JP2018135406A - Phosphor, light-emitting device, and method for producing phosphor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting device with high productivity at a low cost and to provide the light-emitting device having high luminance.SOLUTION: There is provided a β-type sialon phosphor represented by a formula (1): SiAlON:Eu, provided that 0<a≤3, 0<b≤3 and 0<x≤0.1, and characterized in that a median diameter D50 as measured by a laser diffraction method is 16 μm or less; a diffuse reflectance to light having a wavelength of 800 nm is 90% or more; and a diffuse reflectance to light having a wavelength of 500 nm is 80% or more.SELECTED DRAWING: None

Description

The present invention relates to a method of manufacturing a phosphor used in an LED (Light Emitting Diode), a phosphor, and a light emitting device using the phosphor.

A light-emitting device that obtains white light by combining a blue LED, a green phosphor, a red phosphor, and the like is widely known as a light-emitting device (see Patent Document 1). As a method for producing a phosphor, a production method is generally known in which raw materials are mixed and fired, and then refired or annealed in an inert atmosphere, a reducing atmosphere, or vacuum at a temperature lower than the firing temperature (see Patent Document 2). ). It is known that the fluorescent property of the phosphor is improved by performing this annealing step. Further, it is described that the brightness of the light emitting device can be improved by controlling the particle form of the phosphor (see Patent Document 3).

Japanese Patent No. 4769132 Japanese Patent No. 5508817 Japanese Patent No. 5368985

In light emitting devices such as backlights and illuminations for liquid crystal displays, improvements in color reproducibility, color rendering, and brightness are always required. Further, downsizing of LEDs and improvement of production efficiency are always required. On the other hand, in order to reduce the cost of LEDs by reducing the amount of phosphors used, or when preparing phosphor sheets and phosphor plates that are considered as heat countermeasures that are problematic due to the high output of LEDs There is a need for a phosphor having a small particle size and high brightness so that it can be easily dispersed and applied in a liquid resin.

The present invention provides a phosphor having a small particle size in which the amount of phosphor added to the LED is reduced. Further, the present invention provides a production method capable of obtaining a phosphor having a small particle size with high brightness by firing at a low temperature or in a short time. By using these phosphors, the amount of phosphor used is reduced, the cost is reduced, and a light emitting device with improved brightness and luminous efficiency is provided.

In the present invention, the median diameter D50 measured by the laser diffraction method is 16 μm or less, the diffuse reflectance for light with a wavelength of 800 nm is 90% or more, and the diffuse reflectance for light with a wavelength of 500 nm is 80% or more. It is a β-type sialon phosphor represented by the characteristic formula (1).
Equation _{(1) Si 12-a Al} a O b N 16-b: Eu x
0 <a ≦ 3
0 <b ≦ 3
0 <x ≦ 0.1
The method for producing a β-sialon phosphor as described above, comprising a firing step, a low temperature firing step, and an acid treatment step, wherein the temperature of the firing step is lower than 1950 ° C. Further, in the method for producing the β-sialon phosphor, the maximum temperature holding time in the firing step is 3 hours or less. One or more red phosphors selected from the above β-type sialon phosphors, red phosphors using Mn ⁴⁺ as a light source, nitride red phosphors containing CASN and SCASN, and quantum dot red phosphors; , A light emitting device combined with a blue LED. The light emitting device is a combination of the β-sialon phosphor, a red LED or a red organic EL, and a blue LED. In the above light emitting device, the red phosphor having Mn ⁴⁺ as a light source is made of a fluoride phosphor containing KSF.

When the phosphor is used in the LED, the phosphor is dispersed in a silicone-based or epoxy-based resin, or in a transparent or transparent ceramic that transmits visible light. In that case, when light that excites the phosphor (excitation light) is irradiated, the frequency with which the excitation light strikes the phosphor increases as the specific surface area and cross-sectional area of the phosphor increases, and the excitation light becomes fluorescent. The proportion absorbed by the body increases. Therefore, when the specific surface area and cross-sectional area per unit weight or volume of the phosphor are increased, the absorption rate of the excitation light is increased, and the amount of phosphor added can be reduced. That is, the addition amount can be reduced by using a phosphor having a small particle diameter. In addition, when using a phosphor sheet or phosphor plate, if the phosphor has a small particle size, not only can the amount of phosphor added be reduced to reduce costs, but also the thickness of the phosphor sheet or phosphor plate is reduced. Heat dissipation is improved. Moreover, since it becomes easy to disperse | distribute to liquid resin as it is a small particle size, and to coat resin with spray application or fluorescent substance, workability | operativity is improved. In addition, the clogging of the nozzle that passes when coating is also improved by making the particle size small.

