JP5697387B2 - Method for producing β-sialon - Google Patents

Description

  The present invention relates to a method for producing β-sialon suitable as, for example, a phosphor.

  A light-emitting device that combines a light-emitting element that emits primary light and a phosphor that absorbs primary light and emits secondary light requires low power consumption, downsizing, high emission intensity, and wide color reproducibility. It is attracting attention as a next-generation light-emitting device, and is actively researched and developed.

  For example, a white LED that obtains white light by combining a semiconductor light-emitting element that emits blue to violet short-wavelength visible light and a phosphor and mixing the light emitted from the semiconductor light-emitting element and light that has been wavelength-converted by the phosphor is known. It has been.

  In Patent Document 1, a combination of a semiconductor light-emitting element that emits blue to violet short-wavelength visible light and a phosphor allows white light to be emitted by mixing the light emitted from the semiconductor light-emitting element and the light wavelength-converted by the phosphor. A white LED for obtaining the above is disclosed.

  Regarding phosphors, silicates, phosphates, aluminates, and sulfides are widely used as base materials, and transition metals or rare earth metals are used as the emission center.

  In recent years, white LEDs have been increasingly demanded for higher output, phosphor heat resistance and durability. This is due to a decrease in luminance and color of white LEDs due to a decrease in luminance of the phosphor due to a temperature increase in the use environment and deterioration of the phosphor due to exposure to an excitation source of blue light or ultraviolet light for a long time. The background is the problem of misalignment.

  Recently, phosphors of nitride or oxynitride having a stable crystal structure have attracted attention as phosphors having a small decrease in luminance due to temperature rise and excellent durability.

  As a nitride or oxynitride phosphor, sialon which is a solid solution of silicon nitride is typical. Similar to the crystal structure of silicon nitride, sialon has two types of crystal systems, α-type and β-type. And it is known that the alpha sialon which dissolves a specific rare earth element has a useful fluorescence characteristic, and application to white LED etc. is examined (refer patent documents 2-4).

  Moreover, it has been found that β-sialon which dissolves rare earth elements also has similar fluorescence characteristics (see Patent Document 5).

β-type sialon is a solid solution of β-type silicon nitride in which Al is substituted at the Si position and O is substituted at the N position. Since there are two amounts of atoms in the unit cell (unit cell), Si _6-z Al _z O _z N _8-z is used as a general formula. Here, the composition z is 0 <z <4.2 , the solid solution range is very wide, and the molar ratio of (Si, Al) / (N, O) must be maintained at 3/4. is there. The crystal structure of β-type silicon nitride is defined as a structure having symmetry of P6 ₃ or P6 ₃ / m and having an ideal atomic position (see Patent Document 5). In general, as a raw material, β-sialon can be obtained by heating by adding silicon oxide and aluminum nitride or aluminum oxide and aluminum nitride in addition to silicon nitride.

When europium (Eu ²⁺ ) is included in the crystal structure of β-sialon, it is excited by ultraviolet to blue light and becomes a phosphor that emits green light of 520 to 550 nm, and as a green light emitting component of a light emitting device such as a white LED. It can be used and is known as β-sialon in which Eu ²⁺ is dissolved. Β-SiAlON which is a solid solution of the Eu ^2+, among the phosphors solid solution Eu ^2+, since the emission spectrum is very sharp, blue, green, image processing and displaying apparatus narrowband emission of red are required Or it is a material suitable for the backlight light source of a liquid crystal display panel.

Japanese Patent No. 2927279 Japanese Patent No. 3668770 Japanese Patent No. 3726131 JP 2003-124527 A JP 2005-255895 A JP 2008-303331 A

  By the way, unlike a lighting application, a light emitting device used for a backlight light source such as an image processing display device or a liquid crystal display is desired to have a narrow emission spectrum width of three primary colors of blue, green, and red. From white light, the three primary colors can be obtained through a filter that transmits only the three primary colors. However, in order to use it as a backlight for a liquid crystal display or the like, green or red light having a narrow emission spectrum width is used as a phosphor. What emits light is required.

However, β-sialon, which is a solid solution of Eu ²⁺ produced using metallic silicon, aluminum nitride, and europium oxide, has an emission peak wavelength shifted from green to red, that is, a long wavelength side. In order to use it as a light source, it has been required to shorten the emission spectrum. At the same time, it has been required to further narrow the emission spectrum.

However, there is a trade-off relationship between the emission intensity of β-sialon in which Eu ²⁺ is dissolved and the emission spectrum having a shorter wavelength and a narrower band. When the emission intensity is increased, the emission peak of the emission spectrum becomes longer and the spectrum width is widened, so that the color reproduction range is narrowed when used for backlight applications of liquid crystal displays. On the other hand, when the emission spectrum is shortened and narrowed, sufficient luminance cannot be obtained.

