concentration, the hydrofluoric acid concentration in the hydrofluoric acid treatment step, the hydrofluoric acid treatment time, the heating temperature and heating time in the heating step after the hydrofluoric acid treatment, etc.

The surface-coated fluorescent particles according to this embodiment can suppress the decrease in fluorescence intensity in a water-exposed environment, and ideally can suppress the decrease in fluorescence intensity in a high humidity environment such as 90% RH or above, and more ideally can suppress the decrease in fluorescence intensity in a high temperature and high humidity environment.

The coating portion preferably constitutes at least a portion of the surface of the above-mentioned fluorescent particle. Furthermore, the coating portion preferably includes a fluorine compound containing fluorine element, and more preferably includes a fluorine compound containing fluorine element and aluminum element. In the fluorine-containing compound, it is ideal that the fluorine element and the aluminum element are directly covalently bonded. More specifically, the fluorine-containing compound preferably contains one or both of (NH ₄ ) ₃ AlF ₆ or AlF _3. Moreover, the fluorine-containing compound can also be composed of a single compound containing fluorine element and aluminum element. By constituting at least a portion of the outermost surface of the fluorescent particle, the moisture resistance of the fluorescent body constituting the particle can be improved. Moreover, from the perspective of further improving the moisture resistance of the fluorescent body, it is more ideal that the coating portion contains AlF ₃ .

The aspect of the coating part is not particularly limited, as long as the coating part covers at least a part of the particle surface, or covers the entire particle surface. As for the aspect of the coating part, for example, a plurality of granular fluorine-containing compounds are dispersed on the surface of the fluorescent particle, and a fluorine-containing compound continuously covers the surface of the fluorescent particle.

In the surface-coated fluorescent particles of this embodiment, the diffuse reflectivity relative to light irradiation with a wavelength of 300nm is, for example, preferably 56% or more, more preferably 58% or more, and even more preferably 60% or more. In addition, in the surface-coated fluorescent particles, the diffuse reflectivity relative to light irradiation at the peak wavelength of the fluorescent spectrum is, for example, preferably 85% or more, and even more preferably 86% or more. By having such characteristics, the luminous efficiency can be further improved and the luminous intensity can be further increased.

For example, when the surface-coated fluorescent particles of this embodiment are excited by blue light with a wavelength of 455nm, the peak wavelength is preferably within the range of 640nm to 670nm, and the half-value width is preferably 45nm to 60nm. With such characteristics, excellent color rendering and color reproducibility can be expected.

For example, when the surface-coated fluorescent particles of this embodiment are excited by blue light of wavelength 455nm, the color purity of the luminescent color is preferably such that the x value in the CIE-xy chromaticity diagram meets 0.680≦x＜0.735. By having such characteristics, excellent color rendering and color reproducibility can be expected. If the x value is 0.680 or more, red luminescence with better color purity can be expected. If the x value is 0.735 or more, it will exceed the maximum value in the CIE-xy chromaticity diagram. It is preferably within the above range.

(Method for producing surface-coated fluorescent particles) The surface-coated fluorescent particles of this embodiment can be produced by the following steps: a mixing step of mixing raw materials, a calcining step of calcining the mixture obtained in the mixing step, and an acid treatment step of mixing the calcined product obtained in the calcining step with an acid solution. In addition to the above steps, a fluorine treatment step of mixing the calcined product obtained in the acid treatment step and a compound containing fluorine element, and a heating step of heating the result obtained in the fluorine treatment step can be added.

(Mixing step) The mixing step is a step of mixing the raw materials weighed in such a way that the target surface-coated fluorescent particles can be obtained to obtain a powdered raw material mixture. There is no particular limitation on the method of mixing the raw materials, and for example, the raw materials may be mixed thoroughly using a mixing device such as a mortar, a ball mill, a V-type mixer, or a planetary roller. In addition, for strontium nitride, lithium nitride, etc., which react violently with moisture or oxygen in the air, it is more appropriate to operate in a glove box whose interior is replaced with an inert gas environment or using a mixing device.

