Inter- and intra-molecular energy transfer during sensitization of Eu(DBM)3Phen luminescence by Tb(DBM)3Phen in PMMA

A series of Eu(DBM)(3)Phen and Tb(DBM)(3)Phen co-doped poly(methyl methacrylate) (EuxTby-PMMA, subscript x and y denote molar ratio of the ion to repeating unit of PMMA in each sample) were prepared with different Eu/Tb contents. During luminescence measurement of these samples, it was found that for Eu0.010Tb0-PM[MA the maximum excitation was found to be at 363 nm, and for Eu0Tb0.010-PMMA the maximum excitation at 274 nm. This difference reveals that there is different intra-molecular energy transfer mechanism for these two complexes, which contain the same ligands but different central ions. For Eu0.0050Tby-PMMA (y = 0, 5.0 x 10(-6), 3.0 x 10(-5), 5.0 x 10(-6), 3.0 x 10(-4), 4.0 x 10-4, 1.0 X 10(-3) 4.0 x 10(-3), 1.0 X 10(-2), 2.0 x 10-2 4.0 x 10(-2) 6.0 x 10(-2) and 8.0 x 10(-2), respectively), enhanced luminescence of Eu3+ at 612 nm for 5 Do -> F-7(2) was observed at the concentration of TB3+ higher than 0.0048 mol/L. At this Tb 31 content, the minimum intensity of the luminescence of Eu(DBM)3Phen was observed, which comes from the balance between absorption consumption of ligands in Tb(DBM)3Phen and sensitizing in luminescence of EU3+ by Tb3+. EuxTb0.010-PMMA (x = 0, 5.0 x 10(-3), 8.0 X 10(-3), 9.0 X 10(-3), 0.013, 0.020, 0.030, 0.040 and 0.060) showed a gradually increasing emission of Eu3+ at 5 3 5 nm along with decreasing of Tb (3+) emission at 546 nm, which resulted from a fast intra-molecular energy transfer from 5 D, to 5 Do of EU3+ and an inter-molecular energy transfer from the triplet state of DBM in Tb(DBM)3Phen to 5 D I of EU3+,, and the latter energy transfer process is directly dependent on the distance between two kinds of ions. Based on observation above, it was realized that there will be a critical distance between two kinds of complexes in each EuxTby-PMMA sample, which determines the minimum concentration of Tb(DBM)3Phen for the sensitization in luminescence of the sample. To give a vivid picture for this complex system, a model for the sensitization of EuxTby-PMMA was established in terms of Perrin formulation. The radius of the quenching sphere, which corresponds to the critical distance between Eu3+ and Tb 31, was found to be 1.633 nm for the sensitization in EuxTby-PMMA. (c) 2007 Elsevier B.V. All rights reserved.