Additive coloration of cadmium fluoride crystals

摘要

This paper discusses the process of additive coloration of cadmium fluoride crystals doped with ions of the third column of Mendeleev's periodic system. In this crystal, unlike all other ionic crystals, the electrons introduced by this procedure are localized in the conduction band or on hydrogenlike orbitals centered at impurities. For two of the impurities of the indicated group, gallium and indium, the electrons may also be localized on an inner atomlike shell; these bistable impurities are of special interest in connection with the fact that CdF2:Ga and CdF2: In crystals are photochromic. Possible methods are discussed for the additive coloration of cadmium fluoride crystals (in hydrogen, in metal vapor, and in vapor mixtures, in an ampule and in a thermal tube) and for bleaching colored crystals. Comparison of the character of the color distribution over the volume of colored and partially bleached crystals indicated that the defect whose diffusion forms the basis of the process of additive coloration of cadmium fluoride crystals is mobile; this is an anion vacancy. (c) 2006 Optical Society of America.