BLUE COLORATION OF EVAPORATED-FILMS OF SODIUM-CHLORIDE BY ELECTRON-IRRADIATION

Coloration of evaporated films of NaCl has been studied by electron irradiation at various temperatures from 20 to 300°C. As for single crystals of NaCl, blue coloration has been obtained above about 80°C and ascribed to the formation of X or colloidal centers. In the earlier stage of coloration, the growth rate of coloration in the films is several times larger than that in the crystals. The extinction bands in the blue range are narrower in the films than those in the crystals. These results can be explained by assuming that the many more crystal imperfections in the polycrystalline NaCl films offer a large number of nucleation sites for F-center aggregation. Thermal and optical stabilities of the extinction bands enable us to use them for the highly persistent display or memory of an image. © 1990 The Japan Society of Applied Physics.