CN100543110C - Method for preparing rare earth-doped yttrium aluminum garnet phosphor by heterogeneous precipitation of oxalic acid - Google Patents

Abstract

The invention discloses a method for preparing rare earth-doped yttrium aluminum garnet fluorescent powder by heterogeneous precipitation of oxalic acid, which relates to a fluorescent powder. Provided is a method for preparing rare earth doped yttrium aluminum garnet fluorescent powder by heterogeneous precipitation of oxalic acid. Prepare the metal ion solution and ammonium bicarbonate solution first, and then prepare the metal ion precipitate, vacuum filter or vacuum filter the suspension after the precipitation reaction is completed, wash the precipitate with deionized water, and then wash with absolute ethanol, After obtaining the white precipitate, it is dried, and the dried precipitate is mixed with a flux, and under a reducing atmosphere, the powder after the mixing is reacted in a solid state under a reducing atmosphere to obtain a YAG:Ce powder, and the first heat-treated The YAG:Ce powder is sintered in a reducing atmosphere, and the sintered powder is sequentially ground, washed with water, washed with acid, washed with alkali, washed with water, and dried to obtain the target product YAG:Ce phosphor.

Description

Method for preparing rare earth-doped yttrium aluminum garnet phosphor by heterogeneous precipitation of oxalic acid

technical field

The present invention relates to a fluorescent powder, in particular to a generalized cerium-doped yttrium aluminum garnet (YAG:Ce) prepared by oxalic acid heterogeneous precipitation method and applicable to white light-emitting diodes (light-emitting diodes, LEDs). phosphor method.

Background technique

In the 1990s, the technical breakthrough and industrialization of GaN:In chip blue LEDs greatly promoted the development of white LEDs. The white light LED based on the doped semiconductor compound GaN:In has the advantages of small solidification, shock resistance, not easy to damage, short instant start and response time (μs), energy saving, long life (10,000 hours), and no pollution. At present, the luminous efficiency of white LED has greatly exceeded that of incandescent lamps, and it is expected to reach and surpass fluorescent lamps in the future, and develop into the fourth generation of lighting sources to realize energy-saving green lighting. YAG:Ce phosphor can effectively absorb the blue light of the LED chip and excite yellow light, which can be mixed with the unabsorbed blue light to obtain white light. This "blue plus yellow" scheme to manufacture white LEDs was proposed in 1999 by "Nichia Chemical Industry Co., Ltd." (Nichia). Nichia’s white light LED patents are mainly US 5998925 and US6069440 in the United States; TW 383508 in Taiwan; ZL 02800161.3 in China, which is a light-emitting diode that uses YAG:Ce phosphor and doped semiconductor nitride wafer at the same time patent. This 'blue plus yellow' scheme is currently the mainstream of white LED manufacturing. Therefore, the progress of YAG:Ce phosphor preparation technology is of great significance to the development of white light LED.

Preparation of generalized YAG:Ce powder with complete particle shape, particle size (D ₅₀ , the same below) of 3-15 μm, narrow particle size distribution, low degree of agglomeration and high luminous intensity is one of the keys to white LED technology . At present, the following methods are commonly used to prepare YAG:Ce phosphors at home and abroad:

1. Solid phase reaction method: The solid phase reaction method is one of the methods developed earlier. This method has the advantages of simple process, high efficiency, low cost and easy batch production, and is the most commonly used method in industrial production at present. This method requires the reactants to be heat-treated at high temperature (generally about 1600°C) for a long time, and the sintered agglomerated product should be crushed by mechanical method and then sieved. The luminescent powder prepared in this way has irregular appearance and damaged surface structure. Even after long-term high-temperature heat treatment, the interdiffusion of ions between heterogeneous solid reactants may not be complete, and the chemical composition inside the product may not be uniform and accurate. All these factors will lead to the reduction of luminous efficiency. Representative literature such as:

1.Bando K.Development of high-bright and pure-white LED lamps.J.Light & Vis.Env., 1998, (1)[The author is an engineer from Nichia Chemical Industry Co., Ltd. A method for preparing generalized YAG:Ce phosphor by reaction method. Quoted from: Translated by Yang Xiaowei. Development of high-brightness, pure white LED lamps. China Lighting Appliances, 2000, (1): 27-29].

2. The Chinese invention patent with the patent number ZL 02800161.3 (the patentee is Nichia Chemical Industry Co., Ltd., and the patent describes the method of preparing generalized YAG:Ce phosphor by solid-state reaction method).

3. The Chinese invention patent application with the publication number CN1880402A (the applicant is Xiamen Tongshida Lighting Co., Ltd., and the inventors are Wei Lan and Han Junxiang. This application discloses the method for preparing YAG:Ce phosphor by solid-state reaction method, and mentions the use of yttrium , Cerium and other oxalates as raw materials).

