Structural, optical and thermal properties of transition metal ions doped bismuth borate glasses

Bismuth borate glasses with composition 20Bi(2)O(3)center dot 80B(2)O(3) containing 2.0 mol% of transition metal ions having magnetic character (Cu2+, Co2+, Ni2+, and Fe3+) prepared by the melt-quench technique have been investigated for their structural, thermal and optical properties. Glass formation is confirmed by x-ray diffraction (XRD). The density (D) and molar volume (V-m) of prepared have been measured and correlated with the structural changes. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) are carried out in the temperature range of 200-1000 degrees C. The glass transition temperature (T-g) and glass melting temperature (T-m) are found to increase on adding transition metal ions (TMIs) to the bismuth borate glass matrix indicating the decreased glass fragility. The absence of weight loss observed from the TGA thermographs shows that the synthesized compositions are non-volatile. Study of infrared (IR) spectroscopy in mid-IR range (400-4000 cm(-1)) reveals an increase in tetrahedrally coordinated boron atoms and hence formation of nonbridging oxygens (NBOs). The optical band gap (E-opt) band tailing parameter (B) and Urbach energy (DE) are calculated and reported from the optical absorption results. A decrease in optical band gap is observed on adding transition metal ions to pure bismuth borate glass.