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 the luminescence of exciton polaritons are compared with those of the optical phonon sideband. The temporal behaviors are consistently analyzed by taking into account the diffusive motion of polaritons, and the decay-time constants are obtained as a function of the luminescence photon energy. The decay time changes from 50 ps around the longitudinal exciton energy up to 140 ps at the energy a little below the transverse exciton one. The change is ascribed to intraband relaxation of polaritons toward the bottleneck region. [S0163-1829(95)03108-7].