Fluorescence measurements were performed at different temperatures to increase the resolving capabilities of time-resolved laser-induced fluorescence for uranium speciation. This spectroscopic technique was used to determine the fluorescence lifetimes of the uranyl ion and the species UO<sub>2</sub>OH<sup>+</sup>, (UO<sub>2</sub>)<sub>2</sub>(OH)<sup>2</sup><sub>2</sub><sup>+</sup>, and (UO<sub>2</sub>)<sub>3</sub> (OH)<sup>+</sup><sub>5</sub> in 0.5 M NaClO<sub>4</sub> solutions at different pH and total uranium concentration and in the temperature range from 10 to 60 °C. The temperature dependence of the lifetimes was found to follow the Arrhenius law, and the activation energy of the process was determined for each species. The influence of temperature on the equilibrium constants of the uranium hydroxo-complexes was also considered.
Veronique Eliet, Ingmar Grenthe, and Giovanni Bidoglio, "Time-Resolved Laser-Induced Fluorescence of Uranium(VI) Hydroxo-Complexes at Different Temperatures," Appl. Spectrosc. 54, 99-105 (2000)