Relationship between absorption edge and local structure around bismuth ions in bismuth-containing ternary phosphate and borate glasses

Abstract

Relationship between the absorption edge energy and glass structure around bismuth ions has been studied in ternary bismuth phosphate and borate glasses by using Raman spectroscopy. Absorption edge energy shifted toward lower energy with increasing theoretical basicity in both phosphate and borate glasses. Raman peaks related to bismuth ions were observed at 150, 270, 390, 570 and 640 cm⁻¹ in borate glasses, and at 160, 240, 320, 380, 480, 550 and 590 cm⁻¹ in phosphate glasses. All peaks related to bismuth ions, except for the peak at around 150 cm⁻¹ in the borate glass (160 cm⁻¹ in the phosphate glass), shifted toward higher wavenumber with increasing theoretical basicity of glass, which suggests a decrease in Bi–O bond length, that is, an increase in bond strength by increasing electron donation. Absorption edge energy had a negative linear relationship with those peaks positions, which was consistent with the increase of electron donation. In contrast, the peaks at both 150 cm⁻¹ in the borate glasses and 160 cm⁻¹ in phosphate glasses shifted toward lower wavenumber with basicity, and the position had a positive linear relationship with the absorption edge energy. The band assigned to a translational mode might indicate the existence of peculiar structure such as a cluster of bismuth oxygen polyhedra, which could be isolated from the glass network resulting in a different correlation to basicity.