Optical spectroscopy, thermal quenching and electron-vibrational interaction of the octahedrally coordinated Eu²⁺ ion in SrAl ₂B₂O₇

The spectroscopic properties of the six-fold (octahedral) coordinated Eu²⁺ in SrAl₂B₂O₇ have been investigated. Relevant optical parameters such as the Stokes shift, crystal-field splitting, the centroid shift and the red-shift of the Eu ²⁺ 4f⁶5d¹ electronic configuration have been estimated from the experimental data. Further, the Huang-Rhys factor and the effective phonon energy, which are responsible for electron-vibrational interactions are theoretically estimated for the Eu²⁺ ion in SrAl₂B₂O₇. The low quenching temperature of the luminescence is connected with the thermally induced photoionization of the Eu²⁺ 4f⁶5d¹ electron. A cross-cutting comparative study of the optical properties of octahedrally coordinated Eu ²⁺ in SrAl₂B₂O₇ and in Cs ₂M²⁺P₂O₇ (M²⁺=Ca ²⁺, Sr²⁺) is also presented.