Neodymium Fluoride

Neodymium fluoride is an inorganic compound composed of fluoride and the rare earth neodymium.

Glass (Optical)
As an optical material, neodymium fluoride is sometime used to make scintillator detectors, used in the preparation of rare earth crystals, laser materials, rare earth fluoride glass, optical fibers, LEDs, phosphors, and as a purple colorant for glass.

Additional Notes:
*Neodymium has a strong absorption band centered at 580 nm, which is very close to the human eye’s maximum level of sensitivity making it useful in protective lenses for welding goggles. – (link)