Stokes and Anti-Stokes D-A Pair Luminescences in PbI2

The luminescence spectrum of PbI 2 is measured in the excitation below the fundamental absorption edge at low temperatures. Phonon-assisted luminescence bands appear on the Stokes side of the excitation energy and these are considered to be associated with the recombination of a donor-acceptor pair accompanied with the emission of optical and acoustic phonons. Also on the anti-Stokes side, strong luminescence bands are observed. It is led to the conclusion that these anti-Stokes luminescences originate from the radiative recombination between an acceptor hole generated by light and an electron of a donor shallower than that neutralized by light.