Phosphors and Picture-Tube Performance

The brightness, contrast, and sharpness of the picture on a color television tube screen is of great importance to the consumer and of major interest to the picture tube designer. Chromacolor has yielded a substantial improvement both in brightness (to over 100 ft-L) and in contrast (by absorbing incident ambient light) due to its negative guard-band, black surround construction. The sharpness of the picture on the screen depends largely on the diameter of the electron beam incident upon the phosphor dots. An improvement in sharpness can be brought about by a reduction in the size of the electron beam; however, such a reduction in diameter will result in an increase in current density. This brings up a question concerning the cathodoluminescence1 of these phosphors: is the emission intensity linear with respect to beam current density in the region of practical beam currents?