It is the simplest and most common oxide of the caesium.

It forms yellow-orange hexagonal crystals.

[1] Caesium oxide is used in photocathodes to detect infrared signals in devices such as image intensifiers, vacuum photodiodes, photomultipliers, and TV camera tubes[3] L. R. Koller described the first modern photoemissive surface in 1929–1930 as a layer of caesium on a layer of caesium oxide on a layer of silver.

[4] It is a good electron emitter; however, its high vapor pressure limits its usefulness.

[5] Elemental magnesium reduces caesium oxide to elemental caesium, forming magnesium oxide as a side-product:[6][7] Cs2O is hygroscopic, forming the corrosive CsOH on contact with water.