Multiphonon resonant Raman scattering and the second-order Raman processes in the excitonic luminescence of ZnO

Multiphonon assisted optical emission processes of ZnO in the vicinity of excitonic luminescence were investigated using the excitation-emission maps and the photoluminescence (PL) excitation spectra recorded at different emission photon energies. Multiphonon resonant Raman scattering (RRS) was found to have the temperature dependence similar to the excitonic luminescence, but not to be influenced by the surface conditions and annealing process. The multiphonon RRS and the longitudinal optical (LO) phonon replicas of PL lines were substantiated to originate from the cascade scattering of exciton polaritons with successively emitting LO phonons. The second-order Raman processes were observed to take part in the capture of exciton polaritons by the defects, forming the neutral donor bound excitons.