Journal of Luminescence 128 (2008) 190–198 Evaluation of intramolecular energy transfer process in the lanthanide(III) bis- and tris-(TTA) complexes: Photoluminescent and triboluminescent behavior Ercules E.S. Teotonio a,Ã , Gerson M. Fett b , Hermi F. Brito b , Wagner M. Faustino c , Gilberto F. de Sa´ d , Maria Cla´udia F.C. Felinto e , Regina H.A. Santos f a Departamento de Quı´mica, Universidade Federal de Goia´s, Campus Catala˜o, CEP 75704-020 Catala˜o, GO, Brazil b Departamento de Quı´mica Fundamental, Instituto de Quı´mica da Universidade de Sa˜o Paulo, CEP 05508-900, Sa˜o Paulo, SP, Brazil c Departamento de Eletroˆnica Quaˆntica, Instituto de Fı´sica Gleb, Universidade Estadual de Campinas, Cidade Universita´ria, CEP 13083-970, Campinas, SP, Brazil d Departamento de Quı´mica Fundamental, Universidade Federal de Pernambuco, Cidade Universita´ria, CEP 50670-910, Recife, PE, Brazil e Instituto de Pesquisas Energe´ticas e Nucleares Travessa R 400 Cidade Universita´ria, CEP 05508-970, Sa˜o Paulo, SP, Brazil f Instituto de Quı´mica de Sa˜o Carlos, USP, C.P. 780, CEP 13560-970, Sa˜o Carlos, SP, Brazil Received 29 January 2007; received in revised form 9 July 2007; accepted 11 July 2007 Available online 20 July 2007 Abstract This work reports the energy transfer mechanism process of [Eu(TTA) 2 (NO 3 )(TPPO) 2 ](bis-TTA complex) and [Eu(TTA) 3 (TPPO) 2 ](tris-TTA complex) based on experimental and theoretical spectroscopic properties, where TTA ¼ 2-thienoyltrifluoroacetone and TPPO ¼ triphenylpho- sphine oxide. These complexes were synthesized and characterized by elemental analyses, infrared spectroscopy and thermogravimetric analysis. The theoretical complexes geometry data by using Sparkle model for the calculation of lanthanide complexes (SMLC) is in agreement with the crystalline structure determined by single-crystal X-ray diffraction analysis. The emission spectra for [Gd(TTA) 3 (TPPO) 2 ] and [Gd(TTA) 2 (NO 3 )(TPPO) 2 ] complexes are associated to T-S 0 transitions centered on coordinated TTA ligands. Experimental luminescent properties of the bis-TTA complex have been quantified through emission intensity parameters O l (l ¼ 2 and 4), spontaneous emission rates (A rad ), luminescence lifetime (t), emission quantum efficiency (Z) and emission quantum yield (q), which were compared with those for tris-TTA complex. The experimental data showed that the intensity parameter value for bis-TTA complex is twice smaller than the one for tris-TTA complex, indicating the less polarizable chemical environment in the system containing nitrate ion. A good agreement between the theoretical and experimental quantum yields for both Eu(III) complexes was obtained. The triboluminescence (TL) of the [Eu(TTA) 2 (NO 3 )(TPPO) 2 ] complexes are discussed in terms of ligand-to-metal energy transfer. r 2007 Elsevier B.V. All rights reserved. Keywords: Lanthanide ions; b-diketonate; Complexes; Photo and Triboluminescence 1. Introduction b-Diketonates is one of the most studied ligands of trivalent lanthanide complexes. This is probably owing to the higher ability of b-diketonate organic ligands to act as luminescence sensitizers for Ln(III) ions and also due to the higher thermodynamic stability presented by their com- plexes. The luminescence properties exhibited by Ln(III)–b-diketonate complexes make it possible to use them in numerous applications, ranging from diagnostic probes in clinical analyses to emitter layers in light-emitting diodes (LEDs) [1–9]. These complexes have also attracted much interest within theoretical chemistry, and have become target of intensive studies in the investigation of intramolecular energy-transfer processes from ligands to Ln(III) ion, and theoretical models used to describe geometric and spectroscopic properties of lanthanide coordination compounds [1,10–12]. It is also important to mention that although some lanthanide b-diketonates ARTICLE IN PRESS www.elsevier.com/locate/jlumin 0022-2313/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jlumin.2007.07.005 Ã Corresponding author. Tel.: +55 64 3441 1503; fax: +55 64 3441 1515. E-mail address: ercules@catalao.ufg.br (E.E.S. Teotonio).