Fluorescence properties of a uranyl(V)-carbonate species [U(V)O2(CO3)3]5− at low temperature

Fluorescence properties of a uranyl(V)-carbonate species in solution are reported for the first time. The fluorescence characteristics of the stable aqueous uranyl(V)-carbonate complex [U(V)O2(CO3)3]5− was determined in a frozen solution (T = 153 K) of 0.5 mM uranium and 1.5 M Na2CO3 at pH 11.8 by time resolved laser-induced fluorescence spectroscopy (TRLFS). Two different wavelengths of 255 nm and 408 nm, respectively were used to independently of each other excite the uranyl(V)-carbonate species. The resulting U(V) fluorescence emission bands were detected between 380 nm and 440 nm, with a maxima at 404.7 nm (excitation with 255 nm) and 413.3 nm (excitation with 408 nm), respectively. It was found that by using an excitation wavelength of 255 nm the corresponding extinction coefficient was much higher and the fluorescence spectrum better structured than the ones excited at 408 nm. The fluorescence lifetime of the uranyl(V)-carbonate species was determined at 153 K as 120 μs. TRLFS investigations at room temperature, however, showed no fluorescence signal at all.