JP5388699B2 - α-type sialon phosphor and light-emitting device using the same - Google Patents

Description

The present invention relates to an α-sialon phosphor that emits blue to green light and a light-emitting device using the same.

In Patent Documents 1 and 2, the α-sialon activated with Ce ³⁺ is shifted to the short wavelength side in both the excitation band and the emission band as compared with the case of bivalent Eu ion activation, and the peak wavelength of excitation is about 400 nm. In the near-ultraviolet region, the peak wavelength of fluorescence is about 500 nm, and it is described that Ce exhibits a very broad blue-green emission characteristic of Ce. However, in this case, it is hardly excited in the blue light region and cannot be applied as a white LED phosphor using a blue LED as an excitation source.

JP 2003-203504 A JP 2004-238506 A

When the α-sialon phosphor activated with Ce ³⁺ is applied to a light emitting device such as a white LED, further improvement in light emission efficiency and longer wavelength of excitation are expected.
An object of the present invention is to use a phosphor having excellent emission efficiency and capable of being excited at a longer wavelength than that of an α-type sialon phosphor activated with Ce ³⁺ exhibiting blue to green emission. The light emitting element is provided.

The present inventor has studied paying attention to the composition of the α-sialon phosphor activated with Ce ³⁺ , and the luminous efficiency is improved by increasing the substitution amount of Al—N with respect to Si—N as compared with the prior art. At the same time, it has been found that the excitation band shifts to the long wavelength side, and the present invention has been achieved.
That is, the present invention have the general _{^{formula: (M a + x, Ce}} 3+ y) Si 12- (m + n) Al (m + n) O n N 16-n (M is Li, Ca, Mg, Y also lanthanide elements (La And at least one element selected from (except for Ce and Ce), where a is the valence of M, m = ax + 3y, Ce ³⁺ is an α-type sialon represented by M), and 1.5 ≦ x + y ≦ 2.25, 0.05 ≦ y ≦ 0.5, an α-type sialon phosphor that can be excited by ultraviolet to blue light, preferably 0 ≦ n ≦ 0.8, and M is Ca is there.

In addition, the α-sialon phosphor of the present invention is a powdery phosphor mainly composed of the α-sialon phosphor, and the α-sialon has a lattice constant a of 0.789 to 0.796 nm and a lattice constant c. Is 0.571 to 0.578 nm, and when evaluated by the powder X-ray diffraction method, the diffraction intensity of the crystal phase other than the α-type sialon does not exceed the diffraction line intensity of the (210) plane of the α-type sialon. Is 10% or less.

Furthermore, the α-sialon phosphor of the present invention has an external quantum efficiency of 20% or more when excited with light having a wavelength of 450 nm.
In addition, the present invention is a light emitting device composed of a light emitting light source and the α-sialon phosphor, and is preferably a LED having a maximum emission wavelength intensity of 240 to 480 nm.

The high m-value α-sialon phosphor activated by Ce ³⁺ of the present invention is excited not only by ultraviolet rays but also by blue light, and can efficiently emit blue-green to green visible light. Particularly, it is suitable for a white LED using a blue LED or an ultraviolet LED as a light source.

The figure which shows the excitation and the fluorescence spectrum of the fluorescent substance which concern on Example 1 and Comparative Example 1. FIG.

α-sialon has the general ^formula: represented by _{M a + x Si 12- (m} + n) Al (m + n) O n N 16-n. Here, M is at least one element selected from Li, Ca, Mg, Y or a lanthanide element (excluding La and Ce). In α-type silicon nitride composed of 4 units of unit cells, m Si—N bonds are replaced with Al—N bonds, and n Si—N bonds are replaced with Al—O bonds. . Further, for charge compensation, M ^{a +} (a is the valence of M and x = m / a) penetrates and dissolves in a large cage-like space of x α-type silicon nitride crystals.

In order to make the α-sialon exhibit fluorescence characteristics, it is necessary to use a part of M as an element that can be dissolved in a solid solution and becomes a luminescent center. Ce ³⁺ has a large ionic radius, and it is difficult to sufficiently dissolve it to stabilize the α-sialon crystal, but it can be sufficiently dissolved to exhibit the function as a luminescent center. In the α-type sialon, by making part of the M site Ce ³⁺ , a phosphor that is excited efficiently by ultraviolet rays and emits blue to green light can be obtained. Solute concentration of Ce ³⁺ have the general _{^{formula: (M a + x, Ce}} 3+ y) Si 12- (m + n) when expressed as _{Al (m + n) O n} N 16-n (m = ax + 3y), Ce 3+ solute It is preferable that y value which is a density | concentration is the range of 0.05-0.5. If the y value is less than 0.05, the contribution to light emission is small, and if it exceeds 0.5, fluorescence concentration quenching due to energy transfer between Ce ³⁺ occurs, which is not preferable.

