RoHS‐Compliant, Cu‐Zn‐In‐Se‐Based Core/Multi‐shell Quantum Dots with Efficient and Tunable Short‐Wave Infrared Emission

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/Al 2 O 3 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.