USOO587958.6A United States Patent (19) 11 Patent Number: 5,879,586 Kitamura et al. (45) Date of Patent: Mar. 9, 1999

54 METHOD FOR PRODUCING ALUMINATE 62-201989 9/1987 Japan. PHOSPHOR 2-170888 7/1990 Japan. 7-268319 10/1995 Japan. 75 Inventors: Koji Kitamura, Osaka; Shozo Oshio, 997600 2/1963 United Kingdom. Nara; Teruaki Shigeta, Osaka; Shigeru 2259095 3/1993 United Kingdom. Horii, Osaka; Takeshi Nishiura, Osaka; Tomizo Matsuoka, Osaka, all OTHER PUBLICATIONS of Japan Verstegen, “A Survey of a Group of Phosphors, Based on 73 Assignee: Matsushita Electric Industrial Co., Hexagonal Aluminate and Gallate Host Lattices”, The Jour Ltd., Osaka, Japan nal of Electrochemical Society, Vol. 121, No. 12 (1974), pp. 1623-1627. 21 Appl. No.: 721,934 22 Filed: Sep. 27, 1996 Primary Examiner Melissa Bonner Attorney, Agent, or Firm Merchant, Gould, Smith, Edell, 30 Foreign Application Priority Data Welter & Schmidt, PA. Sep. 29, 1995 JP Japan ...... T-253917 57 ABSTRACT Mar. 29, 1996 JP Japan ...... 8-O77126 An alkaline earth metal compound containing no fluorine 51 Int. Cl...... C09K11/64; CO9K11/77; atoms in its molecules, a rare earth compound containing no C09K11/55 fluorine atoms in its molecules, and an aluminum compound 52 U.S. Cl...... 252/301.4 R 313/483 containing no fluorine atoms in its molecules are fired in a 58 Field of Search ...... 252/301.4 R; 313/483 high-temperature reducing atmosphere ranging from 1600 to 2000 C., so that an aluminate phosphor, the particle 56) References Cited diameter and shape thereof are controlled, is provided. A U.S. PATENT DOCUMENTS mixture of 22 wt % of barium carbonate, 11 wt % of basic magnesium carbonate, 65 wt % of Spherical alpha-alumina 3.294,699 12/1966 Lange ...... 252/301.4 R of 10 um diameter and 2 wt % of europium oxide is fired in 4,161,457 7/1979 Takahashi et al...... 252/301.4 a mixed gas atmosphere consisting of gaseous hydrogen of 4,246,630 1/1981 Wolfe ...... 252/301.4 R 4,524.300 6/1985 Rutten et al...... 313/487 5 volume 76 and gaseous nitrogen. The temperature is raised 4,631,144 12/1986 Beers et al. ... 252/301.4 R at 400° C./hr, and lowered at 400° C./hr after firing for two 4,795.588 1/1989 Pet et al...... 252/301.4 hours at 1700° C. As a result, a spherical aluminate phosphor 4,806,825 2/1989 Catherall et al...... 313/486 of 10 um diameter, which is expressed by formula (Baoo, Euoo)MgAloO7 is obtained. FOREIGN PATENT DOCUMENTS 0 286 180 10/1988 European Pat. Off.. 24 Claims, 5 Drawing Sheets

Firing temperature (C)

2OOO 18OO 17OO 16OO U.S. Patent Mar. 9, 1999 Sheet 1 of 5 5,879,586

Firing temperature (C)

2OOO 18OO 17OO 16OO 1400 1200

6 10000/T(K)

F1 G. 1 U.S. Patent Mar. 9, 1999 Sheet 2 of 5 5,879,586

5 Firing temperature(C) 2OOO 18OO 17OO 1600 1400 1200 R H Sa Cs Ol --1 2 -r, Ol 3 - O. H. O.1 s 4 5 6 7 8 9 OOOO/TK)

F1 G. 2 U.S. Patent Mar. 9, 1999 Sheet 3 of 5 5,879,586

F/G 3A

FIG 3D 15 U.S. Patent Mar. 9, 1999 Sheet 4 of 5 5,879,586

O ast1 5 1O

O O 5 10 15 2O Average particle diameter of alpha-alumina (pm)

