GB748788A - Improvements in or relating to electric discharge lamps - Google Patents

Abstract

748,788. Luminescent materials; discharge lamps. GENERAL ELECTRIC CO., Ltd., and McKEAG, A. H. July 12, 1954 [July 17, 1953], No. 19855/53. Class 39 (1). A neon filled discharge lamp includes titanium activated calcium magnesium meta-silicate with or without zinc silicate which luminesces under the very short U.V. radiation 736 Š from the neon discharge. The silicate contains calcium oxide and magnesium oxide in equimolecular proportions and is represented by the formula CaO.MgO.2SiO 2 . The titanium is present in the range of 0.01 to 10 per cent, preferably 0.1 to 1 per cent, by weight of the luminescent material. The luminescent material is prepared by mixing the oxides of calcium, magnesium, silicon and titanium, or compounds producing the oxides on heating, and heating the mixture in steam or in a restricted amount of air in a closed vessel at a temperature in the range 1100‹-1350‹ C., preferably 1250 ‹ C. for one hour. Five per cent by weight, preferably 2.5 per cent, of a flux such as calcium chloride and/or calcium sulphate can be used. The material can be mixed with one or more other luminescent materials such as willemite in such proportions as to produce luminescence of colours varying from yellow, through white to pink. The lamp has a tubular envelope so constructed that the current density of the discharge in normal operation is 5-40 milliamps per sq. cm. and the internal diameter of the envelope is from 10-10 mm. In one example the envelope is 20 mm. in diameter and is operated with a current of 60 milliamps. The pressure of the neon filling at room temperature is 2-15 mm., preferably 5 mm. Specification 457,486 is referred to.