JP2009096882A - Phosphor and production method thereof - Google Patents

Abstract

An α-sialon phosphor having a high nitrogen content and a peak at a wavelength of 595 nm or more with excellent luminous efficiency is provided.
A general formula: (Ca _X , Eu _Y ) (Si, Al) ₁₂ (O, N) ₁₆ (where 1.5 <X + Y <2.2 and 0 <Y <0.2, O / N
≦ 0.04), which is a method for producing a phosphor mainly composed of α-sialon, wherein (a) silicon nitride, (b) aluminum nitride, (c) Ca-containing compound, (d) Raw material mixed powder composed of Eu-containing compound and (e) α-sialon is heat-treated at 1650-1850 ° C. in a nitrogen atmosphere to obtain α-sialon, and the average particle size is 15- A method for producing a phosphor, characterized by obtaining a powder of 25 μm.
[Selection figure] None

Description

  The present invention relates to a phosphor that can be used in various light emitting devices such as a white light emitting diode (white LED) using a blue light emitting diode (blue LED) or an ultraviolet light emitting diode (ultraviolet LED), and a manufacturing method thereof.

  White LEDs are small, lightweight, long life, excellent in high-speed response, do not use harmful substances such as mercury in fluorescent lamps, and have a feature of low environmental impact. It is widely used in backlights for small liquid crystal displays and small lighting devices such as flashlights, and is expected to be used in medium and large display light sources and general lighting applications in the future.

  Various types of white LEDs have been proposed, but the most popular at present is a compound semiconductor blue light-emitting diode element and a blue light emitted from the compound semiconductor blue light-emitting diode element. Examples thereof include yttrium aluminate (YAG: Ce) phosphors activated with cerium.

  This type of white LED has a problem of low color rendering properties due to a lack of reddish luminescent components. For this reason, in order to compensate for the red component, there has been proposed a method of using orange to red nitride and oxynitride phosphor together with the YAG phosphor.

As nitride and oxynitride phosphors, α-sialons in which specific rare earth elements are activated are known to have useful fluorescence characteristics, and their application to white LEDs and the like are being studied (patents) References 1-3).
Japanese Patent No. 3668770 JP 2003-124527 A JP 2004-067837 A

  In the α-type sialon, the Si—N bond of the α-type silicon nitride crystal is partially replaced by an Al—N bond and an Al—O bond, and in order to maintain electrical neutrality, a specific element (Ca , And lanthanide metals excluding Li, Mg, Y, or La and Ce) have a structure intruded into the lattice and dissolved. Fluorescence characteristics are exhibited by using a rare earth element as a light emission center for a part of the element that enters and dissolves. Among them, the α-sialon phosphor in which Ca is dissolved and a part thereof is substituted with Eu is excited relatively efficiently in a wide wavelength range from ultraviolet to blue, and emits yellow to orange light.

  The α-sialon is obtained by treating a mixed powder composed of oxides of silicon nitride, aluminum nitride, calcium and europium (including a compound that becomes an oxide by heat treatment) at a high temperature in a nitrogen atmosphere. In such a synthesis method, since an oxide raw material is used, an α-sialon in which a considerable amount of oxygen is dissolved is inevitably formed. The emission color of the α-sialon phosphor obtained in this case is yellow to orange (fluorescence peak wavelength is around 580 nm).

On the other hand, α-sialon having a high nitrogen content synthesized using calcium nitride as a calcium raw material can dissolve calcium at a higher concentration than the conventional α-sialon. In particular, when the Ca solid solution concentration is high, a phosphor having a fluorescence peak wavelength on the higher wavelength side (595 to 650 nm) than the conventional composition can be obtained (Patent Document 4).
JP-A-2005-307012

  When the α-sialon phosphor having a high nitrogen content is applied to a light emitting device such as a white LED, further improvement in luminous efficiency is expected.

  The object of the present invention is to provide a phosphor having a higher nitrogen efficiency and a method for stably producing the α-sialon phosphor having a high nitrogen content having a peak at a wavelength of 595 nm or more. is there.

