Synthesis And Photoluminescence Properties Of SIC Quantum Dots And Their Nanocomposites

Silicon carbide has excellent physical and chemical properties and good biocompatibility. However, it has a low quantum yield due to its indirect bandgap nature. It has been found that when the size of the SiC particle is reduced to below 10 nm, its luminescence intensity increases by several orders of magnitude with respect to that of bulk material owing to the quantum confinement effect. The photoluminescence (PL) spans a wide spectral region. Nevertheless, the luminescence mechanisms of SiC quantum dots (QDs) are still not fully understood. Moreover, the easy aggregation of SiC QDs hampers their wide applications. In this thesis, we report the study of fabrication and luminescence properties of SiC QDs and their nanocomposites.The 3C-SiC QDs with an average size of 1.8-3.7 nm were fabricated by using chemical etching under different etching conditions. A surface state correlated blue luminescence was observed in the 3C-SiC QDs, and its relative intensity increases with decreasing particle size. This blue luminescence diminishes after introduction of KOH into the SiC QDs solution, and recovers after subsequent introduction of HC1 into the solution. Our study shows that this luminescence originates from the surface defect C=O, and that the HO...C=O interaction between hydroxyl and carbonyl groups plays a key role in this luminescence. Another surface state Si-Si was also identified which results in strong light absorption at 267 nm in the SiC QDs and contributes to luminescence of the 3C-SiC QDs through energy transfer.The silica-encapsulated 3C-SiC QDs nanocomposites were fabricated and their PL properties were investigated. The TEM observation shows that one silica sphere contains several 3C-SiC QDs. The nanocomposites show quantum-confinement luminescence belonging to the embedded 3C-SiC QDs, suggesting that there are no new luminescent surface defects formed for the embedded QDs. The PL intensity of the 3C-SiC QDs/SiO2 nanocomposite film is 10 times stronger than that of the pure 3C-SiC QDs film. The blue emitting SiC/SiO2 nanocomposite can serve as a micro light source with potential applications in optoelectronics and life science.The 3C-SiC QDs/CTAB multilayered vesicle nanostructures were synthesized and their PL properties were studied. The Coulomb attraction force between the QD and surrounding CTAB molecules induces the formation of the core/shell nanostructure, and such a formation mechanism is different from the conventional vesicle formation mechanism related to the hydrophilic/hydrophobic interaction. The core/shell nanostructures exhibit strong near-UV PL arising from outer vesicles. The 3C-SiC QDs/CTAB nanostructures are free from direct aggregation of the SiC QDs when they are assembled into a solid film.The 3C-SiC QDs/sodium dodecyl sulfonate (SDS) network-like composite film was synthesized. It exhibits PL with peak wavelength ranging from 417 to 491 nm as the excitation wavelength increases from 260 to 440 nm, implying that the PL has an origin of quantum confinement. The luminescent 3C-SiC QDs/SDS network-like film prevents aggregation of the QDs and shows promise in applications of solid state lighting.The Ag nanoparticle-induced fluorescence enhancement of SiC QDs/SDS nanocomposite was studied. The enhancement in integrated fluorescence intensity reaches astonishing 176-fold under 360 nm excitation. The finite-element method simulation indicates that the strong resonant coupling between the excited SiC QD and localized surface plasmon of the Ag nanoparticle plays a key role in enhancement of the fluorescence. The absorption enhancement caused by light concentration around the Ag nanoparticles contributes very little. These SiC QDs with highly enhanced fluorescence have potential applications in optoelectronic devices.