WO2014057695A1 - 蛍光体の製造方法 - Google Patents
蛍光体の製造方法 Download PDFInfo
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- WO2014057695A1 WO2014057695A1 PCT/JP2013/054526 JP2013054526W WO2014057695A1 WO 2014057695 A1 WO2014057695 A1 WO 2014057695A1 JP 2013054526 W JP2013054526 W JP 2013054526W WO 2014057695 A1 WO2014057695 A1 WO 2014057695A1
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- C01B21/00—Nitrogen; Compounds thereof
- C01B21/082—Compounds containing nitrogen and non-metals and optionally metals
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- C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
- C01B21/0615—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with transition metals other than titanium, zirconium or hafnium
- C01B21/0627—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with transition metals other than titanium, zirconium or hafnium with one or more rare earth metals
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- C01B21/082—Compounds containing nitrogen and non-metals and optionally metals
- C01B21/0821—Oxynitrides of metals, boron or silicon
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- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
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- C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
- C09K11/7728—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing europium
- C09K11/77348—Silicon Aluminium Nitrides or Silicon Aluminium Oxynitrides
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- C01P2002/84—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by UV- or VIS- data
Definitions
- the present invention relates to a method for manufacturing a phosphor. More specifically, the present invention relates to a method for manufacturing a phosphor that has a host crystal having substantially the same crystal structure as a (Sr, Ca) AlSiN 3 crystal and absorbs light from a light emitting element such as an LED to emit red light.
- a white LED Light Emitting Diode
- a blue LED and a YAG (Yttrium Aluminum Garnet) yellow fluorescent light are used.
- Body combinations are known.
- the YAG phosphor has a small amount of red light-emitting component, there is a problem that the color reproducibility is low for lighting applications and the color reproducibility is deteriorated when used for a backlight of an image display device such as a liquid crystal display device.
- Patent Document 1 As a technique for improving the color rendering properties of a white LED, a method of supplementing a red component by using a YAG phosphor and a nitride-based phosphor that emits red has been proposed (see Patent Document 1). . Also, of the nitride-based phosphor emitting red, an inorganic compound having the same crystal structure as CaAlSiN 3 crystal phase as a host crystal, an optically active element, CaAlSiN 3 based nitrides an emission center among others Eu Alternatively, it is known that oxynitride materials emit orange or red with particularly high luminance (see Patent Document 2).
- the CaAlSiN 3 -based nitride phosphor can be manufactured using a mixture of nitrides of each element constituting the phosphor (see Patent Document 3).
- the obtained mixture is fired in a firing furnace using nitrogen gas as an atmospheric gas.
- the (Sr, Ca) AlSiN 3 -based nitride phosphor in which part of Ca in the Eu 2+ activated CaAlSiN 3 -based nitride phosphor is replaced with Sr has a shorter emission wavelength than the CaAlSiN 3 -based nitride phosphor, Since the luminous color is highly visible, it is effective as a red phosphor for high-intensity white LEDs.
- the present invention provides a method for manufacturing a phosphor that can obtain a (Sr, Ca) AlSiN 3 -based nitride phosphor with higher productivity and higher reliability than conventional materials using a nitride raw material.
- the main purpose is to obtain a (Sr, Ca) AlSiN 3 -based nitride phosphor with higher productivity and higher reliability than conventional materials using a nitride raw material.
- the inventor has found that the main crystal phase is SrN, Sr 2 N or a mixture thereof, and the nitrogen content is in a specific range. It has been found that the use of the strontium nitride contained therein makes it possible to produce a phosphor with high productivity and high reliability, and has led to the present invention.
- the phosphor manufacturing method according to the present invention is a phosphor manufacturing method in which a host crystal has a crystal structure substantially the same as a (Sr, Ca) AlSiN 3 crystal, and the raw materials are mixed. And a firing step of firing the mixture obtained by the mixing step, wherein a main crystal phase in a crystal phase analysis by a powder X-ray diffraction method is SrN, Sr 2 N or a part of the raw material A strontium nitride having a nitrogen content of 5 to 12% by mass is used.
