Size- and shape-controlled synthesis of ZnSe nanocrystals using SeO 2 as selenium precursor

Article abstract of DOI:10.1039/c0dt00709a

Here we report a low-cost and "green" phosphine-free route for the size- and shape-controlled synthesis of high-quality zinc blende (cubic) ZnSe nanocrystals. To avoid the use of expensive and toxic solvents such as trioctylphosphine (TOP) or tributylphosphine (TBP), SeO₂ was dispersed in 1-octadecene (ODE) as a chalcogen precursor. It has been found that the temperature and the surface ligand influenced the nucleation, the reaction speed and the formation of different shapes. Absorption spectroscopy, fluorescence spectroscopy, powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for the characterization of the as-synthesized ZnSe nanocrystals. The size-dependent photoluminescence (PL) range of the as-prepared ZnSe nanocrystals was between 390 and 450 nm, with the PL full width at half-maximum (FWHM) well controlled between 14 and 18 nm and PL quantum yields reached up to 40% at room temperature. Moreover, this new selenium precursor can be used to form tetrapod-shaped ZnSe nanocrystals when zinc acetylacetonate was introduced as the zinc precursor with a one-pot method.

Full text of DOI:10.1039/c0dt00709a

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
Size- and shape-controlled synthesis of ZnSe nanocrystals using SeO as
2
selenium precursor†
Huaibin Shen,a,b Jin Zhong Niu,‡ Hongzhe Wang, Xiaomin Li, Lin Song Li* and Xia Chen*
a
a
a
a
b
Received 22nd June 2010, Accepted 14th September 2010
DOI: 10.1039/c0dt00709a
Here we report a low-cost and “green” phosphine-free route for the size- and shape-controlled synthesis
of high-quality zinc blende (cubic) ZnSe nanocrystals. To avoid the use of expensive and toxic solvents
such as trioctylphosphine (TOP) or tributylphosphine (TBP), SeO
2
was dispersed in 1-octadecene
(
ODE) as a chalcogen precursor. It has been found that the temperature and the surface ligand
influenced the nucleation, the reaction speed and the formation of different shapes. Absorption
spectroscopy, fluorescence spectroscopy, powder X-ray diffraction (XRD) and transmission electron
microscopy (TEM) were used for the characterization of the as-synthesized ZnSe nanocrystals. The
size-dependent photoluminescence (PL) range of the as-prepared ZnSe nanocrystals was between 390
and 450 nm, with the PL full width at half-maximum (FWHM) well controlled between 14 and 18 nm
and PL quantum yields reached up to 40% at room temperature. Moreover, this new selenium precursor
can be used to form tetrapod-shaped ZnSe nanocrystals when zinc acetylacetonate was introduced as
the zinc precursor with a one-pot method.
1
3
1
. Introduction
the Se source. Because of the high chemical stability of SeO , it
2
can be directly dissolved in 1-octadecene without protection from
air and the synthesis cost of nanocrystals was reduced. However,
the application of CdSe nanocrystals was limited by the inherent
toxicity of Cd.
Photoluminescent semiconductor nanocrystals have attracted
much attention because of their unique characteristics, such as
size-dependent optoelectronic properties and flexible processing
chemistry. The potential applications of these nanocrystals
include biological fluorescent labels, light emitting diodes, lasers,
and solar cells. Much effort has been devoted to investigate the
synthesis and properties of various semiconductor nanocrystals,
such as CdSe, PbSe, CuInSe , CdTe, and HgTe nanocrystals,
1–5
Here, we use SeO as the Se source to synthesize ZnSe nanocrys-
2
tals. ZnSe (bulk band gap of 2.7 eV) is an environmentally friendly
wide band gap semiconductor. Due to quantum confinement, its
nanocrystals are interesting emitting materials in the ultra violet
to blue range. Some groups have reported the synthesis of high
quality ZnSe and related Cu-, Mn-doped ZnSe nanocrystals with
an emitting window from 400 to 610 nm.