In the mixing step, when the molar ratio of Al is set to 3, the input amount of ^M1 is preferably 1.10 or more in molar ratio. By setting the input amount of ^M1 to 1.10 or more in molar ratio, the ^M1 deficiency in the phosphor due to volatility of ^M1 in the calcination step can be suppressed, ^M1 is less likely to have defects, and the crystallinity of the crystal structure can be maintained well. This result is speculated to obtain a narrowband fluorescence spectrum and improve the luminescence intensity. In addition, in the mixing step, when the molar ratio of Al is set to 3, the input amount of ^M1 is preferably 1.20 or less in molar ratio. By setting the input amount of ^M1 to 1.20 or less in molar ratio, the increase of heterophase containing ^M1 can be suppressed, the heterophase of the acid treatment step can be easily removed, and the luminescence intensity can be improved.

The raw materials used in the mixing step can be selected from the group consisting of metal monomers of metal elements contained in the composition of the phosphor and metal compounds containing the metal elements. As for the metal compounds, for example, nitrides, hydrides, fluorides, oxides, carbonates, chlorides, etc. can be listed. Among them, in view of improving the luminescence intensity of the phosphor, nitrides can be appropriately used for the metal compounds containing ^M1 and ^M2 . Specifically, as for the metal compounds containing ^M1 , for example, _Sr3N2 , _SrN2 , SrN, etc. can be listed. As for the metal compounds containing ^M2 , for example, _Li3N , _LiN3 , etc. can be _listed . Examples of metal compounds containing ^M3 include _Eu2O3 , EuN, and _EuF3 . Examples of metal compounds containing Al include AlN, _AlH3 , _AlF3 , and _LiAlH4 . Furthermore, a flux may be added as necessary. Examples of flux include LiF _{, SrF2} , _BaF2 , and _AlF3 .

(Calcination step) The calcination step is to fill the mixture of the above raw materials into the interior of the calcination container and calcine it. The above calcination container is preferably a structure with improved airtightness, and the interior of the calcination container is preferably filled with an ambient gas of non-oxidizing gas such as argon, helium, hydrogen, and nitrogen. The calcination container is preferably made of a material that is stable under high-temperature ambient gas and difficult to react with the mixture of raw materials and its reaction products. For example, it is preferably a container made of boron nitride, carbon, or a container made of high-melting-point metals such as molybdenum, tungsten, or the like.

[Calcination temperature] The lower limit of the calcination temperature in the calcination 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 calcination temperature is preferably 1500°C or lower, more preferably 1400°C or lower, and even more preferably 1300°C or lower. By making the calcination temperature fall within the above range, the unreacted raw materials after the calcination step can be reduced, and the decomposition of the main crystal phase can be suppressed.

[Type of calcining environment gas] As for the type of calcining environment gas in the calcining step, for example, a gas containing nitrogen as an element can be appropriately used. Specifically, nitrogen and/or ammonia can be listed, and nitrogen is particularly preferred. In addition, inert gases such as argon and helium can also be appropriately used. In addition, the calcining environment gas can be composed of one type of gas or a mixed gas of multiple types of gases.

[Pressure of calcining environment gas] The pressure of calcining environment gas can be selected according to the calcining temperature, and is usually in the range of 0.1MPa･G or more and 10MPa･G or less. The higher the pressure of calcining environment gas, the higher the decomposition temperature of the fluorescent body, but considering industrial productivity, it is more ideal to be 0.5MPa･G or more and 1MPa･G or less.

[Calcination time] The calcination time in the calcination step can be selected within a time range where problems such as the presence of a large amount of unreacted products, insufficient primary particle growth, or sintering between particles do not occur. In the method for producing surface-coated fluorescent particles of the embodiment, the lower limit of the calcination time is preferably 0.5 hours or more, more preferably 1 hour or more, and even more preferably 2 hours or more. In addition, the upper limit of the calcination 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 calcined product obtained by the calcination step may be in various states such as powder or block depending on the raw material blending and calcination conditions. In order to prepare for actual use as surface-coated fluorescent particles, a crushing, pulverizing and/or separation operation step may be provided to make the obtained calcined product into a powder of a predetermined size. In addition, the average particle size of the surface-coated fluorescent particles is preferably adjusted to be greater than 5 μm and less than 30 μm when the surface-coated fluorescent particles are used as LEDs from the viewpoint of obtaining the absorption efficiency of the excitation light and sufficient luminous efficiency. In addition, in order to prevent the impurities from being mixed into the above-mentioned crushing and pulverizing steps, the components of the machine that come into contact with the sintered product are preferably made of high-toughness ceramics such as silicon nitride, aluminum oxide, and silicon aluminum oxynitride.