The inventor conducted an experimental study on the production of Ca—α-sialon phosphor powder having a high nitrogen content activated by Eu ²⁺ . As a result, by adding α-sialon powder synthesized in advance as raw material powder as seed particles for grain growth, larger and smoother particles can be obtained than before, and without pulverizing from the synthesized powder. The inventors have found that by obtaining a powder having a specific particle size, a phosphor having a fluorescence peak at a wavelength of 595 nm or more with excellent luminous efficiency can be obtained, and the present invention has been achieved.

That is, the present invention has the general formula: (Ca _X , Eu _Y ) (Si, Al) ₁₂ (O, N) ₁₆ (where 1.5 <X + Y <2.2 and 0 <Y <0.2, A method for producing a phosphor mainly composed of α-sialon represented by O / N ≦ 0.04), wherein (a) silicon nitride, (b) aluminum nitride, (c) Ca-containing compound, (D) A raw material mixed powder composed of Eu-containing compound and (e) α-sialon is heated in a nitrogen atmosphere at 1650 to 1850 ° C. to obtain α-sialon, and the average particle size is obtained only by classification treatment. Is a method for producing a phosphor, characterized in that a powder of 15 to 25 μm is obtained.

In the method for producing the phosphor of the present invention, the α-sialon contained in the raw material mixed powder has an addition amount of 5 to 30% by mass, an average particle size of 3 to 15 μm, and a specific surface area of 0.2. It is ˜1 m ² / g. Preferably, the solid solution element is Ca.

The phosphor manufacturing method of the present invention is characterized in that the raw material mixed powder is filled in a boron nitride crucible so as to have a bulk density of 0.6 g / cm ³ or less, and heat treatment is performed.

In addition, the present invention provides a general formula: (Ca _X , Eu _Y ) (Si, Al) ₁₂ (O, N) ₁₆ (where 1.5 <X + Y <2.2 and 0 <Y <0.2 , O / N ≦ 0.04), and a phosphor having a specific surface area of 0.1 to 0.35 m ² / g.
In the present invention, the specific surface area is a value obtained by BET multipoint analysis after measurement based on the BET method.

  The method for producing a sialon phosphor having a high nitrogen content according to the present invention is different from the conventional method in that the particle size of the primary particles can be easily obtained by including an α-sialon powder as a nucleus of grain growth in the starting material. Can be increased. The particle form of the finally obtained sialon phosphor powder can be controlled by the particle size of the α-type sialon powder added as a nucleus. Based on this effect, it is possible to stably provide a phosphor having a large primary particle, a smooth particle surface, and excellent emission characteristics.

The phosphor obtained by the production method of the present invention has a specific surface area as small as 0.1 to 0.35 m ² / g, that is, the primary particles are large and have not been pulverized, so that the particle surface is smooth, As a result, the light emission efficiency is excellent at 60% or more.

  Hereinafter, the production method of the present invention will be described in detail.

First, the Eu-activated Ca-α-sialon phosphor that is the final product produced by the production method of the present invention will be described.
In general, an α-type sialon has a specific cation in the lattice in order to maintain electrical neutrality by replacing a part of the Si—N bond in the α-type silicon nitride with an Al—N bond and an Al—O bond. It is a solid solution that has entered, and is represented by the general formula: M _z (Si, Al) ₁₂ (O, N) ₁₆ . Here, M is an element that can enter the lattice, and is Li, Mg, Ca, Y, and a lanthanide metal (excluding La and Ce). The solid solution amount z value of M is a numerical value determined by the Al—N bond substitution rate of the Si—N bond.

  In order to express the fluorescence characteristics, it is necessary to use a part of M as an element that can be dissolved in a solid solution and become a light emission center. In particular, Ca is used as M, and Eu that becomes a light emission center is selected as a part of M. Thus, a phosphor that is excited with light in a wide wavelength range from ultraviolet to blue and exhibits visible light emission of yellow to orange is obtained.

