Physical and linear/nonlinear optical properties of five samples of borophosphate glasses with the nominal compositions of 50B2O3 + (20-x)CaO + 20P2O5 + 10Na2O + XGd2O3: X = 0 mol.%, 0.5 mol.%, 1 mol.%, 1.5 mol.%, and 2.0 mol.%, prepared via the conventional melt quenching technique, were investigated. X = 0 mol.%, 0.5 mol.%, 1 mol.%, 1.5 mol.%, and 2 mol.%. Density (ρBGd-X) increased from 2.31 g/cm3 to 2.60 g/cm3, whereas molar volume (Vm) reduced from 34.80 cm3/mol for BGd-0.0 sample to 33.50 cm3/mol for BGd-2.0 sample. In the UV range, the position of the absorption edge shifted from ~ 395 nm to a deeper wavelength value (at ~ 410 nm) for BGd-0.0 and BGd-2.0, respectively. The indirect ( \(E_{\text{g-indirect}}^{\text{opt.}}\) ) and ( \(E_{\text{g-direct}}^{\text{opt.}}\) ) optical gap energies reduced from 3.62 to 3.23 eV and from 3.92 to 3.72 eV, respectively. Urbach's energy (EU) decreased from 0.35 and 0.39 eV. The optical density was stable in the spectral range (~ 400 to 1100 nm) between 1 and 3 eV. Linear refractive index (n) changed from 2.180 to 2.222. Both static ( \({\varepsilon }^{\text{static}}\) ) and optical ( \({\varepsilon }^{\text{opt.}} \) ) dielectric constants were improved with increasing Gd2O3 content in glass networks. Molar refraction (Rm) increased from 19.385 to 19.451 when the Gd2O3 molar concentration grew from 0.0 mol.% to 1.0 mol.% and then decreased to 19.015 at 2.00 mol.% Gd2O3 concentration. Both molar polarizability (αm) and electronic molar polarizability (αme) have a linear variation with respect to \({R}_{\text{m}}\) . The optical surface resistance (Rs) and thermal emissivity ( \({\varepsilon }_{\text{th}}\) ) increased as Gd2O3 content increased. The nonlinear susceptibility ( \({\chi }^{(3)}\) ) and nonlinear refractive index ( \({n}_{2}\) ) were proportional to each other for all prepared BGd-X samples. Results showed that the suggested BGd-X glasses can be used for optical applications.
