SPATIAL CORRELATION AND PHOTOSTIMULABILITY OF DEFECT CENTERS IN THE X-RAY-STORAGE PHOSPHOR BAFBR-EU2+

Photostimulable x-ray-storage phosphors in the form of image plates are one of the most important applications of defect centers in ionic crystals. Understanding the underlying mechanism, apart from its practical relevance, creates additional insights into the generation and kinematics of radiation defects in this class of materials. In this paper the commercial storage phosphor BaFBr:Eu2+ is investigated. It is shown that x-ray irradiation produces both fluorine and bromine F centers, and aggregates thereof. Only the bromine F centers were found to contribute to the photostimulability, part of which are spatially correlated with an Eu-hole complex, whereas others are uncorrelated. Apart from the photostimulable centers, the nonphotostimulable centers could be identified via their characteristic infrared emission. Numbers can be deduced on the fraction of photostimulable and nonphotostimulable, correlated and uncorrelated centers. These numbers depend on the sample preparation as well as radiation history. The spectroscopic data and methods presented below should help to control better and improve the properties of storage phosphors.