Preparation and Properties of Heavy‐Metal Fluoride Glasses Containing Ytterbium or Lutetium

Beginning with a 19BaF 2 −27ZnF 2 −27YbF 3 −27ThF 4 (mol%) base glass, compositional modifications were made to improve optical properties and glass‐forming ability. Replacement of YbF 3 by LuF 3 removed a strong near‐ir electronic absorption band, and small additions of LiF and NaF improved glass quality. The multicomponent BaF 2 /ThF 4 glasses had higher refractive indices and lower expansion coefficients than fluorozirconate and fluorohafnate glasses. In the 6 to 10 μm region, these materials exhibit absorption coefficients an order of magnitude lower than those reported for other heavy‐metal fluoride glasses.