This study investigates the thermoluminescence produced when calcium sulfate codoped with Eu 3+ and Pr 3+ (CaSO 4 :Eu 3+ ,Pr 3+ ) is irradiated with X-rays. CaSO 4 :Eu 3+ ,Pr 3+ was synthesized by heating CaSO 4 ·2H 2 O:Eu 3+ ,Pr 3+ at 1050°C. The CaSO 4 :Eu 3+ , Pr 3+ 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.

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... moluminescence peaks were observed at 130, 160, 240, 260, and 355°C upon heating CaSO 4 :Eu 3+ ,Pr 3+ . The luminances of the thermoluminescence peaks increased with increasing X-ray irradiation time. Only the luminance of the peak near 100°C decreased when CaSO 4 :Eu 3+ ,Pr 3+ 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.