Transition Metal‐Stabilized Lanthanide Sulfide Nanocrystal Libraries: A New Platform for Solar‐to‐Hydrogen Conversion

Lanthanide (Ln) sulfide semiconductor nanocrystals (NCs) have garnered considerable attention due to their unique optical properties associated with 4f‐orbital participation. However, the scarcity of Ln sulfide‐based NCs with well‐controlled morphology, composition, and crystal phase, arising from the fairly poor affinity between Ln and S elements, has severely hindered their potential applications. Here, we demonstrate a monovalent transition metal cation‐stabilized strategy for the general synthesis of a ternary Ln sulfide nanocrystal library, containing unconventional phases of Ag 2 EuS 2 and AgLnS 2 (Ln = Nd, Sm, Gd, Tb, Dy, Ho) NCs with tunable size and composition via a colloidal thermal decomposition route. Additionally, this approach can be further extended to the synthesis of multicomponent high‐entropy and heterostructured Ln sulfide‐based NCs. As a proof‐of‐concept application, the as‐constructed Ag 2 EuS 2 ‐CdS heteronanorods exhibit improved photocatalytic hydrogen evolution activity, which can be attributed to the interfacial type‐II band alignment for efficient charge separation and transportation. This study expands the scope of rare earth‐based semiconductor materials and provides promising candidates for solar energy conversion applications.