Luminescence of polymer electrolytes containing europium (III)
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M. Assuncao Departamento de Fisica, Universidade de Aveiro, 3800 Aveiro, Portugal
L. Alcacer Departamento de Quimica, Instituto Superior Tecnico, 1096 Lisboa, and Centre for Microsystems, Instituto Superior Tecnico, 1096 Lisboa, Portugal (Received 3 March 1994; accepted 8 August 1994)
The excitation and emission spectra of polymeric matrices—poly(ethylene oxide), PEO, and poly(propylene oxide), PPO—containing different concentrations of EuBr3 were recorded and most of the observed transitions identified. The Stark components of the 7FQ_4, 5Do levels and the corresponding barycenters were calculated based on the emission lines assignment to the 5Do,i —• 7Fo_4 transitions. The spectra were discussed in terms of a C2v local Eu 3+ coordination. The relative intensity of the 5 D 0 —> 7 F 2 hypersensitive transition was related to the electrolyte morphological changes due to increasing europium concentration.
I. INTRODUCTION The interest in polymeric matrices modified by various inorganic salts has grown considerably since the initial reports of Wright1 and Armand.2 The fact that they can be produced as thin films of large areas conjugated with their mechanical properties gives those materials a high technological potential. Polymer electrolytes containing cations of monovalent metals, mainly lithium, conveyed most of the attention especially due to their application in high energy density batteries.3"5 However, more recently, polymeric matrices that include salts of divalent or trivalent elements have drawn some interest as well.6"16 In particular, flexible polymers modified by trivalent rare-earth cations may prove to be materials with relevant luminescent properties.11"16 Initial results have in fact shown that some of these polymer electrolytes are strongly luminescent from 14 K up to room temperature with lifetimes larger than 1 ms at low temperatures.12 Nevertheless, the behavior of the rare-earth cations within the polymeric matrix is, at present, relatively unknown. Following previous work, this paper gives a first detailed description of the luminescence properties of poly(ethylene oxide), PEO, and poly(propylene oxide), PPO, modified by europium bromide (PEO/PPO) n EuBr3, with n being the number of ether oxygen atoms in the polymeric chain per Eu 3+ cation. Some results by Carlos and Videira concerning the local Eu 3+ environment in these polymer electrolytes, in particular a)
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J. Mater. Res., Vol. 10, No. 1, Jan 1995
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the identification of the ion's site symmetry are referred to. The relationship between phological changes induced by the increasing concentration and the relative intensity of hypersensitive transitions is also discussed.
as C2V,14 the moreuropium the ion's
II. EXPERIMENTAL PROCEDURE A. Materials The usual solvent casting technique was used to prepare samples of polymer electrolytes of poly(ethylene oxide), PEO (MW = 5 X 106, Aldrich), and polypropylene oxide), PPO (Zeon Chemicals), containi
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