Simultaneous Enhancement of Luminescence Performance and Stability of Cs ₃ Cu ₂ Cl ₅ Crystals in a Humid Environment by a Doping Strategy

Low-dimensional cesium halide copper-based perovskites have attracted tremendous attention due to their advantages in the optoelectronic field. However, intrinsic factors, such as defects on the Cs₃Cu₂Cl₅ surface, tremendously restrict their applications in a highly humid environment. In this work, a series of Cs₃Cu₂Cl₅ crystals doped with metal ions (Mn²⁺, Ni²⁺, Li⁺, and Rb⁺) has been prepared to enhance their luminescence performance and stability in a highly humid environment. In particular, the Rb⁺-doped Cs₃Cu₂Cl₅ exhibits excellent luminescence intensity, photoluminescence quantum yield (72.55%), and water stability. The Rb⁺ dopant induces shrinkage of lattice constants, a decreased band gap, and fewer structural defects. The structure of Cs₃Cu₂Cl₅ is reinforced by Rb⁺ doping to prevent the inorganic framework from the damage of water molecules. A suitable Huang-Rhys factor contributes to the intense excitation-phonon coupling and reduced electron-phonon coupling. Therefore, the self-trapped excitations (STEs) from the 0D Cs₃Cu₂Cl₅ structure contribute to the enhanced luminescence performance and stability in a highly humid environment. The luminescent mechanism is presented to explain how Rb⁺ doping improves the luminescence properties of the Cs₃Cu₂Cl₅ crystals. Moreover, the Mn²⁺-, Ni²⁺-, and Li⁺-doped samples also demonstrate a higher luminescence intensity than that of the pristine Cs₃Cu₂Cl₅. Finally, the practical applications of Rb⁺-doped Cs₃Cu₂Cl₅ crystals are systematically investigated, revealing that the as-synthesized metal-ion-doped inorganic copper-based perovskites may be potentially applied in fields of anticounterfeiting and green LEDs.