F1 G. 4 U.S. Patent Mar. 9, 1999 Sheet 5 of 5 5,879,586

F1 G. 5 A

F1 G. 5 B

F1 G. 5 C 5,879,586 1 2 METHOD FOR PRODUCING ALUMINATE no fluorine atoms in their molecules, the rare earth com PHOSPHOR pound is an europium compound containing no fluorine atoms in its molecules, and the aluminate phosphor com FIELD OF THE INVENTION prises the materials expressed by the following formula: This invention relates to a method for producing a phos phor used for a fluorescent lamp and a display, etc. BACKGROUND OF THE INVENTION where Aluminate phosphor for tri-band fluorescent lamps, which was developed by J. M. P. J. Verstegen and the others, has 0.03 sws 0.3, 0.8sxs 1.2, 8sys 12, and 14szs20. been commonly used with the spread of tri-band fluorescent lamps. It is preferable that the alkaline earth metal compound is Such an aluminate phosphor is produced by a method, for a magnesium compound containing no fluorine atoms in its example, taught in The Journal of Electrochemical Society 15 molecules, the rare earth compound is a cerium compound 121 (1974) p. 1623–1627. An aluminate phosphor described and a terbium compound containing no fluorine atoms in by a general formula (Baos Eulo)Mg-AlO7 is produced their molecules, and the aluminate phosphor comprises the by firing materials comprising barium carbonate, europium materials expressed by the following formula: oxide, magnesium carbonate and alumina in a hydrogen reducing atmosphere at 1200° C. (CelTb) Mg,Al,O. A fluorine compound like aluminum fluoride or magne sium fluoride is added to the materials So that the crystal where linity of the aluminate phosphor is improved, So as not to deteriorate during a heating treatment when the aluminate phosphor is coated on a device Such as a fluorescent lamp or 25 0.03 sws 0.6,0.8sxs 1.2, 9sys13, and 152s23. a display. The quantity of the fluorine compound is varied to It is also preferable that the alkaline earth metal com control the particle diameter and the shape of the aluminate pound is a Strontium compound containing no fluorine atoms phosphor, So that the phosphor can be coated on the device in its molecules, the rare earth compound is an europium more uniformly. compound containing no fluorine atoms in its molecules, In a conventional method for producing an aluminate and the aluminate phosphor comprises the materials phosphor, a fluorine compound Such as aluminum fluoride is expressed by the following formula: added to improve its crystallinity and to control the diameter and the shape. (Sra(1-1) Euan) AlO. The method, however, costs more than the material cost 35 because of the Sublimation characteristics of the added where fluorine compound. Furthermore, the firing furnace will be corroded and damaged because of the corrosiveness of the fluorine compound. On the other hand, the crystallinity of 0.01 sws 0.6, 11 sixs 17, and 20sys30. the aluminate phosphor does not improve and controlling of 40 It is further preferable that the particle diameter of the the particle diameter and the shape cannot be conducted if aluminum compound containing no fluorine atoms in its the fluorine compound is not added. molecules is the same or Substantially the same as that of the desired aluminate phosphor. SUMMARY OF THE INVENTION It is still preferable that the particle diameter of the In order to solve these and other problems, this invention 45 aluminum compound containing no fluorine atoms in its aims to provide a method for producing an aluminate molecules ranges from 1 to 20 lim. phosphor. According to this method, the crystallinity is It is also preferable that the particle shape of the alumi improved and the diameter and shape of the particles are num compound containing no fluorine atoms in its mol controlled, without adding any fluorine compounds Such as ecules is the same or Substantially the Same as that of the aluminum fluoride. 