Optical and structural properties of Sr–Nb–phosphate glasses

This research studied optical and structural properties of SrO–Nb2O5–P2O5 glasses containing 0 ~ 25 mol% Nb2O5 and 35 ~ 60 mol% SrO using spectra of UV–Vis, FTIR and XPS. Our aim was to work new moldable glasses which are colorless with high refractive index and transmittance, and their correlation with glass structure. Nb2O5 plays the role as an intermediate of glass formation, and transforms the role to network-former or glass-modifier depending on composition. Refractive index increases monotonically with Nb2O5 content at the expense of transmittance, and specific coloring which occurs in ternary compositions with the ratio P2O5/SrO > 1. This effect arises from much increased [Nb3+ and Nb4+] fraction, as quantitatively deconvoluted in Nb3d XPS spectra, in the ligand [NbO6]octahedral which is supported by FTIR and O1s XPS spectra. As the ratio P2O5/SrO ≤ 1, Nb2O5 is more of a network former and [NbO6]octahedral structure turns into [NbO4]tetrahedron with partial Nb–O…(Sr) bonding turns into (Nb–O–Nb)tetrahedron, coloring disappears.