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

Emission and excitation spectra of the luminescence associated with Pb2+ centers in layered crystals have been investigated. Excitation in the absorption band of the center induces an emission band with fine vibrational structures at the energy near the absorption band, and a broad emission band with large Stokes shift. Measurements of the decay time and time-resolved emission spectra reveal that the former band consists of two parts originating from ((3)E(u), (3)A(2u)) and (3)A(1u) states 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 from the excited states of Pb2+ into the perturbed exciton state.