cesiumiodide

Cesium iodide (CsI) is an inorganic compound composed of cesium cations and iodide anions with the chemical formula CsI. It crystallizes in the halite (rock salt) structure, forming cubic crystals that are highly transparent in the visible and near‑infrared regions. The melting point is approximately 820 °C, and it has a density of 5.1 g cm‑³ at room temperature. The compound is soluble in water, with a solubility of about 5 g mL‑¹ at 20 °C, and it readily dissociates into its constituent ions.

CsI is produced industrially by reacting cesium carbonate or cesium hydroxide with hydroiodic acid, or by direct combination of cesium metal and iodine under controlled conditions to avoid contamination. The high purity product is commonly used as a scintillation material in radiation detection because its high atomic number (Z = 55) provides efficient absorption of X‑rays and gamma rays. It is also employed in high‑intensity laser experiments and as a source of iodine in certain spectroscopic applications.

In addition to scientific use, cesium iodide is found in some photographic media and historical photo plates due to its high sensitivity, although it has largely been supplanted by modern digital sensors. The compound should be handled with care; it is toxic if ingested or inhaled, and can cause irritation to skin and eyes. Proper safety precautions, such as gloves and eye protection, are recommended when working with CsI.