Optical spectroscopy, thermal quenching and electron-vibrational interaction of the octahedrally coordinated Eu super(2+) ion in CaAl sub(2)B sub(2)O sub(7) and BaAl sub(2)B sub(2)O sub(7)

The spectroscopic properties of the six-fold coordinated Eu super(2+) in CaAl sub(2)B sub(2)O sub(7) and BaAl sub(2)B sub(2)O sub(7) are investigated and reported in this paper. Relevant optical parameters such as the Stokes shift, crystal-field splitting, the centroid shift and the red shift of the Eu super(2+) 4f super(6)5d super(1) electronic configuration are calculated from the experimental data. Further, the Huang-Rhys factor and the effective phonon energy, which are responsible for the electron-vibrational interaction, are theoretically estimated for the Eu super(2+) ion in CaAl sub(2)B sub(2)O sub(7) and BaAl sub(2)B sub(2)O sub(7). The low quenching temperature of the luminescence in these materials is tentatively connected with the thermally induced promotion of the Eu super(2+) 4f super(6)5d super(1) electron to the host lattice conduction band (photoionization). Evidence for the limited solubility of Eu super(2+) in BaAl sub(2)B sub(2)O sub(7) is presented. A comparative study of the Eu super(2+) luminescence in M super(2+)Al sub(2)B sub(2)O sub(7) (M super(2+) = Ca super(2+), Sr super(2+), Ba super(2+)) family of materials is also presented.