Synthesis and characterization of bismuth phosphate nanoparticle in glass matrix

Glasses having composition 5Li2O–5ZnO– xBi2O3 –(90 − x) P2O5 (x = 5, 10, 15, 20 and 25 mol%) were prepared by the normal melt quenching technique. Nanocomposite glass containing bismuth phosphate BiPO4 nanocrystals was obtained, which can be attributed to homogeneous nucleation process. The formation of BiPO4 nanocrystals was confirmed and characterized by X-ray diffraction patterns (XRD), transmission electron microscopy (TEM), differential scanning calorimetry, optical absorption (UV–Vis) and micro-hardness studies. The morphological analysis by XRD and TEM microscopy showed the formation of hexagonal BiPO4 nanocrystals, and its estimated nanocrystalline sizes were found to be varying from 5.35 to 11.53 nm depending on the Bi2O3 concentrations. The density (ρ) and molar volume (V m) were also determined and found to be in compositional dependence. Glass transition temperature (T g) and glass crystallization temperature (T c) were obtained and found to be increased (from 240.0 to 337.2 °C) with increasing Bi2O3 up to 20 mol% and then decreased (from 337.2 to 331.8 °C) due to the structural changes in the glass network. Effect of BiPO4 content on the optical properties had been investigated. From the UV–Vis spectra, it was observed that the fundamental absorption edge shifts toward lower wavelengths, i.e., blueshifts with increasing Bi2O3 mol% up to 20 mol%, and then shifts toward higher wavelengths, i.e., redshifts beyond 20 mol%. It was also observed that the obtained E opt (for indirect and direct transitions) increases with gradual increase in Bi2O3 content up to 20 mol% and then decreases beyond 20 mol%. This may be due to the introduction of Bi cations into the glass network as a network former up to 20 mol% causing a decrease in ΔE values, beyond 20 mol%, the introduction of Bi ions into the glass network interstitially leads to increase the values of ΔE. The optical properties of the present nanocrystallized glasses showed a quantum size dependence, in which the optical band gap energy (E opt) was changed as a function of BiPO4 nanocrystalline sizes.