2. Sol-gel method: Sol-gel (sol-gel) method is a new technique for preparing inorganic materials developed in the 1960s, and it is a soft chemical synthesis method with broad application prospects. The sol-gel method is divided into two categories: the "aqueous solution sol-gel method" in which the raw material is an inorganic salt and the "alkoxide sol-gel method" in which the raw material is a metal alkoxide; the latter is usually called the "sol-gel method". The basic principle is: the inorganic salt or metal alkoxide is dissolved in the solvent (water or organic solvent) to form a homogeneous solution; the solute and the solvent undergo hydrolysis or alcoholysis reaction, and the reaction product aggregates into particles of about 1nm and forms a sol; the sol is used Evaporation, drying and other methods to transform into a gel; the gel is then dried and calcined to obtain the final product. In the sol-gel method in which the raw material is an aqueous solution of inorganic salt, organic reagents such as citric acid need to be added as a chelating agent for metal ions to form a sol and then a gel, so this method is also called "citric acid sol-gel method". . The alkoxide sol-gel method uses metal alkoxides as raw materials, such as solutions of yttrium methoxyethoxide and aluminum isobutoxide, and forms a gel through mixing, hydrolysis, polycondensation and other reactions. However, the yield of the sol-gel method is low, the powder is easy to agglomerate, and the cost of organic raw materials used is high; organic matter decomposes in a non-oxidizing atmosphere to form simple carbon, and the carbon remaining in the powder will be lost even after high temperature treatment at 1600 °C in the later stage. It cannot be removed, and will greatly affect the body color and luminance of the phosphor. Related documents are:

1. Veith M, Mathur S, Kareiva A, et al. Low temperature synthesis of nanocrystalline Y ₃ Al ₅ O ₁₂ (YAG) and Ce-doped Y ₃ Al ₅ O ₁₂ via different sol-gel methods. J. Mater. Chem. 1999, 12(9): 3069-3079.

2. The Chinese invention patent with the patent number ZL 02136705.1 [the patentees are Zhang Junji, Ning Jinwei, Liu Xuejian, etc., Shanghai Institute of Silicate, Chinese Academy of Sciences. This patent discloses that YAG nanopowder (including fluorescent powder) with general formula Y _3-x Me _x Al ₅ O ₁₂ or Y ₃ Al _5-x Me _x O ₁₂ has been prepared by sol-gel method, wherein Me is a rare earth element Or one or two transition metal elements, 0.01≤x≤0.30. This patent uses metal nitrates and oxides as raw materials, citric acid as gelling agent and fuel, and obtains precursors through sol-gel method and combustion of citric acid, and then heat treatment can obtain doped or undoped YAG nano powder].

3. Precipitation method: Precipitation method is divided into homogeneous precipitation method and heterogeneous precipitation method; the former is usually called co-precipitation method. The non-oxalic acid precipitation method will be described first, and then the oxalic acid precipitation method closely related to the generalized YAG:Ce phosphor will be discussed in detail.

Relevant literature on preparation of generalized YAG:Ce phosphors by precipitation method

(1) Homogeneous precipitation method and non-oxalic acid homogeneous precipitation method: The homogeneous precipitation method uses water-soluble substances as raw materials to form insoluble substances and precipitate them from aqueous solutions through liquid-phase chemical reactions. Add an appropriate precipitant to the mixed metal salt solution (this is called forward precipitation, but reverse precipitation can also be used), and the reaction will form a uniform precipitate. After filtration, washing, drying, and high-temperature heat treatment, the product is obtained. The precipitant is one or a mixture of oxalic acid, ammonium bicarbonate, ammonia water, urea, triethylamine, etc. Compared with the solid-state reaction, this method can produce phosphors with high purity and excellent chemical uniformity at a lower temperature; and the particle size of phosphors can be adjusted by controlling the concentration of reactants, reaction temperature, time, etc.

The non-oxalic acid homogeneous precipitation method is a common method for preparing YAG:Ce powder, but the specific preparation process is different. One of the main differences is the different selection of precipitating agent. The relevant references are as follows:

1. Chiang CC, Tsai MS, Hsiao CS, et al.Synthesis of YAG: Ce phosphor via different aluminum sources and precipitation processes.J.Alloys Compd., 2006, 416(1～2): 265～269 (the article reported Ammonium bicarbonate was used as a precipitating agent to synthesize YAG:Ce phosphor by homogeneous precipitation method).

2. Pan YX, Wu MM, Su Q. Comparative investigation on synthesis and photoluminescence of YAG: Ce phosphor. Mater. Sci. Eng., B, 2004, 106(3): 251～256 (the author of this article is Su Qiang et al. , reported the use of urea as a precipitating agent, using a homogeneous precipitation method to synthesize YAG: Ce phosphor).

3. Miao Chunyan, Li Dongping, Liu Lifang, etc. Synthesis and spectral properties of YAG: Ce ³⁺ . Spectrum Laboratory, 2004, 21(3): 563～565 (the author of this article is an engineer of "Dalian Luming", and reported that the mixed metal ion solution, ammonium bicarbonate and ammonia water mixed solution were dropped into the same reaction vessel at the same time , to synthesize YAG:Ce phosphor).

4. The Chinese invention patent with the patent number ZL 200510071958.0 (the patentee is "Xiamen Kemingda" Wang Jingao. This patent discloses the preparation of YAG:Ce phosphor by homogeneous precipitation method (ammonia water is used as precipitation agent) and citric acid sol-gel method Methods).

(2) Preparation of YAG:Ce phosphor by oxalic acid homogeneous precipitation method

There are many literatures mentioning that oxalic acid can be used as a precipitating agent in the homogeneous precipitation method, some of which are related to the preparation of YAG:Ce phosphor. The relevant references are as follows:

1. The U.S. patent application whose publication number is US Patent 20060145124 (this application was published on July 6, 2006 and is not authorized), uses a homogeneous precipitation method to synthesize YAG:Ce phosphor, and the precipitating agent is ammonium carbonate, and the precipitating agent is mentioned One or more of oxalic acid, ammonia water, and ammonium carbonate can be used; however, details of the oxalic acid precipitation method are not provided.

