Amine ligands control of the optical properties and the shape of thermally grown core/shell CuInS2/ZnS quantum dots

• A ZnS shell was introduced at high temperature at the periphery of CuInS2 QDs.
• Only CuInZnxS2+x QDs prepared in the presence of oleylamine maintained a good PL QY of 22% after thermolysis.
• Thermolysis of CuInZnxS2+x QDs in the presence of oleylamine generates 6.6 nm-sized pyramidally shaped QDs.

A series of CuInZnxS2+x QDs has been successfully synthesized via a non-injection method by varying the amine (oleylamine, dioctylamine, dodecylamine, octadecylamine) during the ZnS shell introduction on the CuInS2 core. The effects of these amines on the photoluminescence (PL) and on the morphology of CuInZnxS2+x QDs were explored. The optical features and structure of the obtained CuInZnxS2+x QDs have been characterized by UV–visible and fluorescence spectroscopies, time resolved PL, HR-TEM, XRD and EDX. After the ZnS shell introduction at 220 °C, CuInZnxS2+x QDs showed greatly improved properties, the PL quantum yield can reach up to 70% using dioctylamine. The formation of CuInZnxS2+x QDs results in a blue shift of both the absorption and PL due to the formation of the alloyed interfacial layer at CuInS2/ZnS during the shell growth. By increasing the reaction temperature to 250 °C (thermolysis of CuInZnxS2+x QDs), marked red-shifts in PL emissions accompanied by morphological changes of the nanocrystals were observed. The use of oleylamine generates 6.6 nm-sized pyramidally-shaped nanocrystals with a PL quantum yield of 22%.

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