Fluorescence of UO22+ in a non-complexing medium:: HClO4/NaClO4 up to 10 M

Time-resolved laser-induced fluorescence spectroscopy has been used to study the properties of excited UO22+ ions (fluorescence lifetimes and emission spectra) in aqueous solutions of non-complexing HCIO4 and NaClO4 (up to a total concentration of 10 M). An increasing amount of HClO4 (NaClO4) leads to an increase (decrease) of the fluorescence lifetime. These dependences cannot be attributed to the formation of inner-sphere complexes. Two models are discussed to interpret the data: (a) A kinetic description with excited state reactions between UO22+ and both H+ and ClO4-. (b) A phenomenological model with the emphasis on energy transfer, processes between the UO22+ ion in its excited state and the surrounding molecules. Additional measurements of the UO22+ lifetime variation induced by chloride ions show that only the phenomenological model is consistent with all the data. (C) 2001 Elsevier Science B.V. All rights reserved.