Phosphors

Abstract

Phosphors by definition are materials that emit photons with a high efficiency and are of practical interest precisely for their luminescence, including cathodoluminescence. The unusual properties of these materials were discovered long before the development of such devices as cathode-ray-tube (CRT)-based instruments, in which phosphors found one of their most important applications. Currently phosphors are also used in fluorescent lamps, electroluminescent flatpanel displays, x-ray screens, scintillators, infrared-to-visible converters, electron microscope fluorescent screens, and color television screens (for a review, see Pappalardo, 1987). In the latter application, for example, ZnS:Ag is used for the blue component, ZnS:Cu, AI for the green component, and Y₂O₃:Eu³⁺ or Y₂O₂S:Eu³⁺ for the red component. In ZnS phosphors, with high CL efficiency, the mechanism of emission is that of donor-acceptor pairs. The emission peak wavelength (i.e., the color) of light produced by a particular phosphor depends on the impurities present in the material. Table 8.1 lists some of the phosphors used in cathode-ray tubes.