(Acid treatment step) The acid solution used in the acid treatment step is preferably an aqueous solution. The contact with the acid solution is generally performed by dispersing the calcined product in an acidic aqueous solution containing one or more of nitric acid, hydrochloric acid, acetic acid, sulfuric acid, formic acid, and phosphoric acid, and stirring for several minutes to several hours. Specifically, the calcined product is dispersed in a mixed solution of an organic solvent and an acid solution, and after stirring for several minutes to several hours, it can be washed with an organic solvent. The acid treatment can dissolve and remove impurity elements contained in the raw materials, impurity elements originating from the calcination container, heterogeneous phases generated in the calcination step, and impurity elements mixed in the pulverization step. At the same time, fine powder can be removed, so the scattering of light can be suppressed, and the light absorption rate of the fluorescent body can be improved. In addition, the organic solvent can use alcohols such as methanol, ethanol, and 2-propanol, and ketones such as acetone. The acidic solution is one or more of nitric acid, hydrochloric acid, acetic acid, sulfuric acid, formic acid, and phosphoric acid. As for the mixing ratio of these solutions, for example, the concentration of the acidic solution relative to the organic solvent can be prepared in a manner of 0.1 volume % or more and 3 volume % or less.

(Fluorine treatment step) In the fluorine treatment step, as for the fluorine-containing compound to be mixed with the calcined product in the acid treatment step, an aqueous solution of hydrofluoric acid can be appropriately used. The lower limit of the concentration of the aqueous solution of hydrofluoric acid 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 aqueous solution of hydrofluoric acid is preferably 38% or less, more preferably 36% or less, and even more preferably 34% or less. By setting the concentration of the aqueous solution of hydrofluoric acid to 25% or more, a coating containing (NH ₄ ) ₃ AlF ₆ can be formed on at least a portion of the outermost surface of the fluorescent particles. On the other hand, by setting the concentration of the aqueous solution of hydrofluoric acid to 38% or less, an excessively intense reaction between the particles and hydrofluoric acid can be suppressed. The mixing of the calcined product after the acid treatment step and the aqueous solution of hydrofluoric acid can be carried out by using a stirring means such as a stirrer. The lower limit of the mixing time of the calcined product and the aqueous solution of hydrofluoric acid is preferably 5 minutes or more, more preferably 10 minutes or more, and more preferably 15 minutes or more. On the other hand, the upper limit of the mixing time of the calcined product and the aqueous solution of hydrofluoric acid is preferably 30 minutes or less, more preferably 25 minutes or less, and even more preferably 20 minutes or less. By making the mixing time of the calcined product and the aqueous solution of hydrofluoric acid fall within the above range, a coating portion containing ( _NH4 ) _3AlF6 can be stably formed on at least a portion of the outermost surface of the _phosphor -containing particles.

(Heating step) When the resultant 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 higher, more preferably 250°C or higher. On the other hand, the upper limit of the heating temperature is preferably 500°C or lower, more preferably 450°C or lower, and even more preferably 400°C or lower. By setting the heating temperature to 220°C or higher, (NH ₄ ) ₃ AlF ₆ can be converted to AlF ₃ by proceeding with the following reaction formula (1). (NH ₄ ) ₃ AlF ₆ →AlF ₃ +3NH ₃ +3HF･･･(1) On the other hand, by making the heating temperature below 500°C, the crystal structure of the phosphor can be well maintained and the luminescence intensity can be improved. 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 making the heating time fall within the above range, (NH ₄ ) ₃ AlF ₆ can be more reliably converted into AlF ₃ with higher moisture resistance. In addition, the heating step is preferably carried out in the atmosphere or in a nitrogen environment. In this way, the substance that heats the ambient gas itself can produce the target substance without hindering the above reaction formula (1).

