1,051,085. Luminescent materials. NATIONAL CASH REGISTER CO. May 28, 1965 [July 31, 1964], No. 22726/65. Heading C4S. [Also in Division H1] Thin films of single or mixed A n B vI compounds are activated by firing them at a temperature between 560‹ and 620‹ C. for from 6- 20 minutes beneath a cover an internal surface of which has been coated with a sintered powder comprising cadmium sulphide or selenide doped with one or more of cadmium, copper and chlorine. In a preferred method films of cadmium sulphide deposited on glass plates at 288‹ C. from an aqueous solution containing in addition thiourea and cadmium chloride are so treated by placing them in recesses in a ceramic holder over which fits a ceramic cover. A mixture consisting of cadmium sulphide or selenide and specified amounts of chlorides of copper and cadmium is fired at 540-640‹ C. for 15-45 minutes and after grinding and milling applied as a paste to the inside of the cover and fired at 300-400‹ C. for 15 minutes to sinter it on. The cover is then placed over the substrate and the assembly heated at 580‹ C. for 10 minutes to dope the films. Films of cadmium selenide and sulphoselenide and zinc sulphoselenide may be activated in a similar manner.