Preparation Of ZnO Nanostructures And Study Of Defects-related Luminescence Properties

As an important wide band-gap semiconductor, ZnO nanostructures exhibit excellent optical properties and have great potential for optoelectronic applications. ZnO nanostructures have large surface area and high defect density. Defects can affect the life of optoelectronic and transmission of electron and photon, and influence the work of the devices. The key problem is to understand the mechanism of the defects in the photoelectric conversion. ZnO nanorods were prepared by chemical solution method and ZnO nanotubes were synthesized basis on defects corrosion mechanism, ZnO quantum dots-orangic nanocomposite materials were prepared by liquid phase. The electron transfer processes were investigated for nanocomposite materials. Detailed results are as follows:1. ZnO nanorods prepared by chemical solution method were annealed thermal treatment under different temperatures in oxygen ambient. Photoluminescence (PL) spectra of all samples show a weak ultraviolet emission (UV) and a strong broad visible emission band. As the annealing temperature increasing from 200 to 600 oC, the asymmetric visible emission band has a redshift and can be deconvoluted into two subband emissions centered at 535 nm (green emission) and 611 nm (orange-red emission) by Gaussian-fitting analysis. PL excitation spectra (PLE) and PL spectra under different excitation energies reveal that green and orange-red emission have a uniform initial state and can be attributed to the electron transition from shallow donor level Zni to accept levels Vo and to Oi. PL spectra of annealled samples in vacuum ambient confirm the visible emission bands are related to Vo and Oi.2. The poor and incomplete morphology of ZnO nanotubes prepared by hydrothermal method are observed. However, low temperature aqueous solution can obtain a large number of ZnO nanotubes. Controllable aspect ratio of ZnO nanotubes can be achieved through regulation the concentration of KOH solution.3. The visible emission bands from green to blue for ZnO quantum dots prepared by liquid phase are observed by change the amount of NaOH. PL spectra of ZnO/PEG nanocomposite show that green emission band has not affected the surface defect states. But blue emission band significantly decreases with increasing concentration of PEG, indicating that the blue emission is attributed to the surface defect states. PL spectra of ZnO/PVK nanocomposite show that green emission of ZnO nanoparticles increase and the emission of PVK reduce. The excited electrons in PVK can be transfered to the conduction band of the ZnO and induce the enhancement of PL spectra of ZnO quantum dots for ZnO conduction band edge (4.2 eV) below LUMO of PVK (2.3 eV). The charge transfer at the interface can lead to the decrease of the radiative recombination rate and result in the PL spectra intensity of PVK reducing. Green and UV emission of ZnO quantum dots increasesing indicates the number of recombined electron-hole (e-h) pair between Zni state and Vo defects state increase.