Self-trapping exciton-polaron

Such renormalization can be obtained in the framework of the small polaron theory [3]. Scoq is the energy gain of exciton localization. Let us note that the condition (20) and, therefore, Eq.(26) is correct for S 5/wo and arbitrary B/ujq for the lowest energy of the exciton polaron. So Eq.(26) can be used to evaluate the energy of a self-trapped exciton when the energy of the vibrational or lattice relaxation is much larger then the exciton bandwidth. 

The ideas just reviewed are used below to discuss the electronic structure of specific azides. Such features of the band structure as the magnitudes of the effective masses and the positions of the band extrema in momentum space are - not sufficiently understood to warrant discussion. It should also be noted that electrons and holes tend to polarize the medium in which they move. If they are not particularly mobile, ionic nuclei have time to adjust to their presence by moving toward or away from them. An electron or hole is then dressed by this polarization and either carries it about (as an electron or hole polaron) or is trapped by it (self-trapping). Young [64] suggested that exciton models in the alkali azides should take the polaron character of electrons and holes into account. No one has yet attempted such a description. While it may be that polaron effects are necessary for a proper understanding of electronic structure, the discussion here is limited to a model involving undressed holes and electrons. 

---