Formation of a Eu(III) borate solid species from a weak Eu(III) borate complex in aqueous solution.

In the presence of polyborates (detected by (11)B-NMR) the formation of a weak Eu(III) borate complex (lg β11 ~ 2, estimated) was observed by time-resolved laser-induced fluorescence spectroscopy (TRLFS). This complex is a precursor for the formation of a solid Eu(III) borate species. The formation of this solid in solution was investigated by TRLFS as a function of the total boron concentration: the lower the total boron concentration, the slower is the solid formation. The solid Eu(III) borate was characterized by IR spectroscopy, powder XRD and solid-state TRLFS. The determination of the europium to boron ratio portends the existence of pentaborate units in the amorphous solid.