Microstructure Control of Zn/ZnO Core/Shell Nanoparticles and Their Temperature-Dependent Blue Emissions

The microstructure of the Zn/ZnO core/shell nanoparticles synthesized by laser ablation in liquid medium can be facilely controlled. With the surfactant concentration increased over the critical micelle concentration, the nanoparticle transformed from pure ZnO to a Zn/ZnO core/shell structure. Further, with a decrease of the applied laser power, the ZnO shell thickness was monotonously reduced till 2.5 nm and the ultrafine ZnO nanocrystals embedded in the nanoshells were also reduced till 1.5 nm, which induced the increase of the disorder degree of the nanoshell lattice. The controlling mechanism was discussed according to the competition of capping protection and the oxidation reaction of laser-induced plasma. Blue photoluminescence from the ZnO nanoshells was observed. The emission band exhibited abnormal red-blue shift and narrowing with increasing temperature. Such temperature-dependent behaviors can be well described by a localization model involving an interstitial zinc defect center. These results indicate that this method provides a convenient and universal way to obtain various metal/oxide core/shell nanoparticles with controllable microstructure, and it will be beneficial to an understanding of the physical origins of the blue emission in nanostructured ZnO as well as to extending its optical and electronic applications.