NEW APPROACH TO THE THEORY OF NONRADIATIVE-TRANSITIONS - PASSING THE SELF-TRAPPING BARRIER

The adiabatic theory of temperature dependence of the self-trapping (ST) rate is developed. It is shown that there exist two types of solutions. They correspond to the classical activational regime and to thermoactivated tunneling. The first solution dominates at high temperatures and results in the Arrhenius law. The second one dominates at low temperatures and is described mathematically in terms of instantons. These general results of the theory are not restricted by any specific models. The theory is developed in an exponential approximation, however, for the low-temperature region the temperature dependence and magnitude of the pre-exponential approximation, however, for the low-temperature region the temperature dependence and magnitude of the pre-exponential factor are found as well. The dependence of the ST rate on the energy of the exciton, as well as a mechanism of the defect production in the course of ST are discussed. In conclusion a comparison with experimental data has been outlined briefly.