Cations Induced Fluorescence Enhancement in Keggin-Al for Quantitative Detection.

The Keggin-Al 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-Al Keggin clusters using photoluminescent spectra. Specifically, we manipulate the electronic structure of ε-Al by introducing Na ions onto the ε-Al surface, encapsulated within a Na-O motif. The Na-ion-modified ε-Al (Na-ε-Al) 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-Al, with a detection limit of 15.4 μM. This correlation facilitates the quantitative and precise determination of Na-ε-Al concentrations via fluorescence. Both experimental characterizations and theoretical calculations underscore the importance of decorated Na ions in regulating the electronic structure of the ε-Al cluster. Lastly, the influence of external anions/cations on the photoluminescent properties of ε-Al 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-Al Keggin clusters through photoluminescent spectra.