Yttrium oxide (Y2O3), which is also know as yttria, is one of the 17 rare earth oxides.

Yttrium oxide is one of the most important compounds of yttrium and accounts for the largest use. It is widely used in making YVO4 europium, and Y2O3 europium phosphors to give the red color in color television tubes.  Yttrium oxide also is used to produce yttrium-iron-garnets, which are very effective microwave filters.

It also has potential use in ceramic and glass formulas, as the oxide has a high melting point and imparts shock resistance and low expansion characteristics to glass. Hard, dense layers are deposited by electron-beam evaporation or sputtering. Typical applications are protection of aluminum and silver mirror coatings, intermediate layer in wide band visible AR coatings and for XeCl (308nm) laser AR and dielectric mirror designs.

Yttrium oxide is the thermodynamically most stable oxide and is suitable for extreme operation conditions. It is used as a coating in metal production. Yttria is often used with zirconia to form Yttria Stabilized Zirconia (YSZ)