that the ZnSe nanocrystals fulfill the aim to solve the above
limits (1) and (2). ZnSe based nanocrystals with or without a
dopant would potentially be an ideal substitute for cadmium
based nanocrystals due to the ultimate elimination of the use
of toxic components. So far, classical preparation methods of
ZnSe nanocrystals require air-free manipulations using a glove box
because of the use of the following air-sensitive compounds as se-
lenium precursors: bis(trimethylsilyl)selenium, organophosphine
selenide, and selenium powder.
used as the reagents to activate the zinc precursors in order to get
high quality ZnSe nanocrystals. To overcome limit (3) mentioned
above, toxic phosphine ligands should be avoided because they
would increase the control cost for the chemical pollution. If
the production cost of nanocrystals could be greatly decreased
through deploying cheap raw materials with lower toxicity, large-
scale preparation and practical applications of nanocrystals will
be accessible.
In this paper, we report not only ZnSe nanocrystals with high
quantum yields (QYs), but also with size and shape controlled
synthesis by using SeO as the selenium precursor. Different
1–11
2
these were the most investigated materials with photoluminescence
windows from visible to near-IR and many successful synthetic
routes have been established.
17–30
These features mean
1
2–16
Currently, research on the controlled synthesis of semiconduc-
tor nanocrystals is not only aimed at high quality, but also attempts
the use of facile, “green”, low-cost, and environmentally friendly
precursors and solvents. This is because there are some shortages
that limit the application of current nanocrystals: (1) containing
heavy metal ions (such as Cd, Hg, and Pb), which are essentially
toxic, (2) containing rare metals (such as In), of which there will
be a shortage, (3) using pyrophoric, toxic, and expensive reagents,
which are not appropriate for industrial synthesis or application
in the future. To overcome these limits, non-toxic and inexpensive
nanocrystals are needed for real applications in the near future.
Recently, a new route to synthesize high quality CdSe nanocrystals
26–29
Also, aliphatic amines must be
27
was established by Chen et al. through the introduction of SeO as
2
a
Key Laboratory for Special Functional Materials, Henan University,
Kaifeng 475004, P. R. China. E-mail: bbbbz@163.com, lsli@henu.edu.cn;
Fax: +86-378-3881358; Tel: +86-378-3881358
b
College of Life Science, Jilin University, Changchun 130021, P. R. China
†
Electronic supplementary information (ESI) available: Additional data.
See DOI: 10.1039/c0dt00709a
Current address for Jin Zhong Niu: Department of Mathematical and
2
reaction temperatures and surface ligands were tested to optimize
the synthesis conditions and octadecylphosphonic acid (ODPA)
was used for the first time to synthesize ZnSe nanocrystals. It has
‡
Physical Sciences, Henan Institute of Engineering, Zhengzhou, 451191,
P. R. China, E-mail: bellniu@yahoo.com.cn.
1
1432 | Dalton Trans., 2010, 39, 11432–11438
This journal is © The Royal Society of Chemistry 2010

View Article Online
been found that the reaction temperature influenced the nucleation
and different ligands and ligand concentrations influenced the
reaction speed. In this method, the environmental effects of the
chemicals have been seriously considered and all of the above three
limits are solved. The PL spectra can be adjusted from 390 nm to
2.2.3 Stock solution for Se precursor
This was made by degassing a mixture of SeO
2
(0.2218 g, 2 mmol)
and 20 mL of ODE in a 50 mL three-neck flask, which was then
◦
heated to 240 C for 10 min in air.
4
50 nm and the full width at half-maximum (FWHM) are in the
range of 14–18 nm. The narrow FWHM and transmission electron
microscopy (TEM) images demonstrated the near monodispersity
of the ZnSe nanocrystals. The photoluminescence QYs of the
as-prepared ZnSe nanocrystals were from 20% to 50%. These
indicated the quality of the as-prepared ZnSe nanocrystals reached
the same high level as that obtained with the methods using
phosphine selenium precursors. Moreover, tetrapod-shaped ZnSe
were synthesized when zinc acetylacetonate was introduced as the
zinc precursor with a non-injection synthesis approach. Cheap
paraffin was used as the reaction solvent, without any toxic organic
phosphines or aliphatic amines being introduced. This made the
synthesis of the ZnSe nanocrystals much cheaper and greener and
the large-scale production of ZnSe nanocrystals therefore becomes
possible.
