Electron thermalization and trapping rates in pure and doped alkali and alkaline-earth iodide crystals studied by picosecond optical absorption
Electron thermalization and trapping rates in pure and doped alkali and alkaline-earth iodide crystals studied by picosecond optical absorption
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通过皮秒光学吸收研究纯和掺杂碱金属和碱土金属碘化物晶体中的电子热化和俘获率
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发表时间：
2014
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影响因子：
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通讯作者：
R. T. Williams
中科院分区：
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作者：
K. Ucer;G. Bizarri;A. Burger;A. Gektin;L. Trefilova;R. T. Williams
虽然在高能粒子停止后，光会在纳秒到微秒的时间内继续从绝缘晶体中发射出来，但决定响应非线性的大部分因素都发生在第一个皮秒。在这个时间尺度上，自由载流子和激子在轨道核心附近处于高密度，因此受到非线性猝灭。热（自由）电子最终冷却到足够低的能量，从而可以开始捕获空穴、掺杂剂或缺陷。在径迹环境中，皮秒时间尺度上确定的俘获载流子的空间分布可以影响整个光脉冲的光产额和初始粒子能量之间的比例。皮秒光谱的光吸收引起的短脉冲的间隙以上的激发提供了一个有用的窗口，在激发人口的关键早期演变过程中发生了什么。激光激发可以被调谐以激发相对于能带边缘初始非常热（$\ensuremath {\sim}$3 eV）或在开始时几乎热化（$\ensuremath {\sim}$0. 1 eV过剩能量）的载流子。本文研究了NaI：Tl（0%，0.1%），CsI：Tl（0%，0.01%，0.04%，0.3%）和$Sr {I} 2}$：Eu（0%，0.2%，0.5%，3%）的未掺杂和掺杂样品。
Although light continues to be emitted from insulating crystals used as scintillators over a period of nanoseconds to microseconds after stopping of an energetic particle, much of what determines the nonlinearity of response goes on in the first picoseconds. On this time scale, free carriers and excitons are at high density near the track core and thus are subject to nonlinear quenching. The hot (free) electrons eventually cool to low enough energy that trapping on holes, dopants, or defects can commence. In the track environment, spatial distributions of trapped carriers determined on the picosecond time scale can influence the proportionality between light yield and the initial particle energy throughout the whole light pulse. Picosecond spectroscopy of optical absorption induced by a short pulse of above-gap excitation provides a useful window on what occurs during the crucial early evolution of excited populations. The laser excitation can be tuned to excite carriers that are initially very hot ($\ensuremath{\sim}$3 eV) relative to the band edges, or that are almost thermalized ($\ensuremath{\sim}$0.1 eV excess energy) at the outset. Undoped and doped samples of NaI:Tl(0%, 0.1%), CsI:Tl(0%, 0.01%, 0.04%, 0.3%), and $\mathrm{Sr}{\mathrm{I}}_{2}$:Eu(0%, 0.2%, 0.5%, 3%) are studied in this work.