Divalent europium in silica gels

Eu2+ has electronic transitions between the 4f(7) ground state and the 4f(6)d(1) first excited state. These transitions are very sensitive to the surroundings in which the ion is embedded. Due to this characteristic, divalent europium has been employed as a sensitive optical probe. For this work we prepared silica gels doped with Eu2+ ions. The doping was achieved in two different ways, as explained in the text. Excitation and emission spectra were taken, and from the excitation data a very small splitting between the T-2g and E-g levels was calculated. This splitting implies that the impurity ions are located in a weak crystalline electric field as can be expected for this kind of amorphous materials. (C) 1998 Elsevier Science S.A.