Effect of high valency cations on high refractive-index and low dispersion characteristics of borate glasses

Refractive indexes of barium borate-based glasses were measured in the wavelength range from 0.265 to 1.710 μm by using the minimum deviation method. Factors affecting the refractive index dispersion are discussed by using the single-oscillator Drude-Voigt equation. Borate glasses are characterized by the larger number N of molecules in a unit volume than that for silicate glasses. The feature of borate glasses, that is, relative high refractive index and low dispersion, is dominated by the number N which is related to the fraction of four-coordinated borons estimated by Greenblatt and Bray. Borate glasses containing high valency cations, e.g., Y³⁺, La³⁺, Ti⁴⁺, Nb⁵⁺, Ta⁵⁺, possess higher refractive indexes and higher dispersion than barium borate binary glasses.