Luminescence of Dipicolinc Complexes of Lanthanide Ions

摘要

The luminescence decay times τ_(lum) of the complexes of the ions Tb(III), Eu(III), Sm(III), Dy(III), and Yb(III) with dipicolinic acid (DPA) dissolved in protonated and deuterated water, methanol, and dimethyl sulfoxide are measured. The values of τ_(lum) for crystals H_3[Ln(DPA)_3]·nH_2O and their aqueous solutions coincide, which points to the identity of the environment in the nearest spheres of an ion in both cases. A comparison of τ_(lum) of solutions of the complexes in H_2O and D_2O, as well as in CH_3OH, CH_3OH, CD_3OD, DMSO_h_6, and DMSO-d_6 shows that the molecular groups in the second and third spheres of an ion, exhibiting high-frequency vibrations, have noticeable effect on the rate constants of nonradiative transitions k_(nr) in the ion. From this comparison, some inferences on the structure of the solvate shell of the Ln(DPA)_3~(3-) complexes in the solvents used are made. The contributions to k_(nr) of Eu(III), Tb(III), Sm(III), Dy(III), Nd(III), and Yb(III) made by OH and CH groups located at different distances from the ion are estimated. It is demonstrated that the dependence of k_(nr) on the distance to the OH and CH groups is steeper for the Eu(III) and Tb(III) ions than for the remaining ions.