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bismuth or indium seed particles in an SLS-type reaction with TOP as
a capping agent. A very similar reaction was reported, where PCl
3
and
LiBH(C
2
H
5
)
3
were added sequentially to a solution of indium stearate at
40
C, followed by heating at 250
C for InP particle growth.
55
The resulting
particles were approximately 3 nm in diameter and zinc blende in structure.
The absorption spectra showed a clear excitonic feature, indicating the
narrow size distribution, although the excitonic peaks were not as sharp as
particles grown in non-coordinating solvents, which was attributed to the
reaction being a slow and continued nucleation process. The emission
spectra consisted of weak band edge emission and lower energy deep trap
emission. A
d
n
1
y
4
n
g
|
3
er etching with HF, the deep trap emission was removed and the
band edge quantum yield was increased from 0.25% to
ca.
20%.
The lack of other obvious precursors has limited the amount of novel
chemistry reported; however, other safer, more readily available suitable
inorganic starting materials have been explored. It is worth noting that
a common capping agent, TOP, has been used as a phosphorus precursor for
InP by catalytic cleavage of the P
C bond, although the mixed product
included indium metal and the particles were large in size with no detailed
optical characteristics reported.
56
Interestingly, TOP has been used to
prepare In/InP nanoneedles in a one-pot reaction, by initially forming
indium nanodroplets that catalysed the decomposition of TOP.
57
The use of Na
3
P as a phosphorus precursor has also been reported with
4-ethylpyridine and TOP as solvents, and InCl
3
as the indium precursor.
58
The resulting material was reportedly 5 nm in diameter and zinc blende in
structure, exhibiting a clear excitonic peak in the absorption spectrum at
approximately 580 nm, although no description of the emissive properties
was provided. Possibly the most successful alternative for silylated phos-
phines is tris(dimethylamino)phosphine, P(NMe
2
)
3
, which has been utilised
as a precursor in the synthesis of TOPO-capped InP at 365
C, using InCl
3
as
a starting material.
59
The resulting materials, approximately 6 nm in
diameter with a large standard deviation of 50%, exhibited a zinc blende
core, with optical properties consistent with quantum con
-
.
nement but
without any excitonic feature in the absorption spectra and with broad
emission. The use of P(NMe
2
)
3
has been extended to the synthesis of InP,
2
4 nm in diameter, in an autoclave, using InCl
3
and DDA (as a capping
agent), and toluene as a solvent.
60
The reaction proceeded at 180
C for 24
hours before the sample was isolated by size-selective precipitation and
etched with HF as described above, giving particles with emission quantum
yields of up to 58%, before the addition of a wide-bandgap shell. Notably,
trap emission was observed a
-
er size-selective precipitation, which was
attributed to the formation of a surface oxide. This explanation is in
contrast with earlier reports, described above, which suggested the oxide
layer was actually essential to forming an emissive species. In this case, the
ZnS shell was, unusually, added a
er the phase transfer step, in water. This
was improved by adding the shell in a second autoclave step.
61
In an
interesting amendment to the synthesis of anisotropic InP, Dorn
et al.
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