2
.3. Synthesis of ZnSe nanocrystals
Using OA as ligand. 2 mL (0.2 mmol) of the Se precursor
◦
and 4 g (5 mL) of paraffin oil was heated to 300 C under a
nitrogen gas flow in a 25 mL flask. Then, 2 mL (0.2 mmol) of Zn
precursor I solution was injected and the temperature was lowered
◦
to 280 C for the nanocrystal growth. Aliquots were taken at
different time intervals and UV-vis and PL spectra were recorded
for each aliquot. The nanocrystals were precipitated twice by
adding the solution to acetone, separated through spinning down
at 6000 rpm for 10 min and then dried under vacuum. The ZnSe
nanocrystals were obtained finally.
Using ODPA as ligand. The only difference between this
synthesis and the one described above was that 2 mL (0.2 mmol)
of Zn Precursor II solution was used in place of Zn precursor I.
2
. Experimental
2.1. Chemicals
2
.4. Synthesis of tetrapod-shaped ZnSe nanocrystals
All reagents were used as received without further experimental
purification. Zinc oxide (ZnO, 99.99% powder), 1-octadecene
Zn(acac) (0.1582 g, 0.6 mmol), 0.6 mL of OA and 3 mL (0.3
2
mmol) of Se precursor were combined in 4 g (5 mL) of paraffin
(
ODE, 90%), octadecylphosphonic acid (ODPA) (98%), and
oleic acid (OA, 90%) were purchased from Aldrich. Selenium
dioxide (SeO , 99.9%), 2, 4-pentanedione (98%), triethylamine
99%), hexanes (analytical grade), methanol (analytical grade),
◦
-1
oil and heated to 280 C at a rate of 20 K min under a nitrogen
flow. Then tetrapod-shaped ZnSe nanocrystals were synthesized.
2
(
ethanol (analytical grade), zinc chlorides (analytical reagent),
and paraffin oil (analytical grade) were obtained from Beijing
Chemical Reagent Ltd., China.
2.5. Characterization
UV-vis absorption and PL spectra were recorded using an Ocean
Optics spectrophotometer (mode PC2000-ISA). PL spectra were
taken using an excitation wavelength of 365 nm. All of the
quantum yields (QYs) data of the nanocrystals (NCs) and dyes
were collected through SPEX F212. PL QYs of nanocrystals
were measured relative to LD 423 (QY = 68% in ethanol).
2
2
.2. Preparation of precursors
.2.1 Synthesis of zinc acetylacetonate [Zn(acac) ]
2
The NC PL QYs were calculated using the formula as QYNC
=
In a typical synthesis, 20 mmol of ZnCl
of deionized water. Under magnetic stirring, 2, 4-pentanedione
5 mL, 50 mmol) was added and kept stirring for 15 min. Zn(acac)
was precipitated after an appropriate amount of triethylamine was
added to the solution. Then, Zn(acac) was washed several times
2
was dissolved in 10 mL
2
2
-ODdye
-ODNC
QYdye(INC/Idye)(nNC) /(ndye) (1–10
/1–10
), where I is the
spectrally integrated emission intensity, n is the refractive index,
and OD is the optical density of the NC or the dye samples
(
2
(
indicated by a subscript). The optical density of the NC samples
2
at the excitation wavelength was within the 0.02–0.05 range.
