ESR studies to elucidate the origin of the RPL emission of undoped-CaSO4

Recent research has shown that CaSO 4 , without any intentional addition of impurities, exhibits remarkable radiophotoluminescence (RPL) properties. However, the origin of the RPL in CaSO 4 has yet to be fully understood. ESR measurements were carried out to identify the defect species responsible for RPL and elucidate the luminescence’s origin. ESR measurements on undoped-CaSO 4 with different radiation sensitivities showed SO 4 − , SO 2 − +SO 3 − , PO 4 2− , Si=O 3 in P 2 O 5 –SiO 2 (E’ center), Al 2 O 3 hole center and Mn 2+ defect species in CaSO 4 . This means that CaSO 4 contains Al 2 O 3 , Mn 2+ , P, and Si as impurities, which are not intentionally added to CaSO 4 . As the results of this study, the different impurity states may influence the radiation sensitivity of the materials. It is suggested that the deliberate addition of P and Si elements, Al 2 O 3 and Mn 2+ could control the RPL properties.