Luminescent CuInS₂ quantum dots by partial cation exchange in Cu_{2- x}S nanocrystals

Here, we show successful partial cation exchange reactions in Cu_2-xS nanocrystals (NCs) yielding luminescent CuInS₂ (CIS) NCs. Our approach of mild reaction conditions ensures slow Cu extraction rates, which results in a balance with the slow In incorporation rate. With this method, we obtain CIS NCs with photoluminescence (PL) far in the near-infrared (NIR), which cannot be directly synthesized by currently available synthesis protocols. We discuss the factors that favor partial, self-limited cation exchange from Cu_2-xS to CIS NCs, rather than complete cation exchange to In₂S₃. The product CIS NCs have the wurtzite crystal structure, which is understood in terms of conservation of the hexagonal close packing of the anionic sublattice of the parent NCs into the product NCs. These results are an important step toward the design of CIS NCs with sizes and shapes that are not attainable by direct synthesis protocols and may thus impact a number of potential applications.