  Among Eu-activated Ca-α-sialon phosphors, orange-red long wavelength light emission is realized by lowering the oxygen content in sialon crystals and increasing the solid solution concentration of Ca (including Eu). The

Specifically, in the general formula: (Ca _X , Eu _Y ) (Si, Al) ₁₂ (O, N) ₁₆ , 1.5 <X + Y <2.2 and O / N ≦ 0.04. When X + Y is 1.5 or less, it is difficult to obtain fluorescence with a peak wavelength of 595 nm or more, and when an α-sialon exceeding 2.2 is produced, a second phase that adversely affects fluorescence characteristics is likely to be generated. . On the other hand, when the O / N ratio exceeds 0.04, it is difficult not only to obtain fluorescence having a peak wavelength of 595 nm or more, but also to reduce the solid solution limit of Ca and Eu, and it becomes difficult to achieve X + Y> 1.5. Further, regarding the solid solution amount Y value of Eu, it is preferable that 0 <Y <0.2 from the viewpoint of the fluorescence peak wavelength and the light emission efficiency.

Next, raw materials for producing the Eu-activated Ca-α-sialon phosphor will be described.
The production method of the present invention is characterized in that, as a raw material powder, in addition to silicon nitride, aluminum nitride, Ca compound and Eu compound used in the production of conventional α-sialon, a pre-synthesized α-sialon is included. is there.

In order to obtain an α-sialon having a high nitrogen content, the Ca compound is preferably all or part of calcium nitride. It is also possible to use CaF ₂ as a part of the Ca raw material. By adding CaF ₂ , sintering between particles can be suppressed and primary particles can be increased, so that it is easy to obtain a suitable particle growth nucleus.

  The Eu compound is preferably a nitride from the viewpoint of increasing the nitrogen content. However, since the compounding ratio of Eu is very small compared with Ca, an oxide or the like may be used.

  The α-sialon (hereinafter also referred to as raw material sialon) previously blended with the raw material powder selectively becomes a starting point for grain formation during the heat treatment, and promotes the growth of primary particles. Addition of α-sialon increases the primary particle size by several to 10 times compared to the case of no addition, and surface smoothening advances, improving crystallinity and suppressing light scattering on the particle surface. , The emission characteristics are improved. Further, the addition of α-sialon to the raw material powder in advance has an effect of suppressing sintering between particles during the synthesis process, and it is possible to produce easily pulverizable sialon. This sialon has an effect of suppressing the generation of fine particles accompanying the pulverization process, which can obtain a powder having a desired particle size without pulverization process and lowers the light emission characteristics.

  The raw material sialon is present in the center of the particle after synthesis, so its contribution to the luminescent properties is small.Therefore, its composition is not particularly limited, but impurities such as iron that contain different luminescent center elements or inhibit luminescence The use of α-sialon powder containing an element is not preferable because it greatly affects the characteristics of the α-sialon phosphor layer formed on the surface. From such a viewpoint, in the present invention, it is preferable to use α-sialon in which the same Ca as the phosphor layer is dissolved, and in particular, α-sialon that matches the chemical composition of the phosphor to be obtained is used. Is preferred.

In addition, since the raw material sialon serves as a starting point for grain growth, it is desirable that the primary particles are sufficiently larger than the other raw material powders and that they do not form coarse secondary particles. From this viewpoint, it is preferable that the average particle diameter is 3 to 15 μm and the specific surface area is 0.2 to ¹ m ² / g. In this range, sufficient grain growth and sintering suppressing effects can be obtained, and the light emission characteristics are not deteriorated.

  The amount of α-sialon added is preferably 5 to 30% by mass. If the added amount of α-sialon is 5% by mass or more, the formation and sintering of new α-sialon particles and the growth of grains will not proceed in the portion other than the added α-sialon particles, and 30 mass If it is not more than%, it is preferable because there are too many basic points for grain growth, the growth of individual particles becomes small, and it becomes difficult to obtain sufficiently large primary particles.

  Each raw material containing the α-sialon described above is mixed so as to have a desired composition (composition represented by the above general formula). As a method of mixing, a method of dry mixing, a method of removing the solvent after wet mixing in an inert solvent that does not substantially react with each component of the raw material, and the like can be employed. In addition, as a mixing apparatus, a V-type mixer, a rocking mixer, a ball mill, a vibration mill, etc. are used suitably.

