Electronic States and Energy Transfer in PbI_2 Clusters Dispersed in CdI_2 Crystals

Abstract

Luminescence associated with small PbI₂ clusters formed inPb_1-xCd_xI₂ solid solutions has been investigated in the rangeof x between 0.4 and 0.9. Time-resolved measurements reveal that theluminescence at the absorption edge of crystals consists of the bandswith short (sub-ns) and long (μ s) decay times. The two bands arefound to originate from the states related to ³P₁ and³P_oof Pb²⁺ ions. The energy split between the two states increaseswith decrease in the size of PbI₂ clusters. The result is explainedby the change in an exchange energy of electron and hole with thecluster size. Dependences of luminescence decay times on theluminescence and excitation energies indicate that energy transfertakes place among clusters. Temperature dependences of luminescencespectra and decay times are interpreted by the energy transferprocess.