Photo- and thermoinduced changes of the optical absorption in Bi 12SiO20 crystals

Results of experiments on changes of optical absorption in Bi 12SiO20 crystals at fixed wavelengths A = 1064 and 633 nm and in wavelength ranges 450-900 and 900-2500 nm at room temperature upon exposure to laser radiation in visible and near-IR ranges and after annealing at temperatures 230-375°C are presented. Enhanced crystal transmittance is observed in the spectral range 490-900 nm after irradiation and thermal annealing. In the spectral range 900-2500 nm, the optical absorption in the crystal increases insignificantly (less than 0.015 cm-1) after thermal annealing. The photo- and thermo-induced changes are retained in the dark for more than 150 h, while crystal irradiation by visible light causes fast absorption relaxation to the initial state. The resonant character of the experimentally observed impurity absorption in the initial Bi 12SiO20 crystals testifies to the presence of defects for which intracenter transitions are possible. The nature of such defects that can present, for example, the donor-acceptor pairs, and their possible contribution to the formation of dynamic photorefractive holograms in Bi12SiO 20 crystals call for further investigations. Copyright © 2009 American Scientific Publishers All rights reserved.