Exciton Luminescence of CuCl, CuBr and CuI Single Crystals

Emission, absorption and reflection spectra have been studied on single crystals of cuprous halides. Three types of emission are observed: 1) resonance emission due to the annihilation of the lowest energy intrinsic exciton, 2) narrow lines due to bound excitons at defects or impurities, 3)broad bands and overlapping equidistant narrow bands. In the excitation spectrum for the resonance emission a structure of equal spacing, which corresponds to the longitudinal optical (LO) phonon energy, is found in the exciton absorption band region at low temperatures below 40°K. The resonance emission bands in CuBr and emission lines belonging to the type 2) in CuI are accompanied by the LO phonon assisted satellite bands. The LO phonon energies are obtained as 210±12, 166±7 and 151±8 cm -1 in CuCI, CuBr and CuI crystals, respectively.