Linear and Nonlinear Optical Characteristics of Bismuth-Modified Lead-Silicate Glasses

Bismuth-modified lead silicate glasses with composition 20PbO∙(80-x)Bi₂O₃∙xSiO₂ (10 ≤ x ≤ 40 mol%) were fabricated by classical melt-quench technique. The density (D), crystalline volume (V_C), and molar volume (V_M) values decrease with a decrease in bismuth concentration. FTIR spectra suggest the formation of [BiO₃], [BiO₆], [SiO₄], [PbO₃], and [PbO₄] structural units. The optical band gap (E_g) values for the studied glass composition are determined to be between 1.93 and 2.12 eV, while their Urbach energy (∆E) values fall between 0.14 and 0.24 eV. A decrease in values of average electronic oxide polarizability (2.84‒1.62 ų), and optical basicity (1.08‒0.64), predict the increase in the covalence nature of the Bi-O bond with the incorporation of SiO₂ in the glass network. The small metallization criterion (0.311 to 0.325) predicts the suitability of the prepared series to be utilized as nonlinear optical materials. The Z-scan approach was utilized to determine the third-order nonlinear optical characteristics, including the nonlinear absorption coefficient (α₂), nonlinear susceptibility (χ⁽³⁾), and nonlinear refractive index (η₂). Optical studies reveal that with the decrease in Bi₂O₃ content, nonbridging oxygens (NBOs) decrease leads to an increase in bandgap and a drop in the nonlinear refractive index. The dynamic range (DR) and limiting threshold values have also been reported from the optical limiting studies of the prepared glasses.