This embodiment, by appropriately adjusting the types 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 after the fluorine treatment, etc., can obtain surface-coated fluorescent particles, which form a coating portion coated on the surface of the fluorescent particles, and the content of fluorine element is 15 mass% or more and 30 mass% or less relative to the entire surface-coated fluorescent particles, and the mass increase rate measured under the above conditions is less than 15%. By the above-described method for manufacturing surface-coated fluorescent particles, nitride fluorescent particles with improved moisture resistance and capable of maintaining luminescence intensity for a longer period of time can be manufactured.

(Light-emitting device) The light-emitting device of the embodiment has the surface-coated fluorescent particles and the light-emitting element of the embodiment described above. As for the light-emitting element, ultraviolet LED, blue LED, fluorescent lamp can be used alone or in combination. It is expected that the light-emitting element can emit light with a wavelength of more than 250nm and less than 550nm, and a blue LED light-emitting element with a wavelength of more than 420nm and less than 500nm is more ideal.

As for the fluorescent particles used in the light-emitting device, in addition to the surface-coated fluorescent particles of the above-mentioned embodiment, fluorescent particles having other luminescent colors can also be used. As for fluorescent particles of other luminescent colors, there are blue luminescent fluorescent particles, green luminescent fluorescent particles, yellow luminescent fluorescent particles, orange luminescent fluorescent particles, and red fluorescent particles, for example: 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. The fluorescent particles that can be used together with the surface-coated fluorescent particles of the above-mentioned embodiment are not particularly limited, and can be appropriately selected according to the brightness or color rendering required by the light-emitting device. By mixing the surface-coated fluorescent particles of the above-mentioned embodiment with fluorescent particles of other luminescent colors, white of various color temperatures such as daylight white or bulb color can be realized. As for the light-emitting device, there are lighting devices, backlight devices, image display devices and signal devices.

The light-emitting device of this embodiment can achieve high light intensity and improve reliability by adopting the surface-coated fluorescent particles of the above-mentioned embodiment.

The above is a description of the embodiments of the present invention, but these are only examples of the present invention, and various structures other than the above can also be adopted. [Embodiment]

Hereinafter, the present invention will be described by way of embodiments and comparative examples, but the present invention is not limited thereto.

(Example 1) A phosphor having _a composition represented by ^{M1aM2bM3cAl3N4} _{-dOd was} ^prepared _to obtain a ^phosphor having ^M1 =Sr, ^M2 =Li, and ^M3 =Eu. _Sr3N2 (manufactured by _{Taiheiyo Cement} Corporation), _Li3N (manufactured by Materion Corporation), AlN (manufactured by Tokuyama Corporation), and _Eu2O3 (manufactured by Shin-Etsu Chemical Co., _Ltd. ) were used as raw materials, and _LiF (manufactured by Wako Pure Chemical Industries, Ltd.) was used as a flux. When the molar ratio of Al was 3, the amount of Sr added was 1.15 of the molar ratio, and the amount of Eu added was 0.0115 of the molar ratio. 5% by mass of LiF was added to 100% by mass of the total amount of the raw material mixture and the flux. Furthermore, Eu is added in such a manner that the amount added when the molar ratio of Al is 3 is 0.0115 of the molar ratio. The following is a specific description of the method for producing the surface-coated fluorescent particles of Example 1. AlN, Eu ₂ O ₃ and LiF are weighed and mixed in the atmosphere, and then the agglomerates are broken up with a nylon sieve with a mesh of 150 μm to obtain a premix. The premix is moved to a glove box in an inert environment gas maintained at a moisture content of less than 1 ppm and an oxygen content of less than 1 ppm. After that, the aforementioned Sr ₃ N ₂ and Li ₃ N are weighed in a chemical stoichiometric ratio (a=1, b=1) such that the a value exceeds 15% and the b value exceeds 20%, and after additional blending and mixing, the agglomerates are broken up with a nylon sieve with a mesh size of 150μm to obtain a raw material mixture of the phosphor. Since Sr and Li are easily dispersed during calcination, a larger amount than the theoretical value is blended. Then, the aforementioned raw material mixture is filled into a cylindrical BN container with a lid (manufactured by Denka Co., Ltd.). Then, the aforementioned container filled with the raw material mixture of the phosphor is taken out of the glove box and placed in an electric furnace with a carbon heater equipped with a graphite heat insulation material (manufactured by Fuji Electric Industries, Ltd.) to carry out the calcination step. At the beginning of the calcination step, the electric furnace was temporarily degassed to a vacuum state, and calcination was started in a pressurized nitrogen atmosphere of 0.8MPa･G at room temperature. After the temperature in the electric furnace reached 1100℃, the temperature was maintained and calcination continued for 8 hours, and then cooled to room temperature. The calcined product was crushed with a mortar, classified and recovered with a nylon sieve with a mesh size of 75μm. As an acid treatment step, the calcined product powder was added to a mixed solution of MeOH (99%) (manufactured by Kokusan Chemical Co., Ltd.) and HNO ₃ (60%) (manufactured by Wako Pure Chemical Industries, Ltd.), and stirred for 3 hours, and then separated to obtain a fluorescent powder. The obtained fluorescent powder was added to a 30% hydrofluoric acid aqueous solution and stirred for 15 minutes to perform a fluorine treatment step. After the fluorine treatment step, the solution was washed with MeOH by decanting until it was neutral, and after filtering to separate the solid and liquid, the solid component was dried and all passed through a sieve with a mesh size of 45 μm to dissolve the agglomerates, thereby obtaining the surface-coated fluorescent particles of Example 1.

