Time-resolved laser-induced fluorescence spectroscopy has been used to stud
y 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 c
annot 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 phenomenologica
l model with the emphasis on energy transfer, processes between the UO22+ i
on in its excited state and the surrounding molecules. Additional measureme
nts of the UO22+ lifetime variation induced by chloride ions show that only
the phenomenological model is consistent with all the data. (C) 2001 Elsev
ier Science B.V. All rights reserved.