Photoluminescence properties of the entire excitonic series in Cu2 O

We investigated the photoluminescence spectra of Cu2O under photoexcitation at 3.05 eV across the violet band gap. The following three features were found: photoluminescence from blue and violet excitons; photoluminescence from yellow excitons of s,d, and f states in addition to p states with a quantum number up to ten; and emissions associated with the inelastic collision of the 1s yellow excitons. The first process is relevant for the separation of radiative and nonradiative decay rates. The second process likely indicates radiative enhancement of high Rydberg yellow excitons. The last process verifies up-conversion of 1s yellow paraexcitons into higher Rydberg states, which is a critical factor impeding the realization of a high-density paraexciton gas towards transition to the Bose-Einstein condensation.