Morphologies, field-emission and ultrafast nonlinear optical behavior of pure and Ag-doped ZnO nanostructures

Pure and Ag-doped ZnO nanofilms with four morphologies, namely nanocone, nanocrystal, nanochips and nanoleaves, have been successfully synthesized by magnetron sputtering method. The composition of the Ag-doped ZnO (AZO) nanostructures was explored by X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). The XRD patterns revealed that the samples exhibited the hexagonal wurtzite structure with preferential orientation along the (002) crystal plane, although the c-axis as preferred orientation decreased with Ag doping. Moreover, we report the photoluminescence, field-emission (FE) and ultrafast nonlinear optical behavior of AZO films. A blue-shift was demonstrated in the UV region of photoluminescence results for the AZO nanostructures. The resulting FE showed that the superior FE properties were attributed to the better morphologies. The ultrafast time resolved optical Kerr gate experiment results showed that AZO was a good candidate for an optical Kerr gate medium due to its ultrafast response and large third-order nonlinear susceptibility. The result of time-resolved photoluminescence showed that the first decay time was about several picoseconds for films, and the slow relaxation process had the lifetime longer than hundred picoseconds. By analyzing the experimental results of the time-resolved photoluminescence experiment, we found the fast decay process could be attributed to the exciton migration and the slow decay to the recombination process of the relaxed excitons.