The Predictive Power of Electronic Polarizability for Tailoring the Refractivity of High-Index Glasses: Optical Basicity Versus the Single Oscillator Model
High-density (∼8 g/cm3) heavy metal oxide glasses composed of PbO, Bi2O3, and Ga2O3 were produced, and refractivity parameters (refractive index and density) were computed and measured. Refractive indices were measured at six discrete wavelengths from 0.633 to 10.59 m using a prism coupler, and data were fitted to the Sellmeier expression. Optical basicity was computed using three models—average electronegativity, ionic-covalent parameter, and energy gap—and the results were used to compute oxygen polarizability and subsequently the refractive index. Single oscillator energy and dispersion energy were calculated from experimental indices and from oxide energy parameters. The predicted glass index dispersion based on oxide oscillator parameters underestimates the measured index by only 3%–4%. The predicted glass index from optical basicity, based on oxide energy gaps, underpredicts the index at 0.633 m by only 2%. The calculated glass energy gap based on this optical basicity overpredicts the experimental optical gap by 6%–10%. Thus, we have shown that the density, the refractive index in the visible, and the energy gap can be reasonably predicted using only composition, optical basicity values for the constituent oxides, and partial molar volume coefficients. The relative contributions of the oxides to the total polarizability were assessed, providing an additional insight into controlling the refractivity of high-index glasses.
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