Size-Dependent Photoionization in Single CdSe/ZnS Nanocrystals
Size-Dependent Photoionization in Single CdSe/ZnS Nanocrystals
复制标题
单 CdSe/ZnS 纳米晶体中尺寸依赖性光电离
DOI：
10.1021/nl402607a
复制
发表时间：
2013
期刊：
影响因子：
10.8
通讯作者：
Nesbitt, David J.
中科院分区：
文献类型：
--
作者：
Early, Kevin T.;Nesbitt, David J.
单一半导体纳米晶体中的荧光间歇现象已经被证明在几十年的时间和概率上遵循幂定律统计。最近，一些研究表明，虽然“关”驻留时间对几乎所有的实验参数都不敏感，但“开”驻留时间在很长一段时间内表现出与泵浦功率有关的指数截断，这表明在高激发功率下双激子光电离几率增强。在这里，我们报告了这种时间截断对纳米晶体半径的依赖关系。我们观察到，随着Cd Se芯半径从1.3nm.3 nm增加到3.5nm.Ponize(R)∝1/R3.5(5)，单脉冲光电离几率从1.8(2)×10-4下降到2.0(7)×10-6，并对双激子形成的电荷喷射几率进行了半径标度.激子波函数的有效质量计算表明，在富陷阱的硫化锌壳层中，分数电子和空穴几率的乘积与纳米晶体的半径相似。讨论了这种表面局域态可能的电荷喷射机制。
Fluorescence intermittency in single semiconductor nanocrystals has been shown to follow power law statistics over many decades in time and in probability. Recently, several studies have shown that, while “off” dwell times are insensitive to almost all experimental parameters, “on” dwell times exhibit a pump-power dependent exponential truncation at long times, suggestive of enhanced biexciton photoionization probabilities at high excitation powers. Here we report the dependence of this on-time truncation on nanocrystal radius. We observe a decrease in the per-pulse photoionization probability from 1.8(2) × 10–4to 2.0(7) × 10–6as the CdSe core radius increases from 1.3 to 3.5 nm, with a radius scaling for the probability for charge ejection arising from biexciton formationPionize(r) ∝ 1/r3.5(5). Effective mass calculations of the exciton wave functions show that the product of fractional electron and hole probabilities in the trap-rich ZnS shell scale similarly with nanocrystal radius. Possible charge ejection mechanisms from such a surface-localized state are discussed.