Optical spectroscopy, thermal quenching and electron–vibrational interaction of the octahedrally coordinated Eu2+ ion in CaAl2B2O7 and BaAl2B2O7

• Spectroscopic properties of Eu2+ in CaAl2B2O7 and BaAl2B2O7 are examined.
• The electron–vibrational interaction parameters are estimated.
• The crystal-field splitting, centroid shift and Stokes shift are estimated.
• A comparative study of Eu2+ optical properties in M2+Al2B2O7 (M2+ = Ca2+, Sr2+, Ba2+) is provided.

The spectroscopic properties of the six-fold coordinated Eu2+ in CaAl2B2O7 and BaAl2B2O7 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 Eu2+ 4f65d1 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 Eu2+ ion in CaAl2B2O7 and BaAl2B2O7. The low quenching temperature of the luminescence in these materials is tentatively connected with the thermally induced promotion of the Eu2+ 4f65d1 electron to the host lattice conduction band (photoionization). Evidence for the limited solubility of Eu2+ in BaAl2B2O7 is presented. A comparative study of the Eu2+ luminescence in M2+Al2B2O7 (M2+ = Ca2+, Sr2+, Ba2+) family of materials is also presented.