Spectral and relaxation features of excitons mixed with excimer quasi-molecular states

For some class of crystals, an excited atomic state gives rise, along with free excitons, to another related type of crystalline excitations also form ed by resonance bindings, viz. an excimer two-atomic quasi-molecule. Such a n exciton polaron, due to its intrinsic vibrational degree of freedom, rath er moves fast through the lattice and mixes with free-exciton states. It is shown that this mixing results in a distortion of the lower part of the ex citon band via splitting it into narrow polaronic subbands corresponding to vibrational levels of the excimer quasi-molecule. This entails essential p hysical consequences involving absorption spectrum and anomalous relaxation phenomena. The theory is in good qualitative agreement with experiment. (C ) 1999 Elsevier Science B.V. All rights reserved.