Preparation of highly crystalline zinc hydroxystannate thin film and investigation of its structure and luminescence behavior with various annealing temperatures

Abstract The Zn-Sn-(OH)x thin film was prepared by sol-gel method at low temperature, and its structure, morphology, and photoluminescence properties were studied as a function of annealing temperature. X-ray diffraction patterns showed that the as-grown film contained highly crystalline zinc hydroxystannate. When it was annealed at 300 °C, zinc hydroxystannate was decomposed, and wurtzite-structured ZnO was formed. High-resolution TEM images and selected electron diffraction patterns further confirmed the formation of wurtzite-structured ZnO after annealing. The scanning electron microscope observed that the as-grown Zn-Sn-(OH)x film contained two layers: the upper layer was a crystalline ZnSn(OH)6 thin film, and the underlying layer was an amorphous Zn-Sn-O ternary composite. After it was annealed at 300 °C, some pyramid-like nanostructures appeared on the film surface. As the annealing temperature was further increased, the areal density of the pyramid-shaped nanostructures decreased, but the diameter and height increased. The photoluminescence spectra showed that the ZnSn(OH)6 film exhibited strong violet and blue-green co-emission. After annealing, the visible emission intensity was obviously reduced, while an ultraviolet emission from ZnO was being appeared. We proposed that the violet emission of ZnSn(OH)6 thin film might be related to the zinc interstitials, and the blue-green emission should come from the electronic transitions related to oxygen vacancy levels.