Alkali earth sulfide phosphors doped with Eu²⁺ and Ce³⁺ for LEDs

CaS:Eu²⁺, SrS:Eu²⁺, CaS:Ce³⁺, SrS:Ce³⁺, CaS:Eu²⁺, Ce³⁺ and SrS:Eu²⁺, Ce³⁺ phosphor samples have been prepared using a solid state chemical reaction method. Emission and excitation spectra of the samples are investigated. SrS:Ce³⁺, CaS:Ce³⁺, SrS:Eu²⁺ and CaS:Eu²⁺ emit greenish blue (482 nm), green (515 nm), orange (606 nm), and red (648 nm) light, respectively. For the co-doped samples, SrS:Eu²⁺, Ce³⁺ and CaS:Eu²⁺, Ce³⁺, energy transfer from Ce³⁺ to Eu²⁺ is observed. Ce³⁺ emission has been totally quenched because of the energy transfer. Eu²⁺ emissions are estimated to be enhanced by 28% and 18% in SrS and CaS hosts, respectively, at the present doping concentration. The samples are also excited by blue light emitting diodes (450 nm) to exam them as potential coating phosphors for the diodes.