In conventional LEDs, the phosphor has a particle size of about 20 to 30 μm and good crystallinity, and has been considered suitable for improving the luminance of the LED. However, as the phosphor particle size increases, The specific surface area and cross-sectional area decreased, the amount of phosphor added to the LED increased, and the cost increased. In addition, since countermeasures against heat are required due to higher output of LEDs, phosphor sheets and phosphor plates have been studied, and the target thickness of the phosphor sheets and phosphor plates is several tens of μm. For this reason, the conventional phosphor having a large particle size is biased toward dispersion of the phosphor, causing localization, which causes variation in characteristics. Further, the surface roughness of the phosphor sheet or the phosphor plate tends to be rough, and the light emission luminance of the LED is lowered. Further, even when the phosphor is dispersed in the resin and applied, if the phosphor is large, the phosphor is difficult to disperse, causing variation in characteristics, and nozzle clogging during application tends to occur. By making the particle size small, nozzle clogging is reduced and phosphor dispersion is less biased, so that variations in LED characteristics can be reduced and the yield of LEDs can be improved.

As a method of reducing the particle size of the phosphor, there is a method of pulverizing, but the phosphor surface becomes rough, defects increase, and the luminance of the phosphor decreases. When the phosphor is irradiated with light having a wavelength that is not absorbed by the phosphor activator (for example, light having a wavelength of 800 nm in the case of β-SiAlON) and the diffuse reflectance is confirmed, absorption of excess light due to defects in the phosphor is confirmed. Things are possible. When the pulverization is carried out strongly, a phosphor having a small particle diameter can be obtained, but at the same time, defects on the surface increase, light having a wavelength of 800 nm is absorbed by the defects, and the diffuse reflectance decreases. In the present invention, the temperature during firing was reduced, and the retention time at the maximum temperature during firing was shortened to suppress particle growth, thereby producing a phosphor having a small particle size. In this manufacturing method, a phosphor with a small particle diameter can be obtained by weak pulverization, defects can be further reduced, and high brightness can be obtained. As a result, absorption of the activator can be suppressed, and absorption of light having a wavelength of 500 nm that is absorbed by the presence of defects and foreign phases can also be suppressed. The fact that light is hardly absorbed suppresses conversion into light having a long wavelength or conversion into heat, and can suppress a decrease in conversion efficiency of a target wavelength.

  By using a phosphor having a small particle size and a high luminance according to this patent, the amount of the phosphor used can be reduced, the cost can be reduced, and a light emitting device having a high luminance can be obtained.

  Examples according to the present invention will be described in detail with reference to tables and comparative examples.

  Examples and comparative examples according to the present invention were prepared as follows.

<Method for producing β-sialon>
As described below, as a method for producing β-sialon, impurities are removed from the powder after firing the raw material after mixing the starting materials, the low-temperature firing step performed after powdering the fired product, and the powder after the low-temperature firing step An acid treatment step was performed.

<Baking process>
The blend composition of Example 1 was such that the molar ratio was Si: Al: O: Eu = 11.42: 0.58: 0.58: 0.06. E10 grade), aluminum nitride powder (E grade made by Tokuyama), aluminum oxide powder (TM-DAR grade made by Daimei Chemical), europium oxide (RU grade made by Shin-Etsu Chemical) were blended. In addition, the amount of nitrogen at this time is uniquely determined by mix | blending each powder by the said molar ratio. In order to make it disperse | distribute, it mixed with the small mill mixer, Then, the sieve with an opening of 150 micrometers was made to pass through, the aggregate was removed, and raw material powder was obtained.

  The raw material powder is filled into a cylindrical boron nitride container with a lid (made by Denka), and baked at 2010 ° C. in a pressurized nitrogen atmosphere of 0.9 MPa for 13 hours in a carbon heater electric furnace. The product was obtained. This product was pulverized with a ball mill (alumina ball), and then passed through a sieve having an opening of 45 μm to obtain a β-sialon product powder.

<Low-temperature firing process>
The produced powder was filled into a cylindrical boron nitride container, and held at 1500 ° C. for 7 hours in an atmospheric pressure argon flow atmosphere in an electric furnace of a carbon heater to obtain a β-type sialon heat-treated powder. The cooling rate was performed under the same conditions in each of the examples and comparative examples.

<Acid treatment process>
The β-sialon heat-treated powder was immersed in a mixed acid of hydrofluoric acid and nitric acid. Then, the mixture is heated and treated at 60 ° C. or more for 3 hours, and then decantation for removing the supernatant and fine powder is repeated until the solution becomes neutral, and the finally obtained precipitate is filtered and dried. A β-sialon of Example 1 was obtained through a sieve having an opening of 45 μm.

