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17 September 2018 Mechanism of ligand-controlled emission in silicon quantum dots (Conference Presentation)
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Though bulk silicon (Si) is an indirect bandgap material and therefore non-emissive, nm-sized Si quantum dots (Si QDs) exhibit direct band-gap characteristics due to quantum confinement. As a result, Si QDs are emissive though their fluorescence is relatively weak and limited to red or near-infrared. Recently, visible and color-tunable emission with up to 90% quantum yield has been achieved through surface-modification of Si QDs with nitrogen-capped ligands. However, the emission mechanism operating in these surface-modified Si QDs is unclear and the factors that determine their emission maxima are still unknown. Here we report that the emission maximum wavelength of these species can be predicted quantitatively from the calculated ground-state dipole moment of the ligand. This is consistent with the origin of the emission being a charge-transfer (CT) transition between the Si surface and the ligand. A detailed study of the photon statistics behavior of isolated Si QDs reveals two types of emission, the dominant one being characteristic of single quantum states and the weaker one being characteristics of a bulk material. Understanding the emission mechanism of these unique systems and how their properties can be tuned synthetically will enable the design of Si QDs with a broader wavelength range and higher quantum yields for applications in light-emitting diodes, bio-imaging and sensing.
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Linda A. Peteanu, Woong Y. So, Qi Li, and Rongchao M. Jin "Mechanism of ligand-controlled emission in silicon quantum dots (Conference Presentation)", Proc. SPIE 10724, Physical Chemistry of Semiconductor Materials and Interfaces XVII, 1072419 (17 September 2018); https://doi.org/10.1117/12.2321662
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