- a classification step of setting the maximum particle size of a part of the raw material strontium nitride to 300 ⁇ m or less may be performed before the mixing step.
- strontium nitride having an oxygen content of 0.2 to 1% by mass can be used as a part of the raw material.
- strontium nitride powder As the raw material, strontium nitride powder, calcium nitride powder, silicon nitride powder, aluminum nitride powder and europium compound powder can be used.
- a heat treatment can be performed as a firing step under a temperature condition of 1500 to 1900 ° C. in a nitrogen atmosphere.
- the yield at the time of production can be improved as compared with the conventional method for producing a (Sr, Ca) AlSiN 3 -based nitride phosphor, and further, there are few heterogeneous phases and the fluorescence relative peak intensity is low.
- a phosphor with high reliability can be manufactured.
- FIG. 2 is a diagram showing an X-ray diffraction pattern of strontium nitride used in Example 1.
- FIG. 6 is a diagram showing an X-ray diffraction pattern of strontium nitride used in Example 2.
- the phosphor manufacturing method includes at least a mixing step of mixing raw materials and a baking step of baking the mixture obtained by the mixing step, and the base crystal is an (Sr, Ca) AlSiN 3 crystal.
- a phosphor having substantially the same crystal structure is manufactured.
- the main crystal phase in the crystal phase analysis by the powder X-ray diffraction method is SrN, Sr 2 N, or a mixture thereof, and strontium nitride having a nitrogen content of 5 to 12% by mass Is used.
- the (Sr, Ca) AlSiN 3 crystal phase has a structure in which the skeleton structure is a combination of (Si, Al) —N 4 tetrahedrons, and has a crystal structure in which Sr atoms and Ca atoms are located in the gaps.
- this (Sr, Ca) AlSiN 3 crystal when a part of Sr 2+ or Ca 2+ located in the gap of the skeleton structure is replaced with Eu 2+ acting as a luminescence center, a red phosphor is obtained.
- the Eu content in the raw material is 0.01 It is preferable to set it to ⁇ 0.3 atomic%.
- a more preferable range of the Eu content in the raw material is 0.04 to 0.2 atomic%, and more preferably 0.06 to 0.15 atomic%.
- the phosphor obtained by the manufacturing method of the present embodiment contains a trace amount of oxygen (O) as an inevitable component. Then, the occupation ratio of Ca and Sr elements, Si / Al ratio, and N / O ratio, etc., which are phosphor composition parameters, are adjusted so that the electrical neutrality is maintained as a whole while maintaining the crystal structure. Is done.
- strontium nitride In a JCPDS (Joint Committee on Power Diffraction Standards) card, which is a database of X-ray diffraction patterns in crystal structure analysis, Sr 2 N, SrN, SrN 2 and Sr 4 N 3 are listed as strontium nitride. Among various strontium nitrides, strontium nitride having a main crystal phase of SrN, Sr 2 N, or a mixture thereof having excellent stability is preferable.
- the crystal phase analysis of strontium nitride can be performed using an X-ray diffraction method.
- the crystal structure can be identified by comparing the X-ray diffraction pattern of strontium nitride with the aforementioned JCPDS card.
- the strontium nitride that is a part of the raw material has a nitrogen content of 5 to 12% by mass.
- the nitrogen content of strontium nitride is less than 5% by mass, the reaction heat due to nitridation of the raw material increases in the firing step described later due to insufficient nitridation of strontium.
- a large amount of agglomerated baked powder is formed, and the yield is reduced in sieving that is classified to an appropriate particle size or less after baking.
- the strontium nitride used as a part of the raw material preferably has an oxygen content of 0.2 to 1% by mass. If the oxygen content of strontium nitride is too large, the fluorescence intensity of the phosphor finally obtained tends to decrease, and it is technically difficult to obtain strontium nitride having a very low oxygen content.
