Theory of Nonradiative Transition of Bistability

Dynamics of the nonradiative transition in bistability centers is studied. The nonradiative transition is induced by an o -diagonal interaction between the two states around the potential crossing region. We propose a model for the lattice relaxation by extending the quantum damping theory to a two level system and analyze the transition dynamics numerically. The transition goes on in two steps; rst during the lattice relaxation process as the phonon wave packet passes the crossing point, then from the relaxed excited state through thermal excitation or quantum tunneling. The persistent photo-conductivity in DX-center and its temperature dependence are also discussed within our model.