High thermal annealing effect on structural and optical properties of ZnO–SiO 2 nanocomposite

The effect of annealing temperature on photoluminescence (PL) of ZnO–SiO2 nanocomposite was investigated. The ZnO–SiO2 nanocomposite was annealed at different temperatures from 600°C to 1000°C with a step of 100°C. High Resolution Transmission Electron Microscope (HR-TEM) pictures showed ZnO nanoparticles of 5nm are capped with amorphous SiO2 matrix. Field Emission Scanning Electron Microscope (FE-SEM) pictures showed that samples exhibit spherical morphology up to 800°C and dumbbell morphology above 800°C. The absorption spectrum of ZnO–SiO2 nanocomposite suffers a blue-shift from 369nm to 365nm with increase of temperature from 800°C to 1000°C. The PL spectrum of ZnO–SiO2 nanocomposite exhibited an UV emission positioned at 396nm. The UV emission intensity increased as the temperature increased from 600°C to 700°C and then decreased for samples annealed at and above 800°C. The XRD results showed that formation of willemite phase starts at 800°C and pure willemite phase formed at 1000°C. The decrease of the intensity of 396nm emission peak at 900°C and 1000°C is due to the collapse of the ZnO hexagonal structure. This is due to the dominant diffusion of Zn into SiO2 at these temperatures. At 1000°C, an emission peak at 388nm is observed in addition to UV emission of ZnO at 396nm and is believed to be originated from the willemite.