2. The U.S. Patent No. US 6869544 mentions that triethylamine and oxalic acid can be used as a precipitating agent, and YAG:Ce phosphor is synthesized by a homogeneous precipitation method; but the examples only mention triethylamine as a precipitating agent.

3. The Chinese invention patent with the patent number ZL 02130949.3 (patentees are Beijing General Research Institute of Nonferrous Metals and Youyan Rare Earth New Materials Co., Ltd., authorized on May 30, 2007). This patent reports the preparation of generalized YAG:Ce phosphors by homogeneous precipitation method, and compares the emission peak position and relative luminance of the powder sample prepared by the oxalic acid homogeneous precipitation method and the applicant's solid state reaction method.

(3) Preparation of phosphors related to YAG:Ce by oxalic acid homogeneous precipitation method. The relevant references are as follows:

1. Chen TM, Chen SC, Yu CJ. Preparation and characterization of garnet phosphoranoparticles derived from oxalate coprecipitation. J. Solid State Chem., 1999, 144: 437-441, this article describes the synthesis of YAG:Tb by oxalic acid homogeneous precipitation Phosphor powder method; use triethylamine to adjust the pH value without using flux.

2. Li Xiaoyun, Lu Tianchang, Liang Shuang. Preparation and optical properties of strontium aluminate long-lasting luminescent powder. Journal of Nanjing University of Chemical Technology (Natural Science Edition). 2001, 21(3): 563-565. This article describes the process of adding oxalic acid and ammonia water at the same time to obtain SrC ₂ O ₄ , Al(OH) ₃ and Eu(OH) ₃ Homogeneous precipitation, SrAl ₂ O ₄ :Eu phosphor is obtained after calcination.

(4) Heterogeneous precipitation method and non-oxalic acid heterogeneous precipitation method: Generally, the heterogeneous precipitation method is often applied to particle coating, and the powder to be coated is usually prepared into a suspension by controlling the pH value and temperature solution; prepare the coating material into its cationic solution; mix the suspension with the cationic solution; add a precipitant to coat the cationic powder on the powder surface in the form of precipitation; after heat treatment, a dense coating film is formed on the powder surface.

Regarding the precipitation method, except for the documents related to oxalic acid, homogeneous precipitation method or co-precipitation method, only the following 4 documents have similarities with the patent of this application, and 2 of them are for the preparation of YAG:Ce powder. The relevant references are as follows:

1. Wang Hongzhi, Gao Lian, Li Weiqun. Preparation of Al ₂ O ₃ -YAG composite ceramics by heterogeneous precipitation method. Journal of Inorganic Materials, 2000, 15(1): 169-173, this article expounds that AlCl ₃ 6H ₂ O is used as aluminum source, in YAG suspension, ammonia water is used as precipitant, aluminum is precipitated on YAG powder , to prepare Al ₂ O ₃ coated YAG composite powder, and then prepare composite ceramics. Compared with the general heterogeneous precipitation method, the present invention is that the coated material is not a finished powder, but a nascent precipitation in a solution.

2. Shi Shikao, Liu Xingren. Soft chemical synthesis of luminescent YAG. Chemical Bulletin. 1998, 4:39-40. The article explains that the aluminum hydroxide precipitate is first prepared; urea is added to the yttrium sulfate solution, and then the aluminum hydroxide precipitate is added. As the pH value increases, the yttrium hydroxide precipitate is formed and mixed with the aluminum hydroxide precipitate; after centrifugation , washed, filtered, and dried to generate precursor powder; YAG powder was obtained after heat treatment. The present invention has the following differences from this patent: (1) the present invention is to prepare YAG:Ce phosphor, and this patent is to prepare undoped YAG powder. (2) The present invention dissolves yttrium oxide into yttrium nitrate and directly uses aluminum nitrate or aluminum chloride. This patent dissolves the oxide into sulfate, and after the sulfate radical is thermally decomposed, there will be residual sulfur element to replace oxygen in YAG Location. (3) The present invention has used two kinds of precipitation agents of oxalic acid and ammonium bicarbonate successively, and this patent is with urea as precipitation agent. (4) The present invention uses oxalic acid to precipitate oxalates of rare earths such as yttrium and cerium in the same solution, and then uses the oxalate precipitation as a crystal nucleus to precipitate aluminum with ammonium bicarbonate. In this patent, aluminum hydroxide is added to the mixed solution of yttrium sulfate and urea, and the aluminum hydroxide acts as a crystal nucleus; this method will cause larger particles caused by the aluminum hydroxide added first, and smaller particles added later, which is not conducive to the formation of Powder precursor with uniform particle size.

3. Yuan FL, Ryu HJ. Ce-doped YAG phosphor powders prepared by co-precipitation and heterogeneous precipitation. J. Mater. Sci. Eng., B, 2004, 104(1): 14～18. Preparation of YAG:Ce phosphor by ammonium bicarbonate heterogeneous precipitation method: first slowly drop the aluminum nitrate solution into the ammonium bicarbonate solution, and after aging for 30 minutes, slowly drop the mixed solution of yttrium nitrate and cerium nitrate into the ammonium bicarbonate In solution, after aging, a precipitate was obtained. The present invention has following difference with this method: (1) the present invention uses two kinds of precipitation agents of oxalic acid and ammonium bicarbonate, and the ammonium bicarbonate that this method only uses a kind of. (2) The solubility product of the yttrium oxalate used in the present invention and cerium oxalate is closer; But the solubility product of these two numerical values and aluminum oxalate differs greatly; And aluminum oxalate exists unstable in aqueous solution. This makes yttrium and cerium precipitate out of the solution before aluminum, and then the aluminum salt is deposited on the outside of the yttrium and cerium salt precipitation with ammonium bicarbonate to form a coating structure. Therefore, the present invention realizes the sequential precipitation of yttrium, cerium and aluminum by controlling the order of adding anions; and this method utilizes the difference in the order of adding metal ions to form a coating structure. (3) The present invention uses the method of forward titration; this article uses the method of reverse titration.

