THE LUMINESCENCE OF EU2-CRYSTALS( IN MAGNESIUM FLUORIDE)

The luminescence of Eu2+ in MgF2 is reported and discussed. The Eu2+ i on shows 4f(6)5d --> 4f(7)(S-8(7/2)) emission in the blue (maximum at 440 nm). Ar low temperatures a vibrational structure is observed in th e excitation and emission spectra. The coupling with low energetic vib rations (27, 64, 110 cm(-1)) is only observed in the emission spectra. In the excitation spectra zero-phonon lines and vibronics for transit ions to different F-7(J) levels of the 4f(6)(F-7(J))5d excited state a re observed. The t(2g)(5d) triplet is split (approximate to 4000 cm(-1 )) into two components. This is explained by a preferential orientatio n of one of the d orbitals in the Mg2+ chain, which lowers its energy. A comparison is made with the f-d luminescence characteristics of MgF 2:Yb2+ and MF(2):Eu2+ (M = Ca,Sr).