Chemistry Reference
In-Depth Information
signi
VI nanomaterials. The
introduction of dialkylphosphines to improve reactions yield unfortunately
also has an adverse e
cantly lower than the synthesis yields of II
-
ect on emission quantum yield and particle size
control due to the fast reaction rate. The use of an alternative reducing agent,
1,2-hexadecanediol, introduced into the reaction with the ODE during
chalcogen injection, resulted in an increase in reaction yield while main-
taining the high-emission quantum yields, due to the controlled growth
rate.
52
The use of a non-coordinating solvent such as ODE has also been
employed in the synthesis of PbSe by Yu
et al.
53
In these reactions, PbO was
complexed with oleic acid in ODE at 150
C, followed by further heating to
180
C. This was followed by injection of TOPSe and growth at 150
C.
Seconds a
d
n
1
y
4
n
g
|
7
er injection, small (3.5 nm diameter) particles could be isolated in
low yields, although a
er 13 minutes large (9 nm) particle could be isolated
in almost 100% yields. The particle exhibited a narrow size distribution
(5
7% standard deviation on materials <10 nm, above which the standard
deviation increased to 10
-
15%) without the need for size-selective precipi-
tation. The particles were crystalline (rock salt) and spherical in shape; in
contrast to other reports, the larger particles (13 nm) still maintained their
spherical morphology. The particles displayed evidence of size-focusing
growth as determined by the half width at half maximum (HWHM) of the
emission pro
-
le, which had a maximum quantum yield of 89%. The particles
displayed band edge emission, with
rst absorption peaks between 1100 nm
and 2520 nm. Similarly, PbSe has been made in ODE using Se(SiMe
3
)
2
as
a precursor under comparable experimental conditions.
34
An interesting method of preparing PbSe has been reported by cation
exchange.
54
In this example, a lead precursor (PbCl
2
) is injected into the
reaction solution containing precursors for SnSe particle formation. As the
tin precursor is extremely reactive, SnSe formation occurs rapidly, which then
exchanged to provide PbSe particles in less than 1 second, allowing full
growth in 5 minutes. The growth can be tuned by varying the injection and
growth temperatures, and by multiple injections of precursor for particles
above 7.5 nm diameter, resulting in QDs with emission from
ca.
1250 nm to
3000 nm.
Although PbSe was the
.
rst lead chalcogenide to be investigated in depth,
other materials have also been reported. Lead sul
de, PbS, with a cubic
crystalline core has also been synthesised from an amendment of the Murray
route to CdS.
55
In this case, PbO was heated to 150
C with oleic acid for
1 hour, under vacuum or an inert gas, until the oleate complex was formed.
To this was added rapidly
via
injection a solution of S(SiMe
3
)
2
in either TOP
or ODE with a Pb : S ratio of 2 : 1. The
ask was then removed from the heat,
and either allowed to cool or returned to the heating source (80
140
C) a
er
nucleation to allow slow particle growth. The particles exhibited absorption
edges between 1200 and 1400 nm, although much smaller particles could be
obtained by drastically reducing the oleic acid concentration, giving particles
with an excitonic feature at
ca.
800 nm. Emission was band edge, with
-
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