The inventors have solid solution composition (m value, n value) of α-sialon obtained by an emission center Ce ³⁺ and focusing on the M ^{a +} to solid solution for charge compensation, the relationship between their emission characteristics intensive Evaluate and efficiently dissolve Ce ³⁺ with a specific solid solution composition to improve the light emission characteristics, and the coordinating environment in the vicinity of Ce ³⁺ changes in response to changes in the solid solution composition. Thus, the inventors have obtained the knowledge that the excitation band has a longer wavelength and that blue excitation, which was difficult with the conventional composition, is possible, and has led to the present invention.

That is, the α-sialon phosphor of the present invention preferably satisfies 1.5 ≦ x + y ≦ 2.25 in the general formula. When x + y is smaller than 1.5, the excitation efficiency with blue light is low, and a sufficiently high emission intensity cannot be obtained even with ultraviolet excitation, and α-sialon with x + y exceeding 2.25 cannot be obtained in a single phase. This is not preferred because it is accompanied by the generation of a second phase that adversely affects the fluorescence properties.

The range that the m value of α-type sialon can take depends on the n value, and the lower the n value, the wider the m value range in which the α-type sialon crystal is maintained thermodynamically. Since the α-sialon of the present invention has a higher m value than before, it is preferable to make the n value as small as possible. In the present invention, by setting the n value to 0.8 or less, the range of the m value can be expanded, and the x + y value is obtained.

According to the study of the present inventor, it is preferable to use Ca as M because α-sialon is stabilized in a wide composition range and excellent in fluorescence characteristics. However, even if a part of Ca is replaced with another element for fine adjustment of the excitation band and emission wavelength, it does not matter as long as there is no significant decrease in fluorescence characteristics.

In the present invention, from the viewpoint of fluorescence emission, it is desirable that the α-sialon crystal phase contains as much as possible high purity and is preferably composed of a single phase. Even if it is a mixture containing the crystal phase of this, as long as a characteristic is not fallen, it is good. According to the study of the present inventor, when evaluated by the powder X-ray diffraction method, the diffraction intensity of the crystal phase other than the α-type sialon is 10% of the diffraction intensity of the (210) plane of the α-type sialon. The following is preferable. The presence of a crystal phase exceeding 10% is not preferable because the light emission characteristics deteriorate.

In addition, since the phosphor of the present invention has components other than α-sialon as described above, the total composition of the phosphor does not necessarily correspond to the solid solution composition of α-sialon. In the α-type sialon crystal, the crystal lattice size increases as the solid solution amount of aluminum and oxygen increases. Therefore, as a result of studying and examining the lattice constant of the α-sialon, good light emission characteristics are obtained when the lattice constant a is in the range of 0.789 to 0.796 nm and the lattice constant c is in the range of 0.571 to 0.578 nm. I found out that

When an excitation spectrum monitored at a wavelength of 500 to 550 nm was measured with a spectrofluorophotometer for an α-sialon phosphor activated with Ce ³⁺ , two peaks were observed near 300 nm and 390 nm as shown in FIG. Is recognized. The peak near 300 nm is based on the fundamental absorption of the α-type sialon base material, and the peak near 390 nm is due to direct excitation of Ce ³⁺ . The α-sialon phosphor of the present invention having the above-described configuration has a feature that the peak on the long wavelength side in the excitation spectrum is shifted to the long wavelength side, and blue light excitation is possible. Specifically, the α-sialon phosphor of the present invention has an external quantum efficiency of 20% or more when excited with light having a wavelength of 450 nm.

Since the α-sialon phosphor of the present invention uses Ce ³⁺ as the emission center, the fluorescence spectrum is broad and its half-value width is 100 nm or more. Moreover, the fluorescence peak wavelength shifts to the long wavelength side together with the excitation wavelength. For example, the fluorescence peak wavelength when excited by near ultraviolet light having a wavelength of 400 nm is 500 to 530 nm, and when excited by blue light having a wavelength of 450 nm, it is 520 to 550 nm.

