GB728179A - Tri-colour phosphor screens - Google Patents

Abstract

728,179. Luminescent screens. RADIO CORPORATION OF AMERICA. March 20, 1953 [March 25, 1952], No. 7800/53. Drawings to Specification. Class 39 (1). A luminescent screen for a colour television receiver has a multiplicity of phosphor triads, in which the red elements are zinc selenide, or zinc cadmium selenide having at least 8 parts Zn to 1 part Cd by weight, plus 0.003 to 0.03 per cent Cu activator, the blue elements are zinc sulphide or zinc seleno-sulphide having at least 8 parts S to 1 part Se by weight plus 0.005 to 0.025 per cent Ag activator, and the green elements are zinc silicate plus 0.1 to 1.0 per cent Mn activator. In the zinc cadmium selenide the ratio of Zn to Cd is preferably 25: 1. The zinc sulphide or seleno-sulphide may have 0.015 per cent Ag activator. The red and blue phosphors are prepared by firing at 750- 1250‹ C., preferably in a nitrogen atmosphere, using 2 per cent of NaCl or NH 4 Cl as a flux. The colour emission shade can be varied by varying the firing temperature and also, in the case of the blue phosphor, by varying the S : Se ratio. The green phosphor is preferably zinc orthosilicate with 0.3 per cent Mn activator. The tri-colour elements may be lines, dots or triangles, and may be disposed in one or more planes, or angularly as on the sides of pyramids, ridges or cells. The screen may be transparent, for example if elements of one colour are on one side and the elements of the other two colours are on the other side, or opaque, and may be flat or curved. The preferred red phosphor comprises 97 parts of Zn Se, 3 parts of Cd Se and 0.01 parts Cu activator. The deepening effect on the colour of increasing the percentage of Cd Se from 1-10 per cent is indicated graphically, Fig. 2 (not shown). Prior art phosphors for colour television receivers are referred to as follows: (a) blueemitting calcium magnesium silicate with 1 per cent Ti activator, (b) red-emitting cadmium borate with 1 per cent Mn activator, (c) redemitting zinc orthophosphate with 1 per cent Mn activator, (d) green zinc silicate with Mn activator (willemite). Phosphor (b) requires a didymium glass filter to correct the colour.