Graphite-Shelled Si Nanoparticles and Their Au/Si Heterodimers: Preparation, Photoluminescence, and Second Harmonic Generation

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• 作者：Chih-Chia Huang ; Kuei-Yi Chuang ; Chin-Jie Huang ; Tzu-Ming Liu ; Chen-Sheng Yeh
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：May 26, 2011
• 年：2011
• 卷：115
• 期：20
• 页码：9952-9960
• 全文大小：1160K
• 年卷期：v.115,no.20(May 26, 2011)
• ISSN：1932-7455

文摘

New structured graphite-shelled Si nanocrystals were prepared by laser ablation in various solvents including H₂O, ethanol, 2-propanol, hexane, octane, octadecene, trioctylamine, toluene, trioctylamine/toluene, and oleylamine/toluene. With the aromatic debris, containing hexagonal carbon rings, from organic media seems to facilitate graphitization process to build up graphitic carbon layers on Si. The luminescent feature was strongly related to the presence of graphite shells. Excited by infrared femtosecond lasers, the graphite-shelled Si nanocrystals showed extraordinarily strong second harmonic generation (SHG). Both fluorescence and SHG signals were growing with the aging days. The single photon-excited fluorescence and quantum yield were increased from as-prepared graphite-shelled Si quantum dots (QDs) (8%) to 30-day aged samples (13.0%). Because of oxidation upon aging, it is suggested that the possible increase of the Si鈥揙 bonds on Si surface could have diminished nonradiative centers resulting in enhancing fluorescence. The SHG signal was also up to 32 times higher than that of as-prepared graphite-shelled Si QDs after the aging process. Such an oxidative aging process likely created strain at the Si/SiO₂ interface, breaking the central symmetry, and allowed the SHG. Additionally, the poling of SiO₂ on the surface of graphite-shelled Si QDs and the transition states of quantum-confined excitons have been addressed for the SHG observation as well. The enhancements of fluorescence and SHG signals have opened an avenue for the applications of graphite-shelled Si QDs as cell biolabeling agents and contrast agents in deep tissue microscopy and tomography. The blue emission of graphite-shelled Si QDs integrated with Rhodamine 610 dye has allowed us to tune luminous spectra giving white light luminescence. The first synthesis of the Au/Si heterodimer nanostructures were formed through replacement reaction between graphite-shelled Si nanocrystals and tetraoctylammonium鈥揂u³⁺ complexes in organic solvent.