Storage and stimulation of radiation-induced defects in X-ray storage phosphors

• Main Author: Zha, Binbing
• Published: University of Edinburgh 1999
• Subjects: 541.3
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.664221

In this thesis we present an experimental investigation of the mechanism of storage and stimulation processes in the x-ray storage phosphors BaFBr:Eu and related materials. Such materials are used in radiography and diffraction equipment to image X-rays, but the factors that govern the trapping and release of the image is still unclear. We used photostimulated luminescence (PSL), spontaneous luminescence (SL), and magnetic measurements to study the formation and release of charged defects of a series of pure and doped materials isomorphous with BaFBr. Samples of the materials BaFX (X = Cl, Br, I) and in both a pure form and doped with the rare earth ions La, Ce, Sm, Eu, Gd, Tb, Dy, Tm and Yb were prepared, together with SrFX:Eu (X = Cl, Br, I) and the non-stoichiometric samples BaF<SUB>1-x</SUB>Br<SUB>1+ </SUB>(x = -0.2, -0.1, 0, 0.1, 0.2) and samples doped with various amounts of oxygen. We also prepared the isomorphous compounds LaOX (X = Cl, Br, I). We designed and built a variable temperature photostimulation and detection system to study the PSL and SL of these materials. The emission spectrum of BaFBr samples doped with most rare earth ions was the same as the pure host material, the exceptions being the dopants Ce, Eu and Yb which showed evidence of transitions involving ions not in the trivalent state. Samples doped with Eu gave the most intense emission spectra due to the correspondence between the energy of recombination of electrons and holes in the host lattice, and the 4f<SUP>6</SUP>5d - 4f<SUP>7</SUP> transition of Eu<SUP>2+</SUP>. Emission spectra of the pure host materials show trends that correspond to trends in trap depths for different lattices.