LUMINESCENCE OF LEAD-ION CENTERS IN CADMIUM IODIDE SINGLE-CRYSTALS

Emission and excitation spectra of the luminescence associated with Pb 2+ centers in layered crystals have been investigated. Excitation in t he absorption band of the center induces an emission band with fine vi brational structures at the energy near the absorption band, and a bro ad emission band with large Stokes shift. Measurements of the decay ti me and time-resolved emission spectra reveal that the former band cons ists of two parts originating from ((3)E(u), (3)A(2u)) and (3)A(1u) st ates of Pb2+ with D-3d symmetry. The low energy broad band is ascribed to the emission from a relaxed state of excitons of CdI2 perturbed by Pb2+. Thermally activated transfer of energy is found to take place f rom the excited states of Pb2+ into the perturbed exciton state.