Nanocrystalline ZnO films prepared by pulsed laser deposition and their abnormal optical properties

Nanocrystalline ZnO films were fabricated by pulse laser deposition. As the filmʹs grain size decreases to small nanosize (20 nm), the film exhibits unique optical properties. The photoluminescence spectrum has three broad emissions located across ultraviolet-violet, yellow-green-orange and red regions. The structures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The results indicate that the nanocrystalline ZnO film with small nanosize has degenerated crystalline quality and various structured defects. These abnormal optical properties were attributed to the abundant structural defects and the quantum confinement effect of the nanocrystalline ZnO films.