  The phosphor of Example 2 was fired at 1920 ° C., further subjected to ball milling after the acid treatment step, and the other steps were treated in the same manner as in Example 1.

  The green phosphor of Example 3 was fired at 1920 ° C., the holding time of the highest temperature during firing was 3 hours, and the other processes were performed in the same manner as in Example 2.

  The phosphor of Comparative Example 1 was subjected to ball mill pulverization after firing under conditions weaker than those of Example 1 (the pulverization time was half or less), and the other processes were performed in the same manner as in Example 1.

  The phosphor of Comparative Example 2 was subjected to ball mill pulverization after firing under conditions stronger than Example 1 (grinding time was twice or more), and further ball milling after the acid treatment step was performed under conditions stronger than Example 2 (pulverization time was reduced). The other processes were carried out in the same manner as in Example 2.

  For the phosphor of Comparative Example 3, ball milling after firing was performed under conditions stronger than Comparative Example 2 (grinding time was twice or more), and ball milling after the acid treatment step was performed under conditions stronger than Comparative Example 2 (pulverization time was reduced). The other processes were carried out in the same manner as in Comparative Example 2.

External quantum efficiency, internal quantum efficiency, and chromaticity X were measured with a spectrophotometer (MCPD-7000 manufactured by Otsuka Electronics Co., Ltd.) and calculated according to the following procedure.
The phosphors of Examples and Comparative Examples were filled so that the surface of the concave cell was smooth, and an integrating sphere was attached. Monochromatic light separated into a wavelength of 455 nm from a light emitting light source (Xe lamp) was introduced into the integrating sphere using an optical fiber. Using this monochromatic light as an excitation source, the phosphor sample was irradiated and the fluorescence spectrum of the sample was measured.
A standard reflector (Spectralon manufactured by Labsphere) having a reflectance of 99% was attached to the sample portion, and the spectrum of excitation light having a wavelength of 455 nm was measured. At that time, the excitation light photon number (Qex) was calculated from the spectrum in the wavelength range of 450 to 465 nm.
A phosphor was attached to the sample portion, and the number of excited reflected light photons (Qref) and the number of fluorescent 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 fluorescent photons was calculated in the range of 465 to 800 nm.
The external quantum efficiency and the internal quantum efficiency were obtained by the following calculation formula.
External quantum efficiency = (Qem / Qex) × 100
Internal quantum efficiency = (Qem / (Qex−Qref)) × 100
Chromaticity X is calculated from CIE chromaticity coordinate x value (chromaticity X) in the XYZ color system defined by JIS Z 8701 according to JIS Z 8724 from the wavelength range data in the range of 465 nm to 780 nm of the fluorescence spectrum. did.
When the standard sample NSG1301 sold by Sialon Co., Ltd. was measured using the above measurement method, the external quantum efficiency was 55.6%, the internal quantum efficiency was 74.8%, and the chromaticity X was 0.356. . The apparatus was calibrated using this sample as a standard.

The particle size was measured by Microtrac MT3300EX II (Microtrack Bell Inc.). 100 g of ion-exchanged water is charged with 0.5 g of a phosphor, and dispersed therein for 3 minutes in an Ultrasonic Homogenizer US-150E (Nippon Seiki Seisakusho, chip size φ20, Amplitude 100%, oscillation frequency 19.5 KHz, amplitude about 31 μm). After the treatment, the particle size was measured with MT3300EX II. The median diameter D50 was determined from the obtained particle size distribution.

The diffuse reflectance was measured by attaching an integrating sphere device (ISV-469) to a UV-visible spectrophotometer (V-550) manufactured by JASCO Corporation. Baseline correction was performed with a standard reflector (Spectralon), a solid sample holder filled with phosphor powder was attached, and diffuse reflectance was measured in the wavelength range of 500 to 850 nm.

When the phosphor of the example and the comparative example is combined with the blue LED to form a white LED, the green phosphor and the red phosphor of the example and the comparative example are in a ratio of chromaticity X0.275 and chromaticity Y0.279. K ₂ SiF ₆ : Mn was mixed to obtain phosphor mixtures according to Examples and Comparative Examples. The red phosphor K ₂ SiF ₆ : Mn used in the examples and comparative examples in Table 1 was prepared under the following conditions.

The method for producing the red phosphor K ₂ SiF ₆ : Mn is a method for producing a phosphor represented by the general formula: A ₂ MF ₆ : Mn, a melting step for dissolving the raw material, and the phosphor from the raw material. The element A is K (potassium), the element M is Si (silicon), F is fluorine, and Mn is manganese.

