Photoluminescence from Carbon/Silica Gel Nanocomposite
Photoluminescence is observed from carbon/silica gel nanocomposite in which nanometer sized carbon particles are dispersed in a silica gel matrix. Precursors of graphite were mixed with the silica gel by the sol—gel method and the nanocomposites were formed at the temperatures from 500 to 1100°C. Porous silica gels are excellent matrices to make composites of silica with carbon materials.
Photoluminescence was observed from the carbon/silica gel nanocomposites using excitation wavelengths from 250 to 520nm and the spectra exhibit two regions of maxima centered at 390 and 490nm. The luminescence centered at 390nm is the blue luminescence and the luminescence centered at 490nm is the green luminescence. As the calcination temperature increased from 500 to 1100°C, the peak intensity of the blue luminescence increased relative to that of the green luminescence. At the same time, a number of sharp peaks became apparent in the green luminescence.
The excitation spectrum for blue luminescence exhibited a different spectrum from that of green luminescence. The carbon in the nanocomposites is probably the main origin of the green luminescence because the green luminescence was not observed from the samples which were heat treated at temperatures above 1100°C. Carbon was removed after heat treated of the silica gel matrix at temperatures above 1100°C. There were at least four peaks in the green luminescence and these peaks could be excited stepwise by varying the excitation wavelength. However, the silica gel matrix has considerable influence on the blue luminescence, because the blue luminescence could be observed from the samples which did not include carbon, and a similar blue luminescence was observed from pure silica glass. The lifetime of the blue luminescence became longer gradually as the calcination temperature increased from 500 to 900°C, however, the lifetime near 490 nm remained almost constant in the temperature range between 500 and 800°C.
KeywordsExcitation Spectrum Calcination Temperature Photoluminescence Spectrum Silica Glass Scanning Near Field Optical Microscope
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