Improvements in sources of light comprising an electric discharge device and luminescent material adapted to be excited by the discharge therein

摘要

506,165. Luminescent materials. GENERAL ELECTRIC CO., Ltd., McKEAG, A. H., and RANDALL, J. T. Oct. 20, 1937, No. 28623. [Class 39 (i)] An electrical gas discharge device contains luminescent magnesium tungstate and/or zinc tungstate mixed with free magnesium and/or zinc oxide to prevent discolouration and loss of efficiency of the tungstates. In one method of preparation magnesium or zinc oxide is mixed with tungstic oxide in the proportion of 11 molecules to 10 molecules and the mixture heated in an oxidizing atmosphere at about 1150‹ C. for 1 hour and then ground and sieved. In another method 1 mol. of material produced by the first method is mixed when dry with 0À9 mols. of magnesium oxide and the mixture heated to 400‹ C. for half an hour. In general the proportion of free magnesium and /or zinc oxide is such that if a moles. of W03 are present, there are present ( 1 +x)a mols. of (MgO+ZnO), where x is not less than 00À5. According to the Provisional Specification, material produced from a mixture in the ratio of 1MgO (or ZnO) to 1WO3 is mixed with MgO (orZnO) amounting to about 10 per cent of that already present and heated to about 1000‹ C. in an oxidizing or neutral gas for 1 hour or more. The Provisional Specification also refers to Specification 504,354 and to the use of magnesium-cadmium tungstate and calcium tungstate.