title: Ultrafast electronic relaxation and charge-carrier localization in CdS/CdSe/CdS quantum-dot quantum-well heterostructures.
abstract: 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.
authors.affiliation: Laser Dynamics Laboratory, Department of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, USA.
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Schill
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Gaddis
authors.forename: Wei
authors.initials: W
authors.lastname: Qian
authors.forename: Mostafa A
authors.initials: MA
authors.lastname: El-Sayed
authors.forename: Ye
authors.initials: Y
authors.lastname: Cai
authors.forename: Valeria T
authors.initials: VT
authors.lastname: Milam
authors.forename: Kenneth
authors.initials: K
authors.lastname: Sandhage
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D004579:Electron Transport; D036103:Nanotechnology / Q000295:instrumentation / Q000379:methods*; D045663:Quantum Dots; D018036:Selenium Compounds / Q000737:chemistry*; D012666:Semiconductors; D055672:Static Electricity; D013440:Sulfides / Q000737:chemistry*; D013997:Time Factors
chemical_list: D019187:Cadmium Compounds; D018036:Selenium Compounds; D013440:Sulfides; C034939:cadmium sulfide; C058667:cadmium selenide