Intra‐Ionic Dual Excited‐State Emissions of Micelle‐Encapsulated Eu(III) for Metal‐Ion Sensing Map

Current lanthanide‐based ratiometric luminescence sensing typically relies on ground‐state splitting of lanthanide ions or dual‐component systems. Herein, a conceptually distinct strategy utilizing the intrinsic excited‐state diversity of the trivalent europium ion (Eu(III)) is introduced for aqueous ratiometric metal‐ion sensing. By encapsulating a rigid [Eu(hfa) 3 (dppy) 2 ] (hfa: hexafluoroacetylacetonate; dppy: 4‐pyridyldiphenylphosphine oxide) complex within micellar environments, the emissions from the dominant 5 D 0 and the higher‐lying 5 D 1 states of Eu(III) are successfully preserved in aqueous media. Using the distinct susceptibility of these two emitting excited states to non‐radiative deactivation pathways induced by metal‐ion coordination [Eu(hfa) 3 (dppy) 2 ] exhibits differential quenching responses to varying divalent metal‐ions (Mn, Fe, Co, Ni, Cu). This allows for the construction of a unique ratiometric metal‐ion sensing map. This study demonstrates the first Eu(III)‐based system employing intra‐ionic excited‐state diversity for discrimination, offering a robust, self‐referenced sensing platform.