Fluorescence spectroscopy of U(VI) in the presence of perchlorate ions

摘要

Time-Resolved Laser-induced Fluorescence spectroscopy (TRLFS) is used to study the properties of excited UO22+ ions (fluorescence lifetimes and emission spectra) in the presence of perchlorate ions (up to 5.5M concentration). The experiments are performed at three perchloric acid concentrations (0.2, 1 and 2 M). Although ClO4- is known not to complex with UO22+, increasing amounts of ClO4- lead to a decrease of the lifetime fur each [H+] series. The emission spectra do not show any spectral shift and the fluorescence intensity is well correlated with the lifetime variation. Three different models are discussed to interpret the data: (a) A model based on the assumption of a chemical equilibrium between UO22+ and ClO4-, both in their ground stares. (b) A model which additionally takes into account excited state reactions of UO22+. (c) A third model which is solely based on photochemical, excited state reactions of UO22+. It is the only one consistent with the present data and results of other studies of the uranium(VI)/perchlorate system. Hence, photochemical reactions, even in the presence of weakly or non-complexing ligands like perchlorate ions, need to be taken into account in TRLFS experiments. [References: 23]