4f/5d Electron-Governed Plasmonics in Monodisperse Rare-Earth Hexaboride Nanocrystals for Low-Energy Near-Infrared Photocatalysis

Abstract Rare earth hexaborides (REB6) have attracted considerable attention owing to their unique structure. However, the ultrarigid boron cage covalent network within this structure poses immense challenges to the controlled synthesis of their nanocrystals, severely hindering the exploration of their electronic properties and promising application directions. Here we successfully synthesize monodisperse LaB6 nanocrystals with tunable sizes down to sub-20 nm, during which the formation of reactive intermediates and a solution chemistry-like reaction pathway facilitate the formation of monodisperse, small-sized nanocrystals. This strategy is subsequently extended to other rare earth elements, resulting in the establishment of a material library containing 13 types of REB6 nanocrystals. Based on the library, REB6 nanocrystals demonstrate localized surface plasmon resonance (LSPR) properties in the near-infrared region, strongly related to 4f/5d electronic configurations of rare earth elements. Furthermore, they prove to be potentially low-energy photocatalysts under near-infrared light. This study fills a critical gap in systematic research on REB6 nanocrystals, highlighting their promise as a novel class of low-energy near-infrared photocatalysts.