In view of the above-described problems, an object of the present invention is to provide a method for producing β-sialon in which Eu ²⁺ is dissolved, which can realize high emission intensity, shortening of the emission spectrum, and narrow-band emission.

In a β-type sialon in which Eu ²⁺ is dissolved in a base crystal of a β-type sialon represented by the general formula: Si _6-z Al _z O _z N _8-z , as shown in Patent Document 6, Eu solid solution By reducing the amount of oxygen dissolved in the β-type sialon crystal, that is, by reducing the z value in the above equation, the emission spectrum can be shortened and narrowed. However, there is a problem that the emission intensity decreases when the z value is lowered.

The present inventors have revealed that studying about emission properties of β-sialon obtained by solid solution Eu ^2+, metal silicon, aluminum nitride, synthetic solid-dissolved β-SiAlON the Eu ²⁺ obtained by firing europium oxide Thus, the inventors have obtained the knowledge that the nitridation reaction of metallic silicon contained in the raw material mixture affects the shortening and narrowing of the emission spectrum, and the present invention has been completed.

In order to achieve the above object, the present invention provides a process for producing β-sialon in which Eu ²⁺ is dissolved as a light-emitting center in β-sialon represented by the general formula Si _6-z Al _z O _z N _8-z. Provided is a method for producing β-sialon, which includes a nitriding treatment step in which a mixture containing silicon, an aluminum compound and europium oxide is heated in a nitrogen atmosphere, and a firing step in which the nitriding mixture is heat-treated.
Here, the processing conditions of the nitriding step are as follows: the heating temperature is in the range of 1450 ° C. or more and 1550 ° C. or less, and the pressure (y) is a relational expression with respect to the heating temperature (x): y ≦ −0.0035x + 5.575. Must meet.

According to the production method of the present invention, it is possible to control variations in the light emission characteristics of β-sialon (hereinafter referred to as β-sialon) in which Eu ²⁺ is dissolved. The β-sialon obtained by the production method of the present invention is excellent as a green phosphor because it is excited in a wide wavelength range from ultraviolet to visible light and emits light in a high emission intensity and a narrow green band. The β-sialon of the present invention has little change in luminance with respect to changes in the use environment, and can be used for various light-emitting elements, particularly white LEDs using ultraviolet LEDs and blue LEDs as light sources, alone or in combination with other phosphors.

It is a graph which shows the relational expression of the result of Experimental Examples 1-3 according to this invention, and the comparative example 1, and nitriding treatment conditions.

The present invention relates to a process for producing β-sialon in which Eu ²⁺ as a luminescent center is dissolved in β-sialon represented by the general formula Si _6-z Al _z O _z N _8-z. A sialon manufacturing method including a nitriding treatment step of heating a mixture containing nitrile in a nitrogen atmosphere and a firing step of heat-treating the nitrided mixture.

  The metal silicon, aluminum compound and europium oxide as raw materials are preferably powders. Metallic silicon may contain iron as an impurity, but is preferably 20 ppm or less, and more preferably 10 ppm or less.

  The aluminum compound refers to one or more aluminum compounds selected from aluminum nitride, aluminum oxide, or an aluminum-containing compound that decomposes by heating to produce aluminum oxide.

In the nitriding treatment, a mixture containing metal silicon, an aluminum compound and europium oxide is subjected to pressure and heat treatment in a nitrogen atmosphere. The treatment condition is that the heating temperature is in the range of 1450 ° C. or more and 1550 ° C. or less, and the pressure (y) needs to satisfy the relational expression with respect to the heating temperature (x): y ≦ −0.0035x + 5.575.
If the heating temperature is low, Eu ²⁺ cannot enter the β-type sialon crystal, which is not preferable.
In addition, the temperature condition or pressure condition of the nitriding treatment affects the shift of the emission wavelength peak of β-sialon to the red side in relation to the firing process which is a subsequent process. When the heating temperature exceeds 1550 ° C. or the pressure (y) in the nitriding process is higher than the value of −0.0035x + 5.575 in relation to the heating temperature (x), the β-type is formed by the subsequent baking. Since the peak of the emission wavelength of sialon shifts to the red side, that is, the long wavelength side, it is not preferable.

The firing step may be performed by heating in a nitrogen atmosphere in accordance with the conditions of a regular method. The heating temperature is preferably in the range of 1850 to 2050 ° C. If the heating temperature is high, Eu ²⁺ can enter the β-sialon crystal, and a β-sialon having sufficient emission intensity can be obtained. If the heating temperature is within the above-mentioned temperature range, it is not necessary to suppress the decomposition of β-sialon by applying a very high nitrogen pressure, and a special apparatus is not required, which is industrially preferable.