50 desired aluminate phosphor. In order to achieve the above-mentioned purpose, the It is preferable that the aluminum compound is spherical method for producing an aluminate phosphor of this inven or Substantially Spherical. tion fires an alkaline earth metal compound, a rare earth It is further preferable that the alkaline earth metal com compound, and an aluminum compound in a reducing pound containing no fluorine atoms in its molecules is at atmosphere at a temperature from 1600 to 2000 C. The 55 least one Selected from the group consisting of oxide, carbonate, basic carbonate, nitrate and chloride of an alkali compounds do not contain fluorine atoms in their molecules. earth metal. It is preferable that the reducing atmosphere is a mixture It is also preferable that the rare earth compound contain of gaseous hydrogen and gaseous nitrogen. ing no fluorine atoms in its molecules is at least one Selected It is also preferable that the concentration of the gaseous 60 from the group consisting of oxide, carbonate, basic Salt, hydrogen ranges from 0.1 to 10 volume 7% of the reducing nitrate and chloride of a rare earth element. atmosphere consisting of the mixture of gaseous hydrogen It is also preferable that the aluminum compound con and gaseous nitrogen. taining no fluorine atoms in its molecules is at least one It is further preferable that the firing time is at least five Selected from the group consisting of oxide, chloride, minutes. 65 nitrate, Sulfate and alkoxide of aluminum. It is preferable that the alkaline earth metal compound is In the method for producing an aluminate phosphor of this a barium compound and a magnesium compound containing invention, an alkaline earth metal compound containing no 5,879,586 3 fluorine atoms in its molecules, a rare earth compound containing no fluorine atoms in its molecules, and an alu minum compound containing no fluorine atoms in its mol (Sr.4(1-Eu 1)AlOy ecules are fired in a high-temperature reducing atmosphere ranging from 1600 to 2000 C., so that the reaction is where promoted and the crystallinity can be improved without using any fluorine compounds. As a result, the crystallinity can be improved without using any fluorine compounds that 0.01 sws 0.6, 11 sixs 17, 20sys30. easily Sublimate and corrode, and a quality aluminate phos Accordingly, the europium can luminesce efficiently and the phor can be provided. 1O obtained phosphor emits high-luminance blue-green light. Fluorine compounds, which are easily Sublimated and It is preferable in this invention that the aluminum com corroded, are not used in the producing method of this pound containing no fluorine atoms in its molecules has the invention. Therefore, less components will be lost due to Same or Substantially the same particle diameter of the Sublimation in the firing process, and the cost can be desired aluminum phosphor, So that the particle diameter can lowered. In addition to that, corrosion and damage of the 15 be easily controlled in the method for producing aluminum firing furnace can be reduced. phosphor. The reducing atmosphere in the producing method of this It is preferable that the particle diameter of the aluminum invention is a mixture of gaseous hydrogen and gaseous compounds ranges from 1 to 20 um, So that the the aluminate nitrogen, So that a desirable reducing atmosphere can be phosphor will be coated efficiently on a device. provided at a comparatively low cost. It is preferable in this invention that the aluminum com The concentration of the gaseous hydrogen of the reduc pound containing no fluorine atoms in its molecules has the ing atmosphere ranges from 0.1 to 10 Volume 76, So that the Same or Substantially the Same particle shape of the desired Synthesis of the aluminate phosphor can be conducted aluminum phosphor, So that the particle shape can be easily efficiently. controlled in the method for producing aluminum phosphor. The firing time is predetermined to be at least five minutes 25 A spherical or a Substantially spherical aluminum com in the method of this invention, So that the aluminate pound preferably should be used because the Surface area of phosphor can be Synthesized completely in order to provide the phosphor becomes Small, So that the luminance will a quality aluminate phosphor. deteriorate much less when the phosphor is heated in air in It is preferable in the producing method of this invention order to be coated on a device. In