Phosphine-Free Synthesis of Monodisperse and Size-Tunable Silver Selenide Quantum Dots via Thermo-Regulated Selenium Dioxide Reactivity for High-Efficiency NIR-II Emission

Colloidal silver selenide (Ag₂Se) quantum dots (QDs) are promising NIR-II emitters owing to their tunable emission and nontoxic compositions. However, current studies suffer from limited size tunability and poor photoluminescence quantum yields (PL QYs) due to conventional toxic organophosphine-based Se precursors with low reactivity. Here, we demonstrate a thermo-regulated synthetic strategy for size-tunable Ag₂Se QDs employing safe and cost-effective SeO₂ as the Se precursor. The mechanism of tuning the Se precursor reactivity derived from SeO₂ by temperature control is thoroughly elucidated, enabling the controllable synthesis of monodisperse Ag₂Se QDs with tunable absorption spectra and a broad size range from 3 to 15 nm. Furthermore, with a Au alloying strategy, we have successfully achieved tunable NIR-II emission (950-1250 nm) with a record-high PL QY of 53.59% at 1140 nm, along with superior photostability. The results will pave the way for eco-friendly Ag-chalcogenide QDs toward applications in biological and infrared optoelectronics.