Caesium Iodide – CsI

lenses, windows, mirrors, filters and prisms


Caesium Iodide is a very useful material with a transmission range from the visible region out to 70 microns through to a 2mm thick window. CsI is very soft and water-soluble and when humidity is relatively high polished surfaces may be damaged by moisture in the atmosphere. Principally used for Infrared Spectroscopic windows and also for beam splitters in FTIR Instumentation. CsI is also available thallium doped for scintillation applications.

Transmission Range 0.25 – 55 microns
Crystal Structure Caesium chloride
Cleavage Plane None
Colour Colourless
Density 4.526
Melting Point (°) 621
Reflection Loss 13.6% (10µ) for 2 surfaces
Solubility index 44gm/100gm / 0°C
Hardness (Knoop) 20/200 gm indenter
Thermal Conductivity (cal/cm sec°C) 0.13 Wm-1°K-1
Thermal Expansion coefficient (/°C) 50×10-6 (25-50°C)
Caesium Iodide (CsI) windows and Caesium Iodide (CsI) lenses

Download a PDF of this page
Whilst every effort has been made to verify all data provided, no responsibility can be accepted for its accuracy.