addition, it is also that the alkaline earth metal compound is a barium com preferable that a phosphor which is spherical or Substantially pound and a magnesium compound containing no fluorine Spherical is used for a fluorescent lamp or a display etc., atoms in their molecules, the rare earth compound is an because the transmissivity of a visible ray rises and the europium compound containing no fluorine atoms in its radiation efficiency improves. molecules, and the aluminate phosphor is expressed by the It is further preferable that the alkaline earth metal com following formula: 35 pound containing no fluorine atoms in its molecules is at least one Selected from the group consisting of oxide, carbonate, basic Salt, nitrate and chloride of an alkaline earth (BarEu)Mg,Al,O. metal, Since the compounds are comparatively inexpensive, where easily obtained, and comparatively stable. 40 It is also preferable that the rare earth compound contain ing no fluorine atoms in its molecules is at least one Selected 0.03 sws 0.3, 0.8oxides. 50 because the Surface area of the phosphor becomes Small, So For the aluminum compound containing no fluorine that the luminance will deteriorate much less when the atoms in its molecule, oxide, chloride, nitrate and Sulfate of phosphor is heated in air. aluminum and alkoxide of aluminum having C1-C4 alkoxy The aluminum compound for the Spherical aluminate groups are preferably used Since the compounds are com phosphor is, for example, an aluminum compound like paratively inexpensive, easily obtained, and comparatively 55 alpha-alumina which is made spherical by exposing to a stable. high-temperature atmosphere (e.g. by irradiating plasma) The following are preferable examples of aluminum com and then quick-quenching. Another example is a highly pounds containing no fluorine atoms in their molecules: purified spherical alumina named “admafine” by Admatechs aluminum oxide, aluminum chloride, aluminum nitrate, alu Co., Ltd., which is made spherical by a Self-firing method. minum Sulfate, and tri-isopropoxy aluminum. 60 AS the aluminum compound to be the Substantially Spheri Alpha-alumina and gamma-alumina are taken as cal aluminate phosphor, for example, an alumina "Sumico examples of the aluminum oxide. An aluminum compound rundom” by Sumitomo Chemical Company Ltd. can be which is not an oxide is preferably pre-fired in a oxidizing used. "Sumicorundom” is polyhedron (e.g. octahedron) alu atmosphere in order to prevent any elements except oxygen minum oxide manufactured by crystallizing after a gasifying from contaminating as impurities in the phosphor. 65 proceSS. It is difficult to generally predetermine the percentage of It is also preferable that a phosphor which is Spherical or the alkaline earth metal compound, the rare earth compound Substantially Spherical is used for a fluorescent lamp or a 5,879,586 7 display etc., because the transmissivity of a visible ray rises and the radiation efficiency improves. Due to the above TABLE 1. mentioned reasons, aluminate phosphor having desired par ticle diameter and shape can be obtained by the method of Raw materials Weight % this invention by using aluminum compounds whose par Barium carbonate (BaCO) 22.O ticle diameter and shape are Substantially identical to those Europium oxide (Eu2O 2.0 of the produced aluminate phosphor. Basic magnesium carbonate (4MgCO. : Mg(OH), 3H2O) 11.O It is preferable in the producing method of this invention Alpha-alumina (Al2O3) 65.O that the alkaline earth metal compound is a barium com pound and a magnesium compound containing no fluorine Barium carbonate and basic magnesium carbonate were atoms in their molecules, the rare earth compound is an used for the alkaline earth metal compound, alpha-alumina europium compound containing no fluorine atoms in its was used for the aluminum compound, and europium oxide molecules, and the aluminate phosphor is expressed by the was used for the rare earth compound. following formula: The raw materials of the weight% shown in Table 1 were 15 mixed and pulverized in a mortar or in a ball mill. Then the powder was fired in a tube furnace by using a mixture of gaseous