Caesium iodide

Caesium iodide or cesium iodide (chemical formula CsI) is the ionic compound of caesium and iodine. It is 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.[7]

Caesium iodide

CsI crystal

Scintillating CsI crystal

Crystal structure
Names
IUPAC name
Caesium iodide
Other names
Cesium iodide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.223
EC Number
  • 232-145-2
RTECS number
  • FL0350000
UNII
Properties
CsI
Molar mass 259.809 g/mol[2]
Appearance white crystalline solid
Density 4.51 g/cm3[2]
Melting point 632 °C (1,170 °F; 905 K)[2]
Boiling point 1,280 °C (2,340 °F; 1,550 K)[2]
848 g/L (25 °C)[2]
-82.6·10−6 cm3/mol[3]
1.9790 (0.3 µm)
1.7873 (0.59 µm)
1.7694 (0.75 µm)
1.7576 (1 µm)
1.7428 (5 µm)
1.7280 (20 µm)[4]
Structure
CsCl, cP2
Pm3m, No. 221[5]
a = 0.4503 nm
0.0913 nm3
1
Cubic (Cs+)
Cubic (I−)
Thermochemistry
52.8 J/mol·K[6]
123.1 J/mol·K[6]
Std enthalpy of
formation (ΔfH⦵298)
 −346.6 kJ/mol[6]
-340.6 kJ/mol[6]
Hazards
GHS pictograms
GHS Signal word Warning
GHS hazard statements
 H315, H317, H319, H335
P201, P202, P261, P264, P270, P271, P272, P273, P280, P281, P301+312, P302+352, P304+340, P305+351+338, P308+313, P312, P321, P330, P332+313, P333+313, P337+313, P362, P363, P391, P403+233
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
2386 mg/kg (oral, rat)[1]
Related compounds
Other anions
 Caesium fluoride
Caesium chloride
Caesium bromide
Caesium astatide
Other cations
 Lithium iodide
Sodium iodide
Potassium iodide
Rubidium iodide
Francium iodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Synthesis and structure
Monatomic caesium halide wires grown inside double-wall carbon nanotubes.[8]

Bulk caesium iodide crystals have the cubic CsCl crystal structure, but the structure type of nanometer-thin CsI films depends on the substrate material – it is CsCl for mica and NaCl for LiF, NaBr and NaCl substrates.[9]

Caesium iodide atomic chains can be grown inside double-wall carbon nanotubes. In such chains I atoms appear brighter than Cs atoms in electron micrographs despite having a smaller mass. This difference was explained by the charge difference between Cs atoms (positive), inner nanotube walls (negative) and I atoms (negative). As a result, Cs atoms are attracted to the walls and vibrate more strongly than I atoms, which are pushed toward the nanotube axis.[8]

Properties
Solubility of Csl in water[10]
Т (°C) 0 10 20 25 30 40 50 60 70 80 90 100
S (wt%) 30.9 37.2 43.2 45.9 48.6 53.3 57.3 60.7 63.6 65.9 67.7 69.2

Applications

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 low light yield that increases significantly with cooling.[11] 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 is used as a beamsplitter in Fourier transform infrared (FTIR) spectrometers. It has a wider transmission range than the more common potassium bromide beamsplitters, working range into the far infrared. However, optical-quality CsI crystals are very soft and hard to cleave or polish. They should also be coated (typically with germanium) and stored in a desiccator, to minimize interaction with atmospheric water vapors.[12]

In addition to image intensifier input phosphors, caesium iodide is often also used in medicine as the scintillating material in flat panel x-ray detectors.[13]

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References
  1. Cesium iodide. U.S. National Library of Medicine
  2. Haynes, p. 4.57
  3. Haynes, p. 4.132
  4. Haynes, p. 10.240
  5. Huang, Tzuen-Luh; Ruoff, Arthur L. (1984). "Equation of state and high-pressure phase transition of CsI". Physical Review B. 29 (2): 1112. Bibcode:1984PhRvB..29.1112H. doi:10.1103/PhysRevB.29.1112.
  6. Haynes, p. 5.10
  7. Kowalski, M. P.; Fritz, G. G.; Cruddace, R. G.; Unzicker, A. E.; Swanson, N. (1986). "Quantum efficiency of cesium iodide photocathodes at soft x-ray and extreme ultraviolet wavelengths". Applied Optics. 25 (14): 2440. Bibcode:1986ApOpt..25.2440K. doi:10.1364/AO.25.002440. PMID 18231513.
  8. Senga, Ryosuke; Komsa, Hannu-Pekka; Liu, Zheng; Hirose-Takai, Kaori; Krasheninnikov, Arkady V.; Suenaga, Kazu (2014). "Atomic structure and dynamic behaviour of truly one-dimensional ionic chains inside carbon nanotubes". Nature Materials. 13 (11): 1050–4. Bibcode:2014NatMa..13.1050S. doi:10.1038/nmat4069. PMID 25218060.
  9. Schulz, L. G. (1951). "Polymorphism of cesium and thallium halides". Acta Crystallographica. 4 (6): 487–489. doi:10.1107/S0365110X51001641.
  10. Haynes, p. 5.191
  11. Mikhailik, V.; Kapustyanyk, V.; Tsybulskyi, V.; Rudyk, V.; Kraus, H. (2015). "Luminescence and scintillation properties of CsI: A potential cryogenic scintillator". Physica Status Solidi B. 252 (4): 804–810. arXiv:1411.6246. Bibcode:2015PSSBR.252..804M. doi:10.1002/pssb.201451464.
  12. Sun, Da-Wen (2009). Infrared Spectroscopy for Food Quality Analysis and Control. Academic Press. pp. 158–. ISBN 978-0-08-092087-0.
  13. Lança, Luís; Silva, Augusto (2012). "Digital Radiography Detectors: A Technical Overview" (PDF). Digital Imaging Systems for Plain Radiography. Springer. doi:10.1007/978-1-4614-5067-2_2. ISBN 978-1-4614-5066-5.

Cited sources
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