Lanthanum Fluoride is not often used as an optical material. Lanthanum Fluoride is usually doped with Europium at a nominal level of 0.3% mole. In this form, the usual application is as the active element in an ion-selective electrode for the detection and measurement of Fluoride ions in solution.
Lanthanum Fluoride is grown as small ingots of about 10mm diameter as it is difficult to anneal. Doped with Europium, it is a pale yellow colour.
REFERENCES:
(1) Jones and Shand, J.Crys.Growth. 2 (1968) p3611
(2) Sher, Solomon, Lee, and Meuller. Phys.Rev. 144, p593 (1966)
(3) Electronic Processes in Ionic Crystals (OU Press, NY, 1940) p.41 Optical data are for ordinary ray (o).