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.
