Surface luminescence in ZnO nanoparticles

Spectral and time-resolved photoluminescence (TRPL) measurements were performed on ZnO nanoparticles of different sizes (17–300 nm). Under a low photon energy excitation of 2.33 eV, the time-integrated PL spectra (TIPL) clearly exhibit broad emission in the range of 1.2–2.3 eV. Upon increase of the particle size, a red-shift in the PL peak position was observed. Gaussian analysis indicates that this red-shift corresponds to the increased relative magnitude of the Gaussian combination in the low energy region. In addition, TRPL demonstrates a clear relationship between the particle diameters and the PL decay times. The shortening of the PL lifetime could be explained by a surface states model.