- the raw materials are mixed by a technique such as a dry mixing method or a method of wet mixing in an inert solvent that does not substantially react with each component of the raw material and then removing the solvent.
- a technique such as a dry mixing method or a method of wet mixing in an inert solvent that does not substantially react with each component of the raw material and then removing the solvent.
- the mixing apparatus include a V-type mixer, a rocking mixer, a ball mill, and a vibration mill.
- the raw material in the mixing step is preferably strontium nitride powder, calcium nitride powder, silicon nitride powder, aluminum nitride powder and europium compound powder from the viewpoint of eliminating elements other than the target phosphor composition as much as possible.
- strontium nitride and calcium nitride that is unstable in the atmosphere is preferably performed in a glove box in an inert atmosphere because hydrolysis and oxidation affect phosphor characteristics.
- the ratio of the number of elements in the (Sr, Ca) AlSiN 3 nitride phosphor after firing may not match this stoichiometric composition.
- the reason why the stoichiometric composition at the time of blending does not match the stoichiometric composition after firing is due to a decrease in luminous efficiency due to crystal defect formation during firing. Therefore, it is preferable to adjust the raw material composition in anticipation of changes in the stoichiometric composition due to firing.
- the mixture (raw material mixed powder) obtained at the mixing process is accommodated in a baking container.
- the material of the firing container is preferably boron nitride which is stable even when heated at a high temperature in a nitrogen atmosphere and hardly reacts with the mixture and its reaction product.
- heat treatment is preferably performed under a temperature condition of 1500 to 1900 ° C. in a nitrogen atmosphere. This is because the unreacted residual amount increases if the firing temperature is too low, and the main phase having the same crystal structure as (Sr, Ca) AlSiN 3 decomposes if the firing temperature is too high.
- the firing time is preferably 1 to 24 hours from the viewpoints of reducing unreacted substances, suppressing insufficient grain growth, and preventing the productivity from being lowered.
- the higher the atmospheric pressure in the firing step the higher the decomposition temperature of the phosphor, but in view of industrial productivity, it is preferably less than 1 MPa.
- [Classification process] In the phosphor manufacturing method of the present embodiment, it is preferable to perform a classification step of setting the maximum particle size of a part of the raw material strontium nitride to 300 ⁇ m or less before the mixing step. This is because if the raw material contains strontium nitride having an excessively large particle size, the phosphor synthesis reaction becomes non-homogeneous during firing at a high temperature, causing variations in fluorescence intensity and the generation of heterogeneous phases.
- a method of classifying strontium nitride is preferably a method of passing through a sieve having an opening of 300 ⁇ m or less.
- the phosphor manufacturing method of the present embodiment uses strontium nitride having a main crystal phase of SrN, Sr 2 N or a mixture thereof and a nitrogen content of 5 to 12% by mass.
- the reaction heat due to can be moderately suppressed, and the formation of agglomerated massive calcined powder can be suppressed.
- a phosphor having a particle size suitable for LEDs of 5 to 30 ⁇ m can be obtained.
- This phosphor can be further adjusted in particle size by performing any one of crushing, grinding and classification.
- the crystal phase present in the phosphor is preferably a single crystal phase and less heterogeneous phase.
- the heterophase crystal is preferably 10% by mass or less.
- the mass ratio (mass%) of the different phase can be obtained from the diffraction line intensity of another crystal phase with respect to the strongest diffraction line intensity of the crystal phase when evaluated by the powder X-ray diffraction method.
- a phosphor having mass ratios of Sr 2 Si 5 N 8 and AlN, which are different phases calculated by Rietveld analysis using an X-ray diffractometer is 10% by mass or less. It is done.
