KBr (Potassium Bromide)

Download KBr (Potassium Bromide) Datasheet (PDF, 139 KB)

KBrPotassium bromide (KBr) is one of the most popular materials used in spectroscopy due to the wide transmission range. It corresponds to salt crystals as well as KCl and NaCl. KBr is a monocrystal, soft and stable to thermal influence however should be avoided from a contact with water and spirit solutions, glycerin, and acids. Due to material hygroscopicity the polished parts require storage in desiccator or in sealed package with silica gel in a warm room.


  • IR / FTIR spectroscopy

Product types:

  • Plane-parallel windows and wedges
  • Beamsplitter substrates for FTIR spectroscopy
  • Lenses


Tab.1. Typical specification of KBr optical components

Specification Typical State-of-the-art
Sizes See table in the article Plane Windows and Wedged Windows RFQ (up to 100mm size)
Diameter tolerance, mm +0/-0.25 RFQ
Thickness tolerance, mm +0/-0.25 RFQ
Thickness matching, mm - RFQ
Surface quality, scr/dig 60/40 RFQ
Surface flatness, λ @ 633nm per inch* 2 RFQ
Parallelism (wedge tolerance) 5 arc min RFQ
Coating none RFQ
Packaging Typak®  

Transmission Spectrum


For the optics we use KBr material with absorption less than 0.5% in absorption bands (through reference 3mm thickness).

Tab.2. Refractive index

λ, µm n
0.391 1.594
0.405 1.590
0.486 1.572
0.589 1.560
0.811 1.547
1.701 1.539
8.662 1.529
11.862 1.522
17.400 1.504
18.160 1.501
21.180 1.487
21.830 1.483
23.860 1.471
25.140 1.463

Tab.3. Optical properties

Transmission range, microns 0.22-28 µm
Colour Colourless
Reflection losses (2 surfaces), % 5 µm 8.8
11 µm 8.3
Absorption coefficient, cm-1 10.6 µm ≤0.001
19 µm ≤0.05
26 µm ≤0.33
30 µm ≤0.7
Restrahlen peak, µm 77.6
dN/dT, 10-6/C -40.83
dN/dm = 0, мкм  4.2
Birefringence, nm/cm <30

Tab.4. Physical and mechanical properties

Class / Structure Cubic FCC, NaCl type, Fm3m, (100) cleavage
Density @300K, g/cm2 2.753
Molecular Weight 119.01
Lattice Constant, Å 6.60
Melting Point, C 730
Thermal Conductivity @319K, W/(m x K) 4.816
Thermal Expansion @300K, 10-6/C 43
Hardness, Knoop with 200g indenter in (100) 7
in (110) 5.9
Specific Heat Capacity, J/(kg х К) 435
Debye Temperature, K 174
Dielectric Constant for 102 - 1010 Hz @295К 4.90
@360К 4.97
Bandgap, eV 7.6
Young Modulus (E), GPa 64.79
Shear Modulus (G), GPa 5.08
Bulk Modulus (К), GPa 15.02
Elastic Coefficient C11 = 34.5 C12 = 5.4 C44 = 5.08
Apparent Elastic Limit, MPa 1.1 (160psi)
Poisson Ratio 0.203

Tab.5. Chemical stability / Solubility

in water
(at 0 оС)
53.48 g/100cm3
in acids soluble
in organic solvents:  
glycerin soluble
lower spirits soluble
ether insignificantly soluble

Please pay your attention that this article is for your information only. We do not supply KBr in ingots as well as semi-finished products. Our standard products are polished parts.

For further information on our KBr optical components please see the following: Windows for IR-spectroscopy, FTIR beamsplitter substrates, Packaging or fill in our request form.
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