Structural features and optical properties of CeO₂-containing borosilicate glass based on spectroscopic analysis

Borosilicate glasses with composition 63SiO₂-10B₂O₃-3Al₂O₃-10Na₂O-10K2O-4BaO doped with 1 and 3 mol% cerium oxide (CeO₂) were melted at 1500°C followed by annealing at 550°C after quenching. Spectroscopic analysis of the asprepared glasses using infrared spectroscopy, Raman spectroscopy and UV-visible spectrometry was performed to study the effects of CeO₂ doping on the structure and optical properties of the glass. The vibrational spectra of the glasses reveals appreciable changes in relative intensities as a function of the CeO₂ content. The transmission spectra and the derived parameter plots exhibit red-shift of the cut-off wavelength as well as a reduction in the optical band gap and energy gap tail in varying degrees compared to the base glass. These changes indicate structural modifications of glass network and electronic structural variations arising from doping and the polyvalent state of the cerium cation. As a network modifier, cerium in borosilicate glass gives rise to number of nonbridging oxygens resulting in scission of the Si-O network and incomplete conversion of [BO₃] to [BO₄], whereas elevated cerium concentrations suppress further depolymerization of the Si-O network due to the co-existence of tetravalent and trivalent cerium ions, and hence inhibits further reductions in the optical band gap and energy gap tail. Meanwhile the equilibrium between structural disorder and defect repair stemming from polyvalent cerium is proposed to be responsible for the limited decrement of the energy gap tail.