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

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Vol. 191; no. 2; pp. 91 - 96
• Main Authors: Luo, Yanhua, Yan, Qing, Wu, Si, Wu, Wenxuan, Zhang, Qijin
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25.09.2007
• Subjects: Energy transfer; Lanthanide complexes; Luminescence; Quenching sphere; Sensitization; Quenching sphere; Sensitization; Energy transfer; Lanthanide complexes; Luminescence
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2007.04.008

A series of Eu(DBM) 3Phen and Tb(DBM) 3Phen co-doped poly(methyl methacrylate) (Eu x Tb y -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 Eu 0.010Tb 0-PMMA the maximum excitation was found to be at 363 nm, and for Eu 0Tb 0.010-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 Eu 0.0050Tb y -PMMA ( y = 0, 5.0 × 10 −6, 3.0 × 10 −5, 5.0 × 10 −5, 3.0 × 10 −4, 4.0 × 10 −4, 1.0 × 10 −3, 4.0 × 10 −3, 1.0 × 10 −2, 2.0 × 10 −2, 4.0 × 10 −2, 6.0 × 10 −2 and 8.0 × 10 −2, respectively), enhanced luminescence of Eu 3+ at 612 nm for 5D 0 → 7F 2 was observed at the concentration of Tb 3+ higher than 0.0048 mol/L. At this Tb 3+ 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 Eu 3+ by Tb 3+. Eu x Tb 0.010-PMMA ( x = 0, 5.0 × 10 −3, 8.0 × 10 −3, 9.0 × 10 −3, 0.013, 0.020, 0.030, 0.040 and 0.060) showed a gradually increasing emission of Eu 3+ at 535 nm along with decreasing of Tb 3+ emission at 546 nm, which resulted from a fast intra-molecular energy transfer from 5D 1 to 5D 0 of Eu 3+ and an inter-molecular energy transfer from the triplet state of DBM in Tb(DBM) 3Phen to 5D 1 of Eu 3+, 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 Eu xTb y-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 Eu xTb y-PMMA was established in terms of Perrin formulation. The radius of the quenching sphere, which corresponds to the critical distance between Eu 3+ and Tb 3+, was found to be 1.633 nm for the sensitization in Eu xTb y-PMMA.