EFFECT OF HIGH VALENCY CATIONS ON HIGH REFRACTIVE-INDEX AND LOW-DISPERSION CHARACTERISTICS OF BORATE GLASSES

Refractive indexes of barium berate-based glasses were measured in the wavelength range from 0.265 to 1.710 mu m by using the minimum deviat ion method. Factors affecting the refractive index dispersion are disc ussed by using the single-oscillator Drude-Voigt equation. Berate glas ses are characterized by the larger number N of molecules in a unit vo lume than that for silicate glasses, The feature of berate glasses, th at 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, Berate glasses containing hig h valency cations, e.g., Y3+, La3+, Ti4+, Nb5+, Ta5+, posess higher re fractive indexes and higher dispersion than barium berate binary glass es.