Comparative study on the influence of rare earth ion doping on the structural and optical properties of simple B2O3–Na2O glasses

Abstract In this study, a series of sodium borate glasses with the general composition 50 mol% B₂O₃ – (50–x) mol% Na₂O – x mol% RE₂O₃ (where RE = La, Nd, Gd, Ho, Er, Yb and x = 0 and 1 mol%) were synthesized via the melt-quenching technique. This study aims to systematically investigate the effect of substituting different rare earth ions into a fixed sodium borate glass matrix to understand their role in modifying structural and optical properties. XRD analysis confirmed the amorphous nature of all glass samples. FTIR spectra showed structural transformations marked by an increase in BO₄ units and suppression of boroxol rings with rare earth doping. Density and molar volume increased from 2.42 to 2.49 g/cm 3 and from 27.17 to 27.74 cm 3 /mol, respectively, reflecting the influence of RE ionic radii and field strengths on glass compactness. Optical absorption measurements revealed a shift in the absorption edge, with band gap values ranging from 3.13 to 3.38 eV. Tauc, ASF, and HEM models indicated direct allowed transitions in all samples. The refractive index ranged from 2.299 to 2.361. These results demonstrate that rare earth ions act as effective modifiers, enabling tunable structural and optical properties in sodium borate glass systems, which are promising for photonic and radiation shielding applications.