We investigated the photoluminescence spectra of ${\mathrm{Cu}}_2\mathrm{O}$ 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.

• Received 17 July 2018
• Revised 28 September 2018

DOI:https://doi.org/10.1103/PhysRevB.98.195205