Photoluminescence Enhancement of NIR-II Emissive Ag2S Quantum Dots via Chloride-Mediated Growth and Passivation

Ag 2 S quantum dots (QDs) with high photoluminescence quantum yield (PLQY) in the second near-infrared (NIR-II, 1000–1700 nm) window are urgently pursued. Halide atoms (especially chloride) have been studied as inorganic capping ligands on improving the PLQY of Cd-, Pb-based chalcogenide QDs; however, it remains a challenge to well replace the organic ligand with chloride ligand from silver chalcogenide QDs. Herein, a novel strategy to prepare Ag 2 S QDs with significant photoluminescence (PL) enhancement via chloride-mediated growth and passivation is demonstrated. The oleylamine and oleate ligands on the surface of silver-rich Ag 2 S QDs are readily replaced by chloride ligands due to the smaller size and higher binding affinity with Ag + . Upon partial ligand exchange and chloride passivation, the surface trap states in Ag 2 S QDs are reduced through a decrease of unsaturated surface Ag atoms. Therefore, Ag 2 S QDs with approximately 300-fold enhancement of PL intensity, and a PLQY of 47.6% at 1220 nm emission, and a lifetime of 256 ns are obtained because the nonradiative recombination is inhibited. This work reveals that the passivation of Ag 2 S QDs with chloride ligands is fully feasible, providing new insights into improving the PLQY of silver chalcogenide QDs.