Engineering Excited-State Dynamics in AgInS ₂ Quantum Dots by Gallium Incorporation and GaS _y Shell Passivation

Ternary I–III–VI semiconductor quantum dots (QDs) are being explored as nontoxic alternatives to Cd- and Pb-based QDs for light-harvesting applications. Incorporation of Ga into AgInS 2 reduces the number of defect states and improves its photophysical properties. Growth of a GaS y shell on a Ga-doped AgInS 2 core further suppresses donor–acceptor pair (DAP states) emission and restores band-edge emission. We synthesized the core–shell architecture of AgIn x Ga 1– x S 2 –GaS y QDs to make a direct comparison of the photophysical properties with those of AgInS 2 and AgIn x Ga 1– x S 2 QDs. The photocatalytic activity of these QD systems was evaluated by probing electron transfer to ethyl viologen (EV 2+ ) as an acceptor molecule. In all three cases, ultrafast electron transfer to surface-bound EV 2+ occurred with rate constants on the order of ∼10 11 s –1 . However, the steady-state yield of the reduced product (viz., EV +• ) varied, reflecting the influence of both intrinsic semiconductor properties and competing back electron transfer processes. These findings highlight how incorporation of Ga into AgInS 2 improves the photophysical and photocatalytic properties of ternary semiconductor QDs and exemplifies the role of a core–shell architecture to suppress back electron transfer.