Emission tuning of AgInS2-based core/shell semiconductor quantum dots with type-II and quasi-type-II band alignments

Here, silver indium sulfide (AgInS2)/gallium selenide core/shell quantum dots (QDs) were developed to exhibit red band-edge emission. Previously, we developed AgInS2/gallium sulfide core/shell QDs, which exhibited yellow band-edge photoluminescence (PL). Upon the gallium selenide shell growth, the PL spectra redshifted by more than 100 nm owing to an indirect transition between the core and shell (called the type-II characteristic). After the posttreatment with HCl, the PL wavelength was further redshifted by the formation of Ag-In-S-Se alloyed cores with a narrow bandgap, and the PL intensity increased because of the formation of a quasi-type-II band alignment. In addition, the PL wavelength could be tuned between deep-red and yellow by varying the S/(S + Se) ratio in the Ga-S-Se ternary shells. Based on the long lifetime of the QDs with the alloyed shells, it was suggested that the electronic structure of these alloyed shell QDs is the full type II.