Optical parameters and shielding attitude of sodium fluoride in calcium-borate glasses

Borate glasses with compositions xCaO-(30-x)NaF-70B₂O₃ (x = 0–30 mol%, step 5) were synthesized and characterized to investigate the effects of partially substituting NaF with CaO on radiation shielding ability and optical properties. Density, molar volume, packing density, and free volume were measured and calculated. UV–visible spectroscopy was utilized to determine the optical bandgap and other correlated physical parameters. Moreover, different shielding parameters were evaluated using Phy-X simulation software. From data analyses, it was found that increasing CaO content transformed BO₃ to BO₄ structural units in the borate glass network, keeping the optical bandgap values between 3.76 and 3.55 eV. In addition, the refractive index varied from 2.32 to 2.4, while molar refractivity and Urbach energy were slightly increased with composition. Moreover, the replacement of NaF by CaO enhanced photon interaction cross-sections, reducing the mean free path and half-value layer. The work demonstrated that controlled additions of an intermediate oxide like CaO can tailor the radiation shielding and optical characteristics of borate glasses for potential applications as transparent radiation shielding materials.