Distortion of excitonic states by lattice defects and violation of the quasi-momentum conservation law in excitonic absorption

Abstract

Absorption spectrum, related to creating excitons with nonzero wave vector inside a wide band, is considered for an insulator crystal with lattice defects. It is shown that the main contribution to absorption is determined not by the scattering section of defects but by the exciton state distortion within the core or a close vicinity of a defect. Its contribution to absorption differs from that of an impurity center by a great multiplier dependent on the size of the region of distortion. Due to this, lattice defects with a very low concentration ( ∼10 14 cm −3 ), present even in a perfect crystal, can manifest themselves in luminescence excitation spectrum. This can be used for the diagnostics of lattice defects in insulator crystals (e.g., scintillators) exposed to irradiation.