Biomedical Engineering Reference
In-Depth Information
Table 3.3 Influence of particle size on the wavelength and intensity of the
emission spectrum of ZnO/m-PMMA nanocomposites
Particle size (nm)
Position of first
maximum (nm)
Position of second
maximum (nm)
Intensity ratio of
second to first
maximum
4
495
519
0.89
5
497
530
1.00
6
498
535
1.06
The intensity ratio of peak 2 over peak 1 (I
2
/I
1
) increases with increasing
particle size (Table 3.3):
32
I
2
I
1
¼
kd
2
A
þ
½
3
:
5
where I
1
and I
2
are the intensities of peak 1 and peak 2 respectively and
A=1.120±2
10
3
nm
2
are the values taken
from the experimental fit (Fig. 3.14(b)). The position of the first and the
second intensity maximum as a function of the particle size together with the
intensity ratio of these two peaks is given in Table 3.3. A strong blue shift
with decreasing particle size of the second and a less pronounced one of the
first maximum was observed. Additionally, the intensity ratio of the second
over the first peak increases with increasing particle size.
The observation discussed above can be described by the relation of the
luminescence to the ceramic core and coating. The ceramic core absorbs the
existing UV-quanta and the excitation is transferred from the ceramic core
to the coating, where the emission occurs. The wavelength and intensity of
luminescence of oxide nanocomposites can be tailored by changing the
nanoparticle size as the luminescence of these oxide nanocomposites
depends on the surface. In the case of semiconducting oxides such as
ZnO, a mixture of the quantum confinement mechanism with the surface
interaction mechanism is observed. These composites can be used in
nanophotonic waveguides for the transport of electromagnetic energy using
the Fo¨ rster mechanism.
The low-temperature luminescence of Cr
3+
ions in a silicate glass system
and in nanocrystalline glass-ceramic composites with embedded
10
4
and k=
6
4.9±5
6
-Ga
2
O
3
nanocrystals has been studied.
33
The precursor glass showed a wide range of
crystal fields. Due to octahedrally coordinated Cr
3+
ions located in a weak
crystal field, the spectrum of the precursor glass was dominated by a
broadband
4
T
2
-
4
A
2
transition. The spectra of the glass-ceramic nanocom-
posites showed a crystal-like
2
E-
4
A
2
emission and demonstrated that Cr
3+
ions are located within the crystalline environment. It was observed
33
that
the host glass matrix nucleated with gallium oxide nanocrystals (i.e. glass-
β
