CsI:Tl光轉(zhuǎn)換機(jī)理及余輝特性的研究
發(fā)布時(shí)間：2019-02-12 23:47
【摘要】：對(duì)圖像探測(cè)器來說,CsI:Tl閃爍體是所有已知閃爍材料中最好的選擇。光學(xué)性能好、低成本和易于生長等優(yōu)點(diǎn)使它在未來將有廣闊的應(yīng)用前景。雖然科學(xué)工作者對(duì)CsI:Tl薄膜的鍍膜工藝、閃爍性能以及余輝特性上都有研究,但是對(duì)CsI:Tl薄膜的研究很不系統(tǒng)。本文從第一性原理和能帶理論入手分析摻雜離子Tl+和Eu2+對(duì)CsI:Tl晶體的能帶結(jié)構(gòu)的改變。同時(shí)通過實(shí)驗(yàn)探究制備工藝對(duì)CsI:Tl薄膜的薄膜質(zhì)量、閃爍特性的影響。除此之外,進(jìn)一步分析沉積速率以及摻Eu2+濃度對(duì)CsI:Tl薄膜的余輝特性的影響。理論部分,首先建立CsI:Tl晶胞模型,對(duì)結(jié)構(gòu)進(jìn)行優(yōu)化以后計(jì)算出能帶結(jié)構(gòu)。發(fā)現(xiàn)Tl+的摻入在價(jià)帶靠近禁帶處產(chǎn)生了新的能級(jí),這些新能級(jí)為CsI晶體提供了新的發(fā)光中心,提高了CsI晶體的光轉(zhuǎn)換效率。CsI晶體同時(shí)摻入Tl+和Eu2+時(shí),相比于CsI:Tl晶體中又出現(xiàn)了新的能級(jí),分別是位于禁帶的一個(gè)淺能級(jí),位于價(jià)帶中的一個(gè)能級(jí)和位于價(jià)帶底的深能級(jí)。這些新的能級(jí)提供了新的發(fā)光中心,而且深能級(jí)和淺能級(jí)都能有效的抑制CsI晶體中的余輝,這和實(shí)驗(yàn)結(jié)果也是相符合的。實(shí)驗(yàn)部分分別探索了不同影響因素對(duì)CsI:Tl薄膜的光轉(zhuǎn)換性能以及余輝性能的影響。通過掃描電子顯微鏡和X射線衍射儀對(duì)薄膜表面形貌進(jìn)行分析,發(fā)現(xiàn)沉積速率越快,薄膜越致密,晶粒越細(xì)。但是通過CsI:Tl薄膜的穩(wěn)態(tài)譜進(jìn)行分析,發(fā)現(xiàn)薄膜的光轉(zhuǎn)換特性不僅與沉積速率有關(guān)還與Tl+的損失有關(guān)。另外,實(shí)驗(yàn)結(jié)果表明越厚的薄膜光轉(zhuǎn)換特性越好,而預(yù)沉積相對(duì)直接沉積對(duì)薄膜的發(fā)光性能也有明顯的改善。采用穩(wěn)態(tài)/瞬態(tài)熒光光譜儀對(duì)不同沉積速率的CsI:Tl薄膜進(jìn)行熒光壽命的測(cè)試,測(cè)試結(jié)果顯示余輝時(shí)間隨沉積速率變快先下降再上升。分析發(fā)現(xiàn)這是由于薄膜中的缺陷數(shù)目和Tl+含量綜合影響的結(jié)果。用真空蒸發(fā)鍍膜法制備摻Eu2+的CsI:Tl薄膜。測(cè)試結(jié)果表明其激發(fā)譜和發(fā)射譜都有紅移的現(xiàn)象。通過分析不同Eu2+濃度的CsI:Tl薄膜的熒光壽命譜,發(fā)現(xiàn)Eu2+對(duì)CsI:Tl薄膜的余輝產(chǎn)生了很大的抑制作用,余輝時(shí)間降低了一倍。
[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.
【學(xué)位授予單位】：電子科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TL812;TB383.2
本文編號(hào)：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.
【學(xué)位授予單位】：電子科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TL812;TB383.2
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