The optical fluoride calcium fluoride (CaF2) has a high transmittance for application in the vacuum ultraviolet to near-infrared wavelengths. The material has a wide range of optical applications such as spectral CaF2 windows, CaF2 prisms, and CaF2 lenses. In particular, pure grade CaF2 has useful applications in UV and UV excimer laser windows. CaF2 can also be used as a gamma-ray scintillator doped with europium. Alfa chemistry can custom fabricate optical components of almost any shape and size using CaF2 materials. If you need help, please contact us.
Advantages and Uses of Calcium Fluoride Materials
CaF2 has good optical and thermomechanical properties. Among all fluoride crystal materials, CaF2 is considered one of the hardest materials. Its optical properties of high transmittance, low absorption, and low refractive index in the infrared and ultraviolet regions give it a unique advantage in laser applications.
Fig 1. The cubic structure of calcium fluoride in which calcium is coordinated to eight fluoride anions, each F- ion surrounded by four Ca2+ ions. (Ropp R.C, et al. 2013)
In addition, CaF2 is physically stable and chemically inert, which means that products made from it are highly resistant. It also offers excellent chromatic aberration compensation with both low and ultra-low dispersion.
CaF2 is usually manufactured in different qualities or so-called grades. UV grade CaF2 requires a much higher material purity than materials in the infrared range.
Fig 2. Transmission spectra of calcium fluoride windows. (Ropp R.C, et al. 2013)
Properties of Calcium Fluoride Materials
| Density | 3.18 g/cc |
| Molecular Weight | 78.08 |
| Solubility | 98 x 10-6g/100g water |
| Class/Structure | Cubic (111) cleavage |
| Melting Point | 1360 ℃ |
| Hardness | Knoop 158.3 with 500g indenter |
| Refractive Index | 1.39908 at 5 μm |
| Transmission Range | 0.13 ~ 10 μm |
| Reflection Loss | 5.4% at 5 μm |
| Reststrahlen Peak | 13.5 μm |
| Absorption Coefficient | 7.8x10-4 cm-1 at 2.7 μm |
| dn/dT | -10.6x10-6/℃ |
| Youngs Modulus (E) | 75.7 GPa |
| Shear Modulus (G) | 33.77 GPa |
| Bulk Modulus (K) | 83.71 GPa |
| Thermal Expansion | 18.85 x 10-6/℃ |
| Thermal Conductivity | 9.71 W/m/K |
| Dielectric Constant | 6.76 at 1MHz |
| Specific Heat Capacity | 854 J Kg-1 K-1 |
| Poisson Ratio | 0.26 |
| Elastic Coefficients | C11 = 164, C12 = 53, C44 = 33.7 |
About refractive index parameters.
"No" means ordinary light.
| µm | No | µm | No | µm | No |
|---|---|---|---|---|---|
| 0.149 | 1.58 | 0.161 | 1.549 | 0.195 | 1.5 |
| 0.2 | 1.495 | 0.222 | 1.48 | 0.248 | 1.468 |
| 0.266 | 1.4621 | 0.28 | 1.4584 | 0.3 | 1.454 |
| 0.337 | 1.4481 | 0.4 | 1.4419 | 0.486 | 1.437 |
| 0.588 | 1.4339 | 0.656 | 1.4325 | 0.687 | 1.432 |
| 0.728 | 1.4314 | 0.884 | 1.4298 | 1.014 | 1.4288 |
| 1.1 | 1.4283 | 1.25 | 1.4275 | 1.65 | 1.4256 |
| 1.9 | 1.4244 | 2.058 | 1.4236 | 2.45 | 1.4214 |
| 2.7 | 1.4199 | 2.8 | 1.4192 | 3.05 | 1.4175 |
| 3.4 | 1.4149 | 4 | 1.4096 | 4.4 | 1.4057 |
| 4.8 | 1.4014 | 5 | 1.3991 | 5.304 | 1.3952 |
| 5.893 | 1.3871 | 6.483 | 1.3782 | 7.072 | 1.3681 |
| 7.661 | 1.357 | 8.251 | 1.3444 | 8.84 | 1.3308 |
| 9.429 | 1.3161 | 0.161 | 1.549 | 0.195 | 1.5 |
Reference
- Ropp R.C, et al. (2013). "Group 17 (H, F, Cl, Br, I) Alkaline Earth Compounds." Encyclopedia of the Alkaline Earth Compounds. 2: 25-104.