Infrared-to-visible conversion following sub-band-gap excitation in MgS:Eu,Sm

We report here Eu²⁺{→}Sm³⁺ electron transfer by tunneling in MgS:Eu,Sm. Subsequent to exposure to existing fluorescent or incandescent room light, optically stimulated luminescence which involves infrared-to-visible conversion is observed in this material. Room light excites the 480-nm absorption band of the Eu²⁺ ions which is associated with a transition from the ⁸S11/2(4f) ground state to the t2g excited level. Some of the electrons subsequently tunnel from the t2g level of the Eu²⁺ ions to the Sm³⁺ ions. We also report the optically stimulated luminescence from the V^- centers in this material.