Deactivation mechanism of excited uranium(VI) complexes in aqueous solutions

The rate of luminescence decay of various uranium(VI) complexes has been measured by a nitrogen laser photolysis method in aqueous solutions. It was found that the luminescence consisted of a short- and a long-lived component in aqueous solutions at pH > 3. These components were assigned as the emissions from excited aqua and hydrolysed ions, *UO2+2 and *(UO2)2(OH)2+2, for which the decay constants were defined as k1 and k2, respectively. k1 and k2 were unaffected by either the concentration of UVI ion or the pH. The quenching rate constant, kq, of various UVI complexes (fluoro, sulphato, phosphato complexes as well as aqua ones) was determined in aqueous solutions with various quenching anions, Cl–, Br–, I– and NCS–. The values of kq were well correlated with the redox potentials of quenching anions. The mechanism of the quenching reaction was interpreted on the basis of a linear free-energy relationship.