Calcium fluoride

Calcium fluoride (CaF₂) occurs naturally as the mineral fluorite or fluorspar. It is the world′s main source of fluorine. It is used in the optical industry because of its transparency in both infrared (IR) and ultraviolet (UV) wavelengths (about 0.15 to 9 μm). Due to its low refractive index (n500 = 1.44), it is considered a promising candidate for antireflective coatings. Chemically, CaF₂ is relatively stable; optical components will not be harmed under adverse conditions.

In recent years, calcium fluoride has garnered much interest due to its properties such as stability and lack of hygroscopicity. It can be commonly used in the manufacture of optical and optoelectronic materials such as windows, LEDs, laser diodes, solar cells, vitrines, and lenses because of its excellent optical properties and resistance to abrasion and scratches. CaF₂ is also used as an additive to produce high thermal conductivity aluminum nitride (AlN) ceramics because it acts as a sintering aid at high temperatures and removes residual grain-boundary phases. Doped AIN is used as an excellent material for the development of optoelectronic devices due to its high thermal and electrical conductivities.
In addition, CaF₂ is commonly used as a laser crystal and it is easy to grow in the form of large, good-quality bulk crystals to develop commercial optics. It is also used in ceramic host laser applications because of its cubic structure. Divalent rare-earth ions (Sm⁺²) and trivalent rare-earth ions (Er⁺³, Tm⁺³, and Yb⁺³) are doped with CaF₂ to develop a single crystal for tunable broadband and high-power diode-pumped laser operations.

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