Solution-processed quantum dots (QDs) that absorb and emit in the short-wave infrared (SWIR) region are paramount in optoelectronics and biological imaging. However, most of the efficient SWIR-emitting QDs contain heavy metals including Pb and Hg, which are highly toxic and therefore restrict their deployment in electronics or in biological applications. Alternatively, the existing heavy metal-free QDs are mostly expensive and/or show low photoluminescence quantum yields (PLQYs) and broad emission beyond 1000 nm. Herein, a novel strategy is presented for synthesising Cu-Zn-In-Se/ZnS (CZISe/ZnS) core/shell QDs with tunable PL in the second biological window (915–1320 nm), leveraging the quantum confinement effect. To improve biocompatibility and environmental stability, these core/shell QDs are passivated using a thin shell of amorphous alumina, resulting in a CZISe/ZnS/Al₂O₃ core/shell/shell heterostructure. This surface passivation ensures environmental and photo-stability and yields a remarkably high PLQY of up to 53.5% and very narrow PL spectra with full widths at half maximum down to 102 meV. By employing these QDs in down-conversion SWIR light emitting diodes (LEDs), external photon conversion efficiency of up to 7% at 1070 nm is achieved. This synthetic approach offers a scalable route to efficient, environmentally benign QDs and advances I-III-VI QD-based SWIR technologies.