Huxter Vanessa M, Kovalevskij Vitalij, Scholes Gregory D
Lash-Miller Chemical Laboratories, Center for Quantum Information and Quantum Control, and Institute for Optical Sciences, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada.
J Phys Chem B. 2005 Nov 3;109(43):20060-3. doi: 10.1021/jp0546406.
Evidence for an interaction between the quantum dot exciton fine structure states F = +/-1 is obtained by measuring the dynamics of transitions among those states, exciton spin relaxation or flipping. An ultrafast transient grating experiment based on a crossed-linear polarization grating is reported. By using the quantum dot selection rules for absorption of circularly polarized light, it is demonstrated that it is possible to detect transitions between nominally degenerate fine structure states, even in a rotationally isotropic system. The results for colloidal CdSe quantum dots reveal a strong size dependence for the exciton spin relaxation rate from one bright exciton state (F = +/-1) to the other in CdSe colloidal quantum dots at 293 K, on a time scale ranging from femtoseconds to picoseconds, depending on the quantum dot size. The results are consistent with an interaction between those states attributed to a long-range contribution to the electron-hole exchange interaction.
通过测量量子点激子精细结构态F = ±1之间的跃迁动力学、激子自旋弛豫或翻转，获得了这些态之间相互作用的证据。报道了基于交叉线性偏振光栅的超快瞬态光栅实验。利用量子点对圆偏振光吸收的选择规则，证明即使在旋转各向同性系统中，也有可能检测到名义上简并的精细结构态之间的跃迁。对于胶体CdSe量子点的结果表明，在293K的CdSe胶体量子点中，从一个亮激子态（F = ±1）到另一个亮激子态的激子自旋弛豫率强烈依赖于尺寸，时间尺度从飞秒到皮秒不等，这取决于量子点的大小。这些结果与归因于电子 - 空穴交换相互作用的长程贡献的那些态之间的相互作用一致。