  The fired product is granular or massive. This is combined with pulverization, pulverization and / or classification operations to obtain a powder of a predetermined size. Specific examples of the treatment include a method of obtaining a powder that has passed through a sieve by subjecting the fired product to a sieve classification having an opening of 20 to 45 μm, or a general grinder such as a ball mill, a vibration mill, or a jet mill. And a method of pulverizing to a predetermined particle size. In the latter method, excessive pulverization not only generates fine particles that easily scatter light, but also generates crystal defects on the particle surface, causing a decrease in emission intensity. According to the study by the present inventors, the powder obtained by the treatment only by the sieve classification without performing the pulverization treatment finally showed high luminescence intensity.

  Hereinafter, in “Production of powder mixed raw material” to “Firing process”, a production example of β-sialon in which the relationship between the temperature (x) and the pressure (y) of nitriding is y> −0.0035x + 5.575 Is shown as Comparative Example 1 and Examples of Production satisfying the condition of y ≦ −0.0035x + 5.575 are shown below as Experimental Examples 1 to 3.

First, a comparative example will be described prior to the description of the experimental example of the present invention.
[Comparative Example 1]
"Production of powder mixed raw materials"
Silicon powder (purity 99.999% or more, −45 μm, manufactured by Kojun Chemical Co., Ltd.) 96.41% by mass, aluminum nitride powder (E grade manufactured by Tokuyama Co., Ltd.) 1.16% by mass, and europium oxide powder (Shin-Etsu Chemical Co., Ltd.) (RU grade manufactured) 2.43 mass% was mixed using a mortar and pestle made of a silicon nitride fired body, and further passed through a sieve having a mesh size of 250 μm to remove agglomerates to obtain a powder mixed raw material.

"Nitriding process"
The powder mixed raw material is filled into a cylindrical boron nitride container (made by Denki Kagaku Kogyo Co., Ltd., “N-1” grade) with a lid having a diameter of 40 mm and a height of 30 mm, and a pressure of 0.50 MPa is applied in an electric furnace of a carbon heater. Heat treatment was performed at 1550 ° C. for 8 hours in a nitrogen atmosphere. The heating rate during heating was 20 ° C./min from room temperature to 1200 ° C., and 0.5 ° C./min from 1200 to 1550 ° C. The obtained product was massive and was pulverized using a mortar and pestle made of a silicon nitride fired body. The pulverized powder was classified with a sieve having an opening of 45 μm, and the powder of 45 μm or less was used as Eu solid solution aluminum-containing silicon nitride powder for β-type sialon firing. Further, the obtained Eu solid solution aluminum-containing silicon nitride powder was passed through a sieve having an opening of 250 μm to obtain a powder mixed raw material for Eu solid solution β-sialon.

"Baking process"
Powder mixed raw material for Eu solid solution β-type sialon is filled into a cylindrical boron nitride vessel (“N-1” grade, manufactured by Denki Kagaku Kogyo Co., Ltd.) with a lid 60 mm in diameter and 30 mm in height, and an electric furnace for a carbon heater Then, heat treatment was performed at 2000 ° C. for 8 hours in a pressurized nitrogen atmosphere of 0.8 MPa. The obtained product was a green loosely agglomerated lump, which could be lightly unraveled manually. In this way, after mild crushing, it was passed through a sieve having an opening of 45 μm to obtain β-sialon of Comparative Example 1.

[Experimental Example 1]
Β-sialon was obtained under the same conditions as in Comparative Example 1 except that the heating temperature for nitriding was 1450 ° C. and the pressure condition was 0.5 MPa.

[Experiment 2]
Β-sialon was obtained under the same conditions as in Comparative Example 1 except that the heating temperature for nitriding was 1550 ° C. and the pressure condition was 0.15 MPa.

[Experiment 3]
A β-sialon was obtained under the same conditions as in Comparative Example 1 except that the heating temperature for nitriding was 1450 ° C. and the pressure condition was 0.15 MPa.

"Measurement method and result of luminescence characteristics"
The light emission characteristics of β-sialon were evaluated as follows. First, β-sialon powder was filled into a concave cell, the surface was smoothed, and an integrating sphere was attached. Monochromatic light that was split into a predetermined wavelength 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, a β-type sialon sample was irradiated, and the spectrophotometer (MCPD-7000, manufactured by Otsuka Electronics Co., Ltd.) was used to measure the spectrum of the fluorescence and reflected light of the sample. In this example, blue light having a wavelength of 455 nm was used as the monochromatic light.

