The theoretical optical basicity is found to increase from0.93 to 1.15 while the optical
band gap decreases from 2.86 down to 2.30 eV with the addition of Bi2O3. The formation of
metallic bismuth in these glasses during melting in air has been confirmed by the XRD, TEM,
selected area electron diffraction (SAED) and high resolution TEM (HRTEM) analyses.