GB650458A - Improvements in photographic recording and luminescent materials therefor - Google Patents

Abstract

650,458. Luminescent material. URBACH, F. March 25,1947, No. 8160. Convention date, May 3, 1946. Drawings to Specification. [Class 39 (i)] Phosphors with high sensitivity to infra-red stimulation of their luminescence comprise a matrix, the major portion of which is a sulphide or sulphides of one or more of the metals magnesium, calcium, zinc, strontium, cadmium and barium, activated by at least two activators, one dominant and the other auxiliary, preferably selected from the metals samarium, europium, cerium, manganese, bismuth, lead, copper, vanadium, tin, iron, antimony, prµsodymium, neodymium, silver and nickel. The rules of selection governing emission and stimulation are described. The sulphide may include a selenide, sulphate, oxide, carbonate or polysulphide. The sulphate present should exceed 10 per cent of weight of flux materials; the oxide should not exceed 5 per cent of the phosphor. Amount of sulphate present is controlled by firing in a reducing atmosphere or by controlling air or oxygen present, or by direct reduction with illuminating gas, carbon disulphide, nitrogen, hydrogen or hydrogen sulphide, or by including starch, sugar or other organic compounds in the firing charge. Calcium fluoride is instanced as a fluxing addition. The finished phosphor may include 20 per cent magnesium oxide as a filler after which it is reheated to a low temperature. It may also be mixed with methyl methacrylate and a solvent and sprayed or moulded into flat or curved sheets. Gadolinium and some of the other rare or very rare earths may be added as auxiliary activators. There are figures showing excitation, stimulation and emission spectra of certain phosphors. Specifications 650,455, 650,456, 650,457 and 650,459 and U.S.A. Specification 2,074,226 are referred to.