Energy features of bound polaron states in colored NaCl and KBr crystals

Abstract

Thermoionization of bound polaron states in γ-irradiated KBr and NaCl crystals is studied in the temperature range 71–104 K. It is shown that the complex shape of the thermoionization curves in this temperature range is determined by the presence of three types of electron traps that are unstable (each trap decays according to an exponential law) and one type of stable trap. This explains a sharp break on the dependence of the logarithm of the lifetime on the reciprocal temperature, which is observed for a KBr crystal, as well as a number of discrepancies in the results obtained by other authors. The physical parameters (activation energy H for thermoionization, the optical absorption peak Eop, the spectral photoionization threshold Ei, and the energies of phonons participating in the optical absorption, Lop, and in photoionization, Lphc) obtained in the present paper and in our earlier studies on KCl, NaCl, and KBr crystals are analyzed, and the relations between these quantities predicted by available theories are considered.