Thermoluminescence of Eu³⁺,Pr³⁺ codoped calcium sulfate by X-ray irradiation

Abstract

This study investigates the thermoluminescence produced when calcium sulfate codoped with Eu³⁺ and Pr³⁺ (CaSO₄:Eu³⁺,Pr³⁺) is irradiated with X-rays. CaSO₄:Eu³⁺,Pr³⁺ was synthesized by heating CaSO₄·2H₂O:Eu³⁺,Pr³⁺ at 1050°C. The CaSO₄:Eu³⁺,Pr³⁺ exhibited red emission upon X-ray irradiation and subsequently emitted an afterglow. The afterglow time was lengthened by adding Li⁺ ions to the phosphor, and the afterglow time for a Li/Ca atomic ratio of 0.002 was 120 min. Thermoluminescence peaks were observed at 130, 160, 240, 260, and 355°C upon heating CaSO₄:Eu³⁺,Pr³⁺. The luminances of the thermoluminescence peaks increased with increasing X-ray irradiation time. Only the luminance of the peak near 100°C decreased when CaSO₄:Eu³⁺,Pr³⁺ was irradiated with X-rays. Therefore, the afterglow is considered to have originated from the thermoluminescence peak near 100°C that had a trap depth of about 0.20 eV.