Quantum effect and up-conversion luminescence of ZnO-SiO2 composite films synthesized by sol-gel technique

ZnO thin films and ZnOSiO2 composite films were deposited on glass substrates by solgel method. Atomic force microscope images showed that ZnO nanoparticles havd spherical shape of relativly small size. The ultravioletvisible transmittance spectra showed that the transmittance of ZnOSiO2 composite film is about 85% in visible range and the transmittance begins to drop at about 330 nm and reaches zero around 290 nm. Due to quantum effect, the absorption edge has an obvious blue shift. Photoluminescence spectra measurement indicated that ZnOSiO2 composite film excited by a Xe lamp with different wavelength has a UV emission around 290 nm coming from combination of free excitons, which is in agreement with the ultravioletvisible transmittance measurement result. Meanwhile, two photon and three photon absorption and upconversion luminescence were observed in the ZnOSiO2 composite film.