- the phosphor obtained by the manufacturing method of the present embodiment can be used in a light emitting device composed of a light emission source and a phosphor. Since this phosphor has a light emission characteristic having a fluorescence peak at a wavelength of 620 to 650 nm by irradiating with ultraviolet light or visible light having a wavelength of 350 to 500 nm as an excitation source, a light emitting light source such as an ultraviolet LED or a blue LED White light can be obtained by combining with the above, or further combining with green to yellow phosphor and / or blue phosphor as necessary.
- the phosphor obtained by the manufacturing method of the present embodiment has substantially the same crystal structure as the (Sr, Ca) AlSiN 3 crystal phase having excellent stability, so that there is little decrease in luminance at high temperatures and exposure to high temperatures. However, it is not deteriorated, has excellent heat resistance, and has excellent long-term stability in an oxidizing atmosphere and a moisture environment. For this reason, the light-emitting device using this phosphor can realize a high luminance and a long life with a small decrease in luminance and color shift.
- phosphors of Examples and Comparative Examples were produced using strontium nitride having different main crystal phases or nitrogen contents, and the characteristics thereof were evaluated.
- Example 1 ⁇ Manufacture of strontium nitride> Metal strontium (Strem Chemicals Inc. 38-0074 grade, purity 99.9%) was placed on an alumina boat in a glove box where the atmosphere was replaced with nitrogen, and then the alumina boat was set in a quartz tube. Both ends were closed, and metal strontium was taken out from the glove box together with the quartz tube. After setting the quartz tube in a tubular furnace, the quartz tube was evacuated with nitrogen gas piping, quartz tube and nitrogen gas line.
- Metal strontium (Strem Chemicals Inc. 38-0074 grade, purity 99.9%) was placed on an alumina boat in a glove box where the atmosphere was replaced with nitrogen, and then the alumina boat was set in a quartz tube. Both ends were closed, and metal strontium was taken out from the glove box together with the quartz tube. After setting the quartz tube in a tubular furnace, the quartz tube was evacuated with nitrogen gas piping, quartz tube and nitrogen gas line.
- Nitrogen gas was introduced into the quartz tube, heated to 600 ° C. while flowing nitrogen, held at the temperature for 3 hours, then raised to 850 ° C., held at the temperature for 1 hour, then stopped and cooled. Both ends of the quartz tube were closed, and the strontium nitrided in the glove box was collected, and classified into those that passed through a sieve having an opening of 290 ⁇ m to obtain strontium nitride.
- ⁇ -type silicon nitride powder (SN-E10 grade manufactured by Ube Industries, Ltd., oxygen content 1.0 mass%) 52.2 mass%, aluminum nitride powder (E grade manufactured by Tokuyama Corporation), (Oxygen content 0.8 mass%) 45.8 mass% and europium oxide (RU grade made by Shin-Etsu Chemical Co., Ltd.) 2.0 mass% were employed.
- This raw material was subjected to ball mill mixing using ethanol as a solvent. For ball mill mixing, nylon pots and silicon nitride balls were used. After mixing with the ball mill, the solvent was removed by drying, and the mixture was classified only through a sieve having an opening of 75 ⁇ m to remove aggregates.
- the energization to the electric furnace was stopped and the manufactured phosphor was cooled to room temperature.
- the phosphor at room temperature was crushed by a ball mill and divided into only those that passed through a vibrating sieve having an opening of 45 ⁇ m.
- the yield at the time of classification was 98% by mass. After the classified phosphor was washed with water, fine powder was removed by further classification.
- Heterogeneous phase Sr 2 Si 5 N 8 and AlN are heterogeneous phases of the (Sr, Ca) AlSiN 3 crystal phase that is originally a phosphor to be produced, and Sr 2 by Rietveld analysis using an X-ray diffractometer. The mass ratio of Si 5 N 8 and AlN was calculated. These hetero phases are preferably 10% by mass or less.
- Fluorescence relative peak intensity was evaluated based on the relative value when the peak intensity of the phosphor of Comparative Example 1 described later was taken as 100% using the peak intensity of the fluorescence spectrum as an index.
