Effects of rare earth oxides (La2O3, Gd2O3) on optical and thermal properties in B2O3-La2O3 based glasses

The optical and thermal properties of B2O3-La2O3 based glasses, designed for digital imaging lenses, were investigated as a function of the Gd/(La+Gd) ratio in the glasses. The refractive index decreased gradually with increasing Gd/(La+Gd) ratio, although the change of refractive index was small. The liquidus temperature (LT) showed a minimum of 970 degrees C for the glass with a Gd/(La+Gd) ratio of 0.5. The viscosity at the LT reached a maximum for the glass with a ratio of 0.5, although the viscosity determined at 1040 degrees C for the glasses was found to increase gradually with increasing Gd/ (La+Gd) ratio. X-ray diffraction measurements indicated that the crystalline phase in the glasses below the LT depended strongly on the Gd/(La+Gd) ratio. The effect of the Gd/(La+Gd) ratio on the refractive index, dispersion, density, LT and viscosity is discussed in terms of glass structure.