A Proposed Model of Excitonic Mechanism for Defect Formation in Alkali Halides

Abstract

A new model is proposed for the excitonic mechanism of defect formation in alkali halides by ionizing radiation. The bottleneck governing the time of formation is the non-radiative transition from the second lowest state (2p_z) to the lowest state (1s) of the electron bound by the self-trapped hole. The adiabatic instability of the lower state originating from the mixing and anticrossing of the two states of the electron in the double well potential generates a force squeezing out the central anion pair into [110] direction, which results in the replacement sequence ending as H center on the one hand, and in F center left behind in its ground state (because of node number conservation) on the other hand. The model is consistent with a variety of experimental facts so far reported.