- the fluorescence measurement was performed using a spectrofluorometer (F-7000, manufactured by Hitachi High-Technologies Corporation) corrected with rhodamine B and a sub-standard light source. For the measurement, a solid sample holder attached to the photometer was used, and a fluorescence spectrum at an excitation wavelength of 455 nm was obtained.
- the phosphor of Example 1 had a peak wavelength of the fluorescence spectrum of 630 nm and a half width of 87 nm.
- Example 2 For the phosphors of Examples 2 to 9 and Comparative Example 1 described later, the peak intensity was measured using the same sampling method and conditions as in Example 1.
- Example 2 Under the conditions for nitriding metal strontium in Example 1, heating to about 600 ° C. while flowing nitrogen, holding the temperature for about 3 hours, and then stopping the heating without going through the process of raising the temperature to 850 ° C. Produced a phosphor using strontium nitride powder obtained in the same manner as in Example 1. An X-ray diffraction pattern of strontium nitride used in Example 2 is shown in FIG. When the X-ray diffraction pattern shown in FIG. 2 was compared with a JCPDS card, it was confirmed to be the same as the Sr 2 N crystal phase.
- the phosphor of Example 2 has a lower nitrogen content of strontium nitride than that of Example 1, but the fluorescence peak intensity of the obtained phosphor was almost the same as that of Example 1, and there was little contamination with heterogeneous components.
- Example 3 The same method as in Example 1 using a mixed powder of SrN crystal phase and Sr 2 N crystal phase obtained by mixing strontium nitride used in Example 1 and strontium nitride used in Example 2 at the same mass. A phosphor was manufactured. The phosphor of Example 3 had almost the same fluorescence peak intensity as that of Example 1, and there was little mixing of heterogeneous components.
- Example 4 A phosphor was produced in the same manner as in Example 1 except that the metal strontium in Example 1 was nitrided and then classified with a sieve having an aperture of 77 ⁇ m.
- the oxygen content contained in the strontium nitride is higher than that of Example 1, but the fluorescence peak intensity is suppressed to 10% or less of that in Example 1, and the different phase component There was also little contamination.
- Example 5 A phosphor was produced in the same manner as in Example 1 except that the firing temperature in Example 1 was changed from 1800 ° C. to 1500 ° C. In the phosphor of Example 5, the oxygen content contained in the strontium nitride is higher than that of Example 1, but the fluorescence peak intensity is suppressed to 10% or less compared to Example 1, and the heterogeneous component The contamination was within 10%.
- Example 1 A phosphor was produced in the same manner as in Example 1 except that heating was performed at about 450 ° C. with nitrogen flow and the temperature was maintained for about 3 hours under the conditions of nitriding metal strontium in Example 1, and then heating was stopped and cooling was performed. .
- the nitrogen content of the strontium nitride used at that time was a low value of 3.3% by mass.
- Example 6 A phosphor was produced in the same manner as in Example 1 except that strontium metal in Example 1 was nitrided and passed through a sieve having an aperture of 630 ⁇ m. Compared with Example 1, the phosphor of Example 6 had a sieving yield after firing of 90% or more, but the proportion of the Sr 2 Si 5 N 8 phase, which is a heterogeneous component after firing, was higher than that of Example 1. It exceeded 10 mass%. This is presumably because the phosphor synthesis reaction became inhomogeneous during firing at a high temperature because the particle size of the strontium nitride powder exceeded 300 ⁇ m.
- Example 7 A phosphor was produced in the same manner as in Example 1 except that strontium metal in Example 1 was nitrided and then classified with a sieve having an opening of 45 ⁇ m. In the phosphor of this Example 7, the oxygen content contained in strontium nitride exceeds 1% by mass and the sieving yield after firing is 90% or more, but the fluorescence peak of the obtained phosphor The strength was 15% lower than that of Example 1.
