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cooled to room temperature, the volatiles removed
in vacuo
, and the particles
isolated by centrifugation. The core/shell particles had an inorganic diameter
of between 4.9 and 12.6 nm, up notably from the naked particles which had
diameters between 4.0 and 5.7 nm. The absorption spectra of both naked InP
particles and the InP/ZnS particles were very similar with an extremely small
shi
. The emission of the core particles was weak and predominantly trap
based, while the core/shell particles exhibited band edge emission with
quantum yields of 15%. The particles could be simply phase-transferred
using mercaptoacetic acid, and then conjugated to folic acid. These particles
were then used in the imaging of folate-positive receptor cells, and can be
considered one of the
d
n
1
y
4
n
g
|
3
-
V QDs in bioimaging.
Further work by the same group used sulfur dissolved in OAm and
Zn(CO
2
(C
2
H
5
)CH(CH
2
)
3
CH
3
)
2
in ODE as shell precursors, which were added
dropwise at 210
C to the core particles and the temperature maintained for
45 minutes, followed by direct dissolution of the product in toluene.
150
A
similar method to prepare InP/ZnS has been reported by Narayanaswamy
et al.
151,152
who explored the high temperature decrease in emission and
spectral broadening and the link to coupling the emissive state with acoustic
phonons.
An e
rst reports of the use of III
ective and elegant method of overcoming the prolonged and time-
consuming synthesis is the one-pot reaction to InP/ZnS described by Xu
et al.
153
In this reaction, InP are prepared using ODE and methyl myristate,
CH
3
(CH
2
)
12
COOCH
3
, as solvents with the usual precursors. The obvious
di
erence is the inclusion in the reaction of zinc undecylenate,
Zn(CO
2
(CH
2
)
8
CHCH
2
)
2
, which replaced surface indium ions and blocked
dangling bonds on the resulting InP particles, massively increasing the
quantum yields from under 5% to up to 30%. Once the InP nanoparticles had
been formed, which required just 20 minutes, the reaction
.
ask was cooled
to room temperature, whereupon a single-source precursor, Zn(S
2
CNEt
2
)
2
,
was added and reheated to 240
C for a further 20 minutes. Shell growth
could be also be obtained using further Zn(CO
2
(CH
2
)
8
CHCH
2
)
2
and
C
6
H
11
NCS as precursors. By tuning the reaction conditions, tuneable emis-
sion between 480 and 750 nm with quantum yields of up to 60% could be
achieved. These materials have also been capped with SiO
2
shells and used as
converter materials in down-conversion white-emitting LEDs.
154
A similar approach has been described by Li and Reiss, in which all
precursors (In(CO
2
(CH
2
)
12
CH
3
)
2
, Zn(CO
2
(CH
2
)
16
CH
3
)
2
, P(SiMe
3
)
3
, and
CH
3
(CH
2
)
11
SH) were mixed in ODE and rapidly heated to 300
C under argon,
leading to the
in situ
formation of what was initially suggested to be InP/ZnS
particles, due to the di
erence in precursor reactivity.
155
Particle growth
started with InP core formation followed by shell growth as the thiol
precursors decomposed at 230
C, although indium incorporation into the
particles reportedly continued even during the shell growth step. The optical
properties red-shi
ed from a band edge of 450 nm, with clear excitonic
features clearly observed a
er 3 minutes, which broadened over the duration
of the reaction, with narrow emission shi
ing from
ca.
500
-
600 nm.
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