LUMINESCENCE OF DEFECT-INDUCED LOCALIZED EXCITON-STATES IN PBI2

Luminescence spectra of PbI2 grown from the vapor phase have been investigated at 2 K. A broad emission is observed in the energy region below the exciton absorption edge where an absorption tail spreads toward lower energy. Measurements of the luminescence decay reveal that the decay curve consists of a fast and a slow components. The slow component is supposed to be the recombination of donor-acceptor pairs. The fast component is attributed, from its spectral profile and the dependence of the decay time on the emission energy, to radiative decay of excitons localized by potential fluctuations caused by lattice imperfections. The sample dependence of the luminescence is briefly discussed in relation to the reflection spectra.