Complexes of Eu3+, Gd3+, and Tb3+ with tropolone (tropolone=2-hydroxy-2,4,6-cycloheptatrien-1-one) were synthesized and characterized by C and H elemental analysis, infrared vibrational spectroscopy, X-ray powder diffraction analysis and Raman vibrational spectroscopy. The results show that the complexes are isostructural and have the formula [Ln(trop)3], where Ln=Eu3+, Gd3+ or Tb3+ and trop=tropolone. The characteristic luminescence of the Eu3+ and Tb3+ ions was not observed either upon ligand excitation (300-380nm) or upon direct f-f excitation, not even at 4.2 K. In order to understand this phenomenon the spectroscopic properties of the Gd(trop)3 complex (absorption spectra at 298 K, excitation and emission spectra from 4.2 to 298 K and decay time measurements from 20 to 298 K) were investigated. The emission spectra show three distinct bands, which are ascribed to ligand electronic states: a singlet state, S1 (π-π*), at 24 270 cm-1, and two triplet states, T1 and T2, at 15 630cm-1 and 16 610cm-1, respectively. Both triplet states are situated below the emitting states of the Eu3+ and Tb3+ ions (5Do and 5D4, respectively), thus suppressing the luminescence from these states by back-transfer.
Original languageEnglish
Pages (from-to)2237-2245
JournalSpectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Issue number13
Publication statusPublished - 1 Nov 1998
Externally publishedYes


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