Emergence\nof Near-Infrared Photoluminescence via ZnS\nShell Growth on the AgBiS<sub>2</sub> Nanocrystals

AgBiS<sub>2</sub> nanocrystals (NCs), composed of nontoxic,\nearth-abundant\nmaterials and exhibiting an exceptionally high absorption coefficient\nfrom visible to near-infrared (>10<sup>5</sup> cm<sup>–1</sup>), hold promise for photovoltaics but have lack of photoluminescence\n(PL) due to intrinsic nonradiative recombination and challenging shell\ngrowth. In this study, we reported a facile wet-chemical approach\nfor the epitaxial growth of ZnS shell on AgBiS<sub>2</sub> NCs, which\ntriggered the observation of PL emission in the near-infrared (764\nnm). Since high quality of the core is critical for epitaxial shell\ngrowth, we first obtained rock-salt structured AgBiS<sub>2</sub> NCs\nwith high crystallinity, nearly spherical shape and monodisperse size\ndistribution (<6%) via a dual-ligand approach reacting Ag–Bi\noleate with elemental sulfur in oleylamine. Next, a zincblende ZnS\nshell with a low-lattice mismatch of 4.9% was grown on as-prepared\nAgBiS<sub>2</sub> NCs via a highly reactive zinc (Zn(acac)<sub>2</sub>) precursor that led to a higher photoluminescence quantum yield\n(PLQY) of 15.3%, in comparison with a relatively low reactivity precursor\n(Zn(ac)<sub>2</sub>) resulting in reduced PLQY. The emission from\nAgBiS<sub>2</sub> NCs with ultrastrong absorption, facilitated by\nshell growth, can open up new possibilities in lighting, display,\nand bioimaging.