(Example 2) After fluorine treatment, all the fluorescent powders that passed through a sieve with a mesh size of 45 μm and were freed from agglomerates were subjected to a heat treatment at 300°C for 4 hours in an atmospheric environment. In addition, the same raw material input and procedure as in Example 1 were used to obtain the surface-coated fluorescent particles of Example 2.

(Example 3) After fluorine treatment, all the fluorescent powders that passed through a sieve with a mesh size of 45 μm and were freed from agglomerates were subjected to a heat treatment at 400°C for 4 hours in an atmospheric environment. In addition, the same amount of raw materials and procedures as in Example 1 were used to obtain the surface-coated fluorescent particles of Example 3.

(Comparative Example 1) The fluorine treatment uses a 20% hydrofluoric acid aqueous solution. Other than that, the same raw material input and procedure as in Example 1 are used to obtain the fluorescent particles of Comparative Example 1.

(Comparative Example 2) The fluorine treatment was performed using a 20% hydrofluoric acid aqueous solution. After the fluorine treatment, the fluorescent powder that had all passed through a sieve with a mesh size of 45 μm and was deagglomerated was subjected to a heat treatment at 400°C for 4 hours in an atmospheric environment. In addition, the same raw material input amount and procedure as in Example 1 were used to obtain the fluorescent particles of Comparative Example 2.

For the surface-coated fluorescent particles of _each embodiment and the fluorescent particles of ^each comparative example, _the subscripts _a to d of each element in the chemical composition of all crystalline phases (i.e., general formula: ^{M1aM2bM3cAl3N4} _{-dOd )} were determined. The subscripts a to d ^were determined by analyzing the obtained fluorescent particles using the following method. That is, Sr _, Li, Al and Eu were calculated using the analysis results of an ICP emission spectrometer (CIROS-120 manufactured by SPECTRO Co., Ltd.), and O and N were calculated using an oxygen and nitrogen analyzer (EMGA-920 manufactured by Horiba, Ltd.). The values of a to d for the fluorescent particles of the embodiments and comparative examples are shown in Table 1.

(Content of fluorine element) The content of fluorine element in each embodiment relative to the entire surface-coated fluorescent particles and the content of fluorine element in each comparative example relative to the entire fluorescent particles were calculated from the analysis results obtained using a sample combustion device (Mitsubishi Chemical Analytical Technology Co., Ltd., AQF-2100H) and ion spectrometry (Nippon Dionex K.K. Co., Ltd., ICS1500).

