Quenching behaviour of lanthanides on the ultraviolet fluorescence of uranium(VI)

All of the lanthanides can act as quenchers of the UV fluorescence of uranyl ions in an NaF - LiF flux. Half-concentrations, derived from the semi-logarithmic dependence of the relative fluorescence intensity on the quencher concentration, were found to be constant for Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu(Csub(1/2)ca. 1100 p.p.m.). However, Ce, Pr, Nd and Tb showed different quenching behaviour with half-concentrations lower than 300 p.p.m. This peculiar trend exhibited by these elements may be correlated with their chemical behaviour during fusion in an ambient atmosphere yielding coloured pellets owing to an at least partial formation of a higher oxidation state of the corresponding element. (author)