It is a white hygroscopic powder which can be produced by reacting thorium with fluorine gas.

[1] Despite its (mild) radioactivity, thorium fluoride is used as an antireflection material in multilayered optical coatings.

It has excellent optical transparency in the range 0.35–12 μm, and its radiation is primarily due to alpha particles, which can be easily stopped by a thin cover layer of another material.

[2][3] However, like all alpha emitters, thorium is potentially hazardous if incorporated, which means safety should focus on reducing or eliminating this danger.

in making carbon arc lamps, which provided high-intensity illumination for movie projectors and search lights.