Powder X-ray diffraction (XRD) studies of NCs were carried
out with a Philips X¢ Pert Pro X-ray diffractometer using Cu-
with ethanol and water and finally was dried under vacuum at
◦
5
0 C for further use.
˚
Ka radiation (l = 1.54 A). The specimens were prepared as
2
.2.2 Stock solutions for Zn precursor
follows: about 50 mg of the purified nanocrystals were dissolved in
about 0.5 mL of toluene and then dropped onto a low-scattering
quartz sample-holder, dried in air and kept overnight in a vacuum
dessicator. To get a better signal-to-noise ratio, the XRD data were
collected at a scan rate of 16 s with 0.2 per step. Transmission
electron microscopy (TEM) studies were performed using a JEOL-
Solution for Zn precursor I. A mixture (20 mL in total) of ZnO
(
(
0.16274 g, 2 mmol), oleic acid ( 2.256 g, 8 mmol), and paraffin oil
18.5 mL) was loaded in a 50 mL three-neck flask and heated to
◦
◦
300 C under a nitrogen flow to obtain a clear colourless solution.
1
00CXII electron microscope operating at 100 kV and JEOL
Solution for Zn precursor II. A mixture (20 mL in total) of
JEM-2010 electron microscope operating at 200 kV. The specimens
were prepared as follows: about 10 mL of a particle solution was
dropped onto a 200-mesh carbon coated copper grid and was dried
overnight at ambient conditions.
ZnO (0.16274 g, 2 mmol), ODPA (2.676 g, 8 mmol), and 17.5 mL
of paraffin oil was loaded in a 50 mL three-neck flask and heated
◦
to 300 C under nitrogen to obtain a clear colourless solution.
This journal is © The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 11432–11438 | 11433

View Article Online
3
. Results and discussion
For the synthesis of the ZnSe nanocrystals, SeO
2
was directly
◦
dissolved in ODE at 240 C. This solution is stable for months
and can be used effectively for the synthesis of nanocrystals. Cao
13
0
et al. described a mechanism where Se was produced in the Se-
containing reaction mixture upon reaction with long chain alkanes
at high temperature. Here, for the synthesis of ZnSe nanocrystals,
the possible chemical reaction involved in the formation of ZnSe
nanocrystals is shown in Scheme 1. First, ZnO reacted with OA
to form a Zn–OA solution. Second, SeO
in ODE and then the Zn complex reacted with Se to form the
ZnSe nanocrystals. However, the solubility of SeO in ODE is
2
powder was dissolved
0
2
generally low and, for the synthesis of high quality nanocrystals,
the nucleation and growth stages of the nanocrystals must be
separated by the swift injection of precursors. The volume of
the Se precursors can not be large, in order to facilitate the
injection, and the amount of the Se precursor that participates
in the reaction is limited by the small volume of the Se injection
solution. In this report, the SeO was directly dissolved in ODE
2
at an elevated temperature to act as the reaction solution. ZnO
and OA reacted in ODE to form Zn–OA complex solution,
which acted as the injection solution. This is different from the
traditional injection method, where the chalcogen precursors are
usually used as the injection solution and the solution with the Zn
precursors usually acts as the reaction solution, so our method is
termed as the “inverse injection method”. Using this approach,
the Zn–OA complex has a high solubility in paraffin oil, so the
amount of the Zn precursors injected into the reaction solution
can be very large, which, together with the large amount of SeO
2
dissolved in the large volume of the reaction solution, has led to
the successful large scale synthesis of ZnSe nanocrystals. More
than 2 g (contains the weight of surface ligands) of high quality
ZnSe nanocrystals powder was synthesized with one reaction (See
ESI for experimental details and Fig. S1†). The reaction yield of
the nanocrystals was about 69%.
Fig. 1 Temporal evolution of the absorption and PL spectra of ZnSe
nanocrystals synthesized at 300 C in the presence of OA, OA : Zn ratio is
4 : 1. The numbers mentioned on the right of each spectrum indicate the
heating time.
◦
Scheme 1 Proposed mechanism for the formation of ZnSe nanocrystals
by the reaction of ODE with SeO .
2
Optical properties of ZnSe nanocrystals
Fig. 1 shows the temporal evolution of the absorption and PL
spectra of the ZnSe nanocrystals synthesized as described above.
All of the spectra were recorded by dissolving aliquots in hexanes.
We noted that no extra size-selective precipitation was conducted.
