Lanthanide Grafting Modulates Radiative and Nonradiative Energy Dissipation in a Defect-Rich In-MOF for Dual-Functional Luminescence Sensing and Electromagnetic Wave Absorption

Abstract The dual threats of Cr(VI) water pollution and electromagnetic interference demand multifunctional materials integrating fluorescence sensing with electromagnetic wave absorption (EMA). Herein, Eu3+ and Tb3+ ions were postsynthetically anchored onto a defect-rich In-MOF to construct Eu@In-MOF and Tb@In-MOF with integrated luminescence sensing and microwave absorption functionalities. The characteristic f-f emissions of the lanthanide-functionalized frameworks arise from ligand-mediated sensitization and radiative transitions, while microwave attenuation is associated with dipolar/interfacial polarization, magnetic loss, and impedance matching. The composites exhibit selective fluorescence quenching toward Cr(VI), with detection limits of 7.56 ppb for CrO42– using Eu@In-MOF and 8.39 ppb using Tb@In-MOF. Mechanistic studies indicate that fluorescence quenching involves competitive light absorption and coordination-induced electronic perturbation, accompanied by static and dynamic quenching processes. In the X-band, Tb@In-MOF achieves a minimum reflection loss of −41.26 dB and an effective absorption bandwidth of 3.0 GHz. DFT calculations, together with spectroscopic and electrochemical characterization, reveal that lanthanide coordination regulates the local electronic environment and interfacial charge-transfer behavior of the framework, providing a structural basis for the enhanced polarization-related dielectric response. These results demonstrate that lanthanide coordination enables the coexistence of luminescence sensing and microwave attenuation within an In-MOF platform, providing a strategy for multifunctional MOF-based materials.