High thermal annealing effect on structural and optical properties of ZnO-SiO2 nanocomposite

The effect of annealing temperature on photoluminescence (PL) of ZnO-SiO2 nanocomposite was investigated. The ZnO-Si02 nanocomposite was annealed at different temperatures from 600 degrees C to 1000 degrees C with a step of 100 degrees C. High Resolution Transmission Electron Microscope (HR-TEM) pictures showed ZnO nanoparticles of 5 nm are capped with amorphous SiO2 matrix. Field Emission Scanning Electron Microscope (FE-SEM) pictures showed that samples exhibit spherical morphology up to 800 degrees C and dumbbell morphology above 800 degrees C. The absorption spectrum of ZnO-Si02 nanocomposite suffers a blue shift from 369 nm to 365 nm with increase of temperature from 800 degrees C to 1000 degrees C. The PL spectrum of ZnO-Si02 nanocomposite exhibited an UV emission positioned at 396 nm. The UV emission intensity increased as the temperature increased from 600 degrees C to 700 degrees C and then decreased for samples annealed at and above 800C. The XRD results showed that formation of willemite phase starts at 800 degrees C and pure willemite phase formed at 1000 degrees C. The decrease of the intensity of 396 nm emission peak at 900 degrees C and 1000 degrees C is due to the collapse of the ZnO hexagonal structure. This is due to the dominant diffusion of Zn into Si02 aL these temperatures. AL 1000 degrees C, an emission peak at 388 rim is observed in addition to UV emission of ZnO at 396 rim and is believed to be originated from the vvillemite.