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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Effect of Surface Stoichiometry on Blinking and Hole Trapping Dynamics in CdSe Nanocrystals
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Effect of Surface Stoichiometry on Blinking and Hole Trapping Dynamics in CdSe Nanocrystals

机译：表面化学计量学对CdSe纳米晶体闪烁和空穴俘获动力学的影响

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摘要

We measure the photoinduced carrier dynamics as the surface composition of CdSe nanocrystals is systematically varied from metal rich (similar to 80% surface Cd) to nearly stoichiometric (similar to 50% surface Cd). Using time-resolved optical spectroscopy, we determine that the luminescence lifetime is controlled by the rate of hole trapping at the newly exposed surface selenium atoms. However, the increased rate of the photoluminescence decay is not sufficient to explain the decreased photoluminescence quantum yield, and requires a growing proportion of nanocrystals in a dark or "OFF" state to explain the data. A global kinetic model is proposed that relates the fraction of selenium sites to the rate of hole trapping. A linear relationship between the rate of hole trapping and the fraction of exposed Se sites (x(Se)) is observed within the range of accessible stoichiometries (x(Se) = 0.5.-0.2). Extrapolation to higher surface cadmium fractions suggests that not all Se sites serve as effective hole traps. These results explain the strong nonlinear dependence of the fluorescence yield on the nanocrystal stoichiometry.
机译：我们测量光诱导的载流子动力学，因为CdSe纳米晶体的表面组成从富金属（近似于80％的表面Cd）到接近化学计量（近似50％的表面Cd）变化。使用时间分辨光谱，我们确定发光寿命受新暴露的表面硒原子处的空穴俘获率控制。然而，增加的光致发光衰减速率不足以解释光致发光量子产率的降低，并且需要越来越多比例的处于暗或“关”状态的纳米晶体来解释数据。提出了一个全局动力学模型，该模型将硒位点的比例与空穴捕获的速率联系起来。在可达到的化学计量比（x（Se）= 0.5.-0.2）范围内，观察到了空穴捕获速率与暴露的Se位置分数（x（Se））之间的线性关系。外推到较高的镉含量表明，并非所有的硒位点都可以作为有效的空穴陷阱。这些结果解释了荧光产量对纳米晶体化学计量的强烈非线性依赖性。

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