Enhanced photoluminescence of Au-functionalized ZnO nanorods annealed in a hydrogen atmosphere

Au-functionalized ZnO nanorods were synthesized by carbothermal evaporation of a mixture of ZnO and graphite powders at 900 °C followed by gold (Au) sputter-deposition and thermal annealing. The ZnO nanorods had a rod-like morphology with relatively uniform width and length. The widths and lengths of the nanorods ranged from 50 to 100 nm and 3-4 μm, respectively. The diameters of the Au particles on the nanorods ranged from 5 to 40 nm. The dependence of the photoluminescent properties of Au-functionalized ZnO nanorods on the postannealing atmosphere was examined. Annealing resulted in an increase and decrease in the near-band edge (NBE) and deep level (DL) emission intensities of Au-coated ZnO nanorods, respectively, whereas both the NBE and DL emission intensities of uncoated ZnO nanorods were increased by annealing. The intensity ratio of NBE emission to DL emission of the Au-capped ZnO nanorods was increased ~25 fold by hydrogen annealing. The underlying mechanism for NBE emission enhancement and DL emission suppression of Au-capped ZnO nanorods by postannealing is discussed based on the surface plasmon resonance effect of Au.