4. Matsubara I, Paranthaman M, Allison SW, Cates MR, Beshears DL, Holcomb DE. Preparation of Cr-doped Y ₃ Al ₅ O ₁₂ phosphors by heterogeneous precipitation methods and their luminescent properties. J. Mater. Res. Bull., 2000 , 35(2): 217-224. This article describes the preparation of Cr-doped YAG by heterogeneous precipitation method, and the precipitating agent is urea. First mix the aluminum sulfate solution and urea, heat and stir to form a precipitate, centrifuge, wash with water, wash with isopropanol, and dry; prepare the precipitate into aluminum hydroxide suspension, add urea; prepare yttrium sulfate and chromium sulfate into a solution ; While stirring and heating the aluminum hydroxide suspension, add a mixed solution of yttrium sulfate and chromium sulfate; after precipitation, wash with water and isopropanol. The present invention differs from this method in that: (1) the precipitation agent is different. The present invention uses oxalic acid and two kinds of precipitation agents of ammonium bicarbonate successively, and what this method used is urea. (2) The order of precipitation is different from that of the precipitate. In the present invention, after the precipitation of yttrium oxalate and cerium oxalate is generated, ammonium bicarbonate is used to precipitate aluminum ions to form a structure of aluminum coating yttrium and cerium; and the method is to form aluminum hydroxide precipitation first, and then use aluminum hydroxide as a nucleating agent , yttrium and chromium ions were precipitated with urea to form a structure of yttrium and cerium-coated aluminum. (3) The prepared products are different. The present invention is to prepare YAG:Ce fluorescent powder, Ce is in the position of Y, is the active center, and emits yellow light; and what is prepared by this method is YAG:Cr, and Cr is in the position of Al, and emits red light. (4) Since the method is dried after generating aluminum hydroxide, agglomeration has occurred when aluminum hydroxide is used as the seed crystal, and the secondary particle size of the particles is relatively large, which makes the powder particles after coating become larger, and the entire precursor The bulk powder has larger particles, which is not conducive to obtaining finer powder, and will increase the diffusion distance of metal ions, making the formation of YAG phase more difficult.

(5) Oxalic acid heterogeneous precipitation method: Literature search found that in the process of preparing fluorescent powder by precipitation method, the method using oxalic acid as precipitant is generally homogeneous precipitation method; only the world intellectual property rights of international publication number WO/04/079790 The patent is a heterogeneous precipitation method using oxalic acid and ammonia water. For YAG:Ce powder, the generalized oxalic acid heterogeneous precipitation method can also include that yttrium and cerium are first precipitated by oxalic acid homogeneous precipitation method, and then mixed with solid aluminum oxide or hydroxide to form A macroscopically heterogeneous phase was obtained, and YAG:Ce powder was obtained after high temperature treatment. The relevant references are as follows:

1. Publication number is US Patent 20040173807 U.S. patent application (publication number is the world intellectual property patent application of WO/04/079790), has reported in yttrium, aluminum, in the mixed solution of cerium multiion, first adds oxalic acid, makes yttrium and cerium precipitation; after aging, add ammonia water to precipitate aluminum ions; after standing still, pour off the supernatant, centrifuge, and wash with acetone; finally heat treatment. The present invention has following difference with this patent application: (1) the present invention is to use two kinds of precipitation agents of oxalic acid and ammonium bicarbonate, and this patent application is to use oxalic acid and ammoniacal liquor. (2) Ammonium bicarbonate is used to precipitate aluminum ions to form AlOOH or NH ₄ Al(OH) ₂ CO ₃ precipitation, and the latter can be generated as much as possible by controlling the pH value; aluminum ions precipitated by ammonia water, the resulting precipitate is AlOOH. The latter method is more likely to agglomerate the precipitate than the former method, which will affect the performance of the powder. (3) The temperature for preparing the precursor is different. The present invention uses 30～60 ℃, and this patent application uses 75 ℃. (4) The present invention adopts the methods of suction filtration, water washing, and alcohol washing to obtain the precursor; the patent obtains the precursor by standing, removing the supernatant, centrifuging, and washing with acetone; the method of the present invention is relatively simple and practical; the above The method of pouring out the supernatant liquid in the patent application, although it is a common process for producing phosphors by precipitation in industry, has its own advantages; but it is likely to cause some finer precursor powders to be lost. (5) The present invention adopts a staged heat treatment method, first at 900-1200°C, and then at 1300-1600°C for two-stage heat treatment; this patent application adopts a one-stage heat treatment at 1350-1450°C; the two-stage formula has It is beneficial to fully complete the solid-state reaction and sintering and obtain high relative brightness of the phosphor; (6) The present invention has specific experimental parameters, and this application only describes a method.

2. U.S. Patent No. US 4034257. This patent reports adding oxalic acid to the nitric acid aqueous solution of yttrium and cerium to obtain oxalate precipitation, and the oxide obtained after calcining is mixed with alumina and ammonium chloride, and then undergoes solid-state reaction and sintering to prepare YAG: Ce phosphor.

