Influence of excitation density on photoluminescence of zinc oxide with different morphologies and dimensions

Photoluminescence from zinc oxide (ZnO) nanoparticles, nanorods, microparticles, and single crystals was measured under various conditions of ultraviolet excitation. Near-band-gap and deep-level emissions were observed from all samples. The intensities of both emissions from each ZnO sample exhibited a different nonlinear dependence on the excitation density. These differences could be interpreted by the variation of the light scattering and the specific surface areas of the ZnO morphologies. The intensity ratio of the near-band-gap emission to the deep-level emission from the ZnO samples strongly depended on the density of the excitation light. Our results indicated that the intensity ratio of two emissions depends on the sample type (such as the dimension, specific surface area, etc.), as well as the experimental conditions (such as excitation density, radiation area, etc.). Therefore, this ratio could not be simply employed to unequivocally evaluate the quality of the ZnO.