Study On The Visible Luminescence Mechanism Of ZnO Nanopardcles

Due to the excellent photoelectric characteristics of ZnO，it has a good prospect of application in thefield of UV lasers, UV detectors and light emitting diodes. However, the ultraviolet light-emittingefficiency is affected by the emission of visible light seriously，therefore, the visible luminescencemechanism of ZnO has great significance. Although a large number of research groups have carried outextensive researches on the luminescence mechanism of ZnO in the visible region, no general agreementhas been obtained. In this work, we focused on the green and blue light emitting mechanism in ZnOnanoparticles prepared by sol-gel method.We synthesized two kins of ZnO nanoparticles, their emission laid mainly in the green region and theblue region, respectively by the sol-gel method, the surface of the ZnO nanparticles were then modifiedwith different concentrations of PVP. Powders of ZnO nanoparticles were obtained by precipitation methodafter surface modification. The structural and optical properties of the powders were investigated. Thepowders of ZnO nanoparticles were then annealed in atmosphere at400oC to remove PVP on the surface ofthe ZnO nanoparticles, the changes of the structural and optical properties were compared to reveal themechanism of the gree and blue emission.When the surface was modified by PVP, no remarkable changes were observed on the intensity ofgreen emission in the green-emitting ZnO nanoparticles. When PVP was removed by annealing，theintensity of the green emission band decreased obviously, at the same time the UV emission was greatlyenhanced. This might due to the improvement of the crystal quality. Previous researches revealed that thegreen emission had remarkable quantum confinement effect, thus our result supported the idea that thegreen emission was caused mainly by the deep level defects inside the ZnO nanoparticles, not the defectson its surface. As for the blue emission, things were very different. When the PVP concentration wasincreased，the intensity of the blue emission decreased obviously; when PVP was removed，the intensity ofthe blue emission was restored to a large extent. The lower the concentration of PVP，the stronger theintensity of the restored blue emission became. This revaled that unlike the green emission, the blueemission had great dependence on the surface defects.The XRD peak positions of all the samples were not shifted by the annealing，but the Full width at halfmaximum (FWHM) of the diffraction peaks decreased significantly，showing that the crystal quality of theZnO nanoparticles were greatly improved and particle size became larger.