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