Recently, studies involving photoluminescence from silicon nanoparticles have attracted significant interest amongst researchers. This can be attributed to the excellent biocompatibility of silicon nanoparticles that make them suitable for use as biomarkers. In such photoluminescence from semiconductors, only a broad structure appears in their spectra because of the continuous energy states of the conduction and valence bands. The photoluminescence from silicon nanoparticles can be attributed to; the band-to-band transitions resulting from a widen band-gap due to the quantum confinement effect, the transitions involving energy states at the silicon/silica interface or and the adsorption involving photoluminescence. In recently published literature, researchers have been able to observe peaked structures in the photoluminescence spectra of silicon nanoparticles nano powders in hexane. However, these peaked structures are yet to be attributed to the vibronic bands of the absorbed species.
Dr. Masanori Maeda, Professor Taketoshi Matsumoto, and Professor Hikaru Kobayashi from the Institute of Scientific and Industrial Research at Osaka University in Japan investigated the photoluminescence from vibrational excited-states for organic molecules adsorbed on silicon nanoparticles. They purposed to observe photoluminescence transitions with energies higher than the (0, 0) transition of 9,10-dimethylanthracene (DMA) adsorbed on silicon nanoparticles and attribute them to the transitions from the vibrational excited-states of DMA. Their work is now published in the research journal, Phys. Chem. Chem. Phys.
The research team employed the bead milling method to fabricate silicon nanoparticles from stamp the silicon-generated swarf generated during the slicing of silicon ingots via the use of a fixed-abrasive wire saw method. The team then performed the three step milling method in 2-propanol to produce minute silicon nanoparticles. They then proceeded to disperse the silicon nanoparticles in hexane plus water after filtration using a Teflon membrane filter. Eventually, the research team measured the quantum efficiencies of the photoluminescence, the photoluminescence’s ultra-violet and visible-light absorption spectra and its lifetime.
The authors observed that the photoluminescence spectra possessed vibronic bands that were seen to originate from the vibrational states of DMA. The team also noted that the photoluminescence excitation spectra possessed peaked structures with broad structures, and the former and latter structures were attributed to the incident light absorption by the DMA and silicon nanoparticles, respectively. Additionally, the team realized that when light was absorbed by the silicon nanoparticles, a hole and an electron separately transferred to DMA due to their long lifetime in the silicon nanoparticles.
The study has successfully presented the fabrication of silicon nanoparticles from silicon swarf using the bead milling method. This work has shown that the adsorption of 9,10-dimethylanthracene on silicon nanoparticles enhances the photoluminescence intensity by about 60 000 times that of DMA in hexane. Moreover, it has also been shown that in cases where a hole an electron is first transferred to DMA, photoluminescence peaks with energies higher than the (0, 0) peak are observed, and they are attributed to photoluminescence from vibrationally excited states.
M. Maeda, T. Matsumoto, H. Kobayashi. Photoluminescence from vibrational excited-states for organic molecules adsorbed on Si nanoparticles. Phys.Chem.Chem.Phys., 2017, 19, 21856
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