Associate Professor, Department of Chemistry, Faculty of Science, Kobe University
White light emission from SiO2 glass prepared from nanometer-sized silica particles
The strong photoluminescence (PL) observed at room temperature in the visible region from porous silicon as well as from its silicon-based nanostructures has stimulated numerous research works in the development of silicon-based materials for optoelectronic and display applications. In these samples, the visible PL is generally attributed to the presence of nanoscale silicon aggregates, although the precise mechanism of such an efficient PL emission is still a matter of considerable debate.
Recently, we found that transparent “pure” bulk SiO2 glass, prepared from nanometer-sized silica particles using a viscous sintering procedure, exhibited intense broadband light emission unlike normal SiO2 glass. Intense PL, which appeared white to the naked eye, was observed in the wavelength range from ~350 to ~700 nm, depending on processing conditions. The resultant PL is quite stable after prolonged exposure to the atmosphere and shows no appreciable light-induced degradation. In this work, we used nonporous amorphous fumed silica (specific surface area = 390±40 m2/g; particle size 7 nm) as a starting material. The as-received fumed silica powder was pressed in a uniaxial press to form a disk-shaped pellet. To remove surface hydroxyl groups from the as-received samples, we then dehydrated the pellets at temperatures from 1000 to 1100 °C. It has also been found that during the heating procedure, fine silica particles coalesce into bulk-like transparent silica glass. The density of the heat-treated samples was almost identical to normal bulk silica glass (2.20 g/cm3), indicating that the resulting silica glass is not porous. However, the materials that formed showed intense visible PL unlike normal bulk silica glass, suggesting a highly defective nature of the present silica glass samples.
The present bulk SiO2 glass hence is a new class of silicon-oxide-based luminescent materials that do not contain silicon nanostructures. Possible mechanisms that are responsible for its PL are now being investigated using ab initio quantum-chemical methods.
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| Fig. 1 Large Image |
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| Visible emission from transparent silica glass prepared from nanometer-sized silica particles excited at 266 nm (Nd: YAG laser; energy: 2 mJ/cm2; pulse width 7 ns). |
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| Fig. 2 Large Image |
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| PL spectrum of transparent silica glass prepared from nanometer-sized silica particles excited at 266 nm (Nd: YAG laser; energy: 2 mJ/cm2; pulse width 7 ns). |
Relevant papers
- Uchino, T. & Yamada, T.,
White Light Emission from Transparent SiO2 Glass Prepared from Nanometer-Sized Silica Particles
Appl. Phys. Lett. 85, 1164 (2004). - Uchino, T., Aboshi, A., Kohara, S., Ohishi, Y., Sakashita, M. & Aoki, K.
Microscopic Structure of Nanometer-Sized Silica Particles
Phys. Rev. B 69, 155409 (2004) - Uchino, T., Sakoh, A., Azuma, M., Kohara, S., Takahashi, M., Takano, M. & Yoko, T.
Anelastic Compression of Nanometer-Sized Silica Particles under High Pressure: A High Energy X-ray Diffraction Measurement
Phys. Rev. B 67, 092202 (2003).
