PNNL

Abstract

The dynamics of the formation of self-trapped excitons (STEs) and Frenkel pairs upon band-gap excitation have been studied in NaC1 by femtosecond time-resolved spectroscopy at temperatures ranging from 6 to 330K. We found that the primary yield of Frenkel pairs was governed by the process of exciton relaxation that terminated within 10 ps of excitation for all temperatures studied. The yield increases with temperature, and is anticorrelated with the yield of triplet STEs, showing a strong effect of temperature on branching during exciton relaxation. We discuss the mechanism of the temperature-dependent branching of excitons based on the present results and knowledge accumulated from studies of other crystals.