GB775188A - Improvements relating to fluorescent materials - Google Patents

Abstract

775,188. Luminescent materials. SIEMENS BROS. & CO., Ltd. June 3, 1955 [June 25, 1954], No. 18733/54. Class 39(1). Luminescent material, luminescing red in response to radiation of 2537Š, comprises calcium pyrophosphate activated by thallium and manganese in which phosphorus pentoxide is present in excess of stoichrometric proportion, e.g. there may be present 1À2-1À25 gram mols. of phosphorus pentoxide for 2 gram mols. of calcium oxide. The material can be prepared by mixing calcium hydrogen phosphate, diammonium hydrogen phosphate and compounds of thallium and manganese, such as the oxide, nitrate or carbonate, and firing the mixture in air at a temperature between 800‹C. and 1100‹C. preferably 900‹C. The proportion of thallium lies between 0À0075 and 0À0225 gram atoms, of manganese between 0À015 and 0À025 gram atoms and of diammonium hydrogen phosphate between 0À2 and 0À25 gram mols., per gram mols. of calcium hydrogen phosphate. The calcium pyrophosphate may be prepared by igniting a mixture of calcium carbonate and diammonium hydrogen phosphate or by igniting calcium hydrogen phosphate alone. The calcium hydrogen phosphate can be prepared by precipitation from solutions of calcium chloride and diammonium hydrogen phosphate. The excess of phosphorus pentoxide can be obtained by adding diammonium hydrogen phosphate to the calcium pyrophosphate obtained by igniting calcium hydrogren phosphate or by increasing the amount of diammonium hydrogen phosphate above that in the stoichrometric formula when the calcium hydrogen phosphate is obtained by precipitation.