JP7634649B2 - Phosphor particles, composite and light-emitting device - Google Patents

Description

The present invention relates to phosphor particles, composites and light-emitting devices.

A fluoride phosphor represented by K ₂ SiF ₆ :Mn (often abbreviated as "KSF phosphor") is known as a phosphor capable of converting blue light emitted from a blue light-emitting diode into red light. This phosphor is efficiently excited by blue light. In addition, the half-width of the emission spectrum of this phosphor is narrow and sharp. Therefore, by using this phosphor as a red phosphor, a white LED with high brightness and excellent color rendering and color reproducibility can be realized.

An example of a prior art for fluoride phosphors is Patent Document 1. Patent Document 1 describes a fluoride phosphor whose composition is expressed by the general formula A ₂ M _(1-n) F ₆ :Mn ⁴⁺ _n , whose bulk density is 0.80 g/cm ³ or more, and whose mass median diameter is 30 μm or less. In the general formula, 0<n≦0.1, the element A is one or more alkali metal elements containing K, and the element M is Si alone, Ge alone, or a combination of Si and one or more elements selected from the group consisting of Ge, Sn, Ti, Zr, and Hf.

Furthermore, as a prior art for fluoride phosphors, Patent Document 2 can also be mentioned. Patent Document ₂ describes a phosphor characterized by comprising a crystal having a structure in which a transition metal is substituted as an activator in part of a host crystal represented by _A2BF6 (wherein A is K, Na, Rb or Cs, and B is Si, Ge, Sn, Ti or Zr, excluding combinations of K and Si, K and Ge, and K and Ti).

JP 2019-001897 A International Publication No. 2009/119486

As white LEDs become more widespread, there is a demand for further improvement in the luminescent properties of fluoride phosphors.

The inventors conducted various studies with the goal of obtaining a fluoride phosphor with good luminescence characteristics.

The inventors have completed the invention provided below and solved the above problem.

According to the present invention, the following phosphor particles are provided:

A phosphor particle having a composition represented by the following general formula (1):
A phosphor particle having at least one micro-depression on its surface.
General formula (1): A ₂ MF ₆ :Mn
In general formula (1),
Element A is one or more alkali metal elements containing K,
The element M is Si alone, Ge alone, or a combination of Si with one or more elements selected from the group consisting of Ge, Sn, Ti, Zr, and Hf.

Further, according to the present invention,
There is provided a composite material comprising the above phosphor powder and an encapsulant that encapsulates the phosphor powder.

Further, according to the present invention,
There is provided a light emitting device including a light emitting element that emits excitation light and the above composite that converts the wavelength of the excitation light.

The present invention provides a fluoride phosphor with good luminescence properties.

FIG. 4 is a diagram for explaining the shape of minute recesses. FIG. 1 illustrates an example of a light emitting device. 1 is an electron microscope image of phosphor particles produced in Example 1. 1 is an electron microscope image of phosphor particles produced in Example 2. 1 is an electron microscope image of phosphor particles produced in Comparative Example 1.

Below, an embodiment of the present invention will be described in detail with reference to the drawings. All drawings are for illustrative purposes only. The shapes and dimensional ratios of each component in the drawings do not necessarily correspond to the actual objects.

<Phosphor particles>
The composition of the phosphor particles of this embodiment is represented by the following general formula (1): With this composition, the phosphor particles of this embodiment convert blue light normally emitted from a blue LED into red light.
General formula (1): A ₂ MF ₆ :Mn
In general formula (1),
Element A is one or more alkali metal elements containing K,
The element M is Si alone, Ge alone, or a combination of Si with one or more elements selected from the group consisting of Ge, Sn, Ti, Zr, and Hf.

In terms of "shape," the phosphor particle of this embodiment has at least one microscopic depression on its surface.

When blue light is irradiated onto the phosphor particles of this embodiment, it is assumed that the blue light "penetrates" into the micro-recesses, converting the blue light into red light without waste. This is assumed to improve the light emission characteristics.

