The incomplete 4f subshells of the lanthanide ions Ce³⁺ to Yb³⁺ result in a variety of magnetic and spectroscopic properties that are of interest from both a theoretical and practical perspective. For example, gadolinium (Gd³⁺) coordination complexes are administered to patients in order to enhance images obtained using MRI (Magnetic Resonance Imaging) instruments. Similarly, the fluorescence behavior of the lanthanide ions, especially Eu³⁺ and Tb³⁺, are used to generate the images on a color TV screen.

The fluorescence properties in particular make these ions excellent probes of systems in which they are either already present, or into which they can be incorporated. The fluorescence is easily observed, has a relatively long lifetime (~0.1 to 10 msec) and exhibits very sharp lines. In the case of the europium ion, each unique chemical species present in solution or in the solid state results in a single peak in the fluorescence excitation spectrum. For example, when the two calcium ions that are normally present in the muscle protein parvalbumin are replaced by Eu³⁺ ions, two fluorescence peaks are observed in the excitation spectrum, one for each calcium ion binding site. The wavelength at which the fluorescence peaks appear in the excitation spectrum, the lifetime of the fluorescence signal and the number of peaks present in the emission spectrum, all contain information that can be used to characterize the protein environment.

We are interested in using the unique fluorescence properties of these ions to probe a wide variety of systems, including calcium-binding proteins that play a role in many important biological processes, and inorganic materials such as the YBa₂Cu₃O_7-x high temperature superconductors and their analogs for which it is possible to replace the yttrium ion (Y³⁺) with the Eu³⁺ ion.

H-Y.D. Ke* and E.R. Birnbaum, 1995 "Many-Body Nonradiative Energy Transfer in a Crystalline Europium(III) EDTA Complex," J. Luminescence, 63, 9-17.

H-Y.D. Ke*, E.R. Birnbaum, D.W. Darnall and G.D. Rayson, 1992 "Characterization of the Carboxy Groups on Datura innoxia Using Eu(III) Luminescence," Environ. Sci. Technol. 26, 782-788.

C.L. Trevino*, W.A. Palmisano*, E.R. Birnbaum and M.T. Henzl, 1990, "Eu³⁺ Luminescence Studies of Oncomodulin. The Origin of the pH-Dependent Behavior," J. Biological Chem., 265, 9694.