  In the obtained emission spectrum, the chromaticity coordinates CIEx and CIEy in the XYZ color system defined by JIS Z8701 were calculated from the data in the wavelength range of 465 to 780 nm when the excitation wavelength was 455 nm, according to JIS Z8724. .

  The quantum efficiency was determined as the emission intensity as follows. First, a standard reflector (Labsphere, Spectralon) with a reflectance of 99% is set on the sample part, and the spectrum of the excitation light is measured. When the excitation wavelength is 455 nm, the excitation light is obtained from the spectrum in the wavelength range of 450 to 465 nm. The number of photons (Qex) was calculated. Next, β-sialon was set in 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 when the excitation light was 455 nm.

  The external quantum efficiency (= Qem / Qex × 100), the absorption rate (= (Qex−Qref) × 100), and the internal quantum efficiency (= Qem / (Qex−Qref) × 100) are obtained from the obtained three types of photons. Asked.

  Further, the relative peak intensity, which is another measured value indicating the emission intensity, was measured as follows. The peak height of the phosphor with the peak height of the emission spectrum of YAG: Ce (P46Y3; manufactured by Kasei Optonix Co., Ltd.) as 100% was expressed as a relative peak intensity (%). Table 1 shows the measurement results of the absorption rate, internal quantum efficiency, external quantum efficiency, chromaticity, and relative peak intensity of β-sialons of Comparative Example 1 and Experimental Examples 1 to 3.

  As shown in Table 1, when excited with blue light having a wavelength of 455 nm, the absorption rate, internal quantum efficiency, and external quantum efficiency of β-sialon of Comparative Example 1 were 71.9%, 41.3%, and 29.7, respectively. CIEx (chromaticity x) was 0.308, and the emission intensity was 136%. In Experimental Examples 1 to 3, the CIEx value is small, and the CIEx value and the CIEy value are almost the same, and the longer wavelength is suppressed compared to Comparative Example 1, and the blue side, that is, the shorter wavelength side is shifted. I understand that.

FIG. 1 shows the results of Comparative Example 1 and Experimental Examples 1 to 3, and the temperature-pressure relational expression obtained based on these results. It can be seen that the comparative example and the experimental examples 1 to 3 are distributed separately with respect to the value of the relational expression y = −0.0035x + 5.575 (where x is the heating temperature and y is the pressure). . That is, by performing nitriding under conditions where the heating temperature is 1450 ° C. or more and 1550 ° C. or less and the pressure (y) is y ≦ −0.0035x + 5.575 (where x is the heating temperature), β-sialon emission The color can be shifted to the blue side, and the light emitting area can be easily controlled to emit green narrow band light.
As described above, in the powder mixed raw material for Eu solid solution β-type sialon, the relational expression of the pressure (y) with the heating temperature (x) in the temperature range of 1450 ° C. to 1550 ° C .: y It can be seen that by performing nitriding in a range satisfying ≦ −0.0035x + 5.575, the wavelength increase is suppressed, and the luminescence intensity is improved without variation in chromaticity.

  The present invention has been described based on the embodiments. However, the embodiments are merely examples, and it is easy for those skilled in the art that various modifications are possible and that such modifications are also within the scope of the present invention. Is understood.

  The β-sialon obtained by the production method of the present invention is excited by a wide range of wavelengths from ultraviolet to blue light, and exhibits high luminance and narrow band green light emission. It can be suitably used as a phosphor, and can be particularly suitably used for an image display device. Furthermore, since there is little decrease in brightness at high temperatures and excellent heat resistance and moisture resistance, when applied to the above-mentioned image display device field, changes in brightness and emission color with respect to changes in the operating environment temperature are small, and long-term Excellent stability can be achieved.

Claims (2)

A method for producing a β-type sialon in which Eu ²⁺ is dissolved as a luminescent center in a β-type sialon represented by the general formula Si _6-z Al _z O _z N _8-z (0 <z <4.2) ,
Seen containing a nitriding process of silicon metal, aluminum compound and a mixture containing europium oxide is heated under a nitrogen atmosphere, and a firing step of heating a mixture that has been nitrided,
The β-type , wherein the heating temperature condition in the nitriding treatment step is in the range of 1450 ° C. or more and 1550 ° C. or less, and the pressure MPa (y) satisfies the relational expression with the heating temperature (x): y ≦ −0.0035x + 5.575 Sialon manufacturing method. The heating temperature of the baking step is from 1,800 to 2025 ° C., the preparation of β-sialon in claim 1, wherein.