Effect of pH on Crystal Size and Photoluminescence Property of ZnO Nanoparticles Prepared by Chemical Precipitation Method

The effects of pH value on crystal size and optical property of zinc oxide nanoparticles prepared by chemical precipitation method were investigated. Prepared samples have been characterized by means of X-ray diffraction, scanning electron microscopy, ultraviolet visible spectrometer and photoluminescence spectrometer. From X-ray diffraction profile, it is found that the particle size of sample increases from 13.8 to 33 nm when the pH value of the solution was increased from 6 to 13. Microstructural study also shows that the particle size increases with pH value. Hexagonal shape of the zinc oxide nanoparticle has been confirmed by the scanning electron microscopy image. The recorded ultraviolet visible spectrum shows excitonic absorption peaks around 381 nm. The energy gap of the prepared samples has been determined from the ultraviolet visible absorption spectrum, effective mass model equation and Tauc's relation. It was found that the energy gap of the prepared samples decreases with increase in pH value. The recorded blue shift confirmed the quantum confinement effect in the prepared zinc oxide samples. Photoluminescence spectrum infers that the increase in pH value shifts the ultraviolet visible emission but not the violet and green emissions.