GB828216A - Improvements in or relating to field responsive phosphors - Google Patents

Abstract

828,216. Luminescent materials. WESTING- HOUSE ELECTRIC CORPORATION. July 2, 1956 [July 8, 1955], No. 20395/56. Class 39(1). A method of preparing an electric field responsive phosphor which is not responsive to U.V. radiations and which can be used in a flashing sign with an illuminated background, comprises mixing-1 mole of at least one of the group ZnS and ZnSe, from 0À05 mole per cent to 2 mole per cent Cu activator, a coactivator of at least one of the group consisting of a halogen, Al, Ga, In and Tl in at least about the same order of magnitude as the Cu activator and not exceeding 10 mole per cent, and from 10-<SP>3</SP> to 10-<SP>2</SP> mole per cent of at least one of the group consisting of Fe, Co, and Ni-and firing the mixture in an inert atmosphere such as nitrogen, neon or argon, at about 800‹C. to 1250‹C. for at least one half hour. The halogen co-activator can be introduced as a halide, e.g. CuI 2 . The fired material can be washed with potassium cyanide, sodium cyanide and acetic acid. It is stated that firing some of the copper activator and the co-activator will be lost and that the amount of copper remaining will be between 10-<SP>2</SP> and 1 mole per cent with equivalent amounts of the co-activator. It is also stated that commercial ZnS or ZnSe, if used, usually contain from 10-<SP>4</SP> to 2 mole per cent of ZnO which is not harmful. Several examples are described. In the construction of the flashing sign with an illuminated background shown in Figs. 1 and 2, the viewing portion 18 of the sign 10 consists of a sheet of glass having applied to its inner surface a coating 20 of tin oxide forming an electrode. Coated over the tin oxide in the form of letters in the phosphor 14 above described, and coated over the remainder of the tin oxide is an organic-type dye or other phosphor 16 which can be excited only by a source 26 of U.V. radiation. Both phosphors are preferably enbedded in a transparent or translucent dielectric material 22 such as methyl methacrylate in the proportion of 1 part phosphor to 3 parts dielectic. A second electrode 24, which may be of aluminium, is coated over the phosphor-embedded dielectric 22. The electrodes 20 and 24 are conneected to an A.C. source, e.g. of 500 volts and a frequency of 60-5000 cycles, which can be alternately energized and de-energized. In a specific example the phosphor 16 comprises a 0À1% solution of Rhodamine B mixed with a plastic such as polyethylene, and the electrodes 20 and 24 are spaced 0À3 mils (0À008 mms.) apart. In a modified construction the phosphor 14 and the dielectric material may be in separate layers, e.g. a layer of phosphor 2 mils (0À05 mms.) thick and a layer of mica 1 mil (0À025 mms.) thick, and mica being transparent if adjacent the electrode 20. Reference has been directed by the Comptroller to Specification 783,613.