Diameter-dependent Luminescence Properties Of One-dimensional ZnO Nanostructures

In recent years, the scientists are very interested in the synthesis of semiconductor nanostructures, the study of the optical properties, the discovery of new materials and the exploration of basic physical problems in nano science in order to develop photoelectric devices. ZnO, as a very important semiconductor compound, has become the focus of extensive research in the field of luminescence materials because of its wide band gap of 3.37 eV and large exciton binding energy of 60 meV at room temperature. And ZnO has very important potential applications in ultraviolet laser and light emitting diode. In addition, one-dimensional ZnO nanostructures have been recognized as an important material for a variety research into fundamental physics phenomena and applied physics issues. So the research of the optical properties for the one-dimensional ZnO nanostructures has important significance not only to scientific research but also to practical application.In this thesis, diameter modulated ZnO nanowires which means tapered nanowires were synthesized via chemical vapor deposition method. The morphologies,structure and optical properties of synthetic samples were characterized by using scanning electron microscopy,X-ray diffraction and Raman spectroscopy. And, the optical properties of tapered ZnO wires at different positions were emphasized. It can be seen that the PL peaks’ energies which are attributed to the near band edge(NBE) emission of ZnO wire are different with the change of diameter by testing the photoluminescence spectra of the single ZnO wire. The two-dimensional photoluminescence(PL) mapping image which obtained by the spatially resolved technique further shows the integrated optical emission properties at each position of the wire. Moreover, a blue shift of the UV emission peak was directly observed as the diameter gradually decreased. Besides that, the two-dimensional PL intensity map for the sample indicates that the PL integrated intensity distribution is not uniform along the wire. Finally, the mechanisms of the blue shift and the intensity distributions for the PL spectrum along the wire are proposed based on PL mapping, the Burstein–Moss effect and semiconductor theory.