Energy transfer in a self-activated host Ca2MgWO6: Enabling sensitizer-mediated NIR-II thermometry and multimode encryption

Rare-earth-doped luminescent materials have attracted extensive attention owing to their unique 4 f electronic configuration and optical properties. However, the research has largely remained confined to single application domains, and developing multifunctional luminescent systems and elucidating energy transfer mechanisms are essential for broadening their applicability. Herein, we select the double perovskite tungstate Ca 2 MgWO 6 as a host material, leveraging the intrinsic W-O charge transfer band to achieve efficient self-activated blue emission. The W-O charge transfer band further serves as an efficient energy transfer channel to activate the luminescence of lanthanide-based trivalent cations (Ln 3 + ), overcoming the limitation posed by mismatched excited-state energy levels among different Ln 3+ ions (i.e., Er 3+ , Ho 3+ , and Tm 3+ ). By introducing Yb 3+ as an energy sensitizer, the fluorescence intensity of Ln 3+ in visible and near-infrared regions under 980 nm excitation is significantly enhanced. Switching the excitation wavelength enables tunable photoluminescence signals, which leverage to design multimodal decodable anti-counterfeiting labels and information storage systems. Moreover, a sensitizer-mediated NIR-II ratiometric optical thermometer is constructed by means of phonon-assisted energy transfer, exhibiting a relative sensitivity of 0.52% K −1 . This work demonstrates a strategy for designing next-generation, high-performance lanthanide luminescent materials that can be employed in various sensing and photonics applications.