Red persistent luminescence excited by visible light in CaS:Eu 2+ ,Tm 3+

Abstract Excitation wavelength dependence of red persistent luminescence in phosphor is reported. Persistent luminescence appears under visible light excitation in the wavelength region of 400–600 nm. Photon energy from white light-emitting diode lamps is possibly stored in this material. This sulfide phosphor is synthesized using iodine vapor. Under iodine vapor, Eu 2+ and Tm 3+ are found to be efficiently included in CaS. The concentration dependence of Eu 2+ is studied, and the optimum concentration is 0.05%. Trap depth of 0.27–0.33 eV contributing to persistent luminescence is evaluated by using thermoluminescence.