Nature of red luminescence in oxygen treated hydrothermally grown zinc oxide nanorods

A strong broad red luminescence (RL) peak centered at 1.69 eV (FWHM=0.57 eV) at 15 K [1.78 eV (FWHM=0.69 eV) at 300 K] is formed in ZnO nanorods hydrothermally grown at low temperature following thermal annealing at 650 °C for 30 min in an O₂ gas environment. The optical properties of this peak were comprehensively studied using a range of characterization techniques, including photoluminescence and cathodoluminescence spectroscopy, X-ray absorption near edge spectroscopy and electron paramagnetic resonance spectroscopy. With decreasing temperature the RL peak position red shifted and its FWHM became narrower in accordance with the configuration coordinate model. Using these results, the RL has been assigned to highly lattice coupled V_Zn-related acceptor-like centers. No correlation was found between the observed red luminescence and nitrogen impurities.