- Example 8 In Example 8, the firing temperature in Example 1 was changed from 1800 ° C. to 1450 ° C., and in Example 9, the firing temperature was changed to 1950 ° C. In each of the phosphors of Examples 8 and 9, the sieve yield after firing was 90% or more. However, in the phosphor of Example 8, the fluorescence peak intensity decreased by 20% or more compared to Example 1. This is probably because the firing temperature was too low and the crystallinity was lowered.
- Example 6 to 9 the sieve yield after firing was 90% or more and the productivity was excellent.
- Example 1 and Example 6 were compared, classification was performed using a sieve having an opening of 300 ⁇ m or less.
- Example 1 using the strontium nitride thus produced was more effective than Example 6 in reducing the content of the different phase. Comparing Example 1 and Example 7, Example 1 in which the oxygen content of strontium nitride was controlled to 0.2 to 1% by mass yielded a red phosphor superior in luminous efficiency to Example 7. It was. Further, when Example 1 is compared with Examples 8 and 9, Example 1 with a firing temperature of 1500 to 1900 ° C. has a higher effect of suppressing the content of different phases than Examples 8 and 9, and the luminous efficiency is improved. An excellent red phosphor was obtained.
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Abstract
Description
本発明の蛍光体の製造方法では、混合工程の前に、原料の一部の窒化ストロンチウムの最大粒径を300μm以下にする分級工程を行ってもよい。
原料の一部として、酸素含有量が0.2~1質量%である窒化ストロンチウムを用いることができる。
前記原料には、窒化ストロンチウム粉末、窒化カルシウム粉末、窒化ケイ素粉末、窒化アルミニウム粉末及びユーロピウム化合物粉末を用いることができる。
本発明の蛍光体の製造方法は、焼成工程として、窒素雰囲気中1500~1900℃の温度条件下での加熱処理を行うことができる。
(Sr,Ca)AlSiN3結晶相は、骨格構造が(Si,Al)-N4正四面体を結合させた構成であり、その間隙にSr原子及びCa原子が位置する結晶構造を有する。この(Sr,Ca)AlSiN3結晶において、骨格構造の間隙に位置するSr2+又はCa2+の一部を、発光中心として作用するEu2+で置換すると、赤色蛍光体となる。
