Luminescence properties of the x-ray storage phosphor BaBr2:Ce3+

Photoluminescence studies on single-crystal samples of the x-ray storage phosphor orthorhombic BaBr2:Ce3+ show the existence of three luminescent Ce sites with distinct emission and excitation spectra. The isolated Ce3+ emits only at low temperatures, while the two other Ce3+ sites are charge compensated and active also at room temperature. One of the charge compensators was identified as a monovalent cation impurity, which was confirmed by the investigation of BaBr2:Ce3+ co-doped with potassium. The same charge-compensated sites serve as efficient emission sources during the read-out of stored images following x-ray exposure. Read-out is a photostimulated luminescence (PSL) process initiated by the excitation of x-ray-induced F-type trapped electron centres in the visible region. There are two different PSL processes, corresponding to the two kinds of charge-compensated Ce centre, each involving trapped electron and trapped hole centres of a slightly different kind in the vicinity of the charge-compensated Ce sites.