TIME-RESOLVED LUMINESCENCE OF EXCITON POLARITONS IN PBI2

Exciton-polariton luminescence in PbI2 single crystals is investigated at 5 K using picosecond time-resolved spectroscopy. Decay curves of t he luminescence of exciton polaritons are compared with those of the o ptical phonon sideband. The temporal behaviors are consistently analyz ed by taking into account the diffusive motion of polaritons, and the decay-time constants are obtained as a function of the luminescence ph oton energy. The decay time changes from 50 ps around the longitudinal exciton energy up to 140 ps at the energy a little below the transver se exciton one. The change is ascribed to intraband relaxation of pola ritons toward the bottleneck region. [S0163-1829(95)03108-7].