Alkali halide crystals and pressed disks doped with divalent europium were prepared and their absorption and fluorescence spectra measured. There are two broad absorption bands in the ultraviolet, peaking at ~250 and 330 mµ, both due to the transition 4ƒ7→ 4ƒ65d1, and attributed, after comparison with the absorption spectra of Eu2+ observed by previous workers in various other media, to the splitting of the 5d orbitals by the crystal field.
In addition to the many sharp bands riding on the main absorption bands, one peaking at 270 mµ has been observed, in complete analogy with the Gd3+ spectrum. The fluorescence emission spectra are identical, irrespective of the wavelength of irradiation (250 or 330 mµ).
R. REISFELD and A. GLASNER, "Absorption and Fluorescence Spectra of Eu2+ in Alkali Halide Crystals," J. Opt. Soc. Am. 54, 331-333 (1964)