PROPERTIES OF MATERIALS FOR SPECTROSCOPY

This table presented courtesy of Spectral Systems
MaterialSWL
(cm-1)
LWL
(cm-1)
Refractive IndexS/DFlatnessPe
Atm
Restrahlen
(cm-1)
Density
g/cc
Solubility
(g/100g)
Melting Point
(°C)
Hardness
kg/mm2
Comments
AgBr 22,000 255
292
2.22@10 80/50 5 0.56 88 6.5 1.2E-05 432 7 Insoluble in water, slightly soluble in sodium hydroxide and some amines. Migrates into base metals. Will blacken under UV radiation. Cold flows and should not be used above 200 °C.
AgCl 24,500 353
404
1.90@10 80/50 5 0.56 123 5.6 5.2E-02 457 10 Insoluble in water, slightly soluble in sodium hydroxide and some amines. Migrates into base metals. Will blacken under UV radiation. Cold flows and should not be used above 200 °C.
Al2O3 40,000 1608
1834
1.76@0.6
1.77@0.6
40/20 1/2 6.1 741 4.0 0 2040 1370 GRAS. Resistant to strong acids and bases. Birefringent. Very durable and may be used at high temperatures.
AMTIR 11,000 593
625
2.50@10 80/50 1 0.27   4.4 0 370 170 Amorphous material. A chalcogenide glass, which, although relatively hard, is also brittle. Insoluble in water and resistant to acids. It is attacked by alkalis.
BaF2 66,600* 691
782
1.45@5 40/20 1/20 0.56 213 4.9 0.17 1280 82 Hard material suitable for high pressure applications. Extremely vulnerable to thermal shock. Very slightly soluble in water. Attacked by ammonium hydroxide, ammonium salts, complex agents such as EDTA, and acids.
CaF2 79,500* 896
1025
1.40@5 40/20 1/20 0.77 286 3.2 0.0017 1360 158 Very hard material similar to BaF 2 , but almost insoluble in water and less vulnerable to thermal shock. Attacked by nitric acid and strong hydroxides, ammonium salts, and complexing agents such as EDTA. Very desirable for near-IR applications as it has no OH absorption bands.
CdTe 17,000 313
340
2.67@10 80/50 1 0.08   6.2 0 1092 56 Hard but very brittle material. Insoluble in water. Attacked by nitric acid.
Cleartran 22,000 690
722
2.20@10 40/20 1/20 2.2 328 4.1 0 1830 240 GRAS. A clear form of ZnS. Properties similar to ZnS.
CsI 42,000 172 1.73@10 80/50 1/10 0.12 69 4.5 44 621 1 Soft and hygroscopic. Generally only used for its extended far-IR transmission. Should only be exposed to anhydrous solvents. Never use with alcohols or aqueous solutions. A hard optical coating can be used to provide some protection. In powdered form it can be used to make pellets. Keep stored in a dessicator or heated cabinet.
Diamond 30,000 2 2.41@0.6 20/10 1 10.9 None 3.5 0 550fp 5700 GRAS. Hard and chemically resistant. Often used in very high pressure applications. High cost limits size to a few mm. Has a characteristic lattice absorption doublet between 1800 and 2700 cm -1 .
Ge 5500 432
574
4.00@10 60/40 1/8 1.0 None 5.3 0 936 780 Hard and brittle. Semiconductor material with low band gap energy. Free electron absorption becomes important at temperatures above about 60 °C and it can become totally opaque at temperatures above 100 °C. Attacked by sulfuric acid and aqua regia. When used as a window it has high reflection losses which can be significantly reduced with BBAR coatings. Used as an ATR prism when low penetration depth is desired.
KBr 48,800 345
388
1.52@10 60/40 1/20 0.02 129 2.8 53 730 6 The most popular IR material. Hygroscopic and can only be used with anhydrous solvents, glycerol or alcohols. Withstands thermal and mechanical shock well. A protective coating can improve its resistance to humidity. Keep stored in a dessicator or heated cabinet.
KCl 55,600 385
439
1.45@10 60/40 1/20 0.05 158 2.0 35 776 7 Hygroscopic and can only be used with anhydrous solvents, glycerol or alcohols. Withstands thermal and mechanical shock fairly well. A protective coating can improve its resistance to humidity. When AR coated can be used as a low cost CO 2 laser window. Keep stored in a dessicator or heated cabinet.
KRS-5 17,900 204
232
2.37@10 60/40 1/1 0.56 74 7.4 0.05 414.5 40 Extremely toxic, even with skin contact. KRS-5 should only be handled with protective gloves or finger cots. A relatively soft material, it cold flows and deforms under pressure. This is enhanced at temperatures above 200 °C. It should only be polished by well-trained professionals. Good chemical resistance.
LiF 96,150* 1105
1286
1.39@0.5 40/20 1/10 0.23 400 2.6 0.27 870 105 Slightly soluble in water. Hard and brittle. Sensitive to thermal shock. Should not be used above 400 °C.
MgF2 90,900* 1271
1457
1.38@0.51.39@0.5 40/20 1/20 1.0 500 3.2 0.0002 1255 415 Almost insoluble in water. Can be used at fairly high pressure. Slightly sensitive to thermal shock. Birefringent. Should not be used above 500 °C.
NaCl 52,600 457
584
1.49@10 40/20 1/20 0.05 200 2.2 36 801 18 Harder and less hygroscopic than KBr but can only be used with anhydrous solvents, glycerol or alcohols. Withstands thermal and mechanical shock fairly well. A protective coating can improve its resistance to humidity. Keep stored in a dessicator or heated cabinet.
Si 8900 624
969
3.41@10 60/40 1/8 1.8 None 2.3 0 1420 1150 Hard material and resistant to most chemicals except for strong acids. Withstands thermal shock. Has a strong phonon absorption band at 590-630 cm -1 . Transmits well at wavenumbers lower than this and well into the far-IR. BBAR coatings are available for the mid-IR region.
SiO2 50,000* 2315
2677
1.53@1 40/20 1/20 4.2   2.6 0 1713 460 GRAS. Resistant to acids and alkalis. Used in the near-IR. Most forms of SiO 2 have OH absorption bands.
ZnS 17,000 690
722
2.20@10 40/20 1/20 1.5 328 4.1 0 1830 240 GRAS. Relatively hard material and resistant to thermal and mechanical shock. Insoluble in water but can be attacked by strong acids and bases.
ZnSe 15,000 461
508
2.40@10 40/20 1/20 1.2 219 5.3 0 1526 120 Hard and brittle. Attacked by strong acids and bases. Resistance can be improved with the use of a hard coating. The most popular material for ATR applications. When AR coated, can be used as CO 2 laser window.
ZrO2 40,000 1431 2.13@1 60/40 1/8 1.1   5.9 0 2700 1250 Hard material with good resistance to chemicals. Cannot be used at high temperatures as a phase change occurs at 1000 °C.