Luminescence Spectroscopic Study of Europium(III) and Terbium(III) with Ethylenediamine in Dimethyl Sulfoxyde

The luminescence excitation and emission spectra of europium(III) and terbium(III) complexes of ethylenediamine (en) in dimethyl sulfoxide have been studied. The 7F-7(0)-->5D0 spectra of Eu(III) and the values of the luminescence decay constant confirmed that trivalent lanthanides form 1:1, 1:2 and 1:3 inner-sphere complexes with en. The quenching of the luminescence of Eu(III) and Tb(III) are linearly proportional to the number of N-H groups attached to the metal ions. The equations are k(obs) (Eu) = 0.759 n(N-H) + 0.416 and k(obs)(Tb) = 0.073 n(N-H) + 0.299. The quenching mechanism is assumed to be the same as that of the O-H group, ie. it involves coupling between the electronic transition energy of Eu(III) or Tb(III) and the vibrational overtones of N-H. Luminescence spectra and decay contents measured between 15 and 80-degrees-C indicate decreased stability of the complexes with increased temperature, in agreement with the reported enthalpies of complexation.