The phosphor particles of this embodiment can be manufactured by using appropriate raw materials and adopting appropriate manufacturing methods and manufacturing conditions. Details of the manufacturing method will be described later, but when obtaining phosphor particles by precipitating them in water, the phosphor particles of this embodiment can be obtained by appropriately selecting and controlling the order in which various raw materials are added to the water and the temperature at which they are added.

We continue our explanation of the phosphor particles of this embodiment.

(Regarding the shape of the micro recesses)
Examples of specific shapes of the micro recesses are shown in microscope images in the Examples section given later, but for the purpose of explanation, FIG. 1 shows a schematic diagram of the micro recesses and their vicinity.

1, the micro recesses are present on a substantially planar surface of the phosphor particle. The micro recesses may be present in a substantially planar portion of the phosphor particle surface, or in a non-planar portion of the phosphor particle surface.
In Fig. 1, the micro recesses become smaller as they become deeper, but the micro recesses are not limited to this form. The micro recesses may have an approximately constant diameter in the depth direction, for example, like a well.
The depth of the minute recess, that is, the distance between the surface of the phosphor particle and the bottom of the minute recess, is preferably 0.5 μm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less.

The shape of the opening of the micro recess, i.e., the "edge" of the micro recess on the surface of the phosphor particle, is not particularly limited, but is preferably triangular. The "triangular shape" here does not have to be a mathematically strict triangular shape, but may be any shape that can be recognized as a triangle from a common sense point of view. For example, some or all of the three sides of the triangle do not have to be strictly straight lines.
The triangle may be an equilateral triangle, an isosceles triangle, or a triangle with all three sides of different lengths.

The maximum diameter of the opening of the minute recess is preferably 0.5 μm to 20 μm, more preferably 1 μm to 10 μm, and is determined by measuring the maximum diameter of the opening in a two-dimensional image of the phosphor particle taken by an electron microscope.
The maximum diameter of the opening in a two-dimensional image of a phosphor particle photographed by an electron microscope varies depending on the direction of the photographed phosphor particle. However, even in consideration of this variation, better light emission characteristics can be obtained if the maximum diameter falls within the above-mentioned numerical range. In other words, the above-mentioned numerical range of 1 μm or more and 20 μm or less is a numerical range that takes into consideration the variation in the maximum diameter that differs depending on the direction in which the phosphor particle is photographed.

(About particle aggregation)
The phosphor particles of this embodiment may be primary particles or secondary particles formed by agglomeration of primary particles. In other words, the phosphor particles of this embodiment may be secondary particles having minute recesses on the surface.
Generally, when phosphor particles are secondary particles, their light emission characteristics tend to deteriorate. However, the phosphor particles of this embodiment have minute recesses, which may suppress the deterioration of the light emission characteristics.

(Regarding the size of the particles themselves)
The major axis of the phosphor particles of this embodiment, as determined from an image taken by an electron microscope, is preferably 3 μm to 150 μm, more preferably 5 μm to 100 μm, and even more preferably 10 μm to 50 μm. By setting the major axis to an appropriate size, better light emission characteristics can be obtained.
An image of a phosphor particle photographed by an electron microscope is a two-dimensional image, and the major axis varies depending on the direction of the photographed phosphor particle. However, even in consideration of this variation, if the major axis falls within the above-mentioned numerical range, better light emission characteristics can be obtained. In other words, the numerical range of 3 μm or more and 150 μm or less is a numerical range that takes into consideration the variation in the major axis, which differs depending on the direction in which the phosphor particle is photographed.

(Composition: Regarding general formula (1))
The element A is one or more alkali metal elements containing K. Specifically, it may be K alone or a combination of K and one or more alkali metal elements selected from Li, Na, Rb, and Cs. From the viewpoint of chemical stability, it is preferable that the content of K in the element A is high (for example, 50 mol % or more of K in the element A), and it is more preferable that the element A is a single element.

Element M is Si alone, Ge alone, or a combination of Si and one or more elements selected from the group consisting of Ge, Sn, Ti, Zr, and Hf. From the viewpoint of chemical stability, it is preferable that the content of Si in element M is high (for example, 50 mol % or more of element M is Si), and it is more preferable that element M is Si alone.

