Synthsis And Optical Properties Of Ce Or Ag-doped ZnO Micro/nano-materials

In this paper, we have synthesized Ce or Ag -doped ZnO micro/nano-materials. The as-synthesized micro/nano-materials were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD), where the morphologies of these doped ZnO micro/nano-materials were controlled by different temperatures. The following conclusions can be drawn from the studies:1). Many Ce-doped ZnO nanostructures were synthesized by sol-gel method combining with chemical vapor deposition, such as: nanowires, nanorods, nanobrushes, nanoscrewdrivers. The length of nanowires is about 20um and the diameter is 200nm; the nanobrushes and nanoscrewdrivers are composed of two parts: a large 3D micron-sized hexagonal prism, and vertical 1D nano-sized nanorod, the diameter of the ZnO base is about 3μm and the length is about 5μm, while the diameter of the nanorod is about 200nm and the length is about 1μm.The XRD pattern shows that Ce-doped ZnO nanostructures have a wurtzite crystallographic phase (as indicated in JCPDS 79-0207), no signals of other impurities. X-ray photoelectron (XPS) spectra analyses suggest the Ce doping should influence the structure of valence band states and the band gap (Eg). The room temperature photoluminescence spectra show a weak ultraviolet (UV) emission and a strong broad green emission. The UV emission corresponds to near-band-edge (NBE) peak which originated from the recombination of the free excitons of ZnO. The origin of visible broad band is related to structural defects and impurities. The enhancement of the green emission band occurs due to the increased defect sites as predicted from the XRD and XPS data.2. Many Ag-doped ZnO nanostructures were synthesized, such as: nanowires arrays, nanorods arrays, nanotubes arrays. The diameter and the lengths of nanorods ~500nm and 15-20um, respectively; the length of nanotubes is 20um and the diameter is about 3um. The SAED indicates that the nanostructures are typical single-crystalline structure and growth along [0001] direction.The typical XRD patterns of the Ag-doped ZnO nanostructures indicate that the samples exhibit high crystallinity of wurtzite crystal structure. Based on the results of SEM, TEM, and XRD, we propose a model of the growth for these nanostructures are V-L-S. The PL of Ag-doped ZnO nanostructures are composed of two parts: a weak UV emission and a strong broad green emission. In our work, oxygen vacancies and zinc interstitials can easily form because N2 was used for transport gas.