CsI:Tl光转换机理及余辉特性的研究
发布时间：2019-02-12 23:47
【摘要】：对图像探测器来说,CsI:Tl闪烁体是所有已知闪烁材料中最好的选择。光学性能好、低成本和易于生长等优点使它在未来将有广阔的应用前景。虽然科学工作者对CsI:Tl薄膜的镀膜工艺、闪烁性能以及余辉特性上都有研究,但是对CsI:Tl薄膜的研究很不系统。本文从第一性原理和能带理论入手分析掺杂离子Tl+和Eu2+对CsI:Tl晶体的能带结构的改变。同时通过实验探究制备工艺对CsI:Tl薄膜的薄膜质量、闪烁特性的影响。除此之外,进一步分析沉积速率以及掺Eu2+浓度对CsI:Tl薄膜的余辉特性的影响。理论部分,首先建立CsI:Tl晶胞模型,对结构进行优化以后计算出能带结构。发现Tl+的掺入在价带靠近禁带处产生了新的能级,这些新能级为CsI晶体提供了新的发光中心,提高了CsI晶体的光转换效率。CsI晶体同时掺入Tl+和Eu2+时,相比于CsI:Tl晶体中又出现了新的能级,分别是位于禁带的一个浅能级,位于价带中的一个能级和位于价带底的深能级。这些新的能级提供了新的发光中心,而且深能级和浅能级都能有效的抑制CsI晶体中的余辉,这和实验结果也是相符合的。实验部分分别探索了不同影响因素对CsI:Tl薄膜的光转换性能以及余辉性能的影响。通过扫描电子显微镜和X射线衍射仪对薄膜表面形貌进行分析,发现沉积速率越快,薄膜越致密,晶粒越细。但是通过CsI:Tl薄膜的稳态谱进行分析,发现薄膜的光转换特性不仅与沉积速率有关还与Tl+的损失有关。另外,实验结果表明越厚的薄膜光转换特性越好,而预沉积相对直接沉积对薄膜的发光性能也有明显的改善。采用稳态/瞬态荧光光谱仪对不同沉积速率的CsI:Tl薄膜进行荧光寿命的测试,测试结果显示余辉时间随沉积速率变快先下降再上升。分析发现这是由于薄膜中的缺陷数目和Tl+含量综合影响的结果。用真空蒸发镀膜法制备掺Eu2+的CsI:Tl薄膜。测试结果表明其激发谱和发射谱都有红移的现象。通过分析不同Eu2+浓度的CsI:Tl薄膜的荧光寿命谱,发现Eu2+对CsI:Tl薄膜的余辉产生了很大的抑制作用,余辉时间降低了一倍。
[Abstract]:For image detectors, CsI:Tl scintillators are the best choice of all known scintillation materials. Because of its good optical properties, low cost and easy growth, it will be widely used in the future. Although scientists have studied the process, scintillation and afterglow properties of CsI:Tl thin films, the study of CsI:Tl thin films is not systematic. Based on the first principle and the energy band theory, the changes of the band structure of the doped ions Tl and Eu2 on the CsI:Tl crystal are analyzed in this paper. At the same time, the effect of preparation process on the quality and scintillation characteristics of CsI:Tl thin films was investigated. In addition, the effects of deposition rate and Eu2 concentration on the afterglow properties of CsI:Tl films were analyzed. In the theoretical part, the CsI:Tl cell model is first established, and the band structure is calculated after the structure is optimized. It is found that the incorporation of Tl produces new energy levels near the gap band in the valence band. These new energy levels provide a new luminescence center for CsI crystals and improve the optical conversion efficiency of CsI crystals. When both Tl and Eu2 are doped in CsI crystals, Compared with the CsI:Tl crystal, a new energy level appears, one in the gap band, one in the valence band and the other at the bottom of the valence band. These new energy levels provide new luminous centers, and both deep and shallow levels can effectively suppress the afterglow in CsI crystals, which is consistent with the experimental results. In the experimental part, the effects of different factors on the optical conversion and afterglow properties of CsI:Tl thin films were investigated. The surface morphology of the films was analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). It was found that the faster the deposition rate was, the denser the film was and the finer the grain size was. However, by analyzing the steady-state spectra of CsI:Tl films, it is found that the optical conversion characteristics of the films are not only related to the deposition rate but also to the loss of Tl. In addition, the experimental results show that the thicker the film is, the better the photoluminescence properties of the films are. The fluorescence lifetime of CsI:Tl films with different deposition rates was measured by steady-state / transient fluorescence spectrometer. The results show that the afterglow time decreases first and then increases with the deposition rate. It is found that this is the result of the combined effect of the number of defects and the content of Tl in the film. Eu2 doped CsI:Tl thin films were prepared by vacuum evaporation deposition. The results show that both the excitation and emission spectra are red-shifted. By analyzing the fluorescence lifetime spectra of CsI:Tl films with different Eu2 concentrations, it is found that Eu2 has a great inhibitory effect on the afterglow of CsI:Tl films, and the afterglow time is reduced by twice.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TL812;TB383.2
