Eu³⁺-Doped Mixed-Ligand UiO-66-Type Metal–Organic Framework for Ratiometric Fluorescence Sensing Fluoride Ions with Ultralow Detection Limit

Abstract

Metal−organic frameworks (MOFs) have emerged as a highly promising platform for various sensing applications due to their tunable structures and functionalities. In the present work, a Eu 3+ -doped mixed-ligand MOF, namely, the Eu 3+ @UiO-66-IPA, exhibited excellent luminescent properties and high fluorescence stability in aqueous media, displaying dual-emission peaks under 395 and 615 nm excitation that were readily visible to the naked eye. Importantly, the presence of fluoride ions (F − ) promoted the "antenna effect" between the ligand and the Eu 3+ centers, which significantly enhanced the emission intensity of the Eu 3+ characteristic peak. In addition, the addition of F − also inhibited the quenching effect of high-energy O−H bonds existing in the aqueous environment. Notably, Eu 3+ @UiO-66-IPA demonstrated exceptional selectivity for F − over a range of competing anions, with a remarkable limit of detection as low as 0.22 μM. The developed Eu 3+ -doped mixed-ligand MOF system offers a highly promising strategy for the simple and accurate sensing of F − in practical applications.