結晶構造解析におけるX線回折パターンのデータベースであるJCPDS(Joint Committee on Power Diffraction Standards)カードには、窒化ストロンチウムとして、Sr2N、SrN、SrN2及びSr4N3が掲載されている。各種窒化ストロンチウムの中でも安定性に優れるSrN、Sr2N又はこれらの混合体を主結晶相とする窒化ストロンチウムが好ましい。
混合工程では、乾式混合する方法、原料各成分と実質的に反応しない不活性溶媒中で湿式混合した後で溶媒を除去する方法などの手法により、原料を混合する。混合装置としては、V型混合機、ロッキングミキサー、ボールミル、振動ミルがある。
焼成工程を行う際は、混合工程で得た混合体(原料混合粉末)を、焼成容器に収納する。焼成容器の材質は、窒素雰囲気下において高温で加熱しても安定で、混合体及びその反応生成物と反応し難い窒化ホウ素が好ましい。
本実施形態の蛍光体の製造方法では、混合工程の前に、原料の一部の窒化ストロンチウムの最大粒径を300μm以下にする分級工程を行うことが好ましい。原料に、粒径があまりに大きい窒化ストロンチウムが含まれていると、高温での焼成時に蛍光体の合成反応が不均質になり、蛍光強度のばらつきや異相の生成を引き起こすためである。窒化ストロンチウムの分級の方法は、目開き300μm以下の篩を通過させる方法が好ましい。
本実施形態の蛍光体の製造方法では、製造された蛍光体に対して不純物除去を目的とした酸処理工程、結晶性向上を目的としたアニール処理工程を行うことが好ましい。
<窒化ストロンチウムの製造>
金属ストロンチウム(Strem Chemicals Inc.製38-0074グレード、純度99.9%)を、雰囲気を窒素置換したグローブボックス内でアルミナボートに載せた後、そのアルミナボートを石英管内にセットし、石英管の両端を閉じて、グローブボックスから石英管ごと金属ストロンチウムを取り出した。石英管を管状炉にセット後、石英管に窒素ガスの配管、石英管及び窒素ガスラインの真空引きを行なった。
得られた窒化ストロンチウムについて、X線回折装置(株式会社リガク製UltimaIV)を用いて、CuKα線による粉末X線回折を行った。得られたX線回折パターンを図1に示す。図1に示すX線回折パターンを、JCPDSカードと照らし合わせたところ、SrN結晶相と同一のものであることが確認された。
窒化ストロンチウムの窒素及び酸素の含有量は、酸素窒素分析装置(堀場製作所製EMGA-920)により測定した。その結果、窒素含有量は11.0質量%、酸素含有量は0.23質量%であった。
(1)混合工程
原料として、α型窒化ケイ素粉末(宇部興産株式会社製SN-E10グレード、酸素含有量1.0質量%)52.2質量%、窒化アルミニウム粉末(トクヤマ株式会社製Eグレード、酸素含有量0.8質量%)45.8質量%、酸化ユーロピウム(信越化学工業株式会社製RUグレード)2.0質量%を採用した。この原料に対し、溶媒にエタノールを使用して、ボールミル混合を行った。ボールミル混合にあっては、ナイロン製ポットと窒化ケイ素製ボールを使用した。ボールミル混合後、溶媒を乾燥除去し、目開き75μmの篩を通ったものだけに分級して、凝集物を取り除いた。
乳鉢で混合して得た混合体を、グローブボックス内で蓋付きの円筒型窒化ホウ素製容器(電気化学工業株式会社製N-1グレード)に充填し、グローブボックスから取り出し、カーボンヒーターの電気炉にセットし、電気炉内を0.1Pa以下まで十分に真空排気した。真空排気したまま、加熱を開始し、600℃で窒素ガスを導入し、炉内雰囲気圧力を0.9MPaとした。窒素ガス導入後もそのまま1800℃まで昇温し、1800℃で4時間の焼成し、蛍光体を製造した。
実施例及び比較例の各蛍光体における蛍光特性を表1に示すと共に、以下にその内容について説明する。
Sr2Si5N8及びAlNは、本来製造すべき蛍光体である(Sr,Ca)AlSiN3結晶相の異相であり、X線回折装置を用いて、リートベルト解析によるSr2Si5N8及びAlNの質量割合を算出した。これら異相は、10質量%以下であることが好ましい。
蛍光相対ピーク強度は、蛍光スペクトルのピーク強度を指標とし、後述する比較例1の蛍光体のピーク強度を100%としたときの相対値により評価した。蛍光測定は、ローダミンBと副標準光源により補正を行った分光蛍光光度計(日立ハイテクノロジーズ社製、F-7000)を用いて行った。測定には、光度計に付属の固体試料ホルダーを使用し、励起波長455nmでの蛍光スペクトルを求めた。実施例1の蛍光体は、蛍光スペクトルのピーク波長が630nmで、半値幅が87nmであった。
