Ag+-induced energy level splitting in Ln-MOFs achieves enhanced Eu3+ emission intensity

In lanthanide (Ln) complexes, the oversight of f-electrons and inner-shell relativistic interactions has constituted a critical gap, limiting a nuanced understanding and modulation of their luminescent properties. Addressing this issue, our study introduces a pioneering series of Ln-based metal-organic frameworks (Ln-MOFs), designated as Ln-TCPP, utilizing tetraphenylpyrazine-derived ligand and Ln³⁺ ions (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) to modulate luminescence through advanced synthesis and theoretical analysis. We particularly emphasize the enhancement of Eu³⁺ luminescence in Ln-TCPP, where incorporating Ag⁺ ions to replace [(CH₃)₂NH₂]⁺ within the Ln-MOFs plays a pivotal role. Theoretically, by employing time-dependent density functional theory (TD-DFT) with full-electron relativistic effects, we demonstrate that Ag⁺ ions induce a splitting in the energy levels of Eu³⁺. This splitting effectively reduces the rate of non-radiative transitions, significantly amplifying Eu³⁺ emission intensity. Our findings not only fill a long-standing void in understanding the all-electron relativistic interaction between f-electrons in Ln-MOFs luminescence but also establish a new strategy for controlling and optimizing the luminescent efficacy of these materials for potential applications.