Facile Synthesis of Highly Luminescent UV-Blue-Emitting ZnSe/ZnS Core/Shell Nanocrystals in Aqueous Media

Unlike that for cadmium based nanocrystals, little research has been found on the synthesis of the UV-blue-emitting ZnSe based QDs with photoluminescence (PL) quantum yield QY) superior to 50%. In this article, high-quality water-dispersible ZnSe/ZnS core/shell nanocrystals have been prepared in aqueous media. The epitaxial overgrowth of the ZnS shell was carried out at 90 degrees C in a reaction flask consisting of the shell precursor compounds (zinc acetae as zinc resource and thiourea as sulfur resource), together with the as prepared ZnSe core nanocrystals and the capping reagent glutathione. The optical features and structure of the obtained ZnSe/ZnS core/shell nanocrystals have been characterized by UV-vis, PL spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy-dispersive X-ray analysis (EDX). The influences of various experimental variables, including amounts of ligand and thiourea as well as pH value, on the growth rate and luminescent properties of the obtained core/shell nanocrystals have been systematically investigated. The PL QY of the as-prepared water-soluble ZnSe/ZnS core/shell QDs is up to 65%, which is one of the best results for the water-soluble UV-blue-emitting semiconductor nanocrystals. In comparison with the plain ZnSe nanocrystals, both the PL QY and the stability against UV irradiation and chemical oxidation of the ZnSe/ZnS core/shell QDs have been greatly improved.