Physical, Optical, and Spectroscopic Characteristics of Mixed Alkali Tetraborate Glasses RO–ZnO–Li 2 B 4 O 7 -K 2 B 4 O 7 : Impact of Alkaline Earth Oxides (R = Mg, Ca)

Alkali tetraborate glasses 10RO-30ZnO-xLi 2 B 4 O 7 -(60-x) K 2 B 4 O 7 (R = Mg, Ca) with x varying from 0 mole% to 60 mole% were synthesized by melt quenching approach at around 1150 °C. Broad and peak less X-ray diffraction spectra confirmed the amorphous nature of synthesized glass samples. Physical and optical properties namely density, molar volume, refractive index, optical band gaps, molar refractivity and Urbach energy values have been reported. The density of the present glass samples improved with increasing x mole% except at the presence of equal amounts of alkali oxides in the glass system. The molar volume decreased continuously with x mole%. Oxygen packing density (OPD) increased with increasing x mole%. The optical energy band gap E opt values with increasing lithium tetraborate in the glass composition have shown a downward trend, where are refractive index values shown upward. FTIR and Raman studies revealed the variation of BO 3 and BO 4 units in the glasses with composition is marginal. EPR spectra of copper ions confirmed the existence of Cu 2+ ions in the ground state d x 2 – y 2 orbital ( 2 B 1g ). The observed non-linear variations of various properties are attributed to the structural changes caused by mixed alkali effect.