Spectroscopy of a samarium(III) activated X-ray storage phosphor

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Copyright: Liu, Zhiqiang
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Abstract
Nanocrystalline BaFCl:Sm3+, as prepared by co-precipitation from aqueous solutions, is an efficient photoluminescent storage phosphor for ionising radiation. It has potential applications in medical imaging and personal radiation monitoring (dosimetry). Upon X-ray, -ray or -irradiation, the Sm3+ ions in BaFCl host are reduced to Sm2+ ions which can be read out efficiently by measuring the narrow 5DJ-7FJ f-f luminescence lines via excitation into the very intense, parity-allowed 4f6-4f55d transition in the blue-violet region of the spectrum. This thesis focuses on investigations of the storage mechanism of the phosphor by a variety of spectroscopic techniques, such as synchrotron X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence spectroscopy, cathodoluminescence microanalysis, synchrotron-based X-ray absorption spectroscopy, high-resolution laser spectroscopy (e.g. spectral hole-burning) and electron spin resonance. The results are further compared with those obtained for microcrystalline BaFCl:Sm3+ prepared by high-temperature sintering. Significant differences in the local coordination environment and spatial distribution of Sm3+ ions between nanocrystalline and microcrystalline BaFCl:Sm3+ are revealed by comparing the photoluminescence and cathodoluminescence spectra of the two samples before and after X-irradiation. For nanocrystalline BaFCl:Sm3+, the X-irradiation induced reduction of Sm3+ to Sm2+ ions and photoionisation of Sm2+ to Sm3+ ions during photobleaching are investigated by monitoring the photoluminescence intensities of both Sm3+ and Sm2+ ions in the two processes. Both processes can be modelled well by a formulation based on dispersive first-order kinetics. The photoionisation of Sm2+ ions is also demonstrated in spectral hole-burning experiments of the X-irradiated nanocrystalline and microcrystalline BaFCl:Sm3+. It is found that non-Sm3+ electronic traps are likely involved in the photoionisation process. In search for defect centres by electron spin resonance spectroscopy, oxygen defects are found to play an important part in the storage mechanism of the phosphor. In addition, some key aspects of the application of the phosphor in personal radiation dosimetry and medical imaging are evaluated. It turns out that the phosphor has a linear and reproducible response within the dose range of practical application and the image generated from the phosphor displays favourable contrast and brightness and a high signal-to-noise ratio.
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Author(s)
Liu, Zhiqiang
Supervisor(s)
Riesen, Hans
Jackson, Gregory
Hutchison, Wayne
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Publication Year
2012
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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