The molar ratio of OA : Zn was 4 : 1 in paraffin oil solution, the
◦
reaction was carried out at 300 C. Under the synthesis conditions
here, ZnSe nanocrystals with PL between 405–450 nm and
narrow FWHM between 14–18 nm were obtained. The PL QYs
of these ZnSe nanocrystals range from 20% to 50% (Fig. 2). Every
absorption spectrum shows up to three feature peaks, indicating
their narrow size distributions. Indeed, TEM studies show that
these nanocrystals have a typical size distribution of approximately
Fig. 2 Quantum yield vs. peak position of ZnSe nanocrystals synthesized
using OA as the ligand (red dot) and ODPA as the ligand (green square).
±8%. With the increase of reaction time, nanocrystals grew
gradually to the maximum mean size of 8.4 nm after 1 h of
1
1434 | Dalton Trans., 2010, 39, 11432–11438
This journal is © The Royal Society of Chemistry 2010

View Article Online
heating. For more prolonged heating time, the size distribution of
the nanocrystals remained the same. The red line in Fig. 3 shows
the sizing information for the ZnSe nanocrystals synthesized
using OA as the ligand, the sizes of the ZnSe nanocrystals were
determined by TEM observation. The fitting curve was used to
determining the average size of a sample by its first absorption
peak position.
Fig. 4 Temporal evolution of the UV-vis absorption spectra of the
◦
as-prepared ZnSe nanocrystals: (a) injection at 280 C, (b) injection at
◦
3
30 C. The numbers mentioned on the right of each spectrum indicate
the heating time.
Fig. 3 Sizing curves of ZnSe nanocrystals, the sizes of the ZnSe
nanocrystals were determined by TEM; using OA as ligands (red dot)
and using ODPA as the ligands (green square). The fitting curves were
used to determine the average size of a sample by its first absorption peak
position.
The influence of the synthesis temperatures has also been
investigated. Fig. 4 reveals that a higher synthesis temperature
leads to the formation of larger sized nanocrystals, indicates by
the red shifted absorption spectra. For example, the first excitonic
◦
absorption feature of the nanocrystals synthesized at 330
C
(
Fig. 4a) is at 406 nm in 30 s, while the first excitonic absorption
◦
features of the nanocrystals synthesized at 280 C (Fig. 4b) and
3
◦
00 C (Fig. 1) are at 392 nm and 401 nm, respectively. The red-
shift of the absorption features at the higher synthesis temperatures
means the growth rate at the higher temperatures is faster. It is
obvious that the absorption peaks in Fig. 1 are sharper than those
in Fig. 4a and b and the absorption spectra in Fig. 1 have more
absorption features. That is to say, the size distribution of the
◦
nanocrystals synthesized at 300 C was better than that of the
nanocrystals synthesized at higher or lower temperatures, maybe
◦
because balanced nucleation and growth were achieved at 300 C.
Effect of ligand concentration and different ligands
The ligand concentration effect was also investigated in this paper.
◦
Fig. 5 shows that under the same temperature of 280 C and the
Fig. 5 Variation of the absorption and PL spectra as a function of time
for ZnSe nanocrystals grown with different amounts of OA at 280 C.
same reaction time, bigger ZnSe nanocrystals were obtained by
only increasing the amount of OA. For example, after 30 s of
reaction, the PL peaks were at 413 nm, 425 nm and 435 nm when
the molar ratios of Zn : OA were 4 : 1, 8 : 1 and 12 : 1, respectively.
The same tendency still remained after the reaction lasted over
0 min. It seems that a larger amount of long chain OA hastens
the growth of the nanocrystals. Generally, the number of nuclei
formed in the initial nucleation stage increased significantly when
◦
2
+
here, Zn was surrounded by more OA molecules with the increase
of OA concentration, maybe the reactivity of the Zn species was
decreased and so fewer nuclei were formed in the initial nucleation
stage. The presence of a lower nuclei concentration and a larger
amount of leftover monomers in the solution leads to a faster
nanocrystal growth rate, which is the same as the observation by
1
31
31
decreasing the initial oleic acid concentration. In our experiments
Yu et al. for the case of CdS nanocrystals.