(Ratio of phosphor particles having micro recesses in phosphor powder)
When phosphor particles are applied to the composite body or light emitting device described below, phosphor powder, which is an aggregate of phosphor particles, is usually used.
The ratio of phosphor particles having at least one micro-depression on the surface in the phosphor powder is, for example, 10% or more, preferably 30% or more, more preferably 50% or more, and even more preferably 75% or more, based on the number of particles. This value can be determined, for example, by checking whether or not at least 50 phosphor particles in an electron microscope image have a micro-depression.

When the cumulative 50% value in a volume-based particle size distribution curve of the phosphor powder is defined as _D50 , _D50 is preferably 10 μm to 40 μm, more preferably 20 μm to 35 μm. A moderate _D50 value makes it easy to obtain sufficient quantum efficiency, and when it is necessary to mix the phosphor powder with a resin or the like to form a film or sheet containing the phosphor in LED package applications, it makes it easy to form a uniform and smooth film or sheet.

In addition, when the cumulative 10% value in the volume-based particle size distribution curve of the phosphor powder _{is D10} , the cumulative 50% value is _D50 , and the cumulative 90% value is _D90 , ( _D90 - _D10 )/ _D50 is preferably 1.2 or less, more preferably 0.9 or less, and further preferably 0.75 or less. There is no particular lower limit, but it is, for example, 0.3 or more, specifically 0.5 or more.
(D ₉₀ -D ₁₀ )/D ₅₀ can be regarded as an index representing the "width" of the particle size distribution. The narrow width of the particle size distribution of the phosphor powder means that the particle size of the phosphor particles in the phosphor powder is relatively "uniform". Therefore, when (D ₉₀ -D ₁₀ )/D ₅₀ is 0.9 or less, for example, when it is necessary to mix the phosphor powder with a resin or the like to form a film or sheet containing the phosphor, it is easy to form a uniform and smooth film or sheet. In addition, nozzle clogging can be suppressed in the manufacture of LED packages.
The volume-based particle size distribution curve can be obtained through measurement by a laser diffraction scattering method. For details of the measurement method, see the examples given later.

<Method of manufacturing phosphor particles>
The phosphor particles of this embodiment can be manufactured by using an appropriate material and selecting an appropriate manufacturing method and manufacturing conditions. A preferred manufacturing procedure will be described below. It is presumed that by adopting the following procedure, localized highs and lows in the degree of supersaturation during crystal growth will probably occur, causing the growth rate to change, resulting in the formation of minute recesses.

(1) Preparation of Hydrofluoric Acid Hydrofluoric acid (aqueous solution of HF) is prepared by pouring it into a corrosion-resistant container. The concentration of hydrogen fluoride is preferably 50 to 60 mass %.

(2) Cooling of hydrofluoric acid and addition of _KHF2 While cooling the hydrofluoric acid prepared in (1) above, add _KHF2 and stir. Then, while continuing stirring, cool the inside of the beaker. Cooling is preferably performed until the temperature inside the beaker is between -35°C and 0°C, more preferably between -15°C and -2°C, and even more preferably between -10°C and -5°C. According to the knowledge of the present inventor, by cooling the inside of the beaker in this way and then performing the steps from (3) onwards, the way in which the crystals grow is controlled, making it easier to obtain phosphor particles having minute recesses.

When carrying out steps (3) and onwards, cooling may be continued, or cooling may be stopped and the temperature may be gradually brought closer to room temperature. Theoretically, the former is considered preferable as it makes it easier to control various factors, but the latter has the advantage in terms of production costs (energy savings).

(3) Simultaneous introduction of raw materials containing Mn and raw materials containing Si The raw materials containing Mn and raw materials containing Si are simultaneously introduced into the beaker cooled in (2) above and stirred. Although the details are unclear, the "simultaneous introduction" of the two raw materials may also be related to the formation of micro-depressions in the phosphor particles.

