The results of refractive-index measurements in ZrF4-BaF2-LaF3-AlF3 glass and the effects of the addition of NaF are described. The dispersion properties are not enhanced by the addition of NaF, as shown by increased material dispersion M at long wavelengths and decreased crossover wavelength λ0.
Richard N. Brown and Joseph J. Hutta, "Material dispersion in high optical quality heavy metal fluoride glasses," Appl. Opt. 24, 4500-4503 (1985)