This thesis presents an exploration of the photophysics of colloidal semiconductor nanocrystals using both linear and non-linear optical measurement techniques. These optical methodologies are used to follow population dynamics in both singly and multiply excited nanocrystal systems as well as determine material properties of the ensemble. Topics covered in the thesis include, the identification and characterization of bulk-like nanocrystals, study of the fine structure states of the lowest energy exciton, single and multiexciton population dynamics, acoustic phonon modes, elasticity and surface stress properties of a colloidal ensemble in solution.Through linear spectroscopy, the properties of both quantum confined and bulk-like colloidal semiconductor nanocrystals are compared. The identification of a model system of bulk-like nanocrystals with a non-standard absorption profile serves to resolve an ambiguity in literature concerning their characterization. The remainder of the thesis is focused on the size-dependent properties of quantum confined CdSe colloidal nanocrystals. The population dynamics and material properties of these systems are studied using a nonlinear optical technique called transient grating. A third order transient grating measurement with a cross-polarized configuration, which follows the relaxation within the fine structure levels of the lowest energy exciton state, is demonstrated and used to compare systems with different crystal field splittings. Transient grating experiments performed with specific polarization sequences allow for selective observation of the dynamics amongst nearly degenerate levels at room temperature. Cross-polarized transient grating is also used to observe a quantized acoustic phonon mode in a series of nanocrystal samples. The observation of this mode allows experimental determination of the elasticity and surface stress of the nanocrystal ensemble in solution. The anisotropic origin of the acoustic phonon is discussed using a combination of theoretical analysis, modelling and experimental data. In addition, third- and fifth-order transient grating experiments are used to study exciton and multiexciton population relaxation dynamics. The work presented here spans the optical and material properties of quantum confined and `bulk' nanocrystals. This thesis attempts to illustrate the broad scope of the observed behaviour of colloidal nanocrystal systems and to contribute to a greater understanding of their physical properties.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OTU.1807/19195 |
| Date | 01 March 2010 |
| Creators | Huxter, Vanessa |
| Contributors | Scholes, Gregory D. |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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