Influence of Mo doping on the luminescence properties and defect states in ZnO nanorods. Comparison with ZnO:Mo thin films

ZnO:Mo powders of nano- and microrods were fabricated by the hydrothermal growth method. ZnO:Mo thin films deposited on a fused silica glass substrate were synthesized for comparison as well. X-ray diffraction and fluorescence (XRD, XRF), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), photo- and radioluminescence (PL, RL) were applied to characterize these materials. The samples were also annealed in air at elevated temperatures to study the defects and luminescence modification. In particular, EPR spectra in the powder and thin film samples were composed of the signals originating from shallow donors before any treatment. The Mo5+ signal appeared after the annealing at 350 degrees C in the powder spectra. It existed prior to the treatment in the thin film samples. New EPR signal appears after X-ray irradiation in the powder samples. Red luminescence occurs in all powder samples. The intensity of this band demonstrated different dependences on the annealing temperatures in the samples with different Mo content. The exciton-related band at 380 nm never observed in the powder samples before the annealing, appears after the annealing at 350 degrees C. The strongest it was in the ZnO:Mo powder with low Mo content.