GB899251A - Image display screens - Google Patents

Abstract

899,251. Luminescent screens. SYLVANIA ELECTRIC PRODUCTS Inc. Oct. 8, 1958 [Oct. 8, 1957], No. 32166/58. Class 39(1). A multi-colour luminescent screen has a poisoning agent, such as iron, cobalt or nickel, diffused into the surface layers of at least the phosphor particles of one colour nearest the electron gun, to reduce the luminescent efficiency of this phosphor, so that low velocity secondary electrons, or electrons deflected by the shadow mask, do not excite the phosphor and cause colour de-saturation. The screen may be prepared by photographic printing techniques, the poisoning agent being contained in the light-hardenable substance associated with the relevant phosphor or being applied to the individual phosphor crystals prior to their application to the screen. Alternatively, the screen may be washed with a solution of the poisoning agent, e.g. 0.1 to 0.00005% by weight aqueous solution of ferric nitrate, after only the one or more phosphors whose light-emitting efficiency is to be reduced, e.g. the green and blue phosphors, have been applied to the panel. The poisoning agent may be in the form of a salt solution. As a final step in the screen-forming process, the screen may be baked above 400‹C. to remove volatile impurities and aid in the diffusion of the poisoning agent into the surface of the phosphor or particles. Suitable known luminescent materials, light-hardenable substances and solvents therefor, are specified. In particular, the luminescent material may comprise sulphides, oxides, tungstates, aluminates, borates, selenides, phosphates or silicates of one or more of zinc, cadmium, beryllium, magnesium, manganese, calcium and strontium, activated by silver, copper or manganese.