TRLFS study of hydrolyzed Eu(III) species

The hydrolysis of Eu(III) and Am(III) begins near neutral pH conditions, above which precipitation occurs due to low solubility. Careful sample characterization steps are a prerequisite for the speciation study of hydrolyzed Eu(III) complexes without the interference of colloidal particles or precipitation. Herein, the hydrolysis reaction of Eu(III) was studied using time-resolved laser fluorescence spectroscopy (TRLFS). Laser-induced breakdown detection was employed to monitor the presence of colloidal particles. The luminescence properties of Eu(III) and precipitated Eu(OH)₃(s) were investigated and comparisons were made to those of aqua Eu³⁺. Parallel factor analysis was applied for the deconvolution of the TRLFS results. Both primary hydrolyzed Eu(III), EuOH²⁺ and precipitated Eu(OH)₃(s) showed distinct luminescence spectral properties, including an enhanced hypersensitive luminescence peak (J = 2). An increased luminescence lifetime was observed for both EuOH²⁺ (τ = 130 ± 1 μs) and precipitated Eu(OH)₃(s) (τ = 158 ± 7 μs) compared to that of aqua Eu³⁺ (τ = 112 ± 1 μs). A formation constant log^*β_1,1 of EuOH²⁺ at I = 0.1 M NaClO₄ and 25 °C was measured to be –8.28 ± 0.22, which was converted to log^*β°_1,1 = –7.87 ± 0.22 at an infinitely diluted condition of I = 0 based on the specific ion interaction theory.