The α-sialon phosphor of the present invention is a known silicon-containing nitride such as a solid phase reaction method, a reduction nitridation method, a method of nitriding metal silicon or an alloy thereof, a gas phase reaction method, a thermal decomposition method of a silicon imide compound, or the like. It can be obtained by an oxynitride synthesis method. As an example, a method for obtaining the Ce ³⁺ activated Ca-α sialon phosphor of the present invention by a solid phase reaction method is illustrated.

As the raw material powder, nitrides and / or oxides of each constituent element (silicon, aluminum, calcium and cerium), and further compounds that become nitrides or oxides after heating are used. These are blended so as to have a predetermined α-sialon composition after the reaction.

As a method of mixing the raw materials described above, 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. However, mixing in the case of using unstable calcium nitride or cerium nitride in the atmosphere is preferably performed in a glove box in an inert atmosphere because hydrolysis and oxidation thereof affect the properties of the synthesized product.

The above raw material mixed 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 heat-treated in a nitrogen atmosphere, whereby a solid solution reaction between the raw material powders is performed. To obtain α-type sialon. The filling of the raw material mixed powder into the container is preferably as bulky as possible from the viewpoint of suppressing interparticle sintering during the solid solution reaction. Specifically, the bulk density is preferably 0.6 g / cm ³ or less when the raw material powder is filled into the container.

The heating temperature varies depending on the composition and cannot be defined unconditionally, but generally a temperature range of 1700 ° C. or more and 2000 ° C. or less is preferable. If the synthesis temperature is lower than 1700 ° C., Ce ³⁺ solid solution in the α-type sialon crystal is insufficient, and if it exceeds 2000 ° C., it is extremely difficult to suppress decomposition of the raw material and α-type sialon. Since a high nitrogen pressure is required, it is not industrially preferable.

Since the α-sialon after synthesis is in the form of a lump, it can be applied to various applications by combining the pulverization, pulverization, and, in some cases, classification operations, into a powder of a predetermined size. In order to use it as a phosphor for white LED, the average particle size is preferably 5 to 30 μm.

The α-sialon phosphor of the present invention is used in a light-emitting device composed of a light-emitting light source and a phosphor, and in particular, by irradiating ultraviolet light or visible light containing a wavelength of 240 to 480 nm as an excitation source, Fluorescence emission having a peak at a wavelength of 500 to 550 nm is shown, and white light can be easily obtained by combining an ultraviolet LED or a blue LED with a phosphor of another color. In particular, the α-sialon phosphor of the present invention exhibits a very broad light emission, so that it is easy to obtain high color rendering white light.

In addition, since the α-sialon phosphor of the present invention has little decrease in luminance at high temperature, a light-emitting device using the α-sialon phosphor has little decrease in luminance and chromaticity deviation, does not deteriorate even when exposed to high temperatures, and further has high heat resistance. Since it is excellent and has excellent long-term stability in an oxidizing atmosphere and moisture environment, the light-emitting device is characterized by high brightness and long life reflecting these.

The light-emitting device of the present invention is configured using at least one light-emitting light source and a phosphor mainly composed of the α-sialon of the present invention. For example, an LED can be manufactured using a known method described in JP-A-5-152609, JP-A-7-99345, Japanese Patent No. 2927279, and the like. In this case, the light emitting light source is preferably an ultraviolet LED or a blue LED that emits light having a wavelength of 240 to 480 nm, particularly preferably an LED that emits light having a wavelength of 390 to 460 nm. Examples of these light emitting elements include GaN and InGaN. Some are made of a nitride semiconductor, and can be a light-emitting light source that emits light of a predetermined wavelength by adjusting the composition.

In the light-emitting device, in addition to the method of using the phosphor of the present invention alone, a light-emitting device that emits a desired color can be configured by using in combination with a phosphor having other fluorescence characteristics.

