Temperature-dependent photoluminescence of Li-doped ZnO

The temperature-dependent photoluminescence of zinc oxide (ZnO) thin film has been investigated in the present work. ZnO films were prepared by sol-gel spin-coating process; films were doped with Li at different ratios. The prepared sample structure was studied by means of XRD analysis, the optical properties were characterized using UV–visible spectroscopy. The photoluminescence (PL) was measured at different temperature ranged from the ambient to 10 K with a step of 10 K. From XRD analysis and optical characterization, we inferred that Li introduction in ZnO network alters its crystallinity and optical bandgap. The obtained results reveal that the PL spectra are composed of a blue emission assigned to the near band emission due to the recombination of donor-bounded exciton and an intense green emission assigned to the bandgap defects. The deconvolution of the green emission reveals that the latter is composed of two peaks involving the oxygen defects interstitial Oi and vacancy Vo. No peak related to Li dopant was detected. The Li doping causes an enhancement of oxygen vacancy defect. We noticed that the NBE peak position shifts to lower energy with increasing the temperature as well as the green emission. An abrupt quenching has been observed in PL spectra due to the contribution of non-radiative recombination. A model based on the thermal generation of electron is proposed to explain the origin of peak position variation.