Spectroscopic Study on Inverse Auger Effect of Semiconductor Quantum Dots

在有机溶剂和水溶剂中合成了不同尺寸的CdTe量子点，并通过几种方法去除了前体。稳态发光光谱作为激发波长的函数进行了检查，并发现量子点的光谱形状是独立的波长，这表明从杂质的自由。利用飞秒钛宝石激光的二次谐波（400 nm）和三次谐波（266 nm）作为激发脉冲，测量了量子点的发光衰减，分析了不同尺寸的CdTe量子点的逆俄歇效应，发现当ω/Eg大于2.5时，出现逆俄歇效应，量子点的寿命变短，并在单个CdTe量子点中形成多载流子。对于尺寸为5.4nm的CdTe量子点（Eg= 1.73eV），逆俄歇效应的量子效率为190%。此外，电子和空穴的有效质量对量子点的逆俄歇效应阈值能量（2.5Eg）也有重要影响。激发强度依赖的瞬态吸收动力学也被检查，以揭示俄歇效应的CdTe量子点，这是由于多载流子的相互作用产生的逆俄歇效应。通过全局分析，可以通过随时间变化的复合率来分析CdTe量子点和纳米线的俄歇效应，发现纳米线的俄歇复合率大于量子点的俄歇复合率。此外，在单粒子光谱的激发强度依赖性显示，俄歇电离的CdTe量子点的闪烁动力学起着主导作用。

Various sized CdTe QDs were synthesized in organic and water solvents, and the precursors were removed by several methods. Steady-state luminescence spectra were examined as a function of excitation wavelength, and the spectral shape of QDs was found to be independent of the wavelength, suggesting the free from an impurity. The second (400nm) and third (266nm) harmonics of femtosecond Ti:sapphire laser were used as excitation pulse to measure the luminescence decay and analyze inverse Auger effect.By using various sized CdTe QDs, we found that inverse Auger effect was observed when ω/Eg is larger than 2.5, in which the lifetime becomes shorter and multicarriers are formed in single CdTe QDs. For 5.4nm sized CdTe QDs (Eg=1.73 eV), the quantum efficiency of inverse Auger effect was 190%. In addition, the effective mass of the electron and hole may play an important role on the threshold energy of 2.5Eg for inverse Auger effect of CdTe QDs. Excitation intensity dependence of transient absorption dynamics was also examined to reveal Auger effect of CdTe QDs that is due to the interaction of muliticarriers generated by inverse Auger effect. The Auger effects of CdTe QDs and nanowires can be analyzed by the time-dependent recombination rate by Global analysis and the Auger recombination rate of nanowires was found to be larger than that of QDs. Furthermore, the excitation intensity dependence in single particle spectroscopy revealed that the Auger ionization plays an dominant role for the blinking dynamics of CdTe QDs.