LnIII/CuI Bimetallic Nanoclusters with Enhanced NIR-II Luminescence

Coinage-metal clusters with excellent luminescence properties have attracted considerable interest due to their intriguing structures and potential applications. However, achieving strong near-infrared (NIR) luminescence in these clusters is highly challenging. Here, we have successfully synthesized the first Ln^III/Cu^I bimetallic clusters, formulated as [LnCu₅₄O₆Cl₃(2-MeO-PhC≡C)₃₆] (ClO₄)₆ (Ln = Yb for YbCu₅₄, Er for ErCu₅₄, and Gd for GdCu₅₄). Single crystal X-ray diffraction showed that the LnCu₅₄ clusters have a three-layered core-shell structure, consisting of (LnO₆)@Cu₁₈Cl₃@Cu₃₆ units protected by 36 2-MeO-PhC≡C^- ligands. Notably, the YbCu₅₄ cluster exhibits significant NIR-II luminescence at 986 nm with the solid quantum efficiency of 33.3%, the highest among Cu clusters with NIR-II emission. This work not only reports the first category of Ln^III/Cu^I clusters but also presents a method to enhance NIR luminescence in coinage-metal clusters through the incorporation of Ln^III ions.