nitrogen and gaseous hydrogen. The flow quantity where of the nitrogen was 380 ml/minute, and that of the hydrogen was 20 ml/minute. The hydrogen concentration was 5 vol ume 76. The temperature was raised at 400 C./hr, and then 0.03 sws 0.3, 0.8sixs 1.2, 8 sys12, and 14szs20. lowered at 400 C./hr after the powder was fired for two hours at 1700 C. As a result, the above-mentioned BAM Accordingly, the europium can luminesce efficiently and the phosphor was Synthesized. During the firing process, the obtained phosphor emits high-luminance blue light. hydrogen concentration can be lowered to 0.1 volume 76 The above-mentioned composition can be obtained by Since hydrogen is easily deoxidized. The hydrogen concen mixing the alkaline earth metal compound, the rare earth 25 tration is preferably 10 volume 76 or less, since if the value compound, and the aluminum compound to have the ratio exceeds 10 Volume 76, its reducing characteristic will pre shown in the above formula and then, firing the mixture in vent the BAM phosphor from being synthesized. The firing the reducing atmosphere. Other compositions also can be takes only five minutes because the diffusing reaction pro obtained using the same process. ceeds fast at a high temperature of 1600 C. or higher. It is preferable in the producing method of this invention The high-crystallization of the BAM phosphor is that the alkaline earth metal compound is a magnesium explained referring to FIG. 1. In FIG. 1, the vertical axis compound containing no fluorine atoms in its molecules, the indicates the half-value width of the 107 face of the BAM rare earth compound is a cerium compound and a terbium phosphor crystals (the strength peak of X-ray diffraction compound containing no fluorine atoms in their molecules, 35 spectrum). and the aluminate phosphor is expressed by the following The half-value width of the X-ray diffraction spectrum formula: indicates the crystallinity of the BAM phosphor. The crys tallinity is higher as the half-value width is smaller. The luminance of the BAM phosphor generally deteriorates 40 during the heating treatment when the phosphor is coated on where a fluorescent lamp or on a display. It has been found from the experiments by the inventors that the deterioration can be reduced as the crystallinity is high. 0.03 sws 0.6,0.8sixs 1.2, 9 sys13, 15szs23. The horizontal axis indicates the inverse of the firing Accordingly, the terbium can luminesce efficiently and the 45 temperature (K) for synthesis of the BAM phosphor. The obtained phosphor emits high-luminance green light. firing temperature ( C.) is indicated for reference on the It is preferable in the producing method of this invention upper side of FIG.1. The A marks in FIG. 1 are the Survey that the alkaline earth metal compound is a strontium data of the half-value width of the BAM phosphor's X-ray compound containing no fluorine atoms in its molecules, the diffraction spectrum. The Solid line (a) is a linear function of rare earth compound is a europium compound containing no 50 the half-value width of the Survey data of the X-ray diffrac fluorine atoms in its molecules, and the aluminate phosphor tion spectrum fitted by using the least Square method. The is expressed by the following formula: broken line (b) is a half-value width of the 107 face of the X-ray diffraction spectrum of a conventional BAM phosphor containing fluorine compounds. 55 As shown by the line (a), the half-value width of the X-ray where diffraction spectrum becomes Smaller as the firing tempera ture of the BAM phosphor of this invention is raised. When the temperature exceeds 1600 C., the width becomes 0.01 sws 0.6, 11 six<17, 20

PATENT NO. : 5,879,586 Page 1 of 1 DATED : March 9, 1999 INVENTOR(S) : Kitamura et al.

It is certified that error appears in the above-identified patent and that said Letters Patent is hereby corrected as shown below:

Column 2 Line 25, “and 152s23.” Should read -- and 15szs23. --

Column 12 Line 10, "(Baw, Euw)Mg,AlO,” should read -- (Baw, Euw)Mg,AlyO, --

Signed and Sealed this Fifteenth Day of April, 2003

JAMES E ROGAN Director of the United States Patent and Trademark Office