Research On Light Conversionmechanism And Afterglow Characteristics Of CsI:Tl

CsI:Tl scintillator is the brightest and most efficient scintillator material ever developed. While a wide variety of new materials is now available, CsI:Tl remains the primary choice due to its excellent properties, low cost, and easy availability. Although scientists have studied on CsI:Tl film about its growth and performance characteristics of both scintillation and afterglow suppression, CsI:Tl film’s study is unsystematic. This paper analyzes the dopant ions Tl+ and Eu2+ for changes in the band structure of the CsI:Tl crystal. Experiment explores the preparation process of the CsI:Tl film about the film quality and the impacts of scintillation characteristics. In addition, further analysis of the impact of Cs I:Tl film of deposition rate and the concentration of Eu2+on the afterglow characteristics is analyzed.Firstly, CsI:Tl cell model is established to research the doping mechanism of Tl+ and Eu2+ theoretically. After optimization of the structure band structure is calculated. It is found that new bands are generated near the band gap in the valence band resulted from the incorporation of Tl+. These new bands in CsI crystals provide new luminescence centers, and improve the light efficiency of CsI crystals. New bands are observed when Tl+ and Eu2+ are doped at the same time, including shallow bands located in the band gap, bands located in valence band and deep bands located in valence band bottom. These new bands provide new luminescence centers, the deep bands and the shallow bands can both effectively suppress the afterglow of CsI crystal, which is consistent with experimental results.Secondly, different influence factors on scintillation and afterglow properties of CsI thin film are researched experimentally. The surface morphology of the films was analyzed by scanning electron microscopy and X-ray diffraction. It is demonstrated that the films become more dense and more fine-grained when the deposition rate are faster. However, it is found that the light-emitting properties of the film are not only related to deposition rate,but also related to the Tl+ content due to the results of the steady-state spectra of CsI:Tl film. In addition, the results show that the light-emitting properties of CsI:Tl film have positive correlation with the thickness of the film. And the pre-deposition process can improve light-emitting properties of thin films.At last, the fluorescence lifetime of CsI:Tl films deposited at different deposition rate are researched using transient fluorescence spectrometer. It is found that the afterglow time increase first and then go down with faster deposition rate. It is due to changes of the number of defects in the film and the combined effects of Tl+ content.Eu2+ doped CsI:Tl films are prepared by vacuum evaporation. Test results show that its excitation spectra and emission spectra have red shift phenomenon. By analyzing the fluorescence lifetime spectroscopy of different Eu2+ concentrations of CsI:Tl film, conclusions can be made that afterglow can be suppressed efficiently though the addition of Eu2+ to the CsI:Tl host lattice because the afterglow time is cut to only the half of former results.