<Raw material in addition process>
The raw material of the phosphor in the step of adding the red phosphor K ₂ SiF ₆ : Mn was K ₂ SiF ₆ powder (Kanto Chemical Co., Inc., Deer Special) and K ₂ MnF ₆ (manufactured by a production method described later). All the raw materials are in powder form. A hydrofluoric acid solution having a concentration of 55% by mass was used as hydrofluoric acid for dissolving these raw materials.

<Manufacturing process of K ₂ MnF ₆ >
The production of K ₂ MnF _{6 is} a product produced by the following production process.
A Teflon (registered trademark) beaker with a capacity of 1 liter is charged with 800 ml of 40 mass% hydrofluoric acid, 260 g of KHF ₂ powder (made by Wako Pure Chemical Industries, Ltd., special grade reagent) and potassium permanganate powder (Wako Pure). 12 g of Yaku Kogyo Co., Ltd., reagent grade 1) was dissolved. While stirring this hydrofluoric acid reaction liquid with a magnetic stirrer, 8 ml of 30% hydrogen peroxide (special grade reagent) was added dropwise little by little. When the dropping amount of the hydrogen peroxide solution exceeded a certain amount, yellow particles started to precipitate, and the color of the reaction solution began to change from purple. After a certain amount of hydrogen peroxide solution was dropped, the stirring was continued for a while, and then the stirring was stopped to precipitate the precipitated particles. After the precipitation, the supernatant liquid was removed, methanol was added, and the mixture was stirred and allowed to stand, the supernatant liquid was removed, and methanol was further added until the liquid became neutral. Thereafter, the precipitated particles were collected by filtration, further dried, and methanol was completely removed by evaporation to obtain 19 g of K ₂ MnF ₆ powder. All these operations were performed at room temperature.

<Dissolution process>
A dissolution process of the red phosphor K ₂ SiF ₆ : Mn will be described. Under normal temperature, 100 ml of 55 mass% hydrofluoric acid was placed in a 500 ml Teflon (registered trademark) beaker, 3 g of K ₂ SiF ₆ powder (Kanto Chemical Co., Ltd., Deer Special Grade) and K ₂ MnF ₆ 0. 5 g was dissolved sequentially. The amount of the raw materials, the general formula A ₂ MF 6: is the addition amount of below the saturation solubility of the phosphor represented by _Mn.

<Reprecipitation process>
To this solution, 150 ml of water was dropped from two places, stirred for 10 minutes with a magnetic stirrer, and then allowed to stand. When allowed to stand, the phosphor deposited at the bottom of the container was precipitated.

The reason why the amount of water is 150 ml is that the concentration of hydrofluoric acid in the hydrofluoric acid solution when water is added in the reprecipitation step is 22% by mass.

<Washing process>
After confirming the presence of the phosphor, the supernatant was removed, washed with 20% by mass of hydrofluoric acid and methanol, the solid part was separated and recovered by filtration, and the remaining methanol was evaporated and removed by drying. .

<Classification process>
For the phosphor after the drying treatment, a nylon sieve having an opening of 75 μm was used, and only those passing through the sieve were classified, and finally 1.3 g of yellow K ₂ SiF ₆ : Mn phosphor powder was obtained. .

<Optical characteristics>
The optical characteristics of the phosphor obtained by the method for producing the red phosphor K ₂ SiF ₆ : Mn will be described. The excitation wavelength of the fluorescence spectrum measured with a spectrofluorometer (F-7000, manufactured by Hitachi High-Technologies Corporation) is 455 nm, and the monitor fluorescence wavelength of the excitation spectrum is 632 nm. This phosphor has two excitation bands of ultraviolet light having a peak wavelength of around 350 nm and blue light having a peak wavelength of around 450 nm, and has a plurality of narrow-band emission in the red region of 600 to 700 nm. The red phosphor had an absorptance, internal quantum efficiency, and external quantum efficiency of 82%, 74%, and 61%, respectively. The chromaticity coordinates (x, y) of the red phosphor were (0.694, 0.306).

For mixing phosphors, a total of 2.5 g was weighed and mixed in a polyethylene bag, and then a rotating and rotating mixer (47.5 g of silicone resin (Toray Dow Corning Co., Ltd. OE6566)) It was mixed with Shintaro Awatori Nertaro (registered trademark) ARE-310).

