Additive coloration of crystals of calcium and cadmium fluorides

The particular features of additive coloration—formation of color centers as a result of annealing in a reducing atmosphere—have been considered for two crystals with fluorite structure, calcium and cadmium fluorides. The significant differences in the processes of coloration of these crystals are related to both the chemical reactions on their surface and the interaction (or absence of such) between the two components diffusing into the crystal bulk: anion vacancies and electrons.