Dynamics of excitons in deformable lattice

Dynamics of excitons in organic and inorganic crystals, with its reflection in the optical spectra, is reviewed with particular attention to the competing dispositions towards localization and delocalization of their translational and internal motions. The nature of the exciton zero-phonon line and its phonon side band, and their roles in the Urbach tail, are described in the context of renormalization theory. Selftrapping, defects formation and charge transfer instability are discussed on the basis of global stability test of ground and excited states manifold of the electronic system in the deformable lattice field.