Multiphonon Instabilities of an Electron-Hole Pair across the Band Gap

Abstract

With the use of a simple adiabatic model in which an electron-hole pair can be annihilated across the band gap under local lattice distortion, we compared the radiative and nonradiative processes, and classified the relaxed excited state into five types considering their roles as recombination channels. They are: the free exciton (F), the self-trapped exciton (S_I or S_II) which was immune from or survived the dynamic nonradiative annihilation on its way from F, the nonluminescent Frenkel defect (S_III), and the unstable state (U), corresponding to the increasing ratio of the exciton lattice relaxation energy to the band gap. The results are not only consistent with the general trend of available experiments on a variety of materials, but will also be useful for the prediction of relevant features of known and unknown materials.