GB829546A - Luminescent material - Google Patents

Abstract

829,546. Luminescent materials. BRITISH THOMSON-HOUSTON CO. Ltd. March 28, 1956 [April 4, 1955], No. 9809/55. Class 39(1). A luminescent material consists of a bariummagnesium silicate activated with manganese. Excess silica may be present and also chlorine up to 0À1% by weight of the total material. The molecular proportion of BaO to MgO can lie between 3 : 2 and 1: 2, every mol of BaO being associated with between 2 and 3 mols of SiO 2 , and every mol of MgO being associated with between ¢ and 1 mol. of SiO 2 , the molecular proportions of Mn lying between 1 and 15 mols. per cent of the total BaO and MgO. The material can be prepared by heating together at temperatures of between 1040‹C. and 1060‹C. in an oxidising atmosphere, e.g. air, a mixture of BaO, MgO, SiO 2 (or compounds of Ba, Mg and Si which break down to produce the oxides) and a maganese compound, with or without a source of chlorine, for a period of at least one hour and then reducing the product to powder. The source of chlorine can be provided by using MnCl 2 as the manganese compound, or by using BaCl 2 in partial substitution for BaO and MnCO 3 as the manganese compound. Other sources of chlorine referred to are NH 4 Cl and MgCl 2 . Another method of preparation of the material consists in preparing a barium disilicate by co-precipitation from a solution of aqueous ammoniacal Ba(OH) 2 and alcoholic tetra-ethyl silicate, mixing the precipitate with MgO, SiO 2 and MnCl 2 . 4 H 2 O and heating in an oxidising atmosphere at a temperature of between 1040‹C. and 1060‹C. for periods of from 1 to 12 hours with intermediate grindings. The molecular ratio of SiO 2 to MgO lies between 1 : 2 and 1 : 1 when the ratio of BaO to MgO is 3 : 2. Up to 20 mols per cent of the barium di-silicate precipitate can be replaced by BaCl 2 . 2H 2 O, the MnCl 2 . 4H 2 O being replaced by MnCO 3 . The barium di-silicate precipitate can be replaced by BaCO 3 and SiO 2 , or BaCO 3 and silicic acid.