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Cesium iodide

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Cesium iodide

Cesium iodide
CAS number 7789-17-5 YesY
ChemSpider 23003 YesY
EC-number 232-145-2
Jmol-3D images Image 1
Molecular formula CsI
Molar mass 259.81 g/mol
Appearance white crystalline solid
Density 4.51 g/cm3, solid
Melting point

621 °C

Boiling point

1277±5 °C

Solubility in water 44 g/100 ml (0 °C)
Refractive index (nD) 1.739
Crystal structure CsCl
Space group Pm3m, No. 221
Lattice constant a = 456.67 pm
Cubic (Cs+)
Cubic (I)
EU Index not listed
Flash point non-flammable
Related compounds
Other anions Caesium fluoride
Caesium chloride
Caesium bromide
Caesium astatide
Other cations Lithium iodide
Sodium iodide
Potassium iodide
Rubidium iodide
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Caesium iodide (CsI) is an ionic compound often used as the input phosphor of an x-ray image intensifier tube found in fluoroscopy equipment. Caesium iodide photocathodes are highly efficient at extreme ultraviolet wavelengths.[1]

An important application of caesium iodide crystals, which are scintillators, is electromagnetic calorimetry in experimental particle physics. Pure CsI is a fast and dense scintillating material with relatively high light yield. It shows two main emission components: one in the near ultraviolet region at the wavelength of 310 nm and one at 460 nm. The drawbacks of CsI are a high temperature gradient and a slight hygroscopicity.

Caesium iodide can be used in Fourier Transform Infrared (FT-IR) spectrometers as a beamsplitter. CsI has a wider transmission range than the more common potassium bromide beamsplitters, extending its usefulness into the far infrared. A problem with optical-quality CsI crystals is that they are very soft with no cleavage, making it difficult to create a flat polished surface. Also, the CsI optical crystals must be stored in a desiccator to prevent water damage to the surfaces, and coated (typically with germanium) to minimise water damage from short term atmospheric exposure during beamsplitter swapouts.

Optical properties

Physical properties


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