The LED chip was mounted by placing the LED chip on the bottom of the concave package body, wire bonding the electrode on the substrate, and injecting a phosphor mixed with silicone resin from a microsyringe. After mounting, it was cured at 150 ° C., and then post-cured at 110 ° C. for 10 hours and sealed. The LED chip having an emission peak wavelength of 448 nm and a chip size of 1.0 mm × 0.5 mm was used. The chromaticity X and chromaticity Y were confirmed with the LED package produced as described above, and the mixing ratio and addition amount of the phosphor were adjusted. In the light emitting devices using the phosphors of Examples and Comparative Examples, the amount of added green phosphor (excluding the red phosphor) was evaluated. The amount of green phosphor added is normalized by the total weight of all the phosphors added and the resin. Further, the amount of green phosphor added in Example 1 is set to 100%, and comparisons are made using the relative ratio in Examples 2 and thereafter. did.

As shown in Example 1 to Example 3 in Table 1, the amount of green phosphor (excluding the red phosphor) used in the light-emitting device was reduced by reducing the D50 of the phosphor to a small particle size. Comparative Example 1 is a particle size that has been generally used in the past, and cost reduction was required, but the amount of green phosphor added was reduced by reducing the particle size as in Example 1 to Example 3. Reduced and led to cost reduction.

Next, Table 2 compares Example 2 and Comparative Example 2 having substantially the same particle size and chromaticity. Comparative Example 2 is a general technique for obtaining a target small particle size by adjustment by pulverization. In Comparative Example 2, the 800 nm diffuse reflectance decreased due to the impact force by pulverization, the 500 nm diffuse reflectance also decreased, and the external quantum efficiency and the internal quantum efficiency also decreased. On the other hand, Example 2 is a method for adjusting crystallite particle growth in a low-temperature firing stage, in which defects generated during firing are suppressed, and a desired small particle size can be obtained with minimal grinding. Therefore, high 800 nm diffuse reflectance, high 500 nm diffuse reflectance, high internal quantum efficiency, and high external quantum efficiency were obtained. Since the phosphor of Example 2 has higher external quantum efficiency than the phosphor of Comparative Example 2, the light-emitting device uses the phosphor of Example 2 to emit light with higher brightness than the phosphor of Comparative Example 2 A device is obtained.

When Example 3 and Comparative Example 3 having substantially the same particle size and chromaticity as shown in Table 3 are compared, Comparative Example 3 is a general technique for obtaining a desired small particle size by adjustment by pulverization. As a result, the 800 nm diffuse reflectance decreased, the 500 nm diffuse reflectance also decreased, and the external quantum efficiency and the internal quantum efficiency also decreased. On the other hand, Example 3 is a method of adjusting the maximum temperature and the holding time in the firing stage, and defects generated during firing are suppressed, and a desired small particle size can be obtained with minimum grinding. Therefore, high 800 nm diffuse reflectance, high 500 nm diffuse reflectance, high internal quantum efficiency, and high external quantum efficiency were obtained. Since the phosphor of Example 3 has higher external quantum efficiency than the phosphor of Comparative Example 3, the light-emitting device uses the phosphor of Example 3 to emit light with higher brightness than the phosphor of Comparative Example 3 A device is obtained.

The phosphor of the present invention, and the phosphor and the light emitting device prepared by the manufacturing method are used as a white light emitting device and a colored light emitting device. The white light emitting device of the present invention is used for a liquid crystal display, a backlight of a liquid crystal panel, an illumination device, a signal device, and an image display device. It is also used for projector applications.

Claims (6)

A median diameter D50 measured by a laser diffraction method is 16 μm or less, a diffuse reflectance for light with a wavelength of 800 nm is 90% or more, and a diffuse reflectance for light with a wavelength of 500 nm is 80% or more. A β-type sialon phosphor represented by (1).
Equation _{(1) Si 12-a Al} a O b N 16-b: Eu x
0 <a ≦ 3
0 <b ≦ 3
0 <x ≦ 0.1 The method for producing a β-type sialon phosphor according to claim 1, comprising a firing step, a low temperature firing step, and an acid treatment step, wherein the temperature of the firing step is lower than 1950 ° C. The method for producing a β-type sialon phosphor according to claim 2, wherein the maximum temperature holding time in the firing step is 3 hours or less. The β-sialon phosphor according to claim 1, a red phosphor using Mn ⁴⁺ as a light source, a nitride red phosphor containing CASN, SCASN, or a quantum dot red phosphor. A light emitting device that combines a red phosphor and a blue LED. The light-emitting device which combined (beta) sialon fluorescent substance of Claim 1, red LED or red organic EL, and blue LED. The light-emitting device according to claim 4, wherein the red phosphor having Mn ⁴⁺ as a light-emitting source is a fluoride phosphor containing KSF.