Structural and optical properties of $(100-x)(Li_2B_4O_7)-x(SrO-Bi_2O_3-0.7Nb_2O_5-0.3V_2O_5)$ glasses and glass nanocrystal composites

Glasses of various compositions in the system $(100-x)({Li_2B_4O_7})-x(SrO-Bi_2O_3-0.7Nb_2O_5-0.3V_2O_5})$ $(10\leq x \leq 60$, in molar ratio) were prepared by splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses (DTA). The amorphous nature of the as-quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X-ray powder diffraction studies. Glass composites comprising strontium bismuth niobate doped with vanadium $(SrBi_2(Nb_{0.7}V_{0.3})_2O{_9{_-_\delta}$ (SBVN)) nanocrystallites were obtained by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. High resolution transmission electron microscopy (HRTEM) of the glass nanocrystal composites (heat-treated at 783 K/6 h) confirm the presence of rod shaped crystallites of SBVN embedded in ${Li_2B_4O_7}$ glass matrix. The optical transmission spectra of these glasses and glass nanocrystal composites of various compositions were recorded in the wavelength range 190–900 nm. Various optical parameters such as optical band gap $(E_{opt})$, Urbach energy $(\Delta E)$, refractive index (n), optical dielectric constant $(\epsilon ^{\prime}_\infty)$ and ratio of carrier concentration to the effective mass $(N/m ^\ast)$ were determined. The effects of composition of the glasses and glass nanocrystal composites on these parameters were studied