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Caesium Iodide CsI
Caesium Iodide (Cesium Iodide) is the material with the deepest known IR transmission, and is sometimes used for components in the widest range spectrophotometers. An extremely soft material, Cesium Iodide is extremely difficult to polish, and so performance is compromised for range. Doped with Thallium, CsI(Tl) is a useful scintillator which emits at a wavelength that is a good match for Silicon photodiodes. Arrays of Cesium Iodide are used in security imaging systems.
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| Transmission Range | 0.25 to 55 μm (1) |
| Refractive Index | 1.73916 at 10 μm (1)(2) |
| Reflection Loss | 13.6% at 10 μm |
| Absorption Coefficient | n/a |
| Reststrahlen Peak | 145.8 μm |
| dn/dT | -99.3 x 10⁻⁶ K⁻¹ (2) |
| dn/dμ | 6 μm |
| Density | 4.51 g/cc |
| Melting Point | 621 °C |
| Thermal Conductivity | 1.1 W m⁻¹ K⁻¹ at 298 K (3) |
| Thermal Expansion | 48.3 x 10⁻⁶ K⁻¹ at 293 K (3) |
| Hardness | Knoop 20 with 200g indenter |
| Specific Heat Capacity | 201 J Kg⁻¹ K⁻¹ (4) |
| Dielectric Constant | 5.65 at 1 MHz |
| Youngs Modulus (E) | 5.3 GPa |
| Shear Modulus (G) | 6.24 GPa |
| Bulk Modulus (K) | 12.67 GPa |
| Elastic Coefficients | C11=24.6 C12=6.7 C44=6.24 |
| Apparent Elastic Limit | 5.6 MPa (810psi) |
| Poisson Ratio | 0.214 |
| Solubility | 44 g/100 g water at 0 °C |
| Molecular Weight | 259.83 |
| Class/Structure | Cubic CsCl, Pm3m, no cleavage, deforms. |
| μm | No | μm | No | μm | No | μm | No |
|---|---|---|---|---|---|---|---|
| 0.5 | 1.8064 | 15.0 | 1.7344 | 29.0 | 1.7101 | 43.0 | 1.6671 |
| 1.0 | 1.7572 | 16.0 | 1.7332 | 30.0 | 1.7077 | 44.0 | 1.6631 |
| 2.0 | 1.7466 | 17.0 | 1.7319 | 31.0 | 1.7052 | 45.0 | 1.6591 |
| 3.0 | 1.7440 | 18.0 | 1.7306 | 32.0 | 1.7027 | 46.0 | 1.6549 |
| 4.0 | 1.7431 | 19.0 | 1.7291 | 33.0 | 1.7000 | 47.0 | 1.6505 |
| 5.0 | 1.7424 | 20.0 | 1.7276 | 34.0 | 1.6972 | 48.0 | 1.6460 |
| 6.0 | 1.7418 | 21.0 | 1.7260 | 35.0 | 1.6943 | 49.0 | 1.6414 |
| 7.0 | 1.7412 | 22.0 | 1.7244 | 36.0 | 1.6913 | 50.0 | 1.6366 |
| 8.0 | 1.7406 | 23.0 | 1.7226 | 37.0 | 1.6882 | ||
| 9.0 | 1.7399 | 24.0 | 1.7207 | 38.0 | 1.6849 | ||
| 10.0 | 1.7392 | 25.0 | 1.7188 | 39.0 | 1.6816 | ||
| 11.0 | 1.7384 | 26.0 | 1.7168 | 40.0 | 1.6781 | ||
| 12.0 | 1.7375 | 27.0 | 1.7147 | 41.0 | 1.6746 | ||
| 13.0 | 1.7365 | 28.0 | 1.7125 | 42.0 | 1.6709 | ||
| 14.0 | 1.7355 |
Caesium Iodide is grown by sealed ampoule Stockbarger techniques with ingots of approximately 70mm diameter. CsI is very soft and pliable.
IUPAC International Union of Pure and applied Chemistry recommends the spelling as Caesium.
REFERENCES:
(1) Handbook Optical Constants, ed Palik, V2, ISBN 0-12-544422-2
(2) Rodney, J.Opt.Soc.Am. V45, p987, 1955
(3) Combes et al, J.Opt.Soc.Am. V41, p215, 1951
(4) Kelly, Bureau of Mines Bulletin, No371, p51, 1934