Schill Alexander W, Gaddis Christopher S, Qian Wei, El-Sayed Mostafa A, Cai Ye, Milam Valeria T, Sandhage Kenneth
Laser Dynamics Laboratory, Department of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, USA.
Nano Lett. 2006 Sep;6(9):1940-9. doi: 10.1021/nl061054v.
The relaxation and localization times of excited electrons in CdS/CdSe/CdS colloidal quantum wells were measured using subpicosecond spectroscopy. HRTEM analysis and steady-state PL demonstrate a narrow size distribution of 5-6 nm epitaxial crystallites. By monitoring the rise time of the stimulated emission as a function of pump intensity, the relaxation times of the electron from the CdS core into the CdSe well are determined and assigned. Two-component rise times in the stimulated emission are attributed to intraband relaxation of carriers generated directly within the CdSe well (fast component) and charge transfer of core-localized carriers across the CdS/CdSe interface (slow component). This is the first reported observation of simultaneous photon absorption in the core and well of a quantum-dot heterostructure. With increasing pump intensity, the charge-transfer channel between the CdS core CdSe well contributes less to the stimulated emission signal because of filling and saturation of the CdSe well state, making the interfacial charge-transfer component less efficient. The interfacial charge-transfer time of the excited electron was determined from the slow component of the stimulated emission build-up time and is found to have a value of 1.2 ps.
利用亚皮秒光谱测量了CdS/CdSe/CdS胶体量子阱中受激电子的弛豫时间和局域时间。高分辨率透射电子显微镜（HRTEM）分析和稳态光致发光（PL）表明外延微晶尺寸分布狭窄，为5 - 6纳米。通过监测受激发射的上升时间作为泵浦强度的函数，确定并归属了电子从CdS核进入CdSe阱的弛豫时间。受激发射中双组分上升时间归因于直接在CdSe阱内产生的载流子的带内弛豫（快组分）以及核局域载流子穿过CdS/CdSe界面的电荷转移（慢组分）。这是首次报道在量子点异质结构的核与阱中同时发生光子吸收的观测结果。随着泵浦强度增加，由于CdSe阱态的填充和饱和，CdS核与CdSe阱之间的电荷转移通道对受激发射信号的贡献减小，使得界面电荷转移组分效率降低。由受激发射建立时间的慢组分确定了受激电子的界面电荷转移时间，其值为1.2皮秒。
