Defect photoluminescence of ZnO nanorods synthesized by chemical methods

We investigated the morphology and properties of ZnO nanorods synthesized at 90 °C from the solutions of zinc nitrate hydrate and hexamethylenetetramine. Three different substrates were used: Si and Zn foil treated with ZnO nanoparticle seeds, and Si/polycrystalline ZnO film. The morphology of the samples was investigated by scanning electron microscopy, while their optical properties were characterized by photoluminescence spectroscopy. The substrate was found to affect the size uniformity and alignment of ZnO nanorods. The nanorods exhibited strong yellow defect emission. In order to investigate the possibility of improving the optical properties, the influence of annealing at different temperatures (200-600 °C) and in different atmospheres (Ar, air, N2, forming gas) was investigated. While annealing in air improved UV-to-visible emission ratio, defect emission remained prominent. However, annealing in forming gas enhanced UV emission and suppressed defect emission.