Effect of Bi3+ ions on physical, thermal, spectroscopic and optical properties of Nd3+ doped sodium diborate glasses

Neodymium doped sodium diborate glasses containing bismuth oxide were prepared by melt quenching method. An effort has been made to understand whether the stiffness of tightly bound diborate groups affect upon the addition of heavy metal oxide. The increase in density and decrease in molar volume with increase of Bi2O3 content indicates the opening of diborate glass structure to achieve better packing and bonding. The mixed bonding such as Bi-O-B may occur during glass formation leads to decrease in its glass transition temperature. The increase in oxygen packing density values also indicates the existence of tight packing of the oxide network. The optical properties are measured using UV-visible spectroscopy. The increase in refractive index is attributed to the increasing number of highly polarizing Bi3+ ions with higher atomic weight and coordination number. The decrease in the optical band gap energy with increase in Bi2O3 content is ascribed to shifting of absorption edge to a longer wavelength region. The IR spectra reveal that the glass network consists of tightly bound diborate and BiO6 octahedral units.