Near-band-edge photoluminescence from ZnO film: Negative thermal quenching and role of adsorbed oxygen

We studied the photoluminescence (PL) spectra in the near-band-edge region of undoped ZnO films as a function of temperature to determine the thermal quenching behavior in the emission intensity. The quenching of the PL intensity was found to change to an increasing intensity with increasing temperature in the temperature region from 40 to 60 K. On the other hand, a reduction of the vacuum in the same temperature region was observed and was attributed to desorption of oxygen molecules from the cryostat finger. Further investigation revealed that the increase in the PL intensity was caused by adsorption of oxygen on the surface of ZnO films resulting in a decrease in the number of non-radiative recombination centers.