PNNL

Abstract

The dynamics of formation of self-trapped excitons (STEs) and Frenkel-pair upon band-gap excitation have been studied in NaCl by femtosecond time-resolved spectroscopy at temperatures ranging from 6 to 297 K. The relative yields of Frenkel-pairs and triplet STEs are governed by the process of exciton relaxation that terminates within 10 ps of excitation at any temperature studied. Although the Frenkel-pair yield increases with temperature, there is no correlation between the formation time of the F center and the decay time of the STE. Therefore, the thermal coversion of the STEs into Frenkel-pairs is not the origin of the temperature-dependent Frenkel-pair yield in NaCl. Temperature-dependent branching during relaxation is shown to be the origin of the temperature effects.