Facile synthesis of homogeneous CuInS2 quantum dots with tunable near-infrared emission

The near-infrared (NIR) and homogeneously emitting CuInS2 quantum dots (QDs) have been successfully prepared by a one-pot thermolysis route using air-stable indium stearate as a precursor/reactant. The CuInS2 QDs exhibit a tunable emission peak in the range of 693-835 nm with a photoluminescence (PL) quantum yield (QY) of up to 8.7%. The QDs with uniform diameter can be assigned to a typical zinc blende structure according to XRD analysis. Time-resolved PL spectroscopy of CuInS2 QDs shows a biexponential trait in which the donor-acceptor recombination (a lifetime of 100-240 nm) occupied 74-92% of the whole PL emission. The type-I structure CuInS2/ZnS core/shell QDs were synthesized in situ for surface passivation, which leads to a dramatic enhancement of PL QY by over six-fold/time (up to 40.1%). The PL decay curve of CuInS2/ZnS QDs retained the biexponential character with a longer lifetime. The as-prepared CuInS2 based QDs with lower toxicity and desirable optical features are good candidates for biomedical fluorescence labelling.