Thermally activated population transfer between two different off-center exciton states in KCl:I

Temperature dependence of emission intensities and lifetimes of hetero-nuclear relaxed excitons [(ClI)-+e], in KCl:I has been studied in the range of 30 - 200 K. From population conversion between the type II and type III configurations observed below 100 K, the energy difference between the two configurations of 13 meV is obtained. An anomalous behavior observed above 100 K suggests that the singlet state above 74 meV from the triplet state of type III is thermally populated to serve as an additional decay channel effective at higher temperatures.