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

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.