Optical Properties of Rare Earth Doped SrS Phosphor: 
A Review
Rare earth (RE) doped SrS phosphor has attracted a lot of attention on a wide range of photo-, cathodo-, thermo-, and electroluminescent applications. Upon doping with different RE elements (e.g., Ce, Pr, Eu, Yb), the luminescence from SrS can be varied over the entire visible region by appropriately choosing the composition of the strontium sulfide host. The main applications include flat panel displays and SrS-based powder electroluminescence (EL) for back lights. Sulfide materials known for providing Eu2+ based red emission band and preferred as a color conversion material in white light emitting diodes are discussed. Especially, the applications of RE doped SrS are described in light of their utility as conversion and storage phosphors. The effect of energy level splitting, EL efficiency, post-annealing, milling time, and impurity on luminescence properties for SrS are also discussed.