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)