Photoluminescence is the result of photons being excited to a higher energy state and returned to a lower energy state with the emission of photons.

Eu3+ doped Y2O3 emits red when impinged with UV wavelength which is used in plasma display panels.

When excited with UV

Eu2+ doped SrGa2S4 emits green.

Eu2+ doped Sr3SiO5 emits blue.

Eu3+ doped SrY2S4 emits red.

The above red-blue-green combinations can be used in white LED's.