Biomedical Engineering Reference
In-Depth Information
3.15
Luminescence spectra of composite 1 (a) and of composite 2 (b)
measured between 10 and 170 K. With temperature rise, the structured
R-lines' emissions overlap with the associated Stokes phonon
sidebands, which become increasingly noticeable. 33
ceramic nanocomposites) indicated the prevailing contribution of the
crystal-like 2 E- 4 A 2 emissions (R-lines) of Cr 3+ ions in a strong crystal
field. The low-temperature studies demonstrated that below 70 K, the
luminescence of Cr 3+ ions could be demonstrated by sharp R-lines of the
2 E- 4 A 2 transition and above 70K the Cr 3+ luminescence can be
transformed to a combination of R-lines and their sidebands as well as a
small contribution of the 4 T 2 - 2 A transition (Fig. 3.15). The conclusion for
the formation of Ga 2 O 3 :Cr 3+ nanocrystallites and the relocation of Cr 3+
ions from the host glass to the nanocrystalline phase comes from the overall
modification of the luminescence profiles from the broad 4 T 2 - 4 A 2 emission
for the as-quenched glass to the narrow R-lines for the glass-ceramic
composites. The presented results help in the formulation of a simple
distribution model in which most of the Cr 3+ ions are located within the
nanocrystalline phase. The developed nanocrystalline glass-ceramics are a
promising new class of Cr 3+ doped oxide glass-based optically active
composite materials.
Soraru` et al. 34 prepared erbium-activated SiC/SiO 2 nanocomposites
doped with Er 3+ . The concentrations of Er 3+ were varied from 1 to
4 mol% and samples were prepared by pyrolysis of sol-gel derived
precursors. The gels were obtained from modified silicon alkoxides
containing Si-CH 3 and Si-H groups. Crack-free, monolithic and transpar-
ent SiCO glass discs were obtained after pyrolysis at temperatures in the
range 800-1300
￿ ￿ ￿ ￿ ￿ ￿
C. Emission in the C-telecommunication band was
observed at room temperature for all the samples upon continuous-wave
excitation at 980 nm. A spectral bandwidth of 48 nm, large enough for
wavelength division multiplexing (WDM) application, was observed for all
the samples. The shape of the 4 I 13/2 - 4 I 15/2 luminescence band appears to be
8
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