Dynamics of light-induced absorption in Bi/sub 12/TiO/sub 20/ crystals at two wavelengths

We demonstrate experimentally that the time evolution of light-induced absorption in Bi/sub 12/TiO/sub 20/ crystals exhibits a complicated behavior at their sequential irradiation by incoherent light from two light-emitting diodes with the wavelengths of 660 and 525 nm. To interpret our results, we propose a novel two-center model of light-induced changes in absorption, including taking into consideration the two-level structure for each defect center and the in-center transitions between inherent levels. Comparison of the experimental results obtained in the frame of this model for Bi/sub 12/TiO/sub 20/ crystals with different stoichiometry leads us to the conclusion that the titanium vacancies may be considered as trap centers, which provide light-induced absorption.