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+ (tau = 130 +/- 1 mu s) and precipitated Eu(OH)(3)(s) (tau = 158 +/- 7 mu s) compared to that of aqua Eu3+ (tau = 112 +/- 1 mu s). A formation constant log*beta(1,1) of EuOH2+ at I = 0.1 M NaClO4 and 25 degrees C was measured to be -8.28 +/- 0.22, which was converted to log*beta degrees(1,1) = -7.87 +/- 0.22 at an infinitely diluted condition of I = 0 based on the specific ion interaction theory.