Energy transfer between lanthanide ions in nanostructures of their complexes. II

摘要

The changes in the luminescence intensity and in the luminescence lifetime of Eu, Th, and Sm complexes with some beta-diketones and 1,10-phenanthroline that occur upon formation of nanostructures with complexes of triply charged ions Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm, and Yb-acceptors of the electronic excitation of luminescing ions-are compared for the first time. Pairs of lanthanide ions are suggested to exist inside nanostructures, which are bound by a bridge at a distance shorter (0.4 nm) in comparison with the size of interacting complexes. For a large number of pairs of donor and acceptor ions, the averaged probabilities (w(t)) of energy transfer between these ions in nanostructures in the solution of each beta-diketone under study are calculated. Based on the comparison of w(t) with the predictions of the theory of the inductive resonance and exchange resonance energy transfer mechanisms, the average distance R between Ln(III) ions interacting in given fragments of nanostructures is estimated for each donor-acceptor pair, and the energy transfer mechanism is identified for the first time. It is shown that energy can be transferred between Ln(III) ions in nanostructures both according to the inductive resonance and via the exchange resonance mechanisms. The type of the transfer mechanism depends on the spectral parameters of interacting ions and on the ability of complexes of given acceptor ions to form heteronuclear nanostructures, whose composition determines the distance R. The variation in the value of R revealed for different ion pairs is explained by the occurrence of exchange resonance interactions between some ions. The overestimated probabilities w(t) for ion pairs characterized precisely by exchange resonance interactions can be explained by the influence of covalent bonds in nanostructures of Ln chelates on pi conjugation of overlapped electronic shells of interacting particles. By using the method of energy transfer between Ln(III) ions of complexes from distant spheres of a structure, the average minimal size of nanostructures formed is estimated to be 2.6-3.4 nm.