Direct observation of edge luminescence excited by long-lived-exciton-polariton propagation in CdS

Low-temperature time-resolved edge-luminescence excitation spectroscopy has been used to probe the exciton-polariton transport properties in CdS crystals of up to 3 mm thickness. We report the first direct experimental observation of edge luminescence excited by long-lived polaritons with lifetimes exceeding 400 ns which propagate from their origin at the front sample surface to the rear surface, appearing as delayed peaks in the temporal response of edge luminescence. The A exciton-polariton group-velocity distribution is obtained. A group-velocity minimum of 6.8×${10}^5$/s corresponding to the ‘‘bottleneck’’ energy has been observed.