Strain‐Activated Shell Phonon Coupling and Defect Passivation for Ultranarrow and Efficient Near‐Infrared‐Emitting CuInZnSe/ZnS Quantum Dots

ABSTRACT Near‐infrared‐emitting copper‐based I‐III‐VI quantum dots (QDs) hold significant promise for photonics and bioapplications, yet their broad photoluminescence (PL) emission severely limits color purity and device efficiency. Herein, we report a hierarchically staged synthesis that decouples and sequentially suppresses defect‐ and phonon‐induced broadening. Starting with Zn‐poor CuInSe 2 QDs via cation exchange, we introduce Zn 2+ alloying to passivate cation vacancies and homogenize composition, forming a defect‐minimized core. Subsequent epitaxial overcoating with a thick ZnS shell strongly localizes excitons, evidenced by suppressed thermal quenching and dominant coupling to a higher‐order longitudinal optical ( LO ) phonon mode of ZnS ( E LO ≈ 141 meV). This shifts recombination from defect‐assisted to near‐band‐edge emission, yielding CuInZnSe/ZnS QDs with an ultranarrow linewidth…