実施例1における金属ストロンチウムの窒化の条件において、窒素フローしながら600℃程度に加熱、3時間程度温度を保持後、850℃まで温度を上げる工程を経ずに、加熱を止め冷却し、それ以外は実施例1と同様の方法で得た窒化ストロンチウム粉末を用いて蛍光体を製造した。実施例2で用いた窒化ストロンチウムのX線回折パターンを図2に示す。図2に示すX線回折パターンを、JCPDSカードと照らし合わせたところ、Sr2N結晶相と同一のものであることが確認された。
実施例1で用いた窒化ストロンチウムと、実施例2で用いた窒化ストロンチウムを同質量で混合して得たSrN結晶相とSr2N結晶相の混合粉を使用し、実施例1と同様の方法で蛍光体を製造した。この実施例3の蛍光体は、蛍光ピーク強度は実施例1とほぼ同等であり、異相成分の混入も少なかった。
実施例1における金属ストロンチウムを窒化後、目開き77μmの篩で分級した以外は、実施例1と同様の方法で蛍光体を製造した。この実施例4の蛍光体は、窒化ストロンチウム中に含まれる酸素含有量が実施例1よりも多いが、蛍光ピーク強度は実施例1に対して10%以下の低下に抑えられており、異相成分の混入も少なかった。
実施例1における焼成温度を1800℃から1500℃に変更した以外は、実施例1と同様の方法で蛍光体を製造した。この実施例5の蛍光体は、窒化ストロンチウム中に含まれる酸素含有量が実施例1よりも多いが、蛍光ピーク強度は実施例1に対して10%以下の低下に抑えられており、異相成分の混入も10%以内であった。
実施例1における金属ストロンチウムの窒化の条件において、窒素フローしながら450℃程度に加熱、3時間程度温度を保持後、加熱を止め冷却した以外は実施例1と同様の方法で蛍光体を製造した。その際用いた窒化ストロンチウムの窒素含有量は3.3質量%と低い値であった。
実施例1における金属ストロンチウムを窒化後、目開き630μmの篩通しを行なった以外は実施例1と同様の方法で蛍光体を製造した。この実施例6の蛍光体は、実施例1と比較して、焼成後の篩通し収率は90%以上であったが、焼成後の異相成分であるSr2Si5N8相の割合が10質量%を超えていた。これは、窒化ストロンチウム粉末の粒径が300μmを超えたことにより、高温での焼成時に蛍光体の合成反応が不均質になったためと考えられる。
実施例1における金属ストロンチウムを窒化後、目開き45μmの篩で分級を行なった以外は実施例1と同様の方法蛍光体を製造した。この実施例7の蛍光体は、窒化ストロンチウム中に含まれる酸素含有量が1質量%を超えており、焼成後の篩通し収率は90%以上であるものの、得られた蛍光体の蛍光ピーク強度が実施例1に対し、15%低下した。
実施例8は実施例1における焼成温度を1800℃から1450℃に変更したものであり、実施例9は焼成温度を1950℃に変更したものである。実施例8,9の蛍光体はいずれも焼成後の篩通し収率は90%以上であった。しかし、実施例8の蛍光体は、蛍光ピーク強度が実施例1に対し20%以上低下した。これは、焼成温度が低すぎて、結晶性が低くなったためと考えられる。
Claims (5)
- 母体結晶が(Sr,Ca)AlSiN3結晶と実質的に同一の結晶構造を有する蛍光体を製造する蛍光体の製造方法であって、
原料を混合する混合工程と、
前記混合工程により得た混合体を焼成する焼成工程と、を有し、
前記原料の一部として、粉末X線回折法による結晶相解析における主結晶相がSrN、Sr2N又はこれらの混合体であり、窒素含有量が5~12質量%である窒化ストロンチウムを用いる蛍光体の製造方法。 - 混合工程の前に、原料の一部である窒化ストロンチウムの最大粒径を300μm以下にする分級工程を有する請求項1に記載の蛍光体の製造方法。
- 原料の一部である窒化ストロンチウムの酸素含有量が0.2~1質量%である請求項1又は2に記載の蛍光体の製造方法。
- 前記原料が、窒化ストロンチウム粉末、窒化カルシウム粉末、窒化ケイ素粉末、窒化アルミニウム粉末及びユーロピウム化合物粉末である請求項1~3のいずれか1項に記載の蛍光体の製造方法。
- 焼成工程が、窒素雰囲気中1500~1900℃の温度条件下での加熱処理である請求項1~4のいずれか1項に記載の蛍光体の製造方法。
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