Sodium fluoride is seldom used for its optical properties, these being inferior to calcium fluoride and lithium fluoride, but it has one of the lowest refractive indexes of all materials in the UV, and is generating considerable interest as a detector material in high energy physics RICH (Ring Imaging Cherenkov) counters. Sodium fluoride may also be used as an a/r coating material.

Formula: NaF

Molecular Weight: 42.0

Crystal Structure: Cubic, NaCl structure. (100) cleavage

Applications: Cherenkov counters

Typical Optical Properties:

Transmission Range: 0.15 to 14 microns

Refractive Index: 1.327 at 0.5 microns

Reflection Loss: 3.8% at 0.5 microns (2 surfaces)

Restrahlen Peak: 35.8 microns

Typical Physical Properties:

Density: 2.726 gm/cc

Melting Point: 980 ^oC

Solubility in Water: 4.22gm/100gm at 18 ^oC

Thermal Conductivity: 3.746 Wm^{-1 o}K^-1 at 0 ^oC

Thermal Expansion: 36 x 10^-6/^oC

Hardness: Knoop 60

Specific Heat Capacity: 1088 J Kgm^{-1 o}K^-1 at 0 ^oC

Dielectric Constant: 6.0

Young’s Modulus: 79.01 GPa

Shear Modulus: 12.7 GPa

Bulk Modulus: 47.9 GPa

Elastic Coefficients: C₁₁ = 90.9 C₁₂ = 26.4 C₄₄ = 12.7

Poisson Ratio: 0.326