3. U.S. Patent No. US 6409938. The patent reports that yttrium and cerium are precipitated with oxalic acid to form a mixed oxalate precipitation of yttrium and cerium; then mixed with alumina and aluminum fluoride, and subjected to high temperature treatment to obtain YAG:Ce phosphor.

4. The Chinese invention patent with the patent number ZL 98124953.1. In the eighth embodiment of this patent, the oxalate of Y ³⁺ and Ce ³⁺ was obtained by homogeneous precipitation method, and the precipitate was mixed with alumina powder, and YAG:Ce phosphor was obtained by high temperature treatment.

Contents of the invention

The object of the present invention is to provide a method for preparing rare earth-doped yttrium aluminum garnet fluorescent powder by heterogeneous precipitation of oxalic acid, in order to obtain a low degree of agglomeration, a particle size of 3-15 μm, a narrow particle size distribution, and no need for ball milling or air flow. It is a rare earth-doped yttrium aluminum garnet phosphor that can be used after crushing, has no damage to the crystal lattice and surface morphology, and has relatively high luminous brightness.

The technical solution of the present invention is to improve the method for preparing generalized YAG:Ce fluorescent powder by heterogeneous precipitation method, adding oxalic acid and ammonium bicarbonate precipitant in sequence, and then performing high-temperature heat treatment.

The chemical formula of the rare earth-doped yttrium aluminum garnet fluorescent powder according to the present invention is Y _3-xyz R _y Al _5-m Ga _m O ₁₂ : _Cex , R′ _z , wherein 0.01≤x≤0.12, 0≤y≤ 1.20, 0≤z≤0.04, 0≤m≤2.00; R is one of the rare earth elements Gd and Sm, R' is one of the rare earth elements of Pr and Dy, and the rare earth doped yttrium aluminum garnet phosphor is also called It is a generalized YAG:Ce phosphor.

The method for preparing rare earth-doped yttrium aluminum garnet fluorescent powder by heterogeneous precipitation of oxalic acid according to the present invention comprises the following steps:

1) Preparation of metal ion mixed solution: Weigh raw material powders of yttrium oxide, gadolinium oxide or samarium oxide, praseodymium oxide or dysprosium oxide with a purity of 4N or more according to the stoichiometric ratio and add them to water to prepare a suspension, and add a little excess concentrated After heating and dissolving nitric acid, add Al(NO ₃ ) ₃ ·9H ₂ O or AlCl ₃ ·6H ₂ O and Ce(NO ₃ ) ₃ ·6H ₂ O according to the stoichiometric ratio to prepare a mixed solution of metal ions.

2) Preparation of ammonium bicarbonate solution: oxalic acid was weighed and dissolved in deionized water to prepare an oxalic acid solution, and ammonium bicarbonate was weighed and dissolved in deionized water to prepare an ammonium bicarbonate solution.

3) Preparation of metal ion precipitate: under the condition of water bath temperature 30-60°C, successively add oxalic acid solution and ammonium bicarbonate solution to metal ion mixed solution, and the speed of adding oxalic acid solution and ammonium bicarbonate solution to metal ion mixed solution is uniform. The pH value of the solution is 1-8mL·min ^-1 , and the pH value of the solution after the precipitation reaction is completed is 8.0-9.0; standing and aging.

4) Suction filtration, washing and dehydration: vacuum suction filtration or vacuum suction filtration of the suspension after the precipitation reaction is completed, wash the precipitate with deionized water, and then with absolute ethanol to obtain a white precipitate and dry it.

5) Adding a fluxing agent: the dried precipitate is mixed with a fluxing agent, and the amount of the fluxing agent is 0.5%-3.0% of the mass of the target product YAG:Ce.

6) The first heat treatment: under a reducing atmosphere, the mixed and ground powder is subjected to a solid state reaction at 900-1200° C. for 1-6 hours under a reducing atmosphere to obtain YAG:Ce powder.

7) The second heat treatment: sinter the YAG:Ce powder that has undergone the first heat treatment at 1300-1600° C. for 1-8 hours in a reducing atmosphere.

8) Powder washing: the sintered powder is sequentially ground, washed with water, pickled with acid, washed with alkali, washed with water, and dried to obtain the target product YAG:Ce phosphor. The target product YAG:Ce phosphor after sintering and powder washing has the characteristics of low degree of agglomeration, particle size of 3-15 μm, narrow particle size distribution and high luminous intensity without mechanical ball milling.

It is best to add a powder washing step between the first heat treatment and the second heat treatment step. The powder washing step is the same as step 8, that is, the powder after the solid phase reaction is ground, washed with water, pickled, alkali washed, washed with water, and dried in sequence. , which is beneficial to further improve the degree of dispersion of the powder.

In step 1), the total concentration of the metal ion mixed solution is preferably 0.2-0.8 mol·L ^-1 .

In step 2), the optimal concentration of the oxalic acid solution is 0.2-1.5 mol·L ^-1 . The optimal amount of oxalic acid is 1.5 to 5 times the total amount of yttrium and cerium (ie the total molar amount). The optimal concentration of the ammonium bicarbonate solution is 0.2-1.5 mol·L ^-1 . The optimal amount of ammonium bicarbonate is 4 to 6 times the total amount of yttrium, cerium and aluminum.

In step 3), the addition rate of the oxalic acid solution and the ammonium bicarbonate solution is 1-8 mL·min ^-1 , and the temperature of the water bath is 30-60°C. After the addition is complete, continue to stir for 1 to 2 hours until the reaction is complete, and the best aging time is 2 to 12 hours.

