Influence of six different RE

This study deals with investigation of the influence of rare-earth (RE³⁺) ions La³⁺, Nd³⁺, Gd³⁺, Ho³⁺, Er³⁺, and Yb³⁺ on the structural, photoluminescent, electrical, and thermal properties of a simple 50%B₂O₃ − 50%Na₂O glass system. The incorporation of 1 mol% RE₂O₃ systematically enhanced optical polarizability, as indicated by the increase in molar refraction (Rm) and nonlinear susceptibility (χ⁽³⁾). The Er³⁺ doped glass is exhibiting the highest value of χ⁽³⁾ ≈ 1.76 × 10⁻¹² esu. The calculated optical basicity, oxide ion polarizability, and metallization criteria confirmed the nonmetallic nature of all compositions. RE addition markedly intensified the photoluminescence emission, particularly for Gd³⁺ (> 2000 a.u.) and Er³⁺ (~ 700 a.u.), accompanied by high correlated color temperature values (CCT > 7600 K). Thermal analyses (TGA/DSC) revealed excellent stability up to 800 °C, with Tg values increasing from 422 °C (base glass) to 450 °C depending on RE type; the Nd³⁺-doped glass showed the highest thermal stability (ΔT ≈ 120 °C), implying superior glass-forming ability. All RE-doped samples displayed paramagnetic behavior, except La³⁺-doped, which remained diamagnetic. The dc conductivity decreased with decreasing ionic radius, consistent with the correlated barrier hopping (CBH) mechanism, while thermal conductivity (0.49–1.78 W m⁻¹ K⁻¹) confirmed their insulating and thermoelectric potential. Overall, the results demonstrate that RE³⁺ ions effectively tailor multifunctional characteristics of sodium borate glasses, highlighting their promise for advanced photonic and energy-related applications.