LAUSR

Gradient core-shell Zn-Cu-In-S/ZnS quantum dots (QDs) with small size and highly efficient photoluminescence were synthesized via multi-step high temperature method involving cation exchange. The procedure starts with the preparation of indium sulfide nanoparticles followed by addition of Cu- and Zn-precursors. At this stage, Zn replace Cu atoms and as a result the concentration of Cu ions in final QDs is only about 5 % of the total In content in QD. Zn incorporation and the formation of gradient ZnS shell dramatically increases photoluminescence quantum yield. Furthermore, formation of ZnS shell improves chemical stability of Cu-In-S QDs as demonstrated by the preparation of polystyrene-QDs composites and labeling of glioma cells. This work provides an effective strategy for obtaining efficient and stable heavy metal-free fluorophores.