Lithium fluoride (LiF) has the highest UV transmission of any material and can be used in special UV optics. It transmits well into the VUV region at the hydrogen Lyman-alpha line (121 nm) and beyond. LiF is the best crystal for examination because of its lattice spacing and its application in X-ray monochromator plates. Using LiF materials, Alfa Chemistry can produce optical elements on demand that are almost any size and form according to customer specifications. Please get in touch with us if you require assistance.
Advantages and Uses of Lithium Fluoride Materials
LiF has high transmittance and is often used to make windows, prisms and lenses in vacuum UV, ultraviolet, visible and infrared light. Its transmission range is from 0.11 microns to 7 microns. The special lattice structure of LiF makes it the most useful crystal for analysis and is often used as an X-ray monochromator plate.
LiF material should be used with care because it is sensitive to thermal shock and is subject to erosion by atmospheric moisture at 400 ℃. Use non-standard permeability enhancement films when coating LiF materials.
The optical LiF materials used by Alfa Chemistry are of single crystal optical quality and are manufactured to customer order.
Fig 1. Transmittance spectra of the LiF crystal colored by 3 keV electrons. Uncolored area experimental transmittance "dashed line"; experimental "vertical bars" and fitted "full line" transmittance spectra through the colored area. (Montecchi M, et al. 1999)
Properties of Lithium Fluoride Materials
| Density | 2.639 g/cc |
| Molecular Weight | 25.94 |
| Solubility | 0.27g / 100g water at 20 ℃ |
| Class/Structure | Cubic FCC, NaCl, Fm3m, (100) cleavage |
| Melting Point | 848 ℃ |
| Hardness | Knoop 102 with 600g indenter |
| Refractive Index | 1.392 at 0.6 μm |
| Transmission Range | 0.12 ~ 6 μm |
| Reflection Loss | 5.2% at 0.6 μm |
| Reststrahlen Peak | 25 μm |
| Absorption Coefficient | 5.9x10-3 cm-1 at 4.3 μm @ 300K |
| dn/dT | -16 x 10-6 at 1.15 μm |
| Youngs Modulus (E) | 64.97 GPa |
| Shear Modulus (G) | 55.14 GPa |
| Bulk Modulus (K) | 62.03 GPa |
| Thermal Expansion | 37 x 10-6 K-1 at 283 K |
| Thermal Conductivity | 4.01 W/m/K at 314 K |
| Specific Heat Capacity | 1562 J Kg-1 K-1 |
| Poisson Ratio | 0.326 |
| Elastic Coefficients | C11=112; C12=46; C44=63.5 |
| Dielectric Constant | 0.1 |
About refractive index parameters.
"No" means ordinary light.
| µm | No | µm | No | µm | No |
|---|---|---|---|---|---|
| 0.106 | 1.9130 | 0.108 | 1.8330 | 0.110 | 1.7770 |
| 0.121 | 1.6240 | 0.130 | 1.5690 | 0.140 | 1.5300 |
| 0.150 | 1.5030 | 0.160 | 1.4840 | 0.170 | 1.4690 |
| 0.180 | 1.4850 | 0.190 | 1.4455 | 0.200 | 1.4391 |
| 0.220 | 1.4291 | 0.250 | 1.4189 | 0.260 | 1.4164 |
| 0.270 | 1.4141 | 0.280 | 1.4121 | 0.290 | 1.4103 |
| 0.300 | 1.4087 | 0.310 | 1.4073 | 0.320 | 1.4060 |
| 0.330 | 1.4048 | 0.340 | 1.4037 | 0.350 | 1.4028 |
| 0.360 | 1.4019 | 0.400 | 1.3989 | 0.500 | 1.3943 |
| 0.600 | 1.3918 | 0.700 | 1.3902 | 0.800 | 1.3890 |
| 0.900 | 1.3880 | 1.000 | 1.3871 | 1.500 | 1.3832 |
| 2.000 | 1.3788 | 2.500 | 1.3733 | 3.000 | 1.3666 |
| 3.500 | 1.3587 | 4.000 | 1.3494 | 4.500 | 1.3388 |
| 5.000 | 1.3266 | 5.100 | 1.3240 | 5.200 | 1.3213 |
Reference
- Montecchi M, et al. (1999). "Optical Characterization of Low Energy Electron Beam Colored LiF Crystals by Spectral Transmittance Measurements." Radiation Measurements. 86(7): 3745.