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

Abstract

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 U^VI ion or the pH. The quenching rate constant, k_q, of various U^VI 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 k_q 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.