Exploring the impact of CuCl2 modification on structural variations and dielectric constant in bismuth borate tellurite glasses

•TeO2 glass series prepared via melt-quenching technique.•FTIR & Raman Spectroscopy analysis revealed formation of non-bridging oxygens.•UV–Vis absorption spectra show transition 2B1g→2B2g for Cu2+ ions.•Metallization criterion values (0.300 – 0.383) exhibit good nonlinear optical applications.•Dielectric constant analysis shows non-Debye type relaxation behaviour. Copper chloride doped boro-tellurite-based glass series with compositions 60TeO2-(25-x) Bi2O3–15B2O3-xCuCl2 (x = 0, 5, 10, 15, and 20) were synthesized using the traditional melt-quench procedure. The X-ray diffraction patterns of the examined glasses reveal their amorphous nature. The effect of CuCl2 addition on the glass network/structural units was studied using vibrational (FTIR/Raman) spectroscopy, and CuCl2 inclusion in the glass matrix resulted in a transformation from compact TeO4 to TeO3 structural units This shows that copper chloride acts as a modifier in the examined glass series, resulting in the creation of non-bridging oxygen (NBOs), meaning that the loosening of the glass network is further supported by a decrease in the glass transition temperature as CuCl2 content increases. UV–Vis DRS spectra of examined glasses reveal an absorption band corresponding to the typical transition of Cu2+ ions from 2B1g → 2B2g, situated in deformed octahedral sites in absorption spectra. As Cu+ concentration rises, the indirect optical band gap values drop from 2.94 eV to 1.75 eV. The metallization criterion values lie between 0.383 and 0.300 suggesting that these glasses are potential candidates for nonlinear optical applications. With an increase in Cu+ concentration, the values of molar refractive index (Rm) and molar electronic polarizability αm increases from 22.412 to 26.205 and 8.894 to 10.398 respectively, which correlate with increasing dielectric constant (ε′) values as the Cu+ amount increases. Further dielectric studies reveal non-Debye-type relaxation behaviour.