In step 4), wash at least 3 times with deionized water and at least 2 times with absolute ethanol. The drying refers to drying at 50-120° C. for 5-20 hours; or vacuum drying, the optimum temperature of vacuum drying is 150° C., and the optimum drying time is 4-8 hours; or freeze-drying is adopted.

In step 5), the fluxing agent is selected from at least one of ammonium fluoride, sodium fluoride, barium fluoride, aluminum fluoride, yttrium fluoride, cerium fluoride, boric acid and cerium chloride.

In step 6), carbon reduction is selected as the reducing atmosphere; or N ₂ —H ₂ mixed gas, N ₂ :H ₂ (volume ratio) is 90-97:10-3; or directly use N ₂ produced by ammonia decomposition furnace —H ₂ mixed gas.

In step 7), _the N ₂ —H ₂ mixed gas is selected as the reducing atmosphere _, and the N ₂ :H ₂ (volume ratio) is 90-97:10-3; gas.

The preparation of YAG:Ce by oxalic acid heterogeneous precipitation method has the following advantages: (1) cerium and yttrium are precipitated together, the two are mixed more uniformly, the diffusion distance of cerium is shortened, cerium is more likely to occupy the position of yttrium, and the doping process is easy to complete , forming a displacement solid solution. For the preparation of YAG:Ce by the homogeneous precipitation method, due to the uniform mixing of yttrium, aluminum and cerium, the presence of a large amount of aluminum will interfere with the diffusion of cerium to the position of yttrium in the lattice, and it is more difficult to form a replacement solid solution than the heterogeneous precipitation method. For the solid phase reaction method, cerium and yttrium are mixed very unevenly, the distance of cerium diffusion is very long, and the doping and solid solution process is difficult to complete; resulting in high heat treatment temperature, long time, serious agglomeration of the solid state reaction method, and the obtained powder undergoes After ball milling, the crystal phase and surface morphology were severely damaged, and the luminescence performance decreased. (2) Haneda et al pointed out [Jimenez-Melendo M, Haneda H, Nozawa H. Ytterbium cation diffusion inyttrium aluminum garnet (YAG)—implications for creep mechanisms. J.Am.Ceram.Soc., 2001, 84(10): 2356 ~2360], although there is no specific data on the interdiffusion coefficient of aluminum and yttrium, but since the volume and mass of aluminum atoms are smaller than that of yttrium, the partial diffusion coefficient of aluminum should be much larger than that of yttrium, and the diffusion of yttrium into the lattice of aluminum It is the controlling step for the reaction kinetics of preparing YAG. The heterogeneous precipitation method used in the present invention results in a powder coating structure: its spherical core contains yttrium (and cerium), and its coating layer contains aluminum. At high temperature, aluminum must diffuse to the yttrium-containing spherical core. As a result of solid-state reaction, it is easy to maintain the original yttrium-containing spherical structure, making the obtained powder particles closer to spherical. The method of making spherical powder reaction products by using the difference in diffusion coefficient has been confirmed by the preparation process of SiC and other powders (Shi Limin, Zhao Hongsheng, Yan Yinghui, etc. Preparation of spherical submicron silicon carbide powder. Silicic acid Acta Salt Sinica, 2006, 34(11): 1397～1401). (3) The applicant of the present invention finds in experiment, the present invention adopts the YAG: Ce precipitate prepared by oxalic acid and ammonium bicarbonate heterogeneous precipitation method, than only with ammonium bicarbonate, or only with urea, or with ammoniacal liquor and The precipitate obtained by the homogeneous precipitation method of ammonium (bicarbonate) is easier to filter and wash, and the dried precursor is also fluffy and easy to grind. This may be due to the more reasonable precipitant used in the present invention. (4) When the powder precursor precipitates are close together, the surface layers of the powder are in contact. Since the powder is a coated structure, the outer surface layer is the same material, they will not form a eutectic during heat treatment, reducing the possibility of agglomeration. Therefore, the powder prepared by this method is obviously less agglomerated than ordinary sol-gel. The applicant of the present invention has observed that the powder prepared by this method is also significantly less agglomerated than the homogeneous precipitation method.

Detailed ways

Example 1

The phosphor powder in this embodiment is Y _2.96 Al ₅ O ₁₂ :Ce _0.04 . Weigh 3.342g of Y ₂ O ₃ into water, add 6.5mL of nitric acid into the Y ₂ O ₃ suspension, heat to dissolve, add 12.072g of AlCl ₃ 6H ₂ O and 0.174g of Ce(NO ₃ ) ₃ 6H ₂ O to make a solution with a total concentration of metal ions of 0.4mol L ^-1 ; weigh 6.304g of oxalic acid and dissolve it in 200mL of deionized water to make an oxalic acid solution; weigh 23.718g of ammonium bicarbonate and dissolve it in 300mL of deionized Ionized water was prepared into ammonium bicarbonate solution; under the condition of constant stirring of the metal salt mixed solution, oxalic acid solution was added to the metal salt mixed solution at a rate of 6 mL·min ^-1 , aged for 1 h, and the temperature of the water bath was kept at 40°C; Under the condition of constant stirring of the solution, add the ammonium bicarbonate solution into the mixed solution at a rate of 6mL·min ^-1 , continue to stir for 2h, age for 2h, and keep the temperature of the water bath at 40°C; Wash with deionized water and absolute ethanol; transfer to an oven for drying at 60°C for 12 hours; grind, add 2.0% of the mass of the target product with sodium fluoride as a flux for mixing and grinding. The precursor is solid-state reacted at 1200°C for 2 hours in a carbon-reducing atmosphere, and then sintered at 1550°C for 4 hours in a mixed gas of N ₂ —H ₂ (volume ratio 96:4), washed with water, acid, alkali, and water. The YAG:Ce fluorescent powder with good luminous performance, particle size of 3-15 μm and narrow particle size distribution is obtained.

