Quenching of the uranyl (UO22+) emission by inorganic ions in solution

Quenching constants (K) of various inorganic ions have been measured for the quenching of the uranyl emission in aqueous acid solution at room temperature. Quenching constants of halogen or halogen-like anions (X–) increase with decrease in their oxidation potentials and a plot of log K against the oxidation potential is linear, suggesting a chemical (redox) quenching process. Static quenching via formation of a non-emissive complex in the ground state is unlikely to be important. Quenching by some metal ions, when the process is favoured by both the spin conservation rule and the exothermicity of the process, is accompanied by sensitized reactions indicating involvement of an electronic energy transfer process. Efficient quenching by many metal cations occurs without chemical changes even when the electronic energy transfer process is forbidden. There is no correlation between the quenching constants and the magnetic moments or atomic weights of the quenchers. There is a correlation between the quenching constants for the cations and their oxidation potentials and a mechanism of physical quenching through weak electron donor–acceptor interactions is suggested.