Defect Induced Changes in the Linear and Non-Linear Optical Properties of ZnO Nanotetrapods

Abstract

Here, we investigate the origin of green luminescence in ZnO nanotetrapods using nonlinear optical z-scan measurements in tandem with photoluminescence measurements. To this end, we synthesized ZnO nanotetrapods using a chemical vapor deposition (CVD) process, annealed at temperatures below 200 C in O2, Ar, and Zn metal vapor and measured the ensuing optical properties. Our z-scan measurements show that all samples exhibit an effective three-photon absorption (3PA). Furthermore, the 3PA coefficient varies with the incident laser intensity consistent with the presence of real mid-gap states. Interestingly, the rate of change for the 3PA coefficient is strongly influenced by the annealing conditions. Annealing in Zn vapor (Ar and O2 leads to an increase (decrease) in green luminescence and the 3PA coefficient, strongly suggesting that the Zn interstitials are involved in the mechanism of green luminescence.