Spontaneous photon echo from bound excitons in CdSe

We have observed spontaneous photon echoes from acceptor bound excitons in CdSe. The ${\mathit{I}}_1$ 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 ${\mathrm{\tau }}_{\mathit{R}}$=500 ps. The bound excitons have negligible interaction with phonons and interact only weakly with free excitons with a collision cross section σ=5.8×${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^2$. With increasing temperature, the dephasing of the bound excitons is determined by thermal release from the impurity bound state.