Highly reactive se precursor for the phosphine-free synthesis of metal selenide nanocrystals

Herein we present a general phosphine-free synthesis of metal selenide nanocrystals. In this method, reduction of elemental Se with sodium borohydride in the presence of hydrophobic alkylamines generated hydrophobic alkylammonium selenide species in situ. The phosphine-free Se precursor was found to be highly reactive and suitable for the synthesis of various metal selenide nanocrystals. Its high reactivity was also exploited to derive core-shell CdSe@CdS quantum dots (QDs) in one-pot synthesis, without the need for prior purification of CdSe cores. This provided a greener and less expensive route to the large-scale synthesis of metal selenide QDs. Our approach also presented a facile route for tuning the surface properties of metal selenides. It was found that the presence of excess elemental sulfur could quench the luminescence of QDs by the trapping of surface electrons. However, the luminescence could be photoactivated via ultraviolet (UV) irradiation. This deactivation-photoactivation process was reversible, and could be applied toward generating a designed photoluminescent pattern on a solid substrate.