GB536305A - Improvements in the production of luminescent materials - Google Patents

Abstract

536,305. Luminescent materials; silica. TRIGGS, W. W. (Harshaw Chemical Co.). Jan. 25, 1940, No. 1540. [Class 39 (i)] [Also in Group III] In the preparation of luminescent silicates, an oxide of arsenic, preferably As 2 O 3 in aqueous solution, or a material producing it on calcination is added to the silica or to the mixture of the silica with the metal oxides and activator, so that the composition contains .003 - .03 per cent of arsenic based on the weight of silica. The activator is preferably manganese in the form of a chloride, an oxide, or an oxide-producing compound such as the nitrate. The metals in the form of oxides or oxide-producing compounds may be zinc, cadmium with or without magnesium, or a mixture of zinc and beryllium. In the latter case, the oxide of one may be mixed with the silicate of the other, and part of the beryllium may be replaced by magnesium in the form of its silicate, oxide or an oxide producing compound. The silica is preferably prepared by precipitation in a non-colloidal state from a solution of ammonium silico-fluoride or fluosilicic acid by concentrated ammonia, or by precipitation from salts or esters by acids. The ingredients are thoroughly mixed in the form of a slurry in a ball-mill, dried and calcined at a high temperature from 1100-1300‹ C in an oxidising atmosphere. -Examples are described of the preparation of luminescent zinc, cadmium, zinc-beryllium and zinc-beryllium-magnesium silicates.