This journal is © The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 11432–11438 | 11435

View Article Online
2
7,30
In previous reports,
the PL ranges of ZnSe nanocrystals were
the HRTEM image of the ZnSe nanocrystals, the (111) planes are
separated by d = 0.32 nm, which is consistent with that of zinc
blende ZnSe. All the ZnSe nanocrystals in the HRTEM images
have well-resolved lattice fringes, which implies good crystallinity.
between 390–450 nm. The smallest ZnSe nanocrystals, synthesized
using OA as the ligand, had a PL peak at 405 nm, it seemed that the
growth speed was accelerated in our reaction. To get small sized
ZnSe nanocrystals, OA was replaced by ODPA to prepare the Zn
precursor, because ODPA should have less reactivity compared
with the unsaturated acid. The promising result indicated that
highly monodisperse ZnSe could be synthesized successfully when
the temperature was still set at 300 C and the growth speed
could be largely decreased. It was shown that the first excitonic
absorption peak was at 377 nm (Fig. 6) when the reaction lasted
Synthesis of tetrapod ZnSe nanocrystals with one-pot method
For the above mentioned hot-injection method, the Zn precursors
were swiftly injected into the reaction solution and ZnSe nuclei
were formed, followed by the further growth of ZnSe nanocrystals,
because of the difference of the chemical potentials between the
crystal surface and the monomers. The swift injection is the key
step to synthesize high quality nanocrystals because it separated
the nucleation and growth stages. Here, we also tried to synthesize
ZnSe nanocrystals by the non-injection one-pot approach using
this new kind of Se precursor. In a non-injection synthesis,
precursors with appropriate reactivity must be chosen carefully
to separate the nucleation and growth stages during the heating
process. The formation of the nanocrystals is based on the concept
of controlling the thermodynamics and kinetics in the nanocrystal
◦
3
0 s and the FWHM of the PL peak was only 14 nm. The
absorption and PL spectra red-shifted as the reaction proceeded
and the FWHM was between 14 and 16 nm through the whole
reaction, with the PL ranging between 390 nm and 424 nm. The PL
QYs can reach up to 40% (Fig. 2, green line). The size information
for the ZnSe nanocrystals synthesized by using ODPA as the ligand
is shown in Fig. 3 (green square line),
13
nucleation stage. We chose zinc acetylacetonate as the Zn
precursor and used a non-injection synthesis approach, high
quality tetrapod-shaped ZnSe nanocrystals were prepared. As
an unfamiliar type of nanocrystals, tetrapod-shaped nanocrystals
32–34
have some unique optoelectronic properties.
Tetrapods could
self-align on a substrate with one arm always pointing towards
one electrode, so that the photogenerated electrons could undergo
less hopping to reach the electrode and the efficiency of the solar
cell would be increased.
The anisotropic growth of the ZnSe nanocrystals took place in
◦
the first 10 min after the temperature reached 280 C. The TEM
image of tetrapod-shaped ZnSe nanocrystals is shown in Fig. 8a.
These ZnSe tetrapods have an average width of 3.4–3.8 nm and an
arm length of 8–9 nm. After 2 h, with the growth of the arms, ZnSe
tetrapods look like dots with an average diameter of about 8–9 nm
(
Fig. 8b). This means that in this stage of the reaction, the arms
grew thicker rather than longer. However, after 8 h of the reaction
◦
with the temperature kept at 280 C, monodisperse and well-
separated dot-shaped nanocrystals with an average size of 10.5
±
10% nm were obtained after the tetrapods broke their branches,
eventually, during the Ostwald ripening process (Fig. 8c). The
corresponding absorption spectra are shown in Figure S2†.
Analysis of powder X-ray diffraction
To further investigate the structure of the differently shaped ZnSe
nanocrystals, their crystallographic properties were determined
using powder X-ray diffraction (XRD) (Fig. 9). Three obvious
diffraction peaks located at 27.4, 45.6, and 54.0 degrees were
corresponded to the (111), (220) and (311) planes of zinc blende
structured ZnSe, respectively. The peaks in our XRD patterns
show broadening phenomena because the synthesized ZnSe
nanocrystals are small. In Fig. 9a, the mean crystal size calculated
from the (111) reflection by the Scherrer formula is 8 nm, which
is smaller than in the corresponding TEM images (Fig. 7c). The
XRD pattern of the tetrapod-shaped ZnSe, shown in Fig. 9b,
confirms the zinc blende structure. The corresponding selected-
area electron diffraction (SAED) pattern of ZnSe tetrapods is
Fig. 6 Temporal evolution of the absorption and PL spectra of the ZnSe
nanocrystals synthesized at 300 C with the molar ratio of ODPA : Zn
being 2 : 1. The numbers mentioned on the right of each spectrum indicate
the heating time.
