title: Enhanced upconversion luminescence from ZnO/Zn hybrid nanostructures induced on a Zn foil by femtosecond laser ablation.
abstract: ZnO/Zn hybrid nanostructures including nanowires and nanonets were induced on a Zn foil by using 400-nm femtosecond (fs) laser pulses with a low repetition rate of 1 kHz and duration of 100 fs. The laser fluence was chosen to be slightly above the ablation threshold of Zn. The luminescence of the formed ZnO/Zn hybrid nanostructures was examined by using fs laser pulses with a high repetition rate of 76 MHz and duration of ~130 fs through both single-photon and multiphoton excitation. While the luminescence spectrum under the single-photon excitation exhibited a single peak at ~480 nm, a broadband upconversion luminescence with many ripples was observed under the multiphoton excitation. More interestingly, the upconversion luminescence of the ZnO/Zn hybrid nanostructures was significantly enhanced by the underlying Zn nanostructures which induced strongly localized electric field. The enhancement of the upconversion luminescence was verified by the short lifetime of only ~79 ps observed for the ZnO/Zn hybrid nanostructures, which is nearly one order of magnitude smaller as compared with the luminescence lifetime of the ZnO nanorods synthesized by using the chemical coprecipitation method. The localization of electric field in the ZnO/Zn hybrid nanostructures was confirmed by the numerical simulations based the finite-difference time-domain technique.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.forename: Cheng-Yun
authors.initials: CY
authors.lastname: Zhang
authors.forename: Xian-Feng
authors.initials: XF
authors.lastname: Li
authors.forename: Jin
authors.initials: J
authors.lastname: Xiang
authors.forename: Shao-Long
authors.initials: SL
authors.lastname: Tie
authors.forename: Sheng
authors.initials: S
authors.lastname: Lan