A dual-emitting mixed-lanthanide MOF with high water-stability for ratiometric fluorescence sensing of Fe³⁺ and ascorbic acid

Herein, we design and prepare a dual-emitting lanthanide metal–organic framework (Eu_0.07Gd_0.03-MOF) based on functionalized ligands, which can be developed as a ratiometric sensor. This self-calibrated material not only displays high water stability but also offers a highly sensitive and color change detection of Fe³⁺ and ascorbic acid at a low limit of detection. Moreover, water stability surveys for Eu_0.07Gd_0.03-MOF indicate that it maintains structural stability and displays at least 90.4% and 87.5% fluorescence intensity after storage in water for 28 days in water at 70 °C for 6 days, as well as in acidic-basic solutions of broad pH range (3–11) for four days. More importantly, the low concentration range of Fe³⁺ and ascorbic acid can be estimated by the ratios of ligand-based emission as an internal reference and Eu³⁺-based emission as the indicator, thus yielding a visually discernible “color-change-recover” effect.