Photoluminescence from vibrational excited-states for organic molecules adsorbed on Si nanoparticles

Significance 

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.

Photoluminescence from vibrational excited-states for organic molecules adsorbed on Si nanoparticles. Advances in Engineering

About the author

Dr. Masanori Maeda is currently a researcher at TEIJIN LIMITED, Japan.
He received his B.S., M.S., and Ph.D, in chemistry from Osaka University in 2010, 2012, 2015, respectively. His research interests include nanomaterials and organic-inorganic composites. He is a member of JSAP.

About the author

Dr. Taketoshi Matsumoto is an Associate Professor in The Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan.  His research is focused on energy related nano-materials and devices.  He has been engaged in research on Li ion batteries, luminous materials, solar cells, ultra-low power thin film transistors and MOS transistors, permanent memories, fuel cells, hydrogen storages and catalysts.

He received his Ph.D. (2001) and M.S. (1998) in Electronic Chemistry from Tokyo Institute of Technology, Japan, and B.S. (1996) in Chemistry from Keio University, Japan.  He was a research fellow of the Japan Society for the Promotion of Science, a Postdoctoral Research Associate in University of Southern California, US, a Lecturer in University of Tsukuba, Japan, a Research Associate in Institute for Molecular Science, Japan, and an Assistant Professor in Osaka University, Japan.

About the author

Dr. Hikaru Kobayashi is a Professor of The Institute of Scientific and Industrial Research, Osaka University. He has been engaged in research on silicon solar cells, low temperature Si oxidation, and fabrication of Si nanopowder and its application to hydrogen generation material, anode material in Li ion batteries, and luminescent material.

He received the B.E. degree in chemistry from Osaka University, in 1979 and the M.E., and Ph.D. degrees in chemistry from Kyoto University, Kyoto, Japan, in 1981, and 1984, respectively.  From 1984 to 1986, he was a Postdoctoral Research Associate in Department of Physics and Astronomy, University of Pennsylvania, PA.  From 1986-1987, he was a Researcher in Matsushita Electronics Corporation Kyoto Research Center, Kyoto, Japan where he was engaged in LSI wiring and gate oxide technology.  From 1987 to 1990, he was a Research Associate in Department of Chemistry, Faculty of Engineering Science, Osaka University where he was engaged in research on silicon solar cells, surface and interface science of silicon, and low temperature silicon oxidation.  From 1990 to 1998, he was an Associate Professor in Department of Chemistry, Faculty of Engineering Science, Osaka University.

Reference

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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