GB440818A - Improvements in or relating to fluorescent material - Google Patents

Abstract

440,818. Fluorescent screens. LEVY, L. A., and WEST, D. W., 31, Shoot-up Hill, Cricklewood, London. July 20, 1934, No. 21333. [Class 98 (i)] A fluorescent material with little afterglow or persistence of latent image, and suitable for the production of X-ray viewing screens, comprises a mixture of zinc sulphide and about 15 to 40 per cent of cadmium sulphide, both in a high state of purity, a small trace of silver with or without manganese as activator, and a minute trace of nickel not greater than about one part in five million as inhibitor of after-glow &c. The sulphides are purified so that the majority of impurities, particularly compounds of the heavy metals such as copper and iron, are absent; and in any event the quantities of impurities present should not exceed one part in a million, excepting nickel which should be present in much smaller proportion. Salts such as ammonium salts which assist in the firing process, and are completely removed therein, are not regarded as impurities in this sense. The activators may be added in the ratio of one part in about 20,000 parts. The ratio of nickel added as inhibitor (including any present as impurity) may be as low as one part in twenty million. The various additions are made in elemental form or as salts at any stage prior to the heating of the sulphides to form the fluorescent material. Specifications 407,318, 410,114, and 424,195 are referred to.