Effect of annealing on the structural, morphological and optical properties of Ga-doped ZnO nanoparticles by reflux precipitation method

Gallium-doped zinc oxide nanoparticles (GZO NPs) were synthesized using reflux precipitation method and annealed at temperatures ranging from 300 to 600 °C. X-ray diffraction study exhibited a highly crystalline GZO NPs with hexagonal wurtzite structure. The highest diffraction peak intensity was displayed by GZO NPs annealed at 300 °C. The crystallite size of the NPs increased from 12 to 25 nm with the increase in annealing temperature (AT) indicating the tendency of large grain growth in the nanoparticles due to annealing. SEM micrographs showed tiny hexagonal particles for unannealed samples which turned into bigger rods with increasing AT. Photoluminescence spectra displayed the highest excitonic peak luminescence for the sample annealed at 300 °C among its annealed counterparts. The minimum reflection was also observed for the sample annealed at 300 °C. The red shift in the UV emission with increasing particle size due to annealing closely followed the red shift in the band edge emission of the reflectance spectra, indicating that the two complement each other. The band gap of GZO NPs decreased from 3.3 to 3.1 eV with an increase in AT, implying that the optical properties of these materials were clearly affected by thermal annealing. We were able to produce better quality GZO NPs with high crystallinity, minimum lattice stress, and lowest % reflectance in both the visible and UV–Vis range at a relatively lower AT of 300 °C using the reflux method which, to the best of our knowledge, is less reported on to synthesize GZO NPs. Keywords: GZO NPs, Optical properties, Temperature, Transparent conducting oxide (TCO)