Power dependent photoluminescence of ZnO

The effect of excitation power on the photoluminescence (PL) of three types of ZnO samples, including a polycrystalline pellet, thin film, and nanowires, was investigated. The intensity ratio of the defect to band edge emission as well as the overall spectral line shape of the defect emission was strongly affected by the excitation power. A blueshift of the defect emissions at high excitation powers was observed, indicating that donor-acceptor transitions are responsible for the defect emissions. The power dependent PL also suggests that comparisons of defect concentrations among ZnO samples may be possible only if the PL spectra are measured under the same excitation power.