Biomedical Engineering Reference
In-Depth Information
3.13
Emission spectra of ZnO/m-PMMA nanocomposites, influenced
by particle size. The spectra show excitation in first order at 325 nm and
at 650 nm in second order. The spectra are stacked and normalized.
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nanoparticles. With respect to nanoparticles, quantum dots based on
sulphides, selenides or tellurides of zinc and cadmium show the best
luminescence efficiency but these materials are toxic and carcinogenic and
show limited thermodynamic stability against oxidation.
Luminescence of oxide nanoparticles is also subjected to rapid aging
caused by the formation of hydroxides at the surface of oxide nanoparticles,
which leads to quenching luminescence. This problem can be reduced by
coating the surface of the oxide nanoparticles with a polymer to protect it
against ambient air or even water. Vollath and Szabo´ demonstrated that
oxide nanoparticles show luminescence provided they are coated with a
polymer or ceramic.
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They synthesized such nanocomposites using the
Karlsruhe microwave plasma process and showed that interaction between
the ceramic core and the organic coating also leads to luminescence. They
found that the carbonyl group attached to the oxide core exhibits strong
luminescence and this depends strongly on particle size: with a decrease in
particle size the luminescence showed a blue shift and narrowing of emission
lines, which predicts a direct correlation between the molecular orbital and
energy bands of the ceramic particle. Figure 3.13 shows the luminescence
spectra of ZnO/m-PMMA nanocomposites with varying size of zinc oxide
nanoparticles. The figure shows a broad emission spectra consisting of two
broad overlapping lines. The splitting is a consequence of the interaction
between ZnO nanoparticles and their surroundings.
A blue shift was observed for both the overlapping luminescence peaks of
the ZnO/m-PMMA nanocomposites with a decrease in nanoparticle size.
