A multi-method characterization of borosilicate glasses doped with 1 up to 10 mol% of Fe, Ti and Sb

Abstract

The model glasses NBS1 and NBS2 are sodium borosilicate glasses of high intrinsic UV transmission. Although both glasses have an SiO2 content of 74 mol%, they possess different matrix structures due to varied Na2O / B2O3 ratios. Nonbridging oxygens occur in the NBS1 but not in the NBS2 glass. Fe, Ti and Sb oxides were added at concentrations of 1 and 10mol% to study valence, coordination and site distribution. XANES, Mössbauer, optical absorption, photoluminescence and EPR spectroscopy provided an insight into the structures and near range environments of the dopants. Large differences were found for the two Fe doped glasses. The presence of nonbridging oxygens in NBS1 glass leads to a higher solubility of the Fe ions and a higher ratio of tetrahedral over octahedral Fe3+ coordination while a clustering of Fe ions resulting in a lowered UV and VIS transmission is observed in NBS2 glass. In Ti doped glasses EPR and XANES spectroscopy shows that most Ti occurs as Ti4+, in four-, five- and sixfold coordination. Optical spectra of Ti4+ display high intensity charge transfer transitions in the UV region. Ti4+ photoluminescence in the visible range is of low intensity. Optical absorption, XANES and Mössbauer spectroscopy could only detect Sb3+ in the antimony doped glasses. The photoluminescence of Sb3+ is much stronger in the NBS1 than in the NBS2 glass.