Luminescence of Localized Excitons in KCl:I at Low Temperatures

Abstract

Temperature dependence of the intensities of 5.88 eV ( Near-Edge ) and 2.64 eV ( Blue-Green ) emission bands in KCl:I has been investigated in crystals containing various amount of iodine impurities under excitation into each of three absorption bands due to isolated I - ions. Localized excitons created on the I - monomer sites have two relaxed states, NE-state ( one-center type ) and BG-state ( two-center type ). It is confirmed that there is a thermal activation process from the NE-state to the BG-state. Fraction of the relaxation rate into the BG-states, γ BG , is found to increase with increasing iodine contents. This means that the relaxation mechanism of the localized exciton is influenced markedly if another iodine ion is present in the vicinity of the localized exciton.