Afterglow mechanism and thermoluminescence of red-emitting CaS:Eu,Pr phosphor with incorporated Li ion upon visible light irradiation

This paper reports on the afterglow mechanism and thermoluminescence (TL) of a red-emitting CaS:Eu²⁺,Pr³⁺ phosphor with incorporated Li⁺ ion upon irradiation by visible light (D₆₅ lamp). In the TL glow curve of the CaS:Eu²⁺,Pr³⁺ phosphor, a TL peak was observed near 120 °C. The luminescence center of the CaS:Eu²⁺,Pr³⁺ phosphor was the Eu²⁺ ion and the trap depth of the CaS:Eu²⁺,Pr³⁺ phosphor with the cation vacancy (Trap 1) which formed by incorporation of the Pr³⁺ ion was 0.202 eV. A cation vacancy (Trap 2) was formed by incorporation of the Li⁺ ion in the CaS:Eu²⁺,Pr³⁺ phosphor. In the TL glow curve of the CaS:Eu²⁺,Pr³⁺ phosphor with incorporated Li⁺ ion, two TL peaks were observed near 120 and 200 °C. The TL luminance of the CaS:Eu²⁺,Pr³⁺ phosphor with incorporated Li⁺ ion increased with an increase in the initial Li/Ca atomic ratio. The two TL peaks moved to the high-temperature side with an increase in heating rate. The cation vacancy (Trap 2) calculated from the Hoogenstraaten method was 0.118 eV. The afterglow time of the CaS:Eu²⁺,Pr³⁺ phosphor with incorporated Li⁺ ion was prolonged by generation of a shallow trap.