Facile, air-insensitive solvothermal synthesis of emission-tunable CuInS2/ZnS quantum dots with high quantum yields

Yellow-to-red emitting CuInS2/ZnS (CIS/ZnS) core/shell quantum dots (QDs) with a maximum photoluminescence quantum yield (QY) of similar to 65% were facilely synthesized via a stepwise, consecutive solvothermal approach. The size-sorting experiments on CIS/ZnS QDs indicated that the ZnS shell was formed with a relatively uniform thickness even though the size of pre-existing CIS core QDs was not monodisperse. CIS core QDs solvothermally grown for different reaction times of 5-6 h exhibited poor QYs of < 8.8% with deep red emissions as a result of donor-acceptor pair (DAP) recombination. Upon shell overcoating, the band gap energies of CIS/ZnS QDs increased by 0.14-0.23 eV, depending on the CIS core growth time. Such increased band gaps were attributed presumably to the reduction of actual CIS core size, originating from the formation of the alloyed interfacial layer at CIS/ZnS during a long shell growth. Compared to CIS core QDs, the emission of CIS/ZnS QDs was markedly blue-shifted by 0.10-0.18 eV. This blue-shift was discussed based on the shift of QD band gap-dependent donor/acceptor energy levels and the donor-acceptor distance-dependent DAP recombination process.