Phonon-absorption recombination luminescence of room-temperature excitons in Cu2O.

We observe two luminescence lines in the range 70\char21{}340 K due to exciton recombination assisted by phonon emission and phonon absorption. The luminescence line shape fits a double Maxwell-Boltzmann distribution at all temperatures, with a temperature that agrees with that of the phonons implied by the relative heights of the two lines. From the fits to the luminescence, we also deduce the variation of the band gap of Cu${}_{2}$O and the exciton-phonon lifetime broadening up to room temperature. The lifetime-broadening data, when compared with time-resolved spectra and data from Ge and GaAs, indicate the existence of a strong two-phonon emission process.