◦
Morphology and structural characterization
From the TEM images in Fig. 7, ZnSe nanocrystals with a PL peak
at 415 nm has an average size of 5 nm. Typical ZnSe nanocrystals
◦
synthesized at 300 C with the zinc precursor injection method
have a standard deviation of about ±8%. When the PL peak is
at 445 nm, the average size is around 8.4 nm. The inset shows
1
1436 | Dalton Trans., 2010, 39, 11432–11438
This journal is © The Royal Society of Chemistry 2010

View Article Online
◦
Fig. 7 TEM and HRTEM images of the as-prepared ZnSe nanocrystals synthesized at 300 C with OA as the ligands. The average particle size
determined from the TEM images is 5 nm (a), 7.2 nm (b) and 8.4 nm (c). (d), (e) and (f) are the corresponding size-distribution histograms obtained from
the TEM images (a), (b) and (c), respectively.
Fig. 8 TEM images of the as-prepared ZnSe tetrapods with reaction times of (a) 5 min, (b) 2 h, (c) 8 h.
shown in the Fig. 9 inset, which can be indexed to a single face-
centered-cubic (fcc) phase.
ligands and reaction temperatures were discussed in detail. The
size-dependent PL was controlled between 390 and 450 nm with
narrow FWHM of between 14–18 nm. Combining with the
TEM images, this demonstrated that the as-synthesized ZnSe
nanocrystals have nearly monodisperse size distribution. The
PL QYs were as high as 40% at room temperature. The ZnSe
nanocrystals reached the same high quality level, comparing with
ZnSe synthesized by the use of phosphine selenium precursors, as
reported before.
4
. Conclusion
In this report, high quality zinc blende dot- and tetrapod- shaped
ZnSe nanocrystals have been prepared by a much cheaper and
greener route. SeO was chosen to directly disperse in 1-octadecene
2
as the chalcogen precursor. The influences of different surface
This journal is © The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 11432–11438 | 11437

View Article Online
5
V. I. Klimov, A. A. Mikhailovsky, S. Xu, A. Malko, J. A. Hollings,
worth, C. A. Leatherdale, H. J. Eisler and M. G. Bawendi, Science,
2
000, 290, 314.
6
7
8
H. Weller, Philos. Trans. R. Soc. London, Ser. A, 2003, 361, 229.
M. Han, X. Gao, J. Z. Su and S. Nie, Nat. Biotechnol., 2001, 19, 631.
I. Gur, N. A. Fromer, M. L. Geier and A. P. Alivisatos, Science, 2005,
3
10, 462.
S. Coe, W. K. Woo, M. G. Bawendi and V. BulovKc, Nature, 2002, 420,
00.
0 L. Zhu, M. Zhu, J. K. Hurst and A. D. Q. Li, J. Am. Chem. Soc., 2005,
9
8
1
1
27, 8968.
1
1
1 D. V. Talapin and C. B. Murray, Science, 2005, 310, 86.
2 B. David, J. J. Li, Y. J. Wang and X. Peng, Angew. Chem., Int. Ed., 2003,
4
2, 5305.
1
1
1
3 O. Chen, X. Chen, Y. A. Yang, J. Lynch, H. M. Wu, J. Q. Zhuang and
Y. C. C a o , Angew. Chem., Int. Ed., 2008, 47, 8638.
4 S. Sapra, A. L. Rogach and J. J. Feldmann, J. Mater. Chem., 2006, 16,
3
391.
5 H. B. Shen, H. Wang, Z. Tang, J. Z. Niu, S. Lou, Z. Du and L. S. Li,
CrystEngComm, 2009, 11, 1733.
