Dec. 27, 1966 H. LANGE 3,294,699 LUMINESCENT ACTIVATED ALUMINATE Filed Jan. 30, 1963

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1. 2 3,294,699 excited by the mercury line 365 mu (millimicrons), the LUMENESCENT EUROPUMACTIVATED luminescent material emits a broad band spectrum with STRONTUMAUMINATE peak response in the green region at about 520 mp. Horst Lange, Berlin-Grunewald, Germany, assignor to The quantum efficiency of a luminescent material ac Patent-Treuhand-Geselschaft fir elektrische Glih cording to the invention amounts to about 88 percent lampen ab.H. when compared with that of magnesium tungstate. With Fied Jan. 30, 1963, Ser. No. 254,969 increasing temperature, the emission intensity decreases Claims priority, application (Germany, Feb. 8, 1962, slowly above 100° C. P 28,763 6 Clains. (C. 252-301.4) A specific example describing the preparation of a O luminescent material in accordance with the invention The present invention relates to an artificial lumines Will now be given. A charge consisting of: cent material for use in electric discharge lamps, in screens of cathode ray tubes or in X-ray screens, as well G. as to an improved method of manufacturing this lumines SrCOs ------13.28 cent material. 5 Al(OH)3 ------15.60 As is generally known, luminescent materials usually Eu2O3 0.53 consist of a base material in which a suitable is intimately mixed and fired three times for one hour each is incorporated. There have already been described time at 1500 C. in a forming gas current. After each luminescent materials consisting of oxides or silicates of firing the preparation is ground thoroughly. Suitably, the alkaline earth metals as the base material and which 20 the forming gas may consist of 4 parts nitrogen and 1 contain an addition of europium as the activator. There part hydrogen by volume. have also been published reports on europium activated The luminescent material obtained may be used in Sulphides of alkaline earth metals and their luminescence well known manner. It may, if desired, be used alone under suitable excitation. or mixed with other luminescent materials in electric dis According to the invention, it has been found that 25 charge lamps or in screens for cathode ray tubes or in good luminescent materials may be obtained if strontium X-ray Screens. aluminate is activated with europium (II) oxide (where What I claim as new and desire to secure by Letters in Eu has a valence of 2). The amount of europium (II) Patent of the United States is: oxide added to the strontium aluminate is between about 1. An artificial luminescent material consisting essen 2 and 8 mol percent, particularly good results being ob 30 tially of strontium aluminate activated with europium tained with a concentration of approximately 3 mol (II) oxide. percent, 2. A luminescent material as defined in claim 1 char The single figure of the drawing is a spectral response acterized in that the concentration of europium (II) curve typical of a strontium aluminate embody oxide in the strontium aluminate lies between 2 and 8 ing the invention. 35 mol percent. For the preparation of luminescent materials accord 3. A luminescent material as defined in claim 1 char ing to the invention, a mixture of , alumi acterized in that the concentration of europium (II) num oxide and europium oxide is fired under reducing oxide in the strontium aluminate is approximately 3 mol conditions. Alternatively, there may be used in the ini percent. tial mixture, instead of strontium oxide and aluminum 40 4. The method of manufacturing an artificial lumines oxide, compounds which produce the oxides of strontium cent material consisting essentially of strontium alumi aluminate when heated. Also, instead of europium ox ide there may be used an europium compound which nate activated with europium (II) oxide comprising mak produces europium oxide when heated. Very suitable ing a mixture of materials from the group consisting of 45 Strontium oxide, aluminum oxide, compounds yielding compounds are for instance the carbonates, hydroxides when heated strontium oxide and aluminum oxide, and and the like. The firing temperature for the mixture of compounds yielding when heated strontium aluminate, initial materials should be in the range of 1400° C. to 1600 C., a firing temperature of about 1500 C. being and a material from the group consisting of europium optimum. oxide and compounds yielding when heated europium 50 oxide, and firing said mixture under reducing conditions Strontium aluminate Serving as the base material for at a temperature in the range of 1400° C. to 1600 C. the luminescent material may deviate in its composition 5. The method defined in claim 4 wherein the firing from the stoichiometric proportion of strontium oxide. is carried out at about 1500 C. to aluminum oxide given by the formula SrAlO4. Such 6. The method defined in claim 4 wherein the firing variations are customary in the chemistry of luminescent 55 is done in a current of a forming gas consisting of ap materials. Thus, it is well known that in compositions proximately 4 parts nitrogen and 1 part hydrogen by suitable as the base material for luminescent materials, the acid components must often be present in excess, for volume. instance to the extent of 10 to 20 percent over stoichio References Cited by the Examiner UNITED STATES PATENTS metric proportions, in order to obtain highest brightness. 60 In the case of strontium aluminate luminescent materials 2,392,814 1/1946. Froelich. ------252-301.4 according to the present invention, it is advantageous to use an excess of aluminum oxide over stoichiometric OTHER REFERENCES proportions for the purpose of increasing intensity. Kroger: "Some Aspects of the Luminescence of Solids,' A luminescent material according to the invention may 65 Elsevier Publ. Co., New York, 1948, pp. 60, 61, 270-272 be excited for instance with ultraviolet rays. It is espe and 292. cially suitable for excitation by long wave ultraviolet rays Such as are emitted by high-pressure mercury lamps. As TOBIAS E. LEVOW, Primary Examiner. shown in the curve of the accompanying drawing repre senting the spectral distribution of the emission from the MAURICE. A. BRENDISI, Examiner. luminescent material 0.9 SrO 1 AlO3 0.03 EuO when 70 R. D. EDMONDS, Assistant Examiner.