Size-dependent radiative decay of excitons in CuCl semiconducting quantum spheres embedded in glasses

We report the radiative-decay behavior of Wannier excitons confined in CuCl semiconducting microcrystallites with radii R of 18--77 A{} in glasses. We have observed that the radiative-decay rate is proportional to R2.1. This confirms the theoretical prediction for the size dependence of the radiative-decay rate of ``zero-dimensional excitons'' in quantum spheres. This decay of the exciton is a super-radiant decay in the sense that a coherent polarization is involved.