1
1
6 Z. A. Peng and X. Peng, J. Am. Chem. Soc., 2001, 123, 183.
7 N. Pradhan, D. M. Battaglia, Y. Liu and X. Peng, Nano Lett., 2007, 7,
3
12.
Fig. 9 X-ray diffraction patterns of the as-prepared ZnSe nanocrystals
a) hot-injection method with PL peak at 445 nm, (b) one-pot method
with the reaction time of 2 h. Inset is the corresponding selected-area
electron diffraction (SAED) pattern of the ZnSe tetrapods. The vertical
bars correspond to JCPDS file No. 80-0021.
1
8 N. Pradhan, D. Goorskey, J. Thessing and X. Peng, J. Am. Chem. Soc.,
(
2005, 127, 17586.
19 N. Pradhan and X. Peng, J. Am. Chem. Soc., 2007, 129, 3339.
2
2
0 M. A. Hines and P. Guyot-Sionnest, J. Phys. Chem. B, 1998, 102, 3655.
1 S. A. Santangelo, E. A. Hinds, V. A. Vlaskin, P. I. Archer and D. R.
Gamelin, J. Am. Chem. Soc., 2007, 129, 3973.
2
2
2
2 L. Zu, D. J. Norris, KT. A. ennedy, S. C. Erwin and A. L. Efros, Nano
Lett., 2006, 6, 334.
3 N. S. Norberg, G. L. Parks, G. M. Salley and D. R. Gamelin, J. Am.
Chem. Soc., 2006, 128, 13195.
4 D. J. Norris, Nano Lett., 2001, 1, 3.
Acknowledgements
This work was supported by the research project of the Na-
tional Natural Science Foundation of China (20771035), Hi-
Tech Research and Development Program of China (863 plan,
25 A. B. Panda, S. Acharya, S. Efrima and Y. Golan, Langmuir, 2007, 23,
765.
2
2
6 P. D. Cozzoli, L. Manna, M. L. Curri, S. Kudera, C. Giannini, M.
Striccoli and A. Agostiano, Chem. Mater., 2005, 17, 1296.
2
006AA03Z3592), Innovation Scientists and Technicians Troop
7 L. S. Li, N. Pradhan, Y. Wang and X. Peng, Nano Lett., 2004, 4, 2261.
Construction Projects of Henan Province and Program for New
Century Excellent Talents in University.
28 D. F Dayne and A. K. Brian, Chem. Mater., 2007, 19, 4943.
2
3
3
9 Q. Dai, N. Xiao, J. Ning, C. Li, D. Li, B. Zou, W. W. Yu, S. Kan, H.
Chen, B. Liu and G. Zou, J. Phys. Chem. C, 2008, 112, 7567.
0 H. B. Shen, H. Z. Wang, X. M. Li, J. Z. Niu, H. Wang, X. Chen and
L. S. Li, Dalton Trans., 2009, 10534.
References
1 W. W. Yu a n d X . Pe n g , Angew. Chem., Int. Ed., 2002, 41, 2368.
1
2
P. Alivisatos, J. Phys. Chem., 1996, 100, 13226.
32 Y. Cui, U. Banin, M. T. Bjork and A. P. Alivisatos, Nano Lett., 2005,
M. Bruchez, M. Moronne, P. Gin, S. Weiss and A. P. Alivisatos, Science,
5, 1519.
1
998, 281, 2013.
33 L. Manna, D. J. Milliron, A. Meisel, E. C. Scher and A. P. Alivisatos,
Nat. Mater., 2003, 2, 382.
34 I. Gur, N. A. Fromer, C. P. Chen, A. G. Kanaras and A. P. Alivisatos,
Nano Lett., 2007, 7, 409.
3
4
W. C. W. Chan and S. M. Nie, Science, 1998, 281, 2016.
W. U. Huynh, J. J. Dittmer and A. P. Alivisatos, Science, 2002, 295,
2
425.
1
1438 | Dalton Trans., 2010, 39, 11432–11438
This journal is © The Royal Society of Chemistry 2010