本文编号：2420919
[Abstract]:For image detectors, CsI:Tl scintillators are the best choice of all known scintillation materials. Because of its good optical properties, low cost and easy growth, it will be widely used in the future. Although scientists have studied the process, scintillation and afterglow properties of CsI:Tl thin films, the study of CsI:Tl thin films is not systematic. Based on the first principle and the energy band theory, the changes of the band structure of the doped ions Tl and Eu2 on the CsI:Tl crystal are analyzed in this paper. At the same time, the effect of preparation process on the quality and scintillation characteristics of CsI:Tl thin films was investigated. In addition, the effects of deposition rate and Eu2 concentration on the afterglow properties of CsI:Tl films were analyzed. In the theoretical part, the CsI:Tl cell model is first established, and the band structure is calculated after the structure is optimized. It is found that the incorporation of Tl produces new energy levels near the gap band in the valence band. These new energy levels provide a new luminescence center for CsI crystals and improve the optical conversion efficiency of CsI crystals. When both Tl and Eu2 are doped in CsI crystals, Compared with the CsI:Tl crystal, a new energy level appears, one in the gap band, one in the valence band and the other at the bottom of the valence band. These new energy levels provide new luminous centers, and both deep and shallow levels can effectively suppress the afterglow in CsI crystals, which is consistent with the experimental results. In the experimental part, the effects of different factors on the optical conversion and afterglow properties of CsI:Tl thin films were investigated. The surface morphology of the films was analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). It was found that the faster the deposition rate was, the denser the film was and the finer the grain size was. However, by analyzing the steady-state spectra of CsI:Tl films, it is found that the optical conversion characteristics of the films are not only related to the deposition rate but also to the loss of Tl. In addition, the experimental results show that the thicker the film is, the better the photoluminescence properties of the films are. The fluorescence lifetime of CsI:Tl films with different deposition rates was measured by steady-state / transient fluorescence spectrometer. The results show that the afterglow time decreases first and then increases with the deposition rate. It is found that this is the result of the combined effect of the number of defects and the content of Tl in the film. Eu2 doped CsI:Tl thin films were prepared by vacuum evaporation deposition. The results show that both the excitation and emission spectra are red-shifted. By analyzing the fluorescence lifetime spectra of CsI:Tl films with different Eu2 concentrations, it is found that Eu2 has a great inhibitory effect on the afterglow of CsI:Tl films, and the afterglow time is reduced by twice.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TL812;TB383.2
【参考文献】
相关期刊论文 前4条
1 董加彬,彭贺新;安检设备中使用的短余辉碘化铯(铊)晶体[J];警察技术;1998年02期
2 顾牡;张敏;刘小林;姚达林;倪晨;黄世明;刘波;;微柱状CsI闪烁薄膜热蒸发生长工艺[J];强激光与粒子束;2010年02期
3 任国浩;;无机闪烁晶体的发展趋势[J];人工晶体学报;2012年S1期
4 李霞;滕晓云;;X射线衍射原理及在材料分析中的应用[J];物理通报;2008年09期
，本文编号：2420919
本文链接：https://www.wllwen.com/kejilunwen/cailiaohuaxuelunwen/2420919.html