Example 2

Compared with embodiment 1, the difference of this embodiment is:

1) The phosphor powder in this example is Y _2.94 Al ₅ O ₁₂ :Ce _0.06 , and the raw materials are 3.319g Y ₂ O ₃ , 18.757g Al(NO ₃ ) ₃ 9H ₂ O and 0.261g Ce(NO ₃ ) ₃ 9H ₂ O;

2) The temperature of the water bath is 60°C;

3) The first heat treatment is solid state reaction at 900°C for 6 hours;

4) The second heat treatment is sintering at 1600°C for 1h.

Example 3

Compared with embodiment 1, the difference of this embodiment is:

1) a solution in which the total concentration of metal ions in the solution is 0.2mol L ⁻¹ ;

2) The temperature of the water bath is 30°C;

3) The adding speed of the oxalic acid solution and the ammonium bicarbonate solution is both 1mL·min ⁻¹ ;

4) Flux accounts for 0.5% of the target product mass, wherein sodium fluoride and boric acid each account for 0.25%.

Example 4

Compared with embodiment 1, the difference of this embodiment is:

1) The phosphor powder in this example is Y _2.92 Al ₅ O ₁₂ :Ce _0.08 , and the raw materials are 3.297g Y ₂ O ₃ , 18.757g Al(NO ₃ ) ₃ 9H ₂ O and 0.348g Ce(NO ₃ ) ₃ . 9H ₂ O;

2) The total concentration of metal ions in the solution is 0.3 mol·L ⁻¹ ;

3) The flux is 1.0% of the target product mass, wherein ammonium fluoride and boric acid each account for 0.5%;

4) N ₂ —H ₂ (volume ratio 90:10) mixed gas for the first heat treatment;

5) The first heat treatment is solid phase reaction at 1000°C for 5 hours;

6) N ₂ —H ₂ mixed gas decomposed directly with ammonia for the second heat treatment;

7) The second heat treatment is sintering at 1500°C for 2 hours.

Example 5

Compared with embodiment 1, the difference of this embodiment is:

1) The phosphor powder in this example is Y _1.90 Gd _1.00 Al ₅ O ₁₂ :Ce _0.10 , and the raw materials are 2.145g Y ₂ O ₃ , 1.813g Gd ₂ O ₃ , 18.757g Al(NO ₃ ) ₃ ·9H ₂ O and 0.435g Ce(NO ₃ ) ₃ 9H ₂ O;

2) The aging time after adding oxalic acid for precipitation is 1.5h;

3) The flux accounts for 3% of the target product mass, wherein sodium fluoride and boric acid each account for 1.5%;

4) N ₂ —H ₂ (volume ratio 97:3) mixed gas for the first heat treatment;

5) The first heat treatment is solid phase reaction at 1100°C for 4 hours;

6) N ₂ —H ₂ (volume ratio 95:5) mixed gas for the second heat treatment;

7) The second heat treatment is sintering at 1450°C for 3h.

Example 6

Compared with embodiment 1, the difference of this embodiment is:

1) The phosphor powder in this example is Y _2.92 Al ₅ O ₁₂ : Ce _0.06 Pr _0.02 , the raw materials are 3.297g Y ₂ O ₃ , 18.757g Al(NO ₃ ) ₃ 9H ₂ O, 0.087g Pr(NO ₃ ) ₃ 6H ₂ O and 0.261 g Ce(NO ₃ ) ₃ 6H ₂ O;

2) The temperature of the water bath is 50°C;

3) The temperature of the first heat treatment is 1150°C for solid phase reaction for 3 hours;

4) The second heat treatment is sintering at 1450°C for 3h.

Example 7

Compared with embodiment 1, the difference of this embodiment is:

1) The phosphor powder in this example is Y _2.94 Al ₄ GaO ₁₂ :Ce _0.06 , the raw materials are 3.319g Y ₂ O ₃ , 15.006g Al(NO ₃ ) ₃ 9H ₂ O, 4.179g Ga(NO ₃ ) ₃ 9H ₂ O and 0.261 g Ce(NO ₃ ) ₃ 6H ₂ O;

2) N ₂ —H ₂ mixed gas directly decomposed by ammonia for the first heat treatment;

3) The first heat treatment is solid state reaction at 950°C for 5 hours;

4) N ₂ —H ₂ mixed gas decomposed directly with ammonia for the second heat treatment;

5) The second heat treatment is sintering at 1600°C for 1h.

Example 8

Compared with embodiment 1, the difference of this embodiment is:

1) The phosphor powder in this example is Y _2.92 Al ₅ O ₁₂ : Ce _0.06 Dy _0.02 , the raw materials are 3.297g Y ₂ O ₃ , 18.757g Al(NO ₃ ) ₃ 9H ₂ O, 0.091g Dy(NO ₃ ) ₃ 6H ₂ O and 0.261 g Ce(NO ₃ ) ₃ 6H ₂ O;

2) The first heat treatment is solid state reaction at 1050°C for 1 hour;

3) The second heat treatment is sintering at 1500°C for 8 hours;

4) N ₂ —H ₂ mixed gas decomposed directly with ammonia for the second heat treatment.