Next, based on an Example and a comparative example, this invention is demonstrated still in detail.
<Example 1>
The composition of the raw material powder is 68.1% by mass of silicon nitride powder (E10 grade) manufactured by Ube Industries, 27.0% by mass of aluminum nitride powder (E grade) manufactured by Tokuyama, and cerium oxide powder manufactured by Yttrium Japan. The mixture was 4.9% by mass, and these were wet-mixed in a silicon nitride pot and balls in an ethanol solvent, and the resulting slurry was suction filtered to remove the solvent and dried to obtain a premixed powder. Next, this premixed powder was put in a glove box under a nitrogen atmosphere, and mixed with calcium nitride powder manufactured by High Purity Chemical Laboratory Co., Ltd. and a mortar to obtain a raw material mixed powder. The mixing ratio was premixed powder: calcium nitride powder = 88.4: 11.6 mass ratio. Above formulation has the general ^{_{formula: (Ca 2+ x Ce 3+ y}} ) Si 12- in _{(m + n) Al (m} + n) O n N 16-n, x = 1.51, y = 0.16, m = 3. 5, n = 0.24 (however, ignoring the impurity oxygen of the nitride raw material powder and calculating that CeO ₂ is reduced to CeO in the firing step).

The raw material mixed 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 1900 ° C. in a pressurized nitrogen atmosphere of 0.8 MPa in a carbon heater electric furnace. Then, the heat treatment was performed for 12 hours. Since calcium nitride contained in the raw material mixed powder is easily hydrolyzed in the air, the crucible filled with the raw material mixed powder is taken out of the glove box and immediately set in an electric furnace and immediately evacuated. Prevented the reaction of calcium nitride.

The composite was a green lump but could be easily crushed with a mortar or the like. Among the crushed materials, those that passed through a sieve having an opening of 150 μm were obtained as phosphor powder.
The obtained phosphor powder was subjected to powder X-ray diffraction measurement (XRD) using an X-ray diffractometer (manufactured by Rigaku Corporation, ULTIMA IV). The main component was α-sialon, and there was an unknown phase peak that was slightly unidentifiable. The maximum diffraction line intensity of the unknown phase was 1.5% with respect to the diffraction line intensity of the (210) plane of α-sialon. Next, the obtained powder X-ray diffraction pattern was subjected to Rietveld analysis by an analysis program JADE manufactured by Rigaku Corporation. As a result of obtaining the lattice constant of the α-type sialon crystal, the lattice constant a was 0.7934 nm, and the lattice constant c was It was 0.5760 nm.

Next, excitation and fluorescence spectra were measured using a spectrofluorometer (F-4500, manufactured by Hitachi High-Technologies Corporation) corrected with rhodamine B and a sub-standard light source. FIG. 1 shows the excitation / fluorescence spectrum of the phosphor of Example 1. The excitation spectrum has two peaks near the wavelength of 290 nm and around the wavelength of 390 nm, and it was found from the spectrum on the long wavelength side that sufficient excitation is possible even with blue light. The fluorescence spectrum was very broad with a half-value width of 100 nm or more, and the peak wavelength depended on the excitation wavelength, with 514 nm for 400 nm excitation and 524 nm for 450 nm excitation.

Furthermore, the light emission characteristics of the phosphor were evaluated by the following methods.
First, phosphor powder was filled into a concave cell so that the surface was smooth, and an integrating sphere was attached. Into this integrating sphere, monochromatic light separated at a predetermined wavelength from a light emitting light source (Xe lamp) was introduced using an optical fiber. Using this monochromatic light as an excitation source, the phosphor 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, near-ultraviolet light having a wavelength of 400 nm and blue light having a wavelength of 450 nm were used as monochromatic light. In the obtained fluorescence spectrum, the XYZ color system defined by JIS Z8701 is determined in accordance with JIS Z8724 from the data in the wavelength range of 410 to 780 nm and 460 to 780 nm for excitation wavelengths of 400 nm and 450 nm, respectively. Chromaticity coordinates CIEx and CIEy were calculated. The chromaticities CIEx and CIEy at the excitation wavelength of 400 nm were 0.283 and 0.509, respectively, and the chromaticity CIEx and CIEy at the excitation wavelength of 450 nm were 0.350 and 0.554, respectively.

Luminous efficiency was determined as follows. First, a standard reflector (Labsphere, Spectralon) having a reflectance of 99% is set on the sample portion, and the spectrum of the excitation light is measured. When the excitation wavelength is 400 nm, the excitation wavelength is in the wavelength range of 395 to 410 nm. Was 450 nm, the excitation light photon number (Q _ex ) was calculated from the spectrum in the wavelength range of 445 to 460 nm. Next, a phosphor was set in the sample portion, and the number of excited reflected light photons (Q _ref ) and the number of fluorescent photons (Q _em ) were calculated from the obtained spectrum data.