  A powder obtained by mixing so as to have a desired composition (hereinafter simply referred to as raw material powder) is filled into a container made of a material having low reactivity with the raw material and the phosphor to be synthesized, for example, a boron nitride container, and a nitrogen atmosphere. Among them, a phosphor is obtained by heating in a temperature range of 1650 to 1850 ° C. for a predetermined time.

  By setting the temperature of the heat treatment to 1650 ° C. or higher, the amount of unreacted product remaining can be suppressed, and primary particles can be sufficiently grown. Suppression can be suppressed.

The filling of the raw material powder into the container is preferably as bulky as possible from the viewpoint of suppressing interparticle sintering during heating. Specifically, the bulk density is preferably 0.6 g / cm ³ or less when the raw material powder is filled into the container.

  In addition, for the heating time in the heat treatment, a time range in which there are many unreacted substances, primary particles are insufficiently grown, or inconvenience that sintering between particles occurs, is selected, According to the study of the present inventors, about 2 to 24 hours is a preferable range.

The α type sialon phosphor obtained by the above-described operation is obtained only by classification to obtain a powder having an average particle size of 15 to 25 μm.
Although the reaction product after the heat treatment partially contains a lump, it maintains the powder state and the sintering between particles is suppressed. A powder having a predetermined average particle size can be obtained in a high yield only by a classification process using a sieve or the like without performing a single pulverization process.

  By the classification treatment, a lump can be removed and a phosphor having a uniform particle size and characteristics can be obtained. In particular, those having an average particle size of 15 to 25 μm have a large primary particle size, a small specific surface area, and good emission intensity. Specifically, a phosphor having a large primary particle size of 3 to 10 μm is obtained. Further, as described above, since this phosphor is made of particles having a smooth surface because it has not been pulverized, the phosphor has a light emission characteristic of 60% or more. Therefore, the phosphor obtained by the production method of the present invention can be suitably applied as, for example, an LED phosphor. That is, if the average particle diameter is 15 μm or more, the light emission intensity is not lowered, and if the average particle diameter is 25 μm or less, uniform dispersion in the resin for sealing the LED is easy, and the light emission intensity and the color tone vary. It can be used practically without producing.

  In the prior art, the average particle size of the primary particles is at most about 2 μm, and since the surface is not smooth after the pulverization operation, only a luminous efficiency of about 50% or less can be obtained.

Next, based on an Example and a comparative example, this invention is demonstrated still in detail.
In the examples and comparative examples, the specific surface area of the particles was measured with a specific surface area measuring device (BELSORP-mini) manufactured by Bell Japan, and the result of BET multipoint analysis was shown. The results of measurement with a laser diffraction / scattering particle size distribution measuring apparatus (LS-230 type) are shown.

<Example 1>
1. Synthesis of α-sialon (raw material sialon) to be contained in raw material powder As a blending composition of raw material powder, silicon nitride powder was 61.2% by mass, aluminum nitride powder was 22.1% by mass, and calcium nitride powder was 9.5% Mass%, calcium fluoride powder was 5.0 mass%, and europium oxide powder was 2.2 mass%. This composition is almost the same as that of the final product, α-sialon. This raw material powder was mixed using a mortar in a glove box under a nitrogen atmosphere.

  Next, the raw material powder is passed through a sieve having an opening of 250 μm in the same glove box, and then filled into a boron nitride crucible, and is heated at 1750 ° C. for 16 hours in an atmospheric pressure nitrogen in a carbon heater electric furnace. Heat treatment was performed. Since the calcium nitride contained in the raw material powder is easily oxidized and hydrolyzed in the air, the crucible filled with the mixed powder is taken out of the glove box and immediately set in an electric furnace, immediately evacuated and nitrided. Prevented calcium reaction.

The product obtained by the heat treatment was in the form of powder, and almost all passed through a sieve having an opening of 45 μm. What passed through this sieve was made into α core powder. The specific surface area of the α core powder was 0.43 m ² / g, and the average particle size was 9.2 μm.

