The nature of the effect of Gd(III) on fluorescence of Ln(III) chelates inwater solutions

The intensity of fluorescence of Eu(III) and Sm(III) ions sensitized by mol ecules of n-benzoyltrifluoroacetone and 1,10-phenanthroline introduced in a water solution in a ratio of 3 : 1 is studied as a function of the ion con centration in the solution. The comparison of the fluorescence decay curves of Eu(III) and Sm(III) in D2O and H2O (pH greater than or equal to 7) solu tions containing 10(-4) M of n-Cl-BTFA and 3 x 10(-5) M of 1,10-phen and th e values of tau (A) of Sm(III) in themselves (51-90 mus) are indicative of an insignificant content of water molecules in the first coordination spher e of ions. The effect of other ions on I-A and tau (A) of Eu(III) ions is s tudied under these conditions. The intensity of fluorescence of Eu(III) in solutions of 10(-4) M Cl-BTFA and 3 x 10(-5) H 1,10-phen is found to increa se by 1-2 orders of magnitude in the presence of Y(III) and Gd(III) ions, a nd the magnitude of this effect is unaffected by deoxygenation of the solut ion. The introduction of a third ion Nd(III) in the solution is shown to at tenuate the influence of Gd(III) on I-A of Eu(III) for Nd(III) concentratio ns commensurable with the Eu(III) concentration in the solution. The streng th of the influence of Gd(III) ions on I-A of Eu(III) is found to depend on the method of preparation of the solution. The analysis of the results obt ained testifies that inhomogeneities consisting of chelates of lanthanide i ons displaced from the water structure appear in water. The presence of the se inhomogeneities results in efficient energy transfer from ligands of Gd( III) chelates to Eu(III) chelates, which is the reason for the increasing I -A of Eu(III). The possibility of using data on the enhancement of I-A of E u(III) in the presence of Gd(III) and on the reduction of tau (A) of Eu(III ) in the presence of Nd(III) For estimating dimensions and structures of di splaced systems is discussed. (C) 2001 MAIK "Nauka/Interperiodica".