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

Abstract Ag₂S 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 Ag₂S 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 Ag₂S 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 Ag₂S QDs are reduced through a decrease of unsaturated surface Ag atoms. Therefore, Ag₂S 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 Ag₂S QDs with chloride ligands is fully feasible, providing new insights into improving the PLQY of silver chalcogenide QDs.