Examples of raw materials containing Mn include hexafluoromanganate, permanganate, oxide (except permanganate), fluoride (except hexafluoromanganate), chloride, sulfate, and nitrate. Among them, fluoride is preferable because Mn can be efficiently substituted at the Si site in the fluoride phosphor and good light emission characteristics can be obtained, and among fluorides, hexafluoromanganate is preferable. Examples of hexafluoromanganate include Na ₂ MnF ₆ , K ₂ MnF ₆ , and Rb ₂ MnF _6. In particular, K ₂ MnF ₆ is preferable because it contains F and K (corresponding to element A) that constitute the fluoride phosphor in addition to Mn.
A preferred example of the raw material containing Si is SiO _2. SiO ₂ is preferred as the raw material containing Si in that it is easily available and can be easily obtained with high purity.

(4) Adding raw materials containing Mn (preferably in multiple batches)
In the above (3), the two raw materials are charged and stirred for 30 to 60 seconds, and then the raw material containing Mn is charged into the beaker.
It is preferable to charge the raw material containing the required amount of Mn in several times (preferably about 2 to 5 times). This is thought to homogenize the element composition in the phosphor particles (avoiding uneven distribution of Mn in the center). This is preferable in terms of further improving the light emission characteristics.
Specific examples of the raw material containing Mn are as explained in (3) above.

The obtained phosphor particles are collected by solid-liquid separation such as by filtration, and washed with an organic solvent such as methanol, ethanol, or acetone. If a fluoride phosphor is washed with water, some of it may be hydrolyzed to produce a brown manganese compound, which may deteriorate the properties of the phosphor. For this reason, it is preferable to use an organic solvent in the washing process.
Furthermore, by washing several times with a hydrofluoric acid reaction solution before washing with an organic solvent, it is possible to dissolve and remove impurities that have been generated in small amounts. The concentration of hydrofluoric acid in the hydrofluoric acid reaction solution used for washing is preferably 5% by mass or more from the viewpoint of suppressing decomposition of the fluoride phosphor, and is preferably 60% by mass or less from the viewpoint of the solubility of the phosphor. After the washing step, it is preferable to thoroughly evaporate the washing solution by drying.
In addition, classification may be performed using a sieve with a specified mesh size, and coarse particles may be removed.

<Composite, Light Emitting Device>
The composite of this embodiment includes the above-mentioned phosphor particles and a sealant that seals the phosphor particles.
Moreover, the light emitting device of the present embodiment includes a light emitting element that emits excitation light, and the above-mentioned composite that converts the wavelength of the excitation light.
The light emitting device of this embodiment is preferably used as, for example, a backlight for a display.

Below, an example of a composite and a light-emitting device is described with reference to Figure 2.

FIG. 2 is a schematic diagram of the light emitting device 1. As shown in FIG.
The light emitting device 1 includes a composite body 10 and a light emitting element 20. The composite body 10 is provided in contact with an upper portion of the light emitting element 20.
The light emitting element 20 is typically a blue LED. Terminals are provided on the bottom of the light emitting element 20. When the terminals are connected to a power source, the light emitting element 20 can emit light.
The excitation light emitted from the light emitting element 20 is wavelength converted by the composite 10. When the excitation light is blue light, the blue light is wavelength converted to red light by the composite 10 containing phosphor particles.

The composite 10 can be composed of the above-mentioned phosphor particles and a sealant that seals the phosphor powder. The composite 10 may further include phosphor particles other than the above-mentioned phosphor particles.
As the encapsulant, for example, various curable resin materials (materials that are cured by heat and/or light) can be used. Any curable resin material can be used as long as it is sufficiently transparent and can provide the optical properties required for a display or lighting device.
Examples of the sealing material include silicone resin materials. Regarding silicone resin materials, curable materials are supplied by Toray Dow Corning Co., Ltd., Shin-Etsu Chemical Co., Ltd., etc., and silicone resin materials are preferred from the viewpoints of high transparency and excellent heat resistance. Examples of the sealing material include epoxy resin materials and urethane resin materials.
The amount of phosphor particles (including the above-mentioned phosphor particles and phosphor particles other than the above-mentioned phosphor particles) in the composite 10 is, for example, 10 to 70% by mass, and preferably 25 to 55% by mass.

The size and shape of the light-emitting element 20 are not particularly limited. Depending on the application of the light-emitting device 1, the light-emitting element 20 can be of any size and shape.

Just to be clear, the light emitting device 1 shown in FIG. 2 is a so-called chip-type light emitting device. The light emitting device to which the phosphor particles of this embodiment are applied is not limited to the chip type, and may be a bullet type, a multi-segment type, or the like.

