Excitation-dependent photoluminescence of ZnO microrods with MgO surface coating

MgO coating ZnO microrods were synthesized by hydrothermal growth method in a two-stage process. The excitation-dependent photoluminescence of uncoated and MgO-coated ZnO microrods was investigated. We found that the MgO coating passivates defect-states on the surface to reduce largely the green emission, thus the ultraviolet emission efficiency is improved significantly. In addition, the monotonous dependences of violet and ultraviolet emissions on excitation wavelengths are found firstly, while the blue and green emissions are likely in saturated states and are nearly independent of excitation wavelengths. This phenomenon can be interpreted by the transition mechanisms and it indicates that the excitation tuning can also be used to further improve ultraviolet emission efficiency. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.