Bismuth's role in quaternary thulium doped tellurite glasses: Achieving optical clarity and radiation shielding

This study explores the impact of bismuth oxide (Bi₂O₃) on the optical and radiation shielding properties of transparent, lead-free thulium-doped bismuth borotellurite radiation shielding glass. The investigated glass composition follows the formula [(TeO₂)₇₅ (B₂O₃)₂₅]_98-x (Bi₂O₃)_x [Tm₂O₃]₂, where x = 0 mol%, 5 mol%, 10 mol%, 15 mol%, 20 mol%, 25 mol%, and 30 mol%. All glass samples remain transparent, with an optical bandgap ($E_{\text{opt}}$) exceeding 3.1 eV, ensuring visible light transmission. Radiation shielding data from Phy-X and XCom reveal interactions of the photoelectric effect, Compton scattering, and pair production, with minimal relative difference in mass attenuation coefficient ($\text{MAC}$) which is between 0.05 and 0.56. At 0.662 MeV photon energy, the 20 mol% and 25 mol% Bi₂O₃ glasses exhibit significantly higher Phy-X $MAC$ values than other samples, except RS 520 glass, which contains 71% PbO. Despite incorporating only up to 25 mol% Bi₂O₃, these glasses outperform others in density, half-value layer ($\text{HVL}$), and mean free path ($\text{MFP}$). Correlating $E_{\text{opt}}$ and $\text{MAC}$, the 20 mol% Bi₂O₃ glass is the best candidate for transparent radiation shielding glass due to its wide optical bandgap which prevents ionization of trapped holes. Significantly, the linkage between $\text{MFP}$ and molar refraction was also discovered based on the particle size influence on both parameters.