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

The embodiments of the present invention will be described in detail based on examples and comparative examples. It should be noted that the present invention is not limited to the examples.

<Ingredients>
The following raw materials were used:
HF: 55% by mass aqueous solution manufactured by Stella Chemifa Corporation K ₂ SiF ₆ : manufactured by Morita Chemical Co., Ltd. K ₂ MnF ₆ : prepared by the method described in paragraph 0042 of JP 2019-001897 A KHF ₂ : special grade reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. SiO ₂ : FB-50R manufactured by Denka Co., Ltd.

<Production of phosphor particles>
Example 1
The phosphor particles were produced according to the following procedure.
(1) At room temperature, 2,100 mL of an aqueous HF solution having a concentration of 55% by mass was placed in a Teflon (registered trademark) beaker.
(2) While cooling the HF aqueous solution, 315 _{g of} KHF was added and stirred. While continuing stirring, the mixture was cooled until the temperature inside the beaker reached -7°C.
(3) 4 g of K ₂ MnF ₆ and 72 g of SiO ₂ were simultaneously added to the beaker at −7° C., and the mixture was stirred for 45 seconds.
(4) While continuing to cool at −7° C., 4 g of K ₂ MnF ₆ was added to the beaker and stirred for 45 seconds.
(5) While continuing to cool at −7° C., 4 g of K ₂ MnF ₆ was further added to the beaker and stirred for 45 seconds.
(6) While continuing to cool at −7° C., 4 g of K ₂ MnF ₆ was further added to the beaker and stirred for 25 minutes.

After the stirring was completed, the solution was left to stand to precipitate the yellow solids. After the precipitation was confirmed, the supernatant was removed, and the yellow solids were washed with hydrofluoric acid having a concentration of about 24% by mass, and then washed with methanol. The washed solids were filtered to separate and recover the solids, and further dried to evaporate and remove the remaining methanol. After the drying process, a nylon sieve with a mesh size of 75 μm was used to classify and recover only the yellow powder that passed through the sieve.
In this manner, phosphor particles were obtained.

Example 2
Phosphor particles were obtained in the same manner as in Example 1, except that cooling was stopped between (2) and (3) above, i.e., from (3) above onwards, the temperature in the beaker was allowed to gradually and naturally approach room temperature.

Fig. 3 shows an electron microscope image of the phosphor particles obtained in Example 1. Fig. 4 shows an electron microscope image of the phosphor particles obtained in Example 2.
As shown in the respective electron microscope images, in Examples 1 and 2, phosphor particles having minute recesses on the surface were obtained.
As can be seen from each electron microscope image, many of the micro recesses had triangular openings. The maximum diameter of the openings confirmed from each electron microscope image (if the openings were triangular, the length of the longest side of the triangle) was within the range of approximately 1 μm to 20 μm. Specifically, the maximum diameter of the triangular openings of the particles circled in FIG. 3 was about 5 μm. Also, the maximum diameter of the triangular openings of the particles circled in FIG. 4 was about 9 μm.
Moreover, secondary particles formed by aggregation of primary particles were confirmed from each electron microscope image, and minute recesses were also confirmed on the surfaces of the secondary particles.
Furthermore, the major axis of the phosphor particles having microscopic recesses on their surfaces in each of the microscopic images was within the range of approximately 10 μm to 100 μm.

(Comparative Example 1)
Referring to the description in Patent Document 2 (WO 2009/119486), phosphor particles were obtained by the following procedure. The following procedure was performed at room temperature.
(1) First, 100 mL of an aqueous HF solution (46-48%), 6 g of KMnO ₄ , and 100 mL of H ₂ O were mixed to obtain a solution.
(2) 0.38 g of a Si wafer having a thickness of 0.635 mm, which had been cut from an n-type dummy wafer, was placed in the above solution and allowed to stand for 48 hours.
(3) The supernatant of the solution after standing was removed, and the remaining solid matter (precipitated crystals and the undissolved Si wafer) was washed with methanol. The undissolved Si wafer was then manually removed.
In this manner, a phosphor powder was obtained.

