Abstract: In a shadow mask cathode ray tube for use with a light pen, the elemental phosphor areas emissive of red light comprise a blend of a red-emissive phosphor with silver-activated cadmium sulphide (CdS:Ag), the CdS:Ag being present in an amount from 10% to 30% by weight of the blend. In the preferred embodiment the blend comprises approximately 20% by weight of CdS:Ag and 80% by weight of industry standard P22R phosphor.

Abstract: In order to permit reliable light pen interaction with a black matrix shadow mask CRT, the conventional black carbon matrix is replaced by an IR phosphor. This provides a component of IR radiation irrespective of the particular color of the visible display at any given point, and such component can be detected by conventional silicon photodetector light pens. Preferably the particle size of the IR phosphor is substantially less than that of the primary color phosphors so as to largely retain both the packing density of the original black matrix and the edge definition at the IR phosphor/primary color phosphor boundaries. The IR phosphor particles are also pigmented with black graphite to retain the light-absorbing qualities of the original black matrix.