Spectroscopic investigations of complexes between Eu(III) and aromatic carboxylic ligands

In order to obtain information on the number and symmetry of the different Eu3+ complexes formed with several hydroxybenzoic acids, ultra-low temperature luminescence measurements at 4.7 K were carried out. Hydroxybenzoic acids were used as simple model compounds for metal binding structures in humic substances (HS). Information on the complexes was extracted from high-resolution total luminescence spectra (TLS), which were obtained by scanning through the 5D0 ← 7F0 transition of Eu(III) with a pulsed dye laser and measuring the emission in the wavelength range of the 5D0 → 7F1 and 5D0 → 7F2 transitions simultaneously. By extracting the crystal field strength parameter Nv(B2q) from the TLS, it was found that Nv(B2q) was not directly correlated with the excitation energy. Further, the symmetry of the individual complexes formed was extracted from the experimental data.