Optical and thermal properties of electron- and hole-trapping sites in the x-ray storage phosphor RbI:X (X=Tl+, In+, Pb2+, Eu2+)

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Abstract
Two-dimensional x-ray detectors based on x-ray storage phosphors are utilized in the field of medicine, biology, and physics. Defect centers and mechanisms contributing to the photostimulated luminescence (PSL) process of the x-ray storage phosphor RbI:X (X=Tl+, In+, Pb2+, Eu2+) are reported. By optical and thermoluminescence spectroscopy the electron and hole storage centers involved in the PSL process were identified. F- and Z type and Tl0 centers turned out to be the occupied electron storage centers, VK− and dopant-related VKA centers the hole-trapping sites. The specific choice of the dopant yields storage phosphors with different physical properties, such as emission characteristics, photostimulation characteristics, and thermal stability of the information storage. At T=300 K the information stored in the RbI:Tl+ phosphor is unstable, in RbI:Eu2+ it is nearly stable and in RbI:In+ stable. A physical model for the PSL as well as for the thermoluminescence is derived. In the Tl+-doped material Tl0 centers were found to act as efficient electron storage centers at temperatures below 180 K with a 4.7 times larger storage capability than F centers.