科研之友
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摘要
Understanding the mechanisms of defect-related photoluminescence in colloidal transparent conducting oxide nanocrystals is important for the development of new multifunctional nanostructures and devices. Here we report a study of the role of NC size, structure, defects, and surface capping on the photoluminescence energy, efficiency, and dynamics of colloidal gamma-Ga(2)O(3) nanocrystals. A strong blue emission (quantum yield similar to 25%) is associated with the presence of the vacancy-defect sites, and assigned to the donor acceptor pair (DAP) recombination. The emission energy and lifetime are generally determined by the donor and acceptor binding energies (which are dependent on the NC structure) and the attractive Coulombic interactions between charged donor and acceptor sites (which are dependent on the defect concentration). Variable temperature photoluminescence measurements reveal that binding energies of the donor and acceptor levels are also size-dependent; in 6.0 +/- 1.0 rim gamma-Ga(2)O(3) nanocrystals donor binding energy was determined to be 205 meV, increasing by ca. 30 meV in 3.3 +/- 0.5 rim nanocrystals. The defect sites on nanocrystal surfaces (OH(-) or O(2-)) also influence DAP recombination by trapping photogenerated valence band holes. Removal of the surface defect sites by capping ligands (dodecylamine and tri-n-octylphosphine oxide) is shown to eliminate this hole-trapping pathway, enhancing a hole capture by the acceptor sites, and increasing the DAP emission intensity. The results of the mechanistic study of the DAP recombination in this work serve as a useful guideline for introducing and manipulating PL properties in oxide nanostructures by controlling the native defect interactions.
- 出版日期2011-9-29
