LASER MODULATION OF PHOTOCHROMIC EFFECT IN CRYSTALS WITH SILLENITE-TYPE STRUCTURE

In sillenite-type crystals at low temperatures the phenomena of effective laser modulation of the photochromic effect (LM PCE) previously investigated in steady-state conditions are found. The lack of effects of spatial excitation transfer during PCE is shown from the kinetics of PCE laser "switching". Conclusions about intracentre behaviour of the above processes are made. The IR laser illumination is found to lead to anomalous LM PCE (optical obscurity of crystals) relative to the previously known steady-state IR effect on PCE (crystal brightening). Based on the LM PCE data, a new model of intracentre optical processes and PCE centers with anomalously strong electron-phonon interaction (EPI) near the centers with a number of excited states is proposed. The idea of the above model is the assumption of non-photoactivity of the ground states of PCE due to strong EPI from which the centers remove at IR illumination. The main regularities of PCE previously known are also explained by the microscopic model proposed with regard to Stokes losses of lattice relaxation.