ZnO has attracted great attentions due to its stimulated emission and optically pumped laser behavior.Recent studies proved that the emission properties of ZnO films are dependent on the growth conditions and certain doping of other elements can improve the luminescence properties greatly.Therefore

suitable dopants and proper growth conditions are of great benefit to current research.In this report

V-doped ZnO thin films were investigated including their microstructures

photoluminescence properties and the effects of post-annealing.The undoped ZnO and 1%V-doped ZnO thin films were prepared on single crystalline Si(100) substrates by sol-gel spin coating method.The spin-coating process was repeated 8 times to increase the thickness of the films

with two-step rapid-annealing(300℃ for 300 s and 550℃ for 300 s) in air.A further annealing at 800℃(post-annealing) was performed after the 8th rapid-annealing.The structures

morphologies

and luminescence properties of the films were investigated by X-ray diffraction(XRD)

scanning electronic microscopy patterns(SEM)

and photoluminescence(PL).According to XRD pattern

no V-related phases were detected in the prepared samples.The crystalline quality of V-doped ZnO thin films was worse than that of undoped sample before post-annealing

in that the doping of V destroyed the structure of ZnO.Whereas

after post-annealing

the crystallinity of V-doped films became better and there appeared diffraction peaks of zinc silicate in the XRD pattern of V-doped films.We attribute the formation of high crystalline of zinc silicate to the catalytic effect of V.Scanning electronic microscopy patterns indicated all samples were compact and homogeneous thin films composed of uniform nano-particulates.The thickness of the films is about 300 nm.As to photoluminescence spectra

measurements of the V-doped samples without post-annealing showed that the intensities of the UV peak and green peak decreased greatly compared with those of pure ZnO films.Nonradiative recombination due to implantation induced damage is obviously dominating.After additional annealing at 800℃ for an hour

the optical quality can be well restored.Both the UV peak and green peak of the V-doped ZnO thin film increased while the former increased more.Moreover

the intensity of UV emission due to exciton recombination for V-doped ZnO films was obviously stronger than that of undoped ZnO thin films

while the intensity of the green peak was on the contrary.During post-annealing

doped V could fill part of defects of ZnO.The origin for the green emission could be attributed to the decrease of defects in the films.At the same time

the post-annealing decreased the quenching centers induced by V-dopant.As a result

the intensity of UV emission for the V-doped ZnO thin film was increased compared with undoped ZnO sample at the same conditions.