(Analysis by X-ray diffraction) The surface-coated fluorescent particles of each example and the fluorescent particles of each comparative example were analyzed by powder X-ray diffraction patterns using CuKα rays using an X-ray diffraction device (Ultima IV manufactured by Rigaku Corporation) to confirm their crystal structures. 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°. Although a small peak corresponding to (NH ₄ ) ₃ AlF ₆ was observed in Comparative Example 1, it was weaker than that in Example 1, and it is considered that the yield was very small. In addition, a peak corresponding to AlF ₃ was observed in Comparative Example 2, but it was weaker than that in Examples 2 and 3, and it can be considered that the yield was very small.

(Surface analysis by XPS) Surface analysis by XPS was performed on the surface-coated fluorescent particles of each embodiment and the fluorescent particles of each comparative example. For the surface-coated fluorescent particles of each embodiment, Al and F were confirmed to exist on the outermost surface of the fluorescent particles and Al and F were covalently bonded. From the surface analysis results obtained by XPS and the analysis by X-ray diffraction, it can be confirmed that the surface-coated fluorescent particles of Example 1 are composed of (NH ₄ ) ₃ AlF ₆ at least in part of the outermost surface of the fluorescent particles, and the surface-coated fluorescent particles of Examples 2 and 3 are composed of AlF ₃ at least in part of the outermost surface of the fluorescent particles.

(Diffuse reflectivity) The diffuse reflectivity is measured by installing an integrating sphere device (ISV-469) on a UV-visible spectrophotometer (V-550) manufactured by JASCO Corporation. A standard reflector (spectralon) is used for baseline calibration, and a solid sample holder filled with surface-coated fluorescent particles of each embodiment or fluorescent particles of each comparative example is installed to measure the diffuse reflectivity of light with a wavelength of 300nm and the diffuse reflectivity of light with a peak wavelength.

(Luminescence characteristics) The chromaticity x is measured using a spectrophotometer (MCPD-7000 manufactured by Otsuka Electronics Co., Ltd.) and calculated using the following procedure. The surface-coated fluorescent particles of each embodiment or the fluorescent particles of each comparative example are filled in a manner to make the surface of the concave cuvette smooth, and an integrating sphere is installed. The blue monochromatic light of 455nm wavelength split from the luminescent light source (Xe lamp) is introduced into the integrating sphere using an optical fiber. The blue monochromatic light is used as an excitation light source to irradiate the fluorescent sample, and the fluorescence spectrum of the sample is measured. The peak wavelength and the half-value width of the peak are calculated from the obtained spectral data. In addition, chromaticity x is calculated from the wavelength domain information in the range of 465nm to 780nm of the fluorescent spectrum information according to JIS Z 8724:2015, and the CIE chromaticity coordinate x value (chromaticity x) in the XYZ color system specified in JIS Z 8781-3:2016 is calculated.

(Mass increase rate measurement) The powder formed by the surface-coated fluorescent particles of each embodiment is stored in an ultra-low humidity drying box with an internal humidity of less than 1%RH so that the powder will not deteriorate further. 1g of the powder formed by the surface-coated fluorescent particles of each embodiment is taken out and evenly spread in a 40mmφ culture dish. The mass of the culture dish containing the powder is measured, and the initial mass W1 of the powder in the culture dish is measured by subtracting the mass of the culture dish measured in advance from the measured mass. Then, a high temperature and high humidity test was carried out using a thermostat (IW-222, manufactured by Yamato Scientific Co., Ltd.) at 60°C and 90%RH for 50 hours. After that, the culture dish was taken out of the thermostat, and the mass of the culture dish containing the powder was measured within 10 minutes. The initial mass W2 of the powder in the culture dish was measured by subtracting the mass of the culture dish measured in advance from the measured mass. Using the obtained W1 and W2, the mass increase rate was calculated by the formula (W2-W1)/W1×100(%). In addition, the mass increase rate was calculated for the fluorescent particles of the comparative example using the same method as above. The results are shown in Table 1.

