Less contribution of nonradiative recombination in ZnO nails compared with rods

Well aligned ZnO nails with small heads and rods arrays have been grown on indium tin oxides (ITO) substrates by a simple hydrothermal method without any metal catalyst or additives. The optical properties of the as-grown ZnO microstructures were investigated by room-temperature and temperature-dependent photoluminescence spectra. From the PL spectra measured in the range of 80–300 K, the origins of near-band-gap UV lines have been identified in terms of bound exciton complexes and the phonon replicas. We also estimated that the activation energy of the temperature quenching for ZnO nails is higher than that of rods, indicating less nonradiative recombination contributes to the emission process in ZnO nails, which was further testified by the time-resolved PL results. Thus, the relative emission intensity ratio between UV and deep level emission in room-temperature PL spectra for nails is 2.3-times higher than that of rods.