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前驱体。研究了稳态发光光谱与激发波长的关系，发现量子点的光谱形状与波长无关，表明其不含杂质。利用飞秒Ti：蓝宝石激光器的第2次（400nm）和第3次（266nm）谐波作为激发脉冲，测量了其发光衰减并分析了反俄歇效应。通过使用不同尺寸的CdTe量子点，我们发现当ω/Eg大于2.5时，存在逆俄歇效应，其寿命变短，单个CdTe量子点形成多载流子。对于5.4nm尺寸的CdTe量子点（Eg=1.73 eV），反俄歇效应的量子效率为190%。此外，电子和空穴的有效质量可能对CdTe量子点反俄歇效应的阈值能量为2.5Eg起重要作用。研究了瞬态吸收动力学对激发强度的依赖性，揭示了CdTe量子点的俄歇效应，这是由反俄歇效应产生的多载流子相互作用引起的。通过全局分析，CdTe量子点和纳米线的俄歇效应可以用随时间变化的复合率来分析，纳米线的俄歇复合率要大于量子点。此外，单粒子光谱的激发强度依赖性表明，俄歇电离对CdTe量子点的闪烁动力学起主导作用。

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.