2. Synthesis and Evaluation of α-Sialon Phosphor As raw material powder, 15% by mass of the α core powder, 53% by mass of silicon nitride powder, 19.1% by mass of aluminum nitride powder, 11% by mass of calcium nitride powder, europium oxide The powder was mixed with 1.9% by mass, mixed in a mortar in a glove box, and passed through a sieve having an opening of 250 μm. About 22 g of this raw material powder was filled into a boron nitride crucible having an internal volume of 88 cm ³ (inner diameter 60 mm × height 30 mm). The bulk density of the raw material mixed powder filled in the crucible was 0.38 g / cm ³ . The boron nitride crucible filled with the raw material powder was taken out of the glove box, quickly set in an electric furnace of a carbon heater, and subjected to heat treatment at 1750 ° C. for 16 hours. The obtained sample was subjected to sieving without pulverization, and the final product (phosphor) was the powder that finally passed through a 45 μm sieve. The composition of this phosphor is (Ca _1.67 , Eu _0.08 ) (Si, Al) ₁₂ (O, N) ₁₆ (x + y = 1.75, O / N = 0.03).
The ratio of the final product to the heat-treated recovered product was 72% by mass. The average particle size of the final product was 17.7 μm. Further, as a result of examining the crystal phase of the phosphor by powder X-ray diffraction measurement using CuKα rays, the only existing crystal phase was α-sialon.

Next, excitation / fluorescence spectrum measurement was performed using a spectrofluorometer (manufactured by Hitachi High-Technologies Corporation, “F4500”). The results are shown in FIG. In the figure, the vertical axis represents the relative light emission intensity.
As can be seen from the figure, the phosphor was excited at a wide range of wavelengths from ultraviolet to blue, and exhibited a fluorescence spectrum having a peak wavelength of 600 nm and a half-value width of 85 nm. Furthermore, total luminous emission spectrum measurement was performed on the phosphor using an integrating sphere (reference: “Illumination Society Journal” Vol. 83, No. 2, 1999, pp. 87-93, “NBS Standard Fluorescence”. "Quantum efficiency measurement of the body" by Kazuaki Okubo et al.). A spectral xenon lamp light source was used as the excitation light. When excited with blue light having a wavelength of 455 nm, the optical absorptance, internal quantum efficiency, and luminous efficiency were 86%, 73%, and 63%, respectively.

Further, this phosphor was observed with a scanning electron microscope (SEM). A scanning electron microscope (SEM) image is shown in FIG. The particle diameter of the primary particles determined from the SEM image was 3 to 10 μm. The specific surface area of this phosphor was 0.24 m ² / g.

<Comparative Example 1>
Except for not adding the α core powder, the same treatment as in Example 1 was performed. That is, the composition of the raw material powder was 62.4 mass% for the silicon nitride powder, 22.5 mass% for the aluminum nitride powder, 12.9 mass% for the calcium nitride powder, and 2.2 mass% for the europium oxide powder. . The bulk density when this raw material mixed powder (22 g) was filled in a boron nitride crucible (inner volume 88 cm ³ ) was 0.41 g / cm ³ . As a result of subjecting the product after heat treatment at 1750 ° C. for 16 hours to sieve classification with an opening of 45 μm, the sieve passing rate was 35% by mass. The average particle size of the final product that passed through the sieve was 11.6 μm, and as a result of powder X-ray diffraction measurement, the existing crystal phase was only α-sialon.

  The excitation / fluorescence spectrum of the obtained phosphor is shown in FIG. The excitation spectrum shape of the phosphor of the comparative example, the peak wavelength and the half width of the fluorescence spectrum were the same as those of the phosphor of the example, and the fluorescence peak intensity was low. When excited with blue light having a wavelength of 450 nm, the optical absorptance, internal quantum efficiency, and luminous efficiency were 77%, 70%, and 54%, respectively.

As can be seen from the SEM image of FIG. 3, the phosphor of the comparative example is composed of secondary particles obtained by sintering a large number of primary particles having a size of 2 μm or less. The specific surface area of this phosphor powder was 0.42 m ² / g.

