Effect of oxygen partial pressure on the photoluminescence properties of sol-gel synthesized nano-structured ZnO thin films

Nanostructured ZnO thin films were prepared by spin coating on glass substrate. The precursor ZnO gel powder was thoroughly characterized by particle size measurement, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy and selected area diffraction pattern analyses. The sol on heating at 450-650 °C resulted in the formation of dried mass with particle size in the range of 30-40 nm. The photoluminescence (PL) peak of ZnO thin film heat treated at 450 °C for different periods appeared at 400 nm. But when the film was heat treated at the same temperature (450 °C) under reducing atmosphere, another PL peak appeared at 443 nm. Heat treatment of the film at 650 °C for 3 h under reducing atmosphere resulted in the appearance of PL peaks at 500 and 555 nm. The PL peaks developed were related to the defect states of zinc oxide lattice developed at different oxygen partial pressures during the heat treatment.