In
xNa
2O·(40-
x)B
2O
3·60SiO
2 (mol%) (
x=5, 10, 15, 20, 25, 30) glasses with 0.25mol% Eu
2O
3 as additive, the local structure around Eu
3+ was explored by employing the phonon sideband spectra of Eu
3+ associated with the
5D
2 ←
7F
0 transition. It was found that the types and fraction of the structural units around Eu
3+ varied with glass composition. Moreover, the B-O vibrational mode of BO
3 unit exists around Eu
3+ when
x≤15, which is not present in the same composition glasses free of Eu
3+. A greatest asymmetry in the surrounding of Eu
3+ 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 Eu
3+. 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.
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