Erbium(III) Oxide, is synthesized from the lanthanide metal erbium. Erbium oxide is a light pink powder in appearance. It is insoluble in water, but soluble in mineral acids. Er2O3 is hygroscopic and will readily absorb moisture and CO2 from the atmosphere. It is a highly insoluble thermally stable Erbium source suitable for glass, optical, and ceramic applications. Erbium Oxide can be also used as a flammable neutron poison for nuclear fuel.