(Luminescence intensity ratio) For the surface-coated fluorescent particles of each embodiment and the fluorescent particles of each comparative example, the luminescence intensity I ₀ before the start of the high temperature and high humidity test was measured. Then, the luminescence intensity I was measured after 50 hours of high temperature and high humidity test in an environment of 60°C and 90%RH. The luminescence intensity ratio I/I ₀ (%) was calculated from the obtained measured values. The results obtained for the luminescence intensity ratio I/I ₀ are shown in Table 1. In addition, the luminescence intensity was measured using a spectrofluorescence photometer (F-7000, manufactured by Hitachi Advanced Technologies Co., Ltd.) calibrated with Rose Bengal B and a substandard light source. That is, the fluorescence spectrum with an excitation wavelength of 455nm was measured using the solid sample holder attached to the photometer. The peak wavelength of the fluorescence spectrum of the surface-coated fluorescent particles of each embodiment and the fluorescent particles of each comparative example is 656 nm. The intensity value at the peak wavelength of the fluorescence spectrum is taken as the luminescence intensity of the surface-coated fluorescent particles or the fluorescent particles.

[Table 1] Embodiment 1 Embodiment 2 Embodiment 3 Comparison Example 1 Comparison Example 2 Input Sr ratio (※1) 1.15 1.15 1.15 1.15 1.15 Fluorescent particle composition (subscripts in the general formula) and the value of d/(a+d) a 0.99 1.00 1.01 0.95 0.94 b 0.97 0.97 0.97 0.97 0.95 c 0.01 0.01 0.008 0.008 0.007 d 0.30 0.07 0.15 0.21 0.31 d/(a+d) 0.23 0.07 0.13 0.18 0.25 Hydrofluoric acid treatment 30% hydrofluoric acid aqueous solution 30% hydrofluoric acid aqueous solution 30% hydrofluoric acid aqueous solution 20% hydrofluoric acid aqueous solution 20% hydrofluoric acid aqueous solution Heating temperature No heat treatment 300℃, 4 hours 400℃, 4 hours No heat treatment 400℃, 4 hours Fluorine content (mass %) 23.1 22.6 20.8 13.6 12.1 Diffuse reflectivity (%) 300nm 76 73 69 74 68 Peak wavelength 93 89 86 93 85 Peak wavelength (nm) 656 656 656 656 656 Half value width (nm) 56 55 54 56 54 CIE x value 0.713 0.710 0.709 0.711 0.711 Weight increase rate after 60℃, 90%RH, 50 hours (%) 10 0 8 60 57 Luminescence intensity ratio after 50 hours of high temperature and high humidity test (%) 92 99 99 20 70 ※1 Sr molar ratio when Al molar ratio is 3

As shown in Table 1, the surface-coated fluorescent particles of Examples 1 to 3, whose mass increase rate is suppressed to be below 15%, can be confirmed to suppress the decrease of the luminous intensity after the high temperature and high humidity test compared with Comparative Examples 1 and 2. It can be considered that Examples 1 to 3 have improved moisture resistance by having a coating portion that makes the mass increase rate below 15%, and can maintain the luminous intensity for a long time. In contrast, it can be confirmed that the fluorescent particles of Comparative Examples 1 and 2 have a mass increase rate exceeding 15%, and the luminous intensity after the high temperature and high humidity test is greatly reduced.

This application claims priority based on Japanese application No. 2019-074460 filed on April 9, 2019, the entire contents of which are incorporated herein in their entirety.

Claims (9)

