Photoluminescent behavior of ZnO nanoparticles in a sandwich-like structure SiOx/ZnO/SiOx

In this work, the multilayered thin films composed of ZnO nanoparticles and SiOx layers were prepared by electron beam evaporation. The evolution behavior of photoluminescent properties of the samples with the increase of ZnO nanolayer thickness and annealing temperature was investigated. The morphology, crystal structures and luminescent properties of the samples were analyzed by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and photoluminescence (PL), respectively. The SEM images revealed that the thin films were multilayer-structured with ZnO nanoparticles sandwiched in SiOx layers. The HRTEM disclosed that the SiOx was amorphous and ZnO was crystalline. The componential analyses showed that ZnO nanoparticles contained many oxygen vacancies and the x for SiOx was 1.96. The pure ZnO thin film showed three strong emission bands (namely, near ultraviolet, green and red emission bands) with nearly identical intensity. However, as for the ZnO nanoparticles sandwiched in SiOx layers, their green emission efficiency was greatly improved and the red emission was suppressed. Annealing treatments at 300 and 400 °C further enhanced the green emission. The largely enhanced green emission was attributed to the strong interaction between ZnO and SiOx.