Cations Induced Fluorescence Enhancement in Keggin-Al₁₃ for Quantitative Detection

The Keggin-Al₁₃ hydroxide clusters serve as pivotal models for elucidating molecular pathways in geochemical reactions. In this study, we presented a strategy aiming at the quantitative detection of ε-Al₁₃ Keggin clusters using photoluminescent spectra. Specifically, we manipulate the electronic structure of ε-Al₁₃ by introducing Na ions onto the ε-Al₁₃ surface, encapsulated within a Na-O₃ motif. The Na-ion-modified ε-Al₁₃ (Na-ε-Al₁₃) cluster demonstrates incredible photoluminescent qualities, with fluorescence excitation and emission peaks centered at 365 and 436 nm, respectively. In addition, the fluorescence intensities display a linear dependence on the concentrations of Na-ε-Al₁₃, with a detection limit of 15.4 μM. This correlation facilitates the quantitative and precise determination of Na-ε-Al₁₃ concentrations via fluorescence. Both experimental characterizations and theoretical calculations underscore the importance of decorated Na ions in regulating the electronic structure of the ε-Al₁₃ cluster. Lastly, the influence of external anions/cations on the photoluminescent properties of ε-Al₁₃ primarily mirrors modifications to the nonradiative decay process, which is regulated via electrostatic interactions. This work demonstrates an effective strategy for quantitative detection of the ε-Al₁₃ Keggin clusters through photoluminescent spectra.