Structural characterizations and optical properties of new Li–Sr–Nb-phosphate glasses

Abstract

A new Li2O–SrO–Nb2O5–P2O5 glass system was prepared by a high-temperature alumina crucible, and structural characterization and optical properties were investigated. Proper content of Li2O and Nb2O5 was employed to replace partial SrO and P2O5 to improve the optical properties. It was observed that the enhancement of the refractive index from 1.75 to 1.85 is mainly due to the Nb2O5 content. An addition of Li2O significantly increases the optical transmittance; optical transparency can be enhanced from 60% to higher than 85% in the UV–visible region with addition of 20–40 mol% Li2O species. However, optical transmittance is monotonically decreased from about 90% to 80% under 10–30 mol% Nb2O5 addition. The 40P2O5–20Nb2O5–20SrO–20Li2O glasses demonstrate the optimum refractive index (n > 1.75) and high optical transparency (>80%) in the UV–visible region.Furthermore, the effect of Nb2O5 on the structural transition was focused on the (60 − y)P2O5–yNb2O5–20SrO–20Li2O vitreous system since the transition of FTIR spectra reveals that the Nb2O5 has more pronounced effect than Li2O in the glass network due to the higher covalent extent and electronegativity. Addition of Nb2O5 generates Nb–O bonds by dissociating P–O chains and results in the decrease in the intensity of the (PO2), (POP), and (PO3) absorption bands. The O1s-XPS analysis shows that Nb2O5 addition dissociates symmetric bridging oxygens in P–O–P bonding and forms asymmetric bridging oxygens in P–O–Nb and non-bridging Nb–O- bonds, in which octahedral [NbO6] unit is eventually substituted by [NbO4] tetrahedral unit in the Li–Sr–Nb phosphate glasses.