Local structure of Eu³⁺ in borosilicate glasses by phonon sideband spectra

InxNa₂O · (40-x)B₂O₃ · 60SiO₂ (mol%) (x = 5, 10, 15, 20, 25, 30) glasses with 0.25mol% Eu₂O₃ as additive, the local structure around Eu³⁺ was explored by employing the phonon sideband spectra of Eu³⁺ associated with the ⁵D₂ ←⁷F₀ transition. It was found that the types and fraction of the structural units around Eu³⁺ varied with glass composition. Moreover, the B-O vibrational mode of BO₃ unit exists around Eu³⁺ when x ≦ 15, which is not present in the same composition glasses free of Eu³⁺. A greatest asymmetry in the surrounding of Eu³⁺ occurs at x = 10, inconsistent with a maximum of some physical properties found in sodium borosilicate glasses at a Na:B ratio of about unity. In addition, various structural units possess different coordination preference to Eu³⁺. The highest theoretical microscopic optical basicity on the oxygen atoms in these units was advocated as a criterion of the coordination preference, which successfully elucidated a series of coordination preference phenomena occurring in silicate, borate and borosilicate glasses.