A study of lanthanide fluorescence shifts caused by near neighbor perturbation

Lanthanide ions, unlike ions formed by the d-block elements, characteristically exhibit narrow electronic spectral features, usually on the order of one to two wavenumbers. The spectral position and intensity of these features are dependent upon the environmental symmetry of the lanthanide ion. Any perturbation in the coordination sphere, such as a change in bond distance, or a shift to another geometrical polyhedron, will ordinarily cause a change in the observed spectrum. These two characteristics (narrow line spectra and environmental sensitivity) make the lanthanide ions particularly useful for the study of symmetry, coordination, and crystal structure in solid and dissolved compounds in which they are a major or a minor constituent. Such compounds could also be employed for the study of impurities, coordination numbers, absorption of solvent molecules, and anything else that might perturb the environment around the lanthanide ion. The present work describes the theoretical background required, the instrumentation employed, the syntheses attempted, and the spectral evaluations completed for several europium-containing molecules. A special emphasis was placed upon europium-containing chelates. Europium was chosen because of its simple-appearing electronic spectrum and its readily excited emission in the visible region of the electromagnetic spectrum.