Electron-phonon interactions in subband excited photoluminescence of hexagonal boron nitride

The h-BN microcrystalline powder with carbon and oxygen impurities have been studied at 83 and 296 K using Raman and photoluminescence (PL) spectroscopies. The observed blue shift of Raman peaks with temperature decreasing have been discussed. Two series of phonon replicas in PL emission spectra with a zero-phonon line at 4.08 eV have been registered under 4.28 eV excitation. The energy levels model of the impurity (C-N-O-N)-complex responsible for observe luminescence was proposed. It was shown that the optically active center retains its electroneutrality in the processes of radiative recombination under subband (in 4.28 eV) or band-to-band excitation. Possible mechanisms of electron-phonon scattering and phonon replicas forming under subband excitation of (C-N-O-N)-complex were analyzed. It was substantiated that at 83 K the longitudinal optical (h omega(LO) = 174 meV) and transverse acoustic (h omega(TA) = 60 meV) phonons at the middle points of high symmetry in the first Brillouin zone participate in the processes of intravalley (M- and K-scattering) and intervalley (K -> M)-scattering, respectively.