Magnesium fluoride (MgF2) is a white crystalline salt composed of one magnesium ion and two fluoride ions.
It is used in the electrolysis of aluminium ore.
Magnesium fluoride is transparent over an extremely wide range of wavelengths. Windows, lenses, and prisms made of this material can be used over the entire range of wavelenths from 0.2 μm (vacuum ultraviolet) to 6 μm (infrared). The cost of producing optical elements from this material—as of 2004 one vendor charged nearly $500 for 25-mm diameter magnesium fluoride lenses and windows—limits its use to specialized applications.
A thin layer of MgF2 is frequently applied to the surfaces of optical elements as a anti-reflective coating.
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