A surface-coated fluorescent particle comprises: a particle containing a fluorescent body ^, and a coating portion _covering the surface of the particle; the fluorescent body has a composition represented by the general formula _{M1aM2bM3cAl3N4 -dOd ,} but ^M1 is one or more elements selected from Sr _, Mg, Ca and Ba, ^M2 is one _or more elements selected from Li ^and Na, ^M3 is one or more elements selected from Eu and Ce, and a, ^b , c, and d meet 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 content of fluorine element is 15 mass % or more and 30 mass % or less relative to the entire surface-coated fluorescent particles, the mass increase rate measured under the following conditions is 15% or less, the diffuse reflectivity relative to irradiation with light of a wavelength of 300nm is 56% or more, and the diffuse reflectivity relative to irradiation with light of a peak wavelength of the fluorescent spectrum is 85% or more; mass increase rate measurement conditions: the initial mass of the powder formed by the surface-coated fluorescent particles is set as W1, the mass of the powder after 50 hours under the conditions of temperature 60°C and humidity 90%RH is set as W2, and the mass increase rate is calculated as (W2-W1)/W1×100(%). A surface-coated fluorescent particle comprises: a particle containing a fluorescent body ^, and a coating portion _covering the surface of the particle; the fluorescent body has a composition represented by the general formula _{M1aM2bM3cAl3N4 -dOd ,} but ^M1 is one or more elements selected from Sr _, Mg, Ca and Ba, ^M2 is one _or more elements selected from Li ^and Na, ^M3 is one or more elements selected from Eu and Ce, and a, ^b , c, and d meet 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 content of fluorine element is 15 mass % or more and 30 mass % or less relative to the entire surface-coated fluorescent particles. The mass increase rate measured under the following conditions is 15% or less. When excited by blue light of wavelength 455nm, the color purity of the luminescent color satisfies the x value of 0.680≦x<0.735 in the CIE-xy chromaticity diagram. The mass increase rate measurement conditions are as follows: the initial mass of the powder formed by the surface-coated fluorescent particles is set as W1, the mass of the powder after 50 hours under the conditions of temperature 60℃ and humidity 90%RH is set as W2, and the mass increase rate is calculated as (W2-W1)/W1×100(%). The surface-coated fluorescent particle of claim 1 or 2, wherein the coating portion constitutes at least a portion of the outermost surface of the particle and comprises a fluorine compound containing fluorine element. The surface-coated fluorescent particles of claim 1 or 2, wherein the coating portion comprises a fluorine compound containing fluorine and aluminum. The surface-coated fluorescent particle of claim 1 or 2, wherein the ^M1 contains at least Sr, the ^M2 contains at least Li, and the ^M3 contains at least Eu. For the surface-coated fluorescent particles of claim 1 or 2, when excited by blue light of wavelength 455nm, the peak wavelength falls within the range of 640nm to 670nm, and the half-value width is 45nm to 60nm. A method for producing surface-coated fluorescent particles is a method for producing surface-coated fluorescent particles as claimed in any one of claims 1 to 6, characterized in that it includes the following steps: a mixing step of mixing raw materials; a calcining step of calcining the mixture obtained by the mixing step; and an acid treatment step of mixing the calcined product obtained by the calcining step with an acidic solution; in the mixing step, when the molar ratio of Al is set to 3, the input amount of ^M1 is greater than 1.10 and less than 1.20 in terms of molar ratio. _A method for producing surface-coated fluorescent particles, comprising a particle containing a fluorescent body and a coating portion covering the surface of the particle ^. The method is characterized in that: the fluorescent body has a composition represented by the general formula ^{M1aM2bM3cAl3N4} _{- dOd} , but ^M1 is one ^or more elements selected from Sr, Mg _, Ca and Ba, ^M2 is one or more elements selected from Li and Na, ^M3 is one or more elements selected from Eu _{and Ce} , and a, b, c, and d meet 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 content of fluorine element is 15 mass % or more and 30 mass % or less relative to the whole surface-coated fluorescent particle, and the mass increase rate measured according to the following conditions is 15% or less; the manufacturing method of the surface-coated fluorescent particle comprises the following steps: a mixing step, mixing raw materials; a calcining step, calcining the mixture obtained by the mixing step; and an acid treatment step, mixing the calcined product obtained by the calcining step and an acidic solution; in the mixing step, the molar ratio of Al is set to 3 when the Mole ratio of Al is 3. ¹ , the molar ratio is 1.10 or more and 1.20 or less, in the acid treatment step, the acid solution uses a hydrofluoric acid aqueous solution with a fluorine concentration of 25% or more; the mass increase rate measurement conditions are: the initial mass of the powder formed by the surface-coated fluorescent particles is set as W1, the mass of the powder after 50 hours under the conditions of temperature 60°C and humidity 90%RH is set as W2, and the mass increase rate is calculated as (W2-W1)/W1×100(%). A light-emitting device comprising: surface-coated fluorescent particles as in any one of claims 1 to 6, and a light-emitting element.