Electrolytic coloration and spectral properties of natural beryl crystals

Natural colorless beryl crystals are colored electrolytically at various coloration temperatures and voltages, which should mainly benefit from the appropriate coloration temperatures and voltages. Characteristic spectral bands of Fe2+, Fe3+, Cr3+ impurity ions and Maxixe-type color centers (CO3- and NO30 radicals) are observed in absorption and/or reflection spectra of colored crystals. Current–time curve for electrolytic coloration and its relationship with electrolytic coloration process is given. Formation and conversion mechanisms of impurity ions, radicals and color centers are discussed.