Figure 5 shows an electron microscope image of the obtained phosphor particles, but no microscopic recesses with openings like those in Figures 3 and 4 could be confirmed.

<Identification: Crystal phase measurement, composition measurement, etc.>
For the phosphor powder (yellow powder) obtained in each example, an X-ray diffraction pattern was obtained using an X-ray diffractometer. The obtained X-ray diffraction pattern was the same as that of K ₂ SiF ₆ crystal. From this, it was confirmed that K ₂ SiF ₆ :Mn was obtained in a single phase.

<Particle size distribution measurement by laser diffraction scattering method>
30 mL of ethanol was measured into a 50 mL beaker, and 0.03 g of phosphor powder was placed therein. The container was then placed in a homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd., product name US-150E) whose output had been adjusted in advance to "Altitude: 100%", and pretreatment was carried out for 3 minutes.
A volume-based particle size distribution curve was obtained for the solution thus prepared using a laser diffraction/scattering type particle size distribution analyzer (manufactured by Microtrackbell, product name MT3300EXII). From the obtained curve, _D10 , _D50 , and _D90 were calculated.

<Evaluation of light emission characteristics (quantum efficiency, etc.)>
A standard reflector (Spectralon, product name, manufactured by Labsphere) with a reflectance of 99% was set at the side opening (φ10 mm) of an integrating sphere (φ60 mm). Monochromatic light separated to a wavelength of 455 nm from a light emission source (Xe lamp) was introduced into this integrating sphere via an optical fiber, and the spectrum of the reflected light was measured with a spectrophotometer (MCPD-7000, product name, manufactured by Otsuka Electronics Co., Ltd.). At this time, the number of excitation light photons (Qex) was calculated from the spectrum in the wavelength range of 450 to 465 nm.
Next, a concave cell was filled with the phosphor powder obtained in each Example so that the surface was smooth, and the cell was set in the opening of an integrating sphere, and monochromatic light with a wavelength of 455 nm was irradiated, and the excitation reflected light and fluorescence spectra were measured by a spectrophotometer. The number of excitation reflected light photons (Qref) and the number of fluorescence photons (Qem) were calculated from the obtained spectrum data. The number of excitation reflected light photons was calculated in the same wavelength range as the number of excitation light photons, and the number of fluorescence photons was calculated in the range of 465 to 800 nm. From the obtained three types of photon numbers, the absorption rate (= (Qex-Qref)/Qex x 100), internal quantum efficiency (= Qem/(Qex-Qref) x 100), and external quantum efficiency (= Qem/Qex x 100) were calculated.

The above results are summarized in Table 2.

As shown in the table above, the luminescence characteristics of the phosphor particles of Examples 1 and 2 were good.

This application claims priority based on Japanese Patent Application No. 2021-052759, filed on March 26, 2021, the disclosure of which is incorporated herein in its entirety.

Claims (5)

A phosphor particle having a composition represented by the following general formula (1):
having at least one micro recess on its surface;
At least one of the micro recesses has an opening having a maximum diameter of 1 μm or more and 20 μm or less,
A phosphor particle having a (D ₉₀ -D ₁₀ )/ D 50 of 1.2 or less, where D ₁₀ is the cumulative 10% value , D ₅₀ is the cumulative 50% value, and D ₉₀ is the cumulative 90% value in a volume-based particle size distribution curve obtained by a laser diffraction _{scattering method} .
General formula (1): A ₂ MF ₆ :Mn
In general formula (1),
Element A is one or more alkali metal elements containing K,
The element M is Si alone, Ge alone, or a combination of Si with one or more elements selected from the group consisting of Ge, Sn, Ti, Zr, and Hf. 2. The phosphor particle according to claim 1 ,
The phosphor particle, wherein the opening of the minute recess has a triangular shape. 3. The phosphor particle according to claim 1 ,
Phosphor particles are secondary particles formed by agglomeration of primary particles. A composite comprising the phosphor particles according to any one of claims 1 to 3 and a sealant that seals the phosphor particles. A light emitting device comprising: a light emitting element that emits excitation light; and the composite according to claim 4 that converts the wavelength of the excitation light.

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