Optical properties of green synthesized ZnO nanocomposites

A green synthesis route using starch as a capping agent was effectively employed to synthesize ZnO nanostructures through chemical bath deposition. Sodium borohydride was used in one of the approaches in synthesis. Broadening of X-ray diffraction peaks suggested formation of nanosize ZnO in agreement with the high resolution transmission electron microscopy images. As-synthesized ZnO nanostructures were polycrystalline having wurtzite type structure. Average size of the particles was about 8 nm which was in close agreement with measurements from optical studies. Starch was found to play a key role in bringing the strong quantum confinement in ZnO particles. Optical absorption edge was found to be around 240-275 nm which exhibited a clear large blue shift and thereby enhancement of band gap energy. A strong green photoluminescence emission at 604.5 nm was observed in ZnO nanoparticles synthesized using sodium borohydride and may be attributed to the defect controlled recombination mechanism.