Impact of visible light illumination on ultraviolet emission from ZnO nanocrystals

The influence of a visible Ar+-laser (488 nm) illumination on photoluminescence (PL) from ZnO nanocrystals excited by He-Cd laser (325 nm) at various excitation intensities and temperatures was investigated. A reversible quenching of the UV near-band-edge emission under Ar+-laser illumination was observed. The quenching effect increases with decreasing temperature and He-Cd laser intensity at fixed intensity of Ar+-laser. It is found that the recovery time of the initial PL intensity depends on temperature and Ar+-laser exposure time. At room temperature the PL restored the initial intensity instantly after the turning off the Ar+-laser illumination; however at 10 K this process took several minutes. The proposed mechanism of the observed quenching effect implies an appearance of the additional recombination channel under a visible light illumination due to the recharging of oxygen-vacancy states in the surface depletion zone.