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Material Lithium Fluoride (LiF)
Lithium Fluoride is used for windows, prisms, and lenses in the visible and infrared where desired transmission is in the 0.104 µm - 7 µm range.
Modest precautions should be taken against moisture and high
energy radiation damage. LiF is attacked by atmospheric moisture
at 400 °C and softens at 600 °C. LiF is sensitive to thermal
shock. Irradiation produces color centers. The material can
be cleaved. Lithium fluoride is grown by vacuum Stockbarger
technique in diameters of 115mm. Although the optical characteristics
are good the structure is not perfect and cleavage is difficult.
For good structure LiF is less commonly grown by the Kyropoulos
method (air-grown) specifically for monochromator plates. Cleavage
is (100) and less commonly (110). LiF is slightly plastic and
can be bent into radius plates.
Properties
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PARAMETER |
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VALUE |
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| OPTICAL |
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Transmission Range |
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0.12 to 8.5 microns |
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Refractive Index |
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1.3943 at 0. 5 microns |
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Reflection Loss |
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5.4% at 0.5 µm (2 surfaces) |
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dn/dT |
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-12.7 x 10-6/ °C at 0.6 microns |
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| PHYSICAL |
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Density |
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2.63905 g/cm3 |
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Melting Point |
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870° C |
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Thermal Conductivity |
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4. 01 W/(m K) at 41 °C |
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Thermal Expansion |
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37 x 10-6/ °C |
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Hardness |
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Knoop 102 to 113 kg/mm2 with 600g indenter |
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Specific Heat Capacity |
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1562 J/(kg K) at 10 °C |
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Dielectric Constant |
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9.1 at 25 °C |
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Young's Modulus (E) |
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64.79 GPa |
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Shear Modulus (G) |
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55.14 GPa |
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Bulk Modulus (K) |
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62.03 GPa |
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Elastic Coefficients |
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C11=97.4 C12=40.4 C44=55.4 |
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Apparent Elastic Limit |
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11.2 MPa |
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Poisson Ratio |
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0.326 |
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| CHEMICAL |
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Solubility |
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0.27g/l00g water at 20 °C |
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Molecular Weight |
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25.94 |
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Class/Structure |
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FCC, NaCl structure. Cleavage (100) |
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REFRACTIVE INDEX
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Wavelength, µm |
0.20 |
0.22 |
0.24 |
0.29 |
0.39 |
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Refractive Index |
1.44 |
1.43 |
1.42 |
1.41 |
1.40 |
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Wavelength, µm |
0.60 |
1.75 |
2.75 |
3.40 |
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Refractive Index |
1.39 |
1.38 |
1.37 |
1.36 |
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