Photoluminescence characteristics of catalyst free ZnO nanowires

Catalyst free ZnO nanowires are grown by thermal evaporation, and are characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD) and photoluminescence (PL). The ultra-violet (UV) emission band observed in the PL of ZnO nanowires grown on ZnO buffer layer is investigated at different temperatures and excitation intensities. The prominently observed transitions at low temperatures are bound exciton (BX), first longitudinal optical (LO) phonon replica of free exciton (FXAn=1 - 1LO) and donor-acceptor pair (DAP). Electron-hole plasma (EHP) emission is observed above 175 K of temperature and above 1.27 MW cm(-2) of excitation intensity which is associated with the thermal ionization of bound excitons. The observed intensity and temperature dependent EHP emission is attributed to spontaneous emission.