Silver chalcogenides (Ag₂E; E = S, Se, or Te) quantum dots (QDs) have emerged as promising candidates for near-infrared (NIR) applications. However, their narrow bandgap and small exciton Bohr radius render the optical properties of Ag₂E QDs highly sensitive to surface and size variations. Moreover, the propensity for the formation of silver impurities and their low solubility product constants pose challenges in their controllable synthesis. Recent advancements have deepened our understanding of the relationship between the multi-hierarchical structure of Ag₂E QDs and their optical properties. Through rational design and precise structural regulation, the performance of Ag₂E QDs has been significantly enhanced across various applications. This review provides a comprehensive overview of historical and current progress in the synthesis and structural regulation of Ag₂E QDs, encompassing aspects such as size control, crystal structure engineering, and surface/interface engineering. Additionally, it discusses outstanding challenges and potential opportunities in this field. The aim of this review is to promote the custom synthesis of Ag₂E QDs for applications in biological imaging, and optoelectronics applications.

Effects of surface chemistry on energy levels or optical properties of semiconductor nanocrystals have attracted considerable attention and show great promise in broad applications. Yet, it remains challenging to controllably tune the photoluminescence (PL) of quantum dots (QDs) by manipulating surface ligands. Herein, we investigated effects of the ligand, glutathione (GSH), on PL properties of near-infrared (NIR) Ag₂Se QDs by “on-surface” manipulation, that is, precisely manipulating the chelating group without dissociating the ligand from the surface. The anchoring of the amino group was found to be controlled by solution pH, whereas the binding of the thiol group to the Ag⁺ was pH independent, maintaining the “on-surface” state of GSH. By tuning the pH-controlled binding of amino groups, the energy level or the bandgap of Ag₂Se QDs could be increased by up to 140 meV. The increased bandgap resulted in the blueshift of PL spectrum, which could be reversibly tuned by up to 75 nm. The pH-mediated tunable PL properties of QDs could also be extended to other nitrogen-containing pH-sensitive groups which could coordinate to the Ag⁺, not limited to the amino group. Our work would facilitate the study of nanocrystal surface chemistry and our model that the binding of amino groups affected energy levels of Ag₂Se QDs might facilitate new insights into the electronic structure and energy level of other QD-ligand complexes.