SPONTANEOUS PHOTON-ECHO FROM BOUND EXCITONS IN CDSE

We have observed spontaneous photon echoes from acceptor bound excitons in CdSe. The I1 line is inhomogeneously broadened to about 1 meV. The homogeneous linewidth is, at low temperature and low excitation density, found to be extremely small and is determined by the recombination lifetime tau-R = 500 ps. The bound excitons have negligible interaction with phonons and interact only weakly with , free excitons with a collision cross section-sigma = 5.8 X 10(-13) cm2. With increasing temperature, the dephasing of the bound excitons is determined by thermal release from the impurity bound state.