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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Synthesis and Ultrafast Study of Cysteine- and Glutathione-Capped Ag_2S Semiconductor Colloidal Nanoparticles
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Synthesis and Ultrafast Study of Cysteine- and Glutathione-Capped Ag_2S Semiconductor Colloidal Nanoparticles

机译：半胱氨酸和谷胱甘肽封端的Ag_2S半导体胶体纳米颗粒的合成和超快研究

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摘要

A new synthetic method has been developed for preparing silver sulfide, Ag_2S, nanoparticles capped with cysteine or glutathione. The average particle diameter has been determined to be around 9 nm using transmission electron microscopy. The ground-state electronic absorption spectra of the Ag_2S nanoparticles show a continuous increase in absorption cross section toward shorter wavelengths starting from the red (600-800 nm). Ultrafast dynamics of photoinduced electrons in these nanoparticles have been measured using femtosecond transient absorption/bleach spectroscopy. In most cases studied, the early time transient profiles feature a pulse-width limited (< 150 fs) rise followed by a fast decay (750 fs) and a slower rise (4.5 ps). The signal has contribution from both transient absorption and transient bleach. On longer time scales, three (Cys-1, Cys-2, and GSH-2) of the four samples studied show a recovery with 4.5 ps time constant that goes above the baseline and then decays gradually toward the baseline with a time constant of > 1 ns. One sample (GSH-1) shows a bleach recovery that gradually approaches the baseline with a similar time constant (> 1 ns) following the fast 4.5 ps rise. An interesting power dependence was observed for all the samples: the transient absorption contribution becomes more dominant over bleach with increasing excitation intensity. A simple four-state kinetic model developed to account for the main features of the dynamics suggests that initial photoexcitation populates the conduction band and depletes the valence band within the laser pulse (< 150 fs). The conduction band electrons are first trapped in shallow trap states with a time constant of 500 fs and then further trapped into deep traps with a constant of 4 ps. The deep trapped electrons finally recombine with the hole with a time constant of > 1 ns. This model suggests that the difference in dynamics observed between the different samples is due to different absorption cross sections of deep trap states. The observed excitation intensity dependence of the dynamics is attributed to shallow trap state saturation at high intensities.
机译：已开发出一种新的合成方法，用于制备半胱氨酸或谷胱甘肽包覆的硫化银Ag_2S纳米颗粒。使用透射电子显微镜已确定平均粒径为约9nm。 Ag_2S纳米粒子的基态电子吸收光谱显示，从红色（600-800 nm）开始，吸收截面朝着较短的波长连续增加。已使用飞秒瞬态吸收/漂白光谱法测量了这些纳米粒子中光诱导电子的超快动力学。在大多数研究的案例中，早期瞬态曲线的特征是脉冲宽度受限（<150 fs）上升，然后是快速衰减（750 fs）和较慢的上升（4.5 ps）。该信号来自瞬态吸收和瞬态漂白。在更长的时间尺度上，所研究的四个样本中的三个（Cys-1，Cys-2和GSH-2）显示出4.5 ps的时间常数恢复，该时间常数高于基线，然后逐渐向基线衰减，时间常数为> 1 ns。一个样品（GSH-1）显示出漂白剂的恢复，其在快速上升4.5 ps后以相似的时间常数（> 1 ns）逐渐接近基线。对于所有样品，都观察到了一个有趣的功率依赖性：随着激发强度的增加，瞬态吸收作用在漂白剂中的作用越来越明显。为说明动力学的主要特征而开发的简单四态动力学模型表明，初始光激发填充了导带，并耗尽了激光脉冲内的价带（<150 fs）。导带电子首先以500 fs的时间常数陷入浅陷阱态，然后以4 ps的常数进一步陷入深陷阱。最终，深陷的电子以大于1 ns的时间常数与空穴复合。该模型表明，在不同样品之间观察到的动力学差异是由于深阱态的吸收截面不同所致。观察到的动力学的激发强度依赖性归因于在高强度下的浅陷阱态饱和。

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