Ligand Engineering Unlock Triplet Sensitized-Upconversion Luminescence of Near-Infrared AgAuSe Quantum Dots

Colloidal quantum dots (QDs) exhibit exceptional triplet sensitization capabilities for near-infrared (NIR)-to-visible photon upconversion (UC) via triplet–triplet annihilation (TTA). Although eco-friendly lead-free QDs hold promise as NIR sensitizers, the development of NIR Ag-based QD TTA-UC system remains in its infancy. In this work, we employ AgAuSe QDs as NIR-harvesting sensitizers and demonstrate that surface ligands dictate the feasibility of triplet energy transfer (TET). Thiol ligands are essential for passivating QD surface to achieve high quantum yield, while their strong affinity with Ag+ and Au+ in AgAuSe QDs inhibits the binding of triplet energy transmitter molecules, thereby preventing TET. In contrast, amine-capped AgAuSe QDs enable efficient TET, achieving an upconversion efficiency of 21.5% (normalized to 100%). Moreover, our strategy is universally applicable to NIR-to-visible UC using other Ag-based QDs such as Ag2S. These findings overcome a critical bottleneck that has impeded TET in Ag-based QDs, thereby unlocking their potential for a new generation of UC materials.