GB792598A - Improvements in luminescent materials - Google Patents

Abstract

792,598. Luminescent materials. THORN ELECTRICAL INDUSTRIES, Ltd. July 12, 1956 [July 12, 1955; March 21, 1956], Nos. 21348/55 and 8893/56. Class 39(1). An artificial luminescent material comprises a halophosphate of calcium and/or strontium having an apatite structure (3M 3 (PO 4 ) 2 .MX 2 M being a bivalent alkaline earth metal and X a halide), as determined by X-ray analysis, and activated with cerium or with cerium and manganese, the proportion by weight of calcium and/or strontium (expressed as calcium), phosphorus and halide in the material being 36-44 per cent phosphorus pentoxide, 13-50 per cent calcium oxide and 9-47 per cent of calcium halide. Preferably these proportions fall within the ranges 38-42 per cent, 15-48 per cent, 11-45 per cent respectively and the proportion of cerium is between 0À05 and 12À5 per cent of the halophosphate. Up to 10 per cent by weight of the calcium and/or strontium, calculated as calcium alone, may be replaced by manganese. The material may include one or more of the alkali metals lithium sodium or potassium, e.g., as a carbonate or chloride in a proportion of up to 10 per cent by weight of alkali metal in the material. The materials may be made by heating at 900‹-1200‹C. a halophosphate matrix or a mixture of materials that will yield the halophosphate matrix on heating (e.g., Ca HPO 4 , CaF 2 and (NH 4 ) 2 HPO 4 ) together with compounds which will on heating incorporate the cerium or cerium and manganese activators in the matrix. Examples are given of firing at 1120‹C.-1150‹C. for three separate periods of half-hour each in a closed silica crucible. The materials when excited with ultraviolet light of 2537‹A wavelength emit luminescence ranging from ultra-violet to pink depending on the starting materials and their relative proportions,