Patent GB-854684-A (GB)
Title: Improvements in or relating to electroluminescent phosphors and the preparation thereof
IPC: H05B33/14
Filed: 1957-12-09
Abstract: 854,684. Luminescent materials. WESTING- HOUSE ELECTRIC CORPORATION. Dec. 9, 1957 [Dec. 24, 1956], No. 38187/57. Class 39(1). Method of preparing electroluminescent zinc sulphide activated by copper and co-activated by chlorine comprises mixing zinc sulphide and a copper compound, the mixture containing from 0À004 to 0À012, preferably 0À008, gram atom of copper per mole of zinc sulphide, firing the mixture in a container at a temperature of from 850‹C. to 1000‹C. for at least one hour while introducing into the container an atmosphere comprising inert gas, or gases such as nitrogen or the noble gases, having mixed therewith at least one of the group consisting of sulphur monochloride vapour which may contain small amounts of higher sulphur chlorides, and mixed sulphur vapour and chlorine in approximately equal gram-atom proportions, and cooling the fired mixture in an atmosphere substantially free from oxygen. Small amounts of sulphur and a chloride may be incorporated in the starting materials. The firing is preferably at a temperature of about 950‹C. for about one and a half hours. The copper compound can be one or more of the acetate, nitrate and sulphate. Small amounts of zinc oxide can be incorporated. Surface layers of the fired product which do not fluoresce under U.V. excitation can be removed and the residium lightly crushed and submitted to a second firing step as above. Non-fluorescing portions of this residium can again be removed and the remainder lightly crushed. Whether a single or a double firing procedure is used the product can be washed in a solution which is a solvent for cuprous sulphide but not for zinc sulphide such as a two-normal solution of potassium or sodium cyanide. The fired or re-fired mixture is lightly crushed to pass through an 8 to 20 mesh screen, boiled in the solvent solution, cooled, decanted, lightly crushed, washed in water, decanted, washed in a solution which is a solvent for zinc oxide but not for zinc sulphide such as a one-normal solution of acetic acid at a temperature of 90‹C., decanted, washed with water, dried at a temperature not exceeding about 140‹C., preferably not exceeding about 120‹C., and screened. The electroluminescent material can be embedded in a dielectric such as P.V.C. acetate and incorporated into an electroluminescent cell. Apparatus for forming the material comprises a furnace 14 containing a silica tube 12 containing a firing tray 10 holding the starting materials. A firing-atmosphere supplying tube 18 is connected through the stoppered end of the tube 12 to the outlet side of a gas-scrubbing bottle 22. Nitrogen is passed through sulphur monochloride in the bottle 22 and passes together with sulphur monochloride vapour into the tube 12. Excess pressures are prevented by the outlet tube 24. Alternatively equal gram atom proportions of sulphur vapour and chlorine are introduced separately into the tube 12 by using a preheating furnace to vaporise the sulphur and then controlling the rate at which the sulphur vapour and chlorine are mixed with an inert gas. Sulphur monochlorine vapour may be mixed with sulphur vapour and chlorine gas and carried by the inert gas into the tube 12. Specification 854,683 is referred to.