Biomedical Engineering Reference
In-Depth Information
3.6
Optical properties of glass-carbon nanotube (CNT)
composites
Fluorescence of single-walled carbon nanotube (SWCNT) bundles has
become an emerging field due to its wide range of application, especially in
fiber optics. We report for the first time
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SWCNT borosilicate glass
composite having strong NIR fluorescence near 0.84-2.03
μ
m with 325 nm
laser excitations. The emission spectrum was 1185 nm wide and contained
three main transmission windows for fiber optic telecommunications, which
strongly indicates the strong potential of this material in broadband fiber
optic telecommunications and fabrication of NIR tunable lasers.
As noted above, the total spectral width of the emission of the composite
was found to be 1185 nm. While analyzing the emission spectra for both
glass and the composite, it was observed that the fluorescence peaks at 844,
1193, 1562 and 2029 nm were generated due to structural defects of SiO
2
.
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Other emission peaks can be considered to be the bandgap fluorescence of
CNT bundles. Fluorescence bands were seen at 1420, 1502, 1635, 1694,
1768, and 1865 nm, together with three shoulders at 954, 1267 and 1318 nm,
although such emissions remain elusive in the base glass spectra (Fig. 3.20).
The high intensities of the bands show that the SWCNT bundles are made
from semiconducting tubes. However, the presence of metallic tubes in a
bundle will rapidly quench the emission. Two extremely strong wide
emission bands were observed around 1121-1350 nm and 1500-1600 nm,
centered at 1267, 1318 and 1562 nm. This is of considerable significance in
fiber optic telecommunications in terms of lowest dispersion and best
transmission. Broadened spectra having a high intensity at 1318 nm and
1562 nm are very important for the ability to carry large amounts of
information at a slightly different wavelength in wavelength division
multiplexing systems. Strong emission from the composite at 954 nm in
the range of 800-1030 nm is also useful for short-range communication
devices like remote controls for audio and video systems.
Researchers have shown that SWCNT fluorescence can be used as a laser
source for optical amplification.
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The total emission of 1185 nm width is
well within the tunable range of conventional NIR lasers like Ti:Saphire
(460 nm) and InGaAs (161 nm). Full width at half maximum data of the
composite, together with the area under the emission curve (
)ofthe
emission bands are shown in Table 3.5. The data show that the composite is
a material with great potential for the fabrication of tunable NIR lasers,
which will be useful as an NIR emitter for fiber optic telecommunications
(800-1600 nm), in light detection and ranging (Lidar) and infrared
countermeasure (IRCM) applications (1800-2100 nm). The fluorescence
from semiconducting SWCNT bundles can be explained by two important
photophysical phenomena - intertube carrier migration
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and the excitonic
σ
