Europium occurrence

Europium is a metallic element discovered in 1901 in Paris by the French scientist Eugene-Anatole Demarcay. It belongs to a series of elements called lanthanides, or 4f elements, extending from lanthanum (atomic number 57) to lutetium (atomic number 71). These elements have low abundances Europium occurrence in Earth s crust is only 2.1 ppm (parts per million), that is, 2.1 grams (0.07 ounces) per metric ton, and in seawater, its concentration is as low as 4 X 10 8 ppm. 

The atomic volumes of the lanthanides, as calculated from their room-temperature lattice parameters, are shown in fig. 3. Basically this is the same plot as given by Klemm and Bommer where the lanthanide contraction is evident, and also the anomalous valence states for cerium (slightly greater than three) and europium and ytterbium (both divalent). Anomalies due to divalency are also evident in many of the physical properties and these will be duly noted throughout the chapter. The occurrence of divalency in europium and ytterbium is a striking confirmation of Hund s rule that half-filled (in the case of divalent europium with a 4f con-... 

The direct electronic excitation of lanthanide ions is very inefficient because of their low absorption coefficients and the occurrence of nonradiative deactivation processes mediated by solvent molecules, particularly by water. Therefore, sensitizing ligands are applied. These sensitizers are often termed as anterma chromo-phores. By using antenna chromophores like acridone or diaiyl ketones, the excitation wavelength for europium complexes, which is usually <370 nm, can be shifted to the visible region [5-7]. 

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