Tuning the optical band gap and shielding efficiency of heavy metal borate glasses through controlled Fe2O3 doping

This work investigates the influence of Fe³⁺ doping (via Fe₂O₃) on the structure, optical, ligand field, and
shielding properties of heavy metal glasses. Structural studies confirmed the addition of Fe³⁺ ions as network
modifiers by causing some structural modifications via increasing density, decreasing molar volume, and
increasing non-bridged oxygen content. By analyzing the optical spectra in the visible light region, the tetrahedral symmetry of Fe³⁺(Td) was confirmed. The generated samples exhibited a characteristic brown hue due to
the electronic transition 6
A1g (S) → 4
T2g (D) of Fe³⁺(Td) ions. Additionally, the absorption bands in the NIR region
confirmed the octahedral symmetry of Fe³⁺(Oh). Increasing Fe₂O₃ concentration strengthens and red-shifts optical bands, suggesting a narrowing band gap and increased disorder (higher Urbach energy). Refractive indices
also rise, indicating enhanced electronic polarization and optical basicity. Ligand field studies reveal improved
Fe³⁺ environments and a tendency for covalent bonding (nephelauxetic effect). Shielding effectiveness tests
revealed a significant improvement, particularly at low energies, for the sample with the highest Fe₂O₃ content,
compared to common shielding materials.