Luminescence spectroscopic study of europium(III) and terbium(III) with ethylenediamine in dimethyl sulfoxide

Abstract

The luminescence excitation and emission spectra of europium(III) and terbium(III) complexes of ethylenediamine (en) in dimethyl sulfoxide have been studied. The ⁷F₀→⁵D₀ spectra of Eu^III and the values of the luminescence decay constant confirmed that trivalent lanthanides from 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, i.e. 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 °C indicate decreased stability of the complexes with increased temperature, in agreement with the reported enthalpies of complexation.