CRYSTAL-FIELD AND FREE-ION ANALYSIS FOR EU-3(+) ION IN LAOF CRYSTAL

The europium doped lanthanum oxyfluoride LaOF:Eu3+ was synthesized by solid reaction method. The fluorescence spectra of the rhombohedral La OF:Eu3+ were recorded in the region 11,800-21,800 cm-1 at 60 K and roo m temperature. The symmetries of the crystal field energy levels were assigned and the crystal field parameters were determined by the simul ation of the crystal field splittings of the 7F0-4 and 5D0-2 multiplet s. The free-ion calculations were performed for Eu3+ in LaOF and also in LaOCl and LaOBr for comparison. It was noted that the crystal field strength decreases when the interatomic distance decreases along the host series LaOBr-LaOCl-LaOF and that the reduction of the free-ion pa rameters demonstrates an 'anti-nephelauxetic series', i.e. the Slater parameters F(k) and the spin-orbit coupling parameter zeta of Eu3+ dim inish from ligand Br- to F- along the above series.