<Examples 2 and 3 and Comparative Examples 2 and 3>
Using the α core powder, silicon nitride powder, aluminum nitride powder, calcium nitride powder, and europium oxide powder prepared in Example 1, the composition shown in Table 1 is used so that it becomes an α-sialon single phase after synthesis. The phosphor powder having the same composition as in Example 1 was obtained by the same treatment as in Example 1. The evaluation results are shown in Tables 2 and 3 together with the results of Example 1 and Comparative Example 1.

As can be seen from the results in Tables 1 to 3, a phosphor having a large average particle size and a small specific surface area was obtained by adding α-sialon as a synthetic raw material. However, when the addition amount of the raw material sialon is 2% by mass and 80% by mass, the average particle size of the phosphor as the final product is 13 μm or less and the specific surface area is 0.8 when compared with the phosphors of Examples 1 to 3. Exceeding 35, a decrease in luminous efficiency was observed.

<Example 4, comparative example 4>
In order to study the influence of the particle size of the raw material sialon on the final product, two types of α-sialon having different particle sizes were prepared. That is, the α nucleus powder produced in Example 1 was subjected to wet ball milling with a silicon nitride pot and balls for 4 hours in an ethanol solvent, filtered and dried to obtain α nucleus powder A. Further, the fine powder contained in the α nucleus powder A was removed by repeating the sedimentation classification using water to obtain α nucleus powder B. The average particle size of α kernel powder A and B are each 1.2 [mu] m, at 3.2 .mu.m, specific surface area were respectively 1.5m ² /g,0.82m ² / g. As raw material sialon, α-nuclear powder B was used in Example 4, and α-nuclear powder A was used in Comparative Example 4, and phosphor powder was obtained by the same method as Example 1. The evaluation results are shown in Tables 4 and 5.

  According to the production method of the present invention, it is possible to produce an orange-red high nitrogen content α-sialon phosphor having excellent emission characteristics and a fluorescent peak wavelength of 595 nm or more with good reproducibility and mass productivity.

  The phosphor of the present invention is an excellent phosphor that is composed of α-sialon having a high nitrogen content and emits orange to red light having a fluorescence peak wavelength of 595 nm or more, and is suitable for various lighting devices such as white LEDs. It is applicable and very useful in industry.

The figure which shows the emission spectrum by the excitation spectrum when the fluorescence intensity of 600 nm of the fluorescent substance which concerns on an Example and a comparative example is measured, and the external excitation light of wavelength 450nm. The photograph which shows the scanning electron microscope (SEM) image of the fluorescent substance which concerns on an Example. The photograph which shows the SEM image of the fluorescent substance which concerns on a comparative example.

Claims (7)

General formula: (Ca _X , Eu _Y ) (Si, Al) ₁₂ (O, N) ₁₆ (where 1.5 <X + Y <2.2 and 0 <Y <0.2, O / N ≦ 0. 04), which is a method for producing a phosphor mainly composed of α-sialon, wherein (a) silicon nitride, (b) aluminum nitride, (c) Ca-containing compound, and (d) Eu-containing compound. And (e) α-sialon is obtained by heat-treating the raw material mixed powder composed of α-sialon in a nitrogen atmosphere at 1650-1850 ° C., and powder having an average particle size of 15-25 μm only by classification treatment A process for producing a phosphor, characterized in that   The method for producing a phosphor according to claim 1, wherein the content of (e) α-sialon in the raw material mixed powder is 5 to 30% by mass. (E) The method for producing a phosphor according to claim 1 or 2, wherein the α-sialon has an average particle diameter of 3 to 15 µm and a specific surface area of 0.2 to ¹ m ² / g.   (E) The method for producing a phosphor according to any one of claims 1 to 3, wherein the α-sialon at least contains Ca as a solid solution. The phosphor production according to any one of claims 1 to 4, wherein the raw material mixed powder is filled in a reaction vessel so as to have a bulk density of 0.6 g / cm ³ or less, and heat treatment is performed. Method. General formula: (Ca _X , Eu _Y ) (Si, Al) ₁₂ (O, N) ₁₆ (where 1.5 <X + Y <2.2 and 0 <Y <0.2, O / N ≦ 0. And a specific surface area of 0.1 to 0.35 m ² / g.   The phosphor according to claim 6, wherein the phosphor has an emission peak wavelength in a wavelength range of 590 nm or more.