The number of excitation reflected light photons is in the same wavelength range as the number of excitation light photons. The number of fluorescent photons is in the wavelength range of 410 to 800 nm when the excitation wavelength is 400 nm, and 455 when the excitation light is 450 nm. Calculation was performed in the range of 800 nm. From the obtained three types of photons, external quantum efficiency (= Q _em / Q _ex × 100), absorption rate (= (Q _ex −Q _ref ) × 100), internal quantum efficiency (= Q _em / (Q _ex − Q _ref ) × 100). When excited by near-ultraviolet light with a wavelength of 400 nm, the absorptance, internal quantum efficiency, and external quantum efficiency are 84.6%, 65.8%, and 55.7%, respectively, and when excited by blue light with a wavelength of 450 nm Were 56.7%, 51.3%, and 29.1%, respectively.

上記の通り、Ｃｅ^３＋を付活したα型サイアロンの固溶組成を特定の範囲とすることにより、発光効率に優れ、青色励起でも十分蛍光発光が可能な青緑〜緑色蛍光体が得られる。
＜実施例５〜７＞
実施例１の配合組成をベースにＣａ２＋の２０ａｔ％を実施例５ではＬｉ＋に、実施例６では、Ｍｇ２＋に、実施例７では、Ｙ３＋に置換する様に原料を配合し、実施例１と同様の方法により蛍光体を作製した。ＸＲＤ測定の結果及び４５０ｎｍの光で励起した場合の外部量子効率及び色度を表４に示す。

<Examples 2-4, Comparative Examples 1-3>
Raw materials were blended so that the obtained α-sialon had the design composition shown in Table 1, and an α-sialon phosphor was synthesized based on the same technique and procedure as in Example 1. The results of XRD measurement are shown in Table 2, and the fluorescence characteristics are shown in Table 3. The excitation spectrum of Comparative Example 1 is shown in FIG.

As described above, by setting the solid solution composition of the α-sialon activated with Ce ³⁺ within a specific range, a blue-green to green phosphor excellent in luminous efficiency and capable of sufficiently emitting fluorescence even with blue excitation can be obtained.
<Examples 5-7>
Based on the blend composition of Example 1, the raw material was blended so that 20 at% of Ca 2+ was replaced with Li + in Example 5, Mg 2+ in Example 6, and Y 3+ in Example 7. A phosphor was prepared by the method described above. Table 4 shows the results of XRD measurement and the external quantum efficiency and chromaticity when excited with 450 nm light.

In particular, the phosphor of the present invention is efficiently excited by ultraviolet to blue light and emits blue-green to green visible light. Therefore, as a phosphor for a light emitting device using an ultraviolet, near ultraviolet, or blue LED as a light source, It is suitable and very useful industrially. The light-emitting device of the present invention uses an α-sialon phosphor that has excellent heat resistance and little temperature change in light-emitting characteristics, and thus is a light-emitting device that has high brightness over a long period of time and can be provided for various applications. It is useful above.

Claims (6)

^Formula: A _{^{(M a + x, Ce 3+}} y) Si 12- (m + n) Al (m + n) O n N 16-n (M is at least Ca, when the valence of M and a, m = ax + 3y, Ce ³⁺ represents an M-site substitution) α-sialon represented by 1.51 ≦ x + y ≦ 2.25, 0.05 ≦ y ≦ 0.5, 0 ≦ n ≦ 0.8, and ultraviolet to blue Α-type sialon phosphor that can be excited by light. A powdery α-sialon phosphor mainly comprising the α-sialon phosphor according to claim 1 . The α-sialon phosphor according to claim 1 or 2, wherein the α-sialon has a lattice constant a of 0.789 to 0.796 nm and a lattice constant c of 0.571 to 0.578 nm. When evaluated by a powder X-ray diffraction method, the diffraction intensity of a crystal phase other than α-sialon is 10% or less of the diffraction intensity of the (210) plane of α-sialon. The α-type sialon phosphor according to any one of claims 1 to 3 . The α-sialon phosphor according to any one of claims 1 to 4 , wherein the external quantum efficiency when excited with light having a wavelength of 450 nm is 20% or more. A light emitting device comprising the α-sialon phosphor according to any one of claims 1 to 5 and an LED having a maximum emission wavelength in the range of 240 to 480 nm as constituent elements.

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