Coherent energy migration in solids. II. Spin-resonance absorption in coherent-wave-packet states and the effects of phonon-exciton scattering

Abstract

A model is presented which describes the effects of phonon-exciton scattering on the coherent migration of Frenkel excitons. The development is such that it provides for experimental verification through the use of electron-spin-resonance techniques. Both qualitative and quantitative information on the mode of exciton migration, the rate of phonon-exciton scattering, and the temperature dependence of phonon-exciton scattering at low temperatures are obtainable from the model. One-dimensional triplet excitons are considered specifically, although the treatment is applicable to other phenomena such as impuriton migration. Three cases are treated. In the first, the exciton dispersion is taken to be much smaller than the acoustic-phonon dispersion. In the second, the exciton and phonon dispersions are taken to be approximately equal, and in the third case, the exciton dispersion is taken to be much larger than the acoustic-phonon dispersion. In each case, the possibility of long-range energy migration is considered and is related to experimental observables. In addition, multidimensional exciton interactions in the spin-orbit-coupled singlet states, and multidimensional exciton interactions in the triplet state are discussed.