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n
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y
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.
Figure 2.2
Absorption and emission spectra of various sizes of InP QDs, showing
a mixture of band edge emission and deep trap emission. Reprinted
with permission from A. A. Guzelian, J. E. B. Katari, A. V. Kadavanich,
U. Banin, K. Hamad, E. Juban, R. H. Wolters, C. C. Arnold and J. R.
Heath,
J. Phys. Chem.
, 1996, 100, 7212. Copyright 1996 American
Chemical Society.
trap emission at lower energies (Figure 2.2), with the smallest particles (2.8
nm in diameter) having the highest quantum yield of up to 0.12%. The oxide
layer on InP particles has also been shown to limit size-selective precipita-
tion.
34
The oxidation of InP is signi
cant as the oxidation has been shown to
extend beyond the surface; the storage of InP in ambient condition for a few
days reportedly resulted in the total oxidation to In
2
O
3
, and this also occurred
in high-quality commercially available InP/ZnS samples, giving evidence of
the formation of both In
2
O
3
and ZnO.
35
2.2.1
Increasing the Emission Quantum Yield of III
V
-
Materials
The low quantum yield for TOPO-capped InP QDs was the major limiting
factor in the use of these materials, and this was attributed to phosphorus
vacancies on the particle surface
36
(although several excellent
routes
to highly luminescent core/shell structures, such as InP/ZnS are described in
'
one-pot
'
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