Engineering Excited-State Dynamics in AgInS ₂ Quantum Dots by Gallium Incorporation and GaS _<i>y</i> 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 AgInS2 reduces the number of defect states and improves its photophysical properties. Growth of a GaSy shell on a Ga-doped AgInS2 core further suppresses donor–acceptor pair (DAP states) emission and restores band-edge emission. We synthesized the core–shell architecture of AgInxGa1–xS2–GaSy QDs to make a direct comparison of the photophysical properties with those of AgInS2 and AgInxGa1–xS2 QDs. The photocatalytic activity of these QD systems was evaluated by probing electron transfer to ethyl viologen (EV2+) as an acceptor molecule. In all three cases, ultrafast electron transfer to surface-bound EV2+ occurred with rate constants on the order of ∼1011 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 AgInS2 improves the photophysical and photocatalytic properties of ternary semiconductor QDs and exemplifies the role of a core–shell architecture to suppress back electron transfer.