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

The introduction of rare earth lanthanide ion (Ln³⁺) impurities into all-inorganic lead-free halide perovskites has captured significant research attention and exhibited great promise in a range of optoelectronic applications. Nevertheless, the successful achievement of Ln³⁺ doping within heterometallic layered double perovskite (LDP) nanocrystals (NCs) remains as an unexplored frontier, accompanied by a lack of understanding. Herein, we report the first colloidal synthesis of Ln³⁺ (Yb³⁺, Er³⁺) doped LDP NCs utilizing a modified hot-injection method. The resulting NCs exhibited proficient NIR PL profiles encompassing both the NIR-I and NIR-II regions, achieved <i>via</i> energy transfer down-conversion mechanisms. Density function theory (DFT) calculations reveal that Ln³⁺dopants exhibit a preference for substituting Sb³⁺ cations, occupying within the LDP crystal lattice while maintaining its structural stability. By leveraging sensitizations of intermediate energy levels, we delved into the mechanisms of energy transfer between the host and dopants, and between different types of dopants, across a series of designed Ln³⁺ doped Cs₄CdSb₂Cl₁₂ or Cs₄MnSb₂Cl₁₂ LDP NCs. Interestingly, doping Er³⁺ ions into Cs₄MnSb₂Cl₁₂LDP NCs yielded distinct photophysical responses, <i>i.e.</i>, brightening the pre-dark states of Er³⁺ dopants, owing to the role of Mn component played as an intermediate energy bridge. This study not only presents a novel model system that advances our understanding of sensitization-induced energy transfer mechanisms in doped semiconductor NCs, but also propels the potential applications of all-inorganic lead-free LDP NCs across a wide array of optoelectronic domains, such as optical data encryption, optical telecommunication, multiplexed NIR detection and imaging.