Radiative and Nonradiative Transitions of Eu 3+ in Binary Solvent Systems

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Abstract
The fluorescence efficiency of the rare-earth ions in solution increases upon deuteration of the solvent(1–3) and is dependent upon the presence in the solvent molecule of such groups as etc. Lower fluorescence quantum yields observed for Eu3+ and Tb3+ in protic solvents were accounted for, at least qualitatively, by electronic excitation energy transfer from the excited rare-earth ion to some of the vibrational modes in the solvent molecule. The fluorescence quantum yield of Dy3+ in solution is also lower in the presence of groups.(7) Furthermore, significant fluorescence enhancement and long fluorescence lifetimes were observed for both Sm3+ and Eu3+ in such aprotic solvents as POCl3:SnCl4, POCl3:ZrCl4 and POCl3:TiCl4, where both the fluorescence intensities and lifetimes were enhanced by a factor of 1000 and 300, respectively, relative to those in aqueous solutions.(8,9) The fluorescence efficiency of Sm3+ and Eu3+ was also found to depend upon the composition of the primary solvation sphere of the ion.(8,9) The low fluorescence quenching efficiency of these aprotic solvents was further emphasized by the observation of fluorescence emission arising from the 5D3-state of Tb3+ in POCl3:SnCl4.(10) The significance of the composition of the solvent and its effect upon the pertinent transition probabilities were also demonstrated in solutions of Eu3+ in DMSO.(6,11) Results obtained in spectroscopic studies of Eu3+ in binary solvent systems in which only one of the components is the solvating species will be reported here.