Chemistry Reference
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reported.
85
The better optical properties were attributed to the use of the
metal alkyl precursors.
In most cases, particles of ZnE (E
Se, S) appeared air sensitive and the
photoluminescence quenched upon oxidation. The use of olive oil, described
earlier as a suitable solvent for the preparation of passivated CdSe particles,
has been applied to the synthesis of ZnSe particles.
115
Here, selenium was
dissolved in hot olive oil (200
C), cooled to room temperature, then injected
into a solution of ZnO in olive oil at 330
C followed by growth and isolation
by quenching in cold acetone. Notably, this reaction was not conducted
under an inert atmosphere. Band edge emission was observed at
ca.
400 nm
with a clear excitonic peak observed in the electronic spectra. The particles
appeared monodispersed, and could be prepared in a
¼
d
n
1
y
4
n
g
|
1
ower-like morphology
by varying the reaction conditions. For such a simple reaction, the resulting
particles were of a notably high quality, and represent a signi
cant method of
preparing ZnSe, which requires relatively high synthesis temperatures when
compared to other QDs. In this case, the olive oil presents a solvent system
that remains in the liquid state for the entire range of temperatures, unlike
the earlier work, which required the use of tetracosane.
109
Zinc telluride (ZnTe) has also been prepared, by a precursor reduction
method,
116
where either Zn(CO
2
CH
3
)
2
or ZnCl
2
was dissolved in benzyl ether
with either oleic acid or OAm followed by the addition at relatively low
temperatures (250
C) of TOPTe and, if the oleic acid is employed, a reducing
agent such as superhydride. The use of the reducing agent was needed as the
use of TOPTe alone was an insu
d
n
4
.
cient source of Te
2
-type intermediate. If
the amine was used, the additional reducing agent was not required, as the
amine was itself a weak reducing agent. The di
erence in reducing agents
resulted in di
ering availabilities of tellurium monomer, and hence resulted
in di
ering particle morphologies. The use of the acid resulted in quasi-
spherical 5 nm particles, while the use of the amine resulted in tetrahedrons
15
-
18 nm in diameter, or rods, depending on reaction conditions.
1.5 HgE (E
S, Se, Te)
Mercury chalcogenides nanomaterials are of interest because of their
unusual electronic structure
117
and the associated emission in the near
infrared region of the spectrum, an area of immense interest.
118
Mercury
sul
¼
de (HgS) is a semiconducting material existing in two polymorphs; the
stable
-HgS (zinc blende, meta-
cinnabar). Estimations of the band gap vary between
a
-HgS (trigonal, cinnabar) and metastable
b
0.1 eV and 0.05 eV,
making the material either a semimetal or a narrow-gap semiconductor.
119,120
Mercury selenide (HgSe) favours the zinc blende structure and has a bandgap
with similarly undetermined values, of between 420 meV and
274
meV.
121,122
Mercury telluride (HgTe) has a reported negative bandgap of
0.32
eV
123
and favours a cubic crystalline form. Strong size quantisation e
ects
are expected in these materials due to the large excitonic radius (
e.g.
,
a
B
for
HgTe
¼
40 nm). Again, di
ering values for the bandgap of HgTe can be found
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