Study on the photo-transfer thermoluminescence in Eu doped potassium chloride
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Study on the photo-transfer thermoluminescence in Eu doped potassium chloride Hector Duran-Munoz1; Raul Perez-Salas2; Thomas Piters2 1
Programa de doctorado en ciencia de materiales. Departamento de Investigación en Polímeros y Materiales. 2 Departamento de Investigación en Física, Universidad de Sonora, PO Box 5-088, 83190 Hermosillo, Sonora México. ABSTRACT In this work a survey of possible optical stimulation processes in irradiated KCl:Eu with a focusing on photo-transfer thermoluminescence (PTTL) effects are shown. For different wavelengths in the range from 180 to 800 nm a cycle of measurements was performed, each comprising of a TL measurement after light irradiation, a TL measurement after beta irradiation for reference purposes and a PTTL measurement. The latter was obtained by applying first a beta irradiation, then a partial readout up to a certain end temperature followed by a monochromatic light irradiation of a specific wavelength and finally a TL measurement. This procedure was repeated for different partial readout end temperatures. From the results the existence of at least four different photo-transfer processes, induced by 310, 245 and 550 nm light are deduced. The photo transfer process induced by an approximate value of 245 nm produced a TL glow peak not seen before in beta or light induced TL. Furthermore it was observed that some of the TL peaks created by light of 240 and 260 nm were strongly sensitized after a beta irradiation and a partial readout. INTRODUCTION Since the 70s it is clear that at room temperature, the principle radiation products in alkali halides are F and H centers generated during the decay of a self trapped exciton [1]. The F center is stable and the H center could stabilize at impurity centers when present. This stabilization effect causes a strong absorption in the visible part of the spectrum due to the presence of F centers. The stability of the radiation products is broken by thermal and optical stimulation. During heating, H centers recombine with the F centers, a process which is evidenced by the removing of the radiation induced coloring. Simultaneously, light is emitted which is known as thermal stimulated luminescence or thermoluminescence (TL). The thermal stimulated recombination occurs in different stages at specific temperatures. Each stage is associated with a (impurity) defect that acts, in this view, as an H-center trap during the irradiation stage. The kinetics of the thermally stimulated recombination process is well investigated and usually described in terms of the band structure of the solid and the redistribution of charge over energy levels within the band gap after ionizing the solid with radiation. While this description is useful for visualizing the kinetic processes in an energy level diagram, its physical base is principally different as the one described above. For example: the description of TL based on energy levels within the band gap requires charge transport while the TL based on the irradiation induced F and H center creation requires
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