Quantum number dependence of the photoluminescence broadening of excitonic Rydberg states in cuprous oxide

We report the first observation of photoluminescence from excitonic Rydberg states with quantum number n up to 7 in Cu₂O. We find that the luminescence linewidths increase at elevated temperatures and under increased laser power, and that the effect is more pronounced for a state with a larger n. The temperature dependence is attributed to scattering by longitudinal-optical phonons, whereas the density dependence is explained by the binary collisions of excitons in the ground (n=1) and excited (n≥2) Rydberg states. The n-dependent broadening is discussed on the basis of the overlap of wave functions and collision cross sections determined by the Bohr radius of Rydberg excitons.