Solution Synthesis and Light-Emitting Applications of One-Dimensional Lead-Free Cerium(III) Metal Halides.

Combining rare earth elements with the halide perovskite structure offers valuable insights into designing nonlead (Pb) luminescent materials. However, most of these compositions tend to form zero-dimensional (0D) networks of metal-halide polyhedra, with higher-dimensional (1D, 2D, and 3D) structures receiving relatively less exploration. Herein, we present synthesis and optical properties of Cs3CeCl6·3H2O, characterized by its unique 1D crystal structure. The conduction band minimum of Cs3CeCl6·3H2O becomes less localized as a result of the increased structural dimension, making it possible for the materials to achieve an efficient electrical injection. For both Cs3CeCl6·3H2O single crystals and nanocrystals, we also observed remarkable luminescence with near-unity photoluminescence quantum yield and exceptional phase stability. Cs3CeCl6·3H2O single crystals demonstrate an X-ray scintillation light yield of 31900 photons/MeV, higher than that of commercial LuAG:Ce (22000 photons/MeV); electrically driven light-emitting diodes fabricated with Cs3CeCl6·3H2O nanocrystals yield the characteristic emission of Ce3+, indicating their potential use in next-generation violet-light-emitting devices.

Organic-Inorganic Hybrid Cuprous-Based Metal Halides with Unique Two-Dimensional Crystal Structure for White Light-Emitting Diodes.

Ternary cuprous (Cu+)-based metal halides, represented by cesium copper iodide (e.g., CsCu2I3 and Cs3Cu2I5), are garnering increasing interest for light-emitting applications owing to their intrinsically high photoluminescence quantum yield and direct bandgap. Toward electrically driven light-emitting diodes (LEDs), it is highly desirable for the light emitters to have a high structural dimensionality as it may favor efficient electrical injection. However, unlike lead-based halide perovskites whose light-emitting units can be facilely arranged in three-dimensional (3D) ways, to date, nearly all ternary Cu+-based metal halides crystallize into 0D or 1D networks of Cu-X (X = Cl, Br, I) polyhedra, whereas 3D and even 2D structures remain mostly uncharted. Here, by employing a fluorinated organic cation, we report a new kind of ternary Cu+-based metal halides, (DFPD)CuX2 (DFPD+ = 4,4-difluoropiperidinium), which exhibits unique 2D layered crystal structure. Theoretical calculations reveal a highly dispersive conduction band of (DFPD)CuBr2, which is beneficial for charge carrier injection. It is also of particular significance to find that the 2D (DFPD)CuBr2 crystals show appealing properties, including improved ambient stability and an efficient warm white-light emission, making it a promising candidate for single-component lighting and display applications.