Effects of polymer coating and thermal annealing on the structural and optical properties of ZnO microrods
The effects of polymer coating and thermal annealing as post-growth treatments on the structural and optical properties of ZnO microrods are presented. Hexagonal ZnO microrods with lengths and diameters ranging from 5.7 to 14.7 µm and 1.4 to 2.3 µm, respectively, are initially synthesized by hydrothermal growth method and then subjected to different post-growth treatments by coating with polyvinylpyrrolidone (PVP) and by annealing in ambient air at 300°C. PVP coating leads to pitted surfaces of the ZnO microrods. Moreover, the ZnO microrods subjected to PVP coating and to annealing in air both have reduced visible emission compared with the as-prepared microrods. However, the as-prepared and the coated microrods exhibit green emission centered around 558 nm, while the annealed ZnO microrods exhibit yellow emission centered around 574 nm. The observed effects of PVP coating and thermal annealing are attributed to the interaction between the PVP molecules and the ZnO surface and to the diffusion of oxygen-related defects, respectively. Regardless of postgrowth treatment, the ZnO microrods exhibit intense and very fast ultraviolet (UV) emissions with lifetimes less than 30 ps which makes them potential building blocks for microstructured scintillator devices.