Claims (6)

1. the oxalic acid non-homogeneous phase deposition prepares the method for rare earth doping yttrium aluminium garnet fluorescent powder, it is characterized in that the chemical formula that the oxalic acid non-homogeneous phase deposition prepares rare earth doping yttrium aluminium garnet fluorescent powder is Y _3-x-y-zR _yAl _5-mGa _mO ₁₂: Ce _x, R ' _z, 0.01≤x≤0.12,0≤y≤1.20,0≤z≤0.04,0≤m≤2.00 wherein; R is a kind of in Gd, the Sm rare earth element, and R ' is a kind of in Pr, the Dy rare earth element; The preparation method may further comprise the steps:

1) preparation of metal ion solution: taking by weighing purity by stoichiometric ratio is that yttrium oxide, gadolinium sesquioxide or Samarium trioxide, Praseodymium trioxide or dysprosium oxide raw material powder more than the 4N adds in the entry, be mixed with suspension liquid, add excessive slightly concentrated nitric acid, after the heating for dissolving, add Al (NO by stoichiometric ratio ₃) ₃9H ₂O or AlCl ₃6H ₂O and Ce (NO ₃) ₃6H ₂O is mixed with metallic ion mixed liquor, and the total concn of metallic ion mixed liquor is 0.2～0.8molL ^-1

2) preparation of ammonium bicarbonate soln: take by weighing oxalic acid and be dissolved in the deionized water, be mixed with oxalic acid solution, take by weighing bicarbonate of ammonia and be dissolved in the deionized water, be mixed with ammonium bicarbonate soln, the concentration of oxalic acid solution is 0.2～1.5molL ^-1, the consumption of oxalic acid is that the total amount of substance of yttrium and cerium is 1.5～5 times of mole total amounts, the concentration of ammonium bicarbonate soln is 0.2～1.5molL ^-1, the consumption of bicarbonate of ammonia is 4～6 times of the total amount of substances of yttrium, cerium and aluminium;

3) preparation of precipitation by metallic ion thing: under the condition of 30～60 ℃ of bath temperatures, successively oxalic acid solution and ammonium bicarbonate soln are added metallic ion mixed liquor, the speed that oxalic acid solution and ammonium bicarbonate soln add metallic ion mixed liquor is 1～8mLmin ^-1, adding the back that finishes and continue to stir 1～2h to reacting completely, the pH value of solution was 8.0～9.0 after precipitin reaction was finished, and is still aging, the aged time is 2～12h;

4) suction filtration, washing and dehydration: suspension liquid decompress filter or vacuum filtration after precipitin reaction finished, with the deionized water wash precipitation, use absolute ethanol washing again, the white depositions after drying;

5) add fusing assistant: with dried throw out and fusing assistant mix grinding, the consumption of fusing assistant is 0.5%～3.0% of a target product YAG:Ce quality;

6) thermal treatment for the first time: under reducing atmosphere,, get the YAG:Ce powder with 900～1200 ℃ of solid state reaction 1～6h under reducing atmosphere of the powder behind the mix grinding;

7) thermal treatment for the second time: will be through the heat treated YAG:Ce powder first time, 1300～1600 ℃ of sintering 1～8h under reducing atmosphere;

8) wash powder: with the powder behind the sintering, through grinding, wash successively, pickling, alkali cleaning, washing, oven dry gets target product YAG:Ce fluorescent material.

2. oxalic acid non-homogeneous phase deposition as claimed in claim 1 prepares the method for rare earth doping yttrium aluminium garnet fluorescent powder, it is characterized in that in the thermal treatment first time and increase between the heat treatment step for the second time washing the powder step, with the powder after the solid state reaction, successively through grinding, washing, pickling, alkali cleaning, washing, oven dry.

3. oxalic acid non-homogeneous phase deposition as claimed in claim 1 prepares the method for rare earth doping yttrium aluminium garnet fluorescent powder, it is characterized in that in step 4), with deionized water wash at least 3 times, with absolute ethanol washing at least 2 times, described drying is meant at 50～120 ℃ of oven dry 5～20h; Or to use vacuum-drying, vacuum drying temperature be 150 ℃, and the exsiccant time is 4～8h; Or employing lyophilize.

4. oxalic acid non-homogeneous phase deposition as claimed in claim 1 prepares the method for rare earth doping yttrium aluminium garnet fluorescent powder, it is characterized in that in step 5) fusing assistant is at least a in Neutral ammonium fluoride, Sodium Fluoride, barium fluoride, aluminum fluoride, yttrium fluoride, cerium fluoride, boric acid and the Cerium II Chloride.

5. oxalic acid non-homogeneous phase deposition as claimed in claim 1 prepares the method for rare earth doping yttrium aluminium garnet fluorescent powder, it is characterized in that in step 6), reducing atmosphere is selected carbon reduction for use; Or N ₂-H ₂Gas mixture, N by volume ₂: H ₂Be 90～97:10～3; Or the N that directly produces with the ammonia decomposing furnace ₂-H ₂Gas mixture.

6. oxalic acid non-homogeneous phase deposition as claimed in claim 1 prepares the method for rare earth doping yttrium aluminium garnet fluorescent powder, it is characterized in that in step 7), reducing atmosphere is selected N for use ₂-H ₂Gas mixture, N by volume ₂: H ₂Be 90～97:10～3; Or the N that directly produces with the ammonia decomposing furnace ₂-H ₂Gas mixture.