Lanthanide Doping into All-Inorganic Heterometallic Halide Layered Double Perovskite Nanocrystals for Multimodal Visible and Near-Infrared Emission

The introduction of lanthanide ions (Ln³⁺) into all-inorganic lead-free halide perovskites has captured significant attention in optoelectronic applications. However, doping Ln³⁺ ions into heterometallic halide layered double perovskite (LDP) nanocrystals (NCs) and their associated doping mechanisms remain unexplored. Herein, we report the first colloidal synthesis of Ln³⁺ (Yb³⁺, Er³⁺)-doped LDP NCs utilizing a modified hot-injection method. The resulting NCs exhibit efficient near-infrared (NIR) photoluminescence in both NIR-I and NIR-II regions, achieved through energy transfer down-conversion mechanisms. Density functional theory calculations reveal that Ln³⁺ dopants preferentially occupy the Sb³⁺ cation positions, resulting in a disruption of local site symmetry of the LDP lattices. By leveraging sensitizations of intermediate energy levels, we delved into a series of Ln³⁺-doped Cs₄M(II)Sb₂Cl₁₂ (M(II): Cd²⁺ or Mn²⁺) LDP NCs via co-doping strategies. Remarkably, we observe a brightening effect of the predark states of Er³⁺ dopant in the Er³⁺-doped Cs₄M(II)Sb₂Cl₁₂ LDP NCs owing to the Mn component acting as an intermediate energy bridge. This study not only advances our understanding of energy transfer mechanisms in doped NCs but also propels all-inorganic LDP NCs for a wider range of optoelectronic applications.