Electrolytic coloration and spectral properties of natural fluorite crystals containing oxygen impurities

Natural fluorite crystals containing oxygen impurities are colored electrolytically by using a pointed cathode and a flat anode at various temperatures and voltages. F and F(2) color centers are produced in colored fluorite crystals. O(2-)-V(a)(+), O(2-)-V(a)(+) aggregate, Yb(2+), Ce(3+) and Sm(2+) absorption bands are observed in absorption spectra of uncolored fluorite crystals. O(2-)-V(a)(+), O(2-)-V(a)(+) aggregate, Yb(2+), Ce(3+), Sm(2+), F, M (F(2)) absorption bands and group of four absorption bands are observed simultaneously in absorption spectra of colored fluorite crystals. Current-time curve for electrolytic coloration of natural fluorite crystal and its relationship with electrolytic coloration process are given. Production and conversion of color centers are explained.