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Abstract
The optical absorption spectra and photochromic effect of Bi12SiO20 pure, Al and Ga doped single crystals and crystals of nonstoichiometric composition have been investigated in the wavelength range between 8,000–26,000 cm−1.
It is suggested that the mechanism of the color centers photo-generation takes place for Bi5+ ions tetrasites according to the following scheme: Bi5+ + 2e → Bi3+. The role of oxygen vacancies and Bi3+, Al3+ and Ga3+ ions in the lattice octasites of Bi12SiO20 crystals in the formation of the optical absorption shoulder is discussed.