Preparation And Photoluminescence Properties Of Mg_xZn_1-xO Nanocrystal Powders And Nanorods

ZnMgO alloy is an important material to construct the heterojunction or superlattice to obtain highperformance laser diode (LD) and light-emitting diode (LED) devices.Mg_xZn_1-xO alloy can form heterostructures with ZnO which can guarantee the function of electropult in wider wavelengths.There have been significant research efforts to study the photoelectric properties of ZnMgO ,However, the model of analyse visible emission of ZnMgO have not set up, and no theory to explain the phenomenon that the visible emission is blue-shifted with increasing Mg-doping concentration.This dissertation mainly studies the photoluminescence of nanocrystalline Mg_xZn_1-xO. Three main factors are considered as following: the concentration of Mg, the annealed atmosphere, the change of XRD structures. The following conclusions can be drawn from the studies:1. Mg_xZn_1-xO nanocrystalline powders were prepared by LCLD reaction. From TEM image, Mg_xZn_1-xO powers are well-proportioned nanograins, ranging from 40 to 60nm.From XRD pattern, it is shown that nanocrystalline powders of this series have a wurtzite crystallographic phase and crystal lattice constants a, c and volume of Mg_xZn_1-xO crystalline cell were calculated. The lattice constants of alloy are ranging with increasing Mg content. Cell volume of Mg_xZn_1-xO has a linear relationship with Mg doping concentration, according with Vegard law, showing Mg ionic is in the substituent of cation.2. The photoluminescence spectra were measured at room temperature to investigate the optical properties of nanocrystals. Photoluminescence of Mg_xZn_1-xO nanocrystals can be attributed to near-bandedge (NBE) emission and lacuna emission. A peak of the UV emissions and lacuna emission is slightly blue-shifted.The strong lacuna emission is blue-shifted with increasing Mg-doping concentration ,And the reason is explained: The Eg of ZnO is 3.18eV, the electrons of the VB transition to the CB, the cavities are captured by VO x, which complex with the electrons of the CB, Then bring the visible light. All of the above, we can get the the mechanism of the visible light which is ZnO.Owing to the Mg_xZn_1-xO alloy, the bottom of conduction is determined by the Zn4s electron states which can shift to a higher energy due to Mg-doping. The energy of Mg2p is higher than that of Zn4s in ZnO, leading to the CB of ZnO:Mg moving to higher energy, higher than that of Zn4s of ZnO. Meanwhile, the environment of O is not changed, the position of VB is fixed, the position of CB leading to higher energy. After the ionic of Mg replace a part of the ionic of Zn, Because the electronegative of the Mg is smaller than that of Zn, which lead to the Eg of VO x to move to the lower energy. We can see the distance that is between the CB and the Eg of VO x is becoming bigger. After the electrons of the CB complex with the cavities of the VO x of Eg ,It can bring the energy bigger than that of ZnO .so the visible light is blue-shiffed.3 Mg_xZn_1-xO nanorods have a different XRD pattern with Mg_xZn_1-xO power. However, no change of profiles and peaks of PL spectrums is observed.