GB735235A - Improvements relating to luminescent screens - Google Patents

Abstract

735,235. Luminescent materials. GENERAL ELECTRIC CO. Aug. 25, 1952 (Aug. 25, 1951], No. 21337/52. Class 39 (1). A method of forming a transparent luminescent screen responsive to the bombardment of electrons, e.g. in a C.R.T., consists in depositing on a supporting surface a film consisting either of a suitable uncombined metal(s) or a suitable halogen compound(s) of a metal(s) together with an activator, and thereafter converting the film on the supporting surface to a luminescent sulphide or selenide of the metal(s). Zinc or a halide(s) thereof or a mixture of zinc and cadmium or of their halides or layers of both such materials may be deposited with suitable activating material to form the film. The metal(s) or halogen compound(s) may be deposited on the supporting surface by vaporization in vacuo and the film converted to a sulphur (selenium) compound by heating to approximately 500‹ C. in contact with sulphur vapour or a gaseous sulphur (selenium) compound such as hydrogen sulphide (selenide). The activator may be copper or silver. In one example, zinc fluoride or bromide activated with manganese is volatilized from the boat-shaped evaporator 2, Fig. 1, contained in the evacuated glass envelope 1, on to the glass or fused quartz base 9 to a thickness of about 0.25 micron. The coated base 9a is then transferred to a tubular reaction oven 10, Fig. 2, heated by the winding 11 to a temperature of about 500‹ C. Hydrogen sulphide or other gaseous sulphur compound is admitted by a conduit 12 and carried away together with reaction by-products by a conduit 13. In another example a mixture of 85 per cent zinc, 0.1 per cent copper and the remainder cadmium is fused in hydrogen and the mixture subjected to the preceding process. In a modification a film of zinc together with an activator of copper may be first applied to the base 9, following which a film of zinc and cadmium together with a copper activator may be applied and the dual film then converted to sulphides.