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Selecting IR Transmitting Materials

 

Prior to selecting a transmitting material for infrared cell use, wavelength range, solubility, and refractive index must be considered. Thermal and mechanical properties of the material are also important. A chart describing transmission ranges, refractive index, and other useful information pertaining to crystal selection is provided in the selection guide for infrared transmitting materials.

Cost is also an important factor. In the following pages you will find economical IR transmitting crystals of the highest quality available.

SELECTION GUIDE FOR INFRARED TRANSMITTING MATERIALS
Materials
Transmission
Range
Index of
Refraction
NaCl Rock Salt
0.25 - 15µm
1.52
Generally considered the most useful cell window. NaCl is low cost and rugged. Hygroscopic.
KBr Potassium
Bromide
0.25 - 25µm
1.53
KBr is an excellent, low cost material with an extended transmission range. It is softer than NaCl; stands thermal and mechanical shock fairly well. Hygroscopic.
AgCl Silver
Chloride
0.4 - 23µm
2.0

Soft material. Darkens under UV radiation, insoluble in water. Used as inexpensive cell windows. Corrosive to metals.

CaF2 Calcium
Fluoride
0.15 - 9µm
1.40
Low index and very low solubility. Makes durable and precise cell for the region in which it transmits. Insoluble in water; resists most acids and alkalides. Do not use with solutions of ammonium salts.
BaF2 Barium
Fluoride
0.2 - 11.5µm
1.46
This material is extremely sensitive to thermal shock. Do not use with solutions of ammonium salts. Insoluble in water; has good resistance to fluorine and fluorides.
CsI Cesium
Iodide
1.5 - 50µm
1.74
Generally easier to handle than cesium bromide. Hygroscopic; does not cleave; easily scratched.
KRS-5 Thallium
Bromide-
Iodide
0.5 - 35µm
2.37
Easily scratched; will cold flow; does not cleave; soluble in bases; insoluble in acids; slightly water soluble. Ideal for ATR work. Do not grind or polish.
ZnSe Zinc
Selenide
1 - 18µm
2.4
Material equals KRS-5 in general usefulness. Insoluble in water and highly resistant to most solvents. Strong interference fringes may occur in short path cells. It is brittle and therefore must be handled with extreme care.
MgF2 Magnesium
Fluoride
0.11 - 7.5µm
1.37 - 1.38
Slightly more soluble than CaF2. Birefringent. Transmits from vacuum ultraviolet into the infrared. Sensitive to thermal shock.
Ge Germanium
2 - 11.5µm
4.0
This high index material should prove highly useful for surface studies and perhaps as a process window. It is chemically inert, hard and brittle. Should be handled with extreme care, tends to fracture.
KCl Potassium
Chloride
0.18 - 20µm
1.46
KCl is similar to NaCl, but not as popular. Our choice over NaCl for basic cell material because it is less hygroscopic, transmits further into the infrared range, and resists thermal shock.
ZnS Irtran-2
Zinc Sulfide
1 - 14µm
2.20
Insoluble in water. Slightly soluble in acids, HNO3, H2SO4, and KOH.
SiO2 Infrasil
Quartz
0.4 - 4µm
1.5 at
3333cm-1
Insoluble in water. Birefringent.