GB830894A - Improvements in luminescent materials - Google Patents

Abstract

830,894. Luminescent materials. BRITISH THOMSON-HOUSTON CO. Ltd. May 7, 1956 [May 6, 1955], No. 13219/55. Class 39(1). A luminescent material comprises lithiummagnesium silicate activated with magnanese. Excess silica and chlorine may be present, the chlorine being limited to 0À1% by weight of the total material. The material is prepared by heating together at a temperature between 800‹C. and 950‹C. in an oxidising atmosphere such as air, a mixture of Li 2 O or Li 2 CO 3 , MgO, SiO 2 and a manganese compound, with or without a source of chlorine, for periods of 1-4 hours with intermediate grinding and mixing, the molecular proportions of Li 2 O : MgO lying between 0À6 : 1 and 1À35 : 1, the molecular proportions of SiO 2 : (Li 2 O + MgO) lying between 0À95 : 2 and 1À5 : 2, preferably between 1 : 2 and 1À25 : 2, and the proportion of manganese lying between 0À05 and 6% preferably between 0À15 and 1À5%, calculated as atoms per total molecules of (Li 2 O + MgO). MnCO 3 can be the manganese compound. The source of chlorine can be provided by using MnCl 2 À4H 2 O as the manganese compound, Mg Cl 2 6H 2 O, HCl, SH 4 Cl or LiCl, the quantity preferably not exceeding 5% of (Li 2 O + MgO) on a molecular basis if other than MnCl 2 4 H 2 O, and preferably 1À2% of MgCl 2 À6H 2 O. It is stated that the X-ray diffraction spectra of the material is that of lithium-magnesium silicate with or without magnesium silicate or a lithium silicate according to the proportions of starting materials used.