Chemistry Reference
In-Depth Information
passivated with the inorganic shell; this was suggested to be due to the
etchant blocking the surface and hindering e
ective growth.
The prototypical shelling material (ZnS) has also been grown on InP dots,
giving materials with signi
rst report of
the preparation of InP/ZnS, Et
2
Zn and S(SiMe
3
)
2
were added to a TOP solu-
tion of InP cores (in equimolar amounts to In and P), then injected into hot
TOP at 200
C, followed by quickly raising the temperature to 260
Cto
induce precursor decomposition. The reaction was then cooled to 100
C for
1 hour, then allowed to cool to room temperature, whereupon the reagents
were diluted with toluene,
cantly improved emission.
145
In the
d
n
1
y
4
n
g
|
3
standing under nitrogen for
several days, slowly allowing up to 2 monolayers of ZnS to grow. The particles
could then be isolated by the usual solvent/non-solvent interactions,
although rapid agglomeration was observed. The absorption spectra of the
core/shell particles lost some de
ltered, and le
very little,
possibly due to the thin shell. The emission quantum yield improves from
negligible emission up to a maximum of 23% a
nition although appeared to shi
er 3 weeks. Electron
microscopy suggested that the shell formation was not complete and that the
increase in emission might be improved upon by better shelling techniques,
although XPS con
rmed the core/shell structure.
146
Langof
et al.
reported
a similar route, where Et
2
Zn and S(SiMe
3
)
2
were added to TOPO-capped
InP in pyridine at 100
C, with the shell growth complete a
er the addition
of the precursors.
147
The
nal InP/ZnS QDs were notably anisotropic, espe-
cially apparent with the larger particles. Interestingly, the particles still
exhibited band edge emission along with band edge recombination at low
temperatures.
The obvious problem with this method of preparing core/shell particles is
the use of dangerous precursor and the prolonged length of time required to
obtain luminescent materials. Xie
et al.
, who reported a simple method for
producing high-quality InP QDs using OA as a capping agent, also reported
a simple shelling method to prepare InP/ZnS, using ODE solutions of sulfur
and Zn(CO
2
(CH
2
)
16
CH
3
)
2
using thermal cycling.
148
In this method, the
precursors were added separately, 10 minutes apart at relatively low
temperatures, followed by periods of heating at high (220
C) temperatures.
This was repeated to build up the shell with di
.
ering amounts of precursor.
Using this method with the high-quality core particles, strong emission (up
to 40% quantum yield) could be achieved, ranging from the blue end of the
visible spectrum to the near infrared. The use of simple precursors was also
explored by Bharali
et al.
in a synthetic procedure that resulted in lumines-
cent InP/ZnS QDs in 6
8 hours.
149
The core particles of InP were prepared
using standard precursors and capped with myristate groups, and although
they were not isolated from the growth solution prior to shell growth, they
were cooled to room temperature and centrifuged to remove waste side
products. The supernatant was then added to a reaction vessel which con-
tained the correct amount of Zn(CO
2
CH
3
)
2
and sulfur to produce a 0.7 nm
shell of ZnS. A
-
er the addition of a solvent (ODE) and degassing at 80
C, the
reaction was then heated to 140
C for 1.5 hours, a
er which the product was
Search WWH ::
Custom Search