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.