Mendeleev
Communications
Mendeleev Commun., 2012, 22, 292–293
Synthesis and characterization of Ni2+-doped
CdSe and CdSe(S) quantum dots
Anna S. Dotsenko,* Sergey G. Dorofeev, Konstantin O. Znamenkov and Denis V. Grigoriev
Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation.
Fax: +7 495 939 0998; e-mail: dorofeev@inorg.chem.msu.ru, annadotsenko@list.ru
DOI: 10.1016/j.mencom.2012.11.003
The Ni-doped CdSe and CdSe(S) nanocrystals were synthesized using oleic and pelargic acids as stabilising agents and investigated
by transmission electron microscopy, optical spectroscopy and inductively coupled plasma atomic emission spectroscopy.
Doped semiconductor nanocrystals (NCs) have attracted con-
siderable attention due to their unique properties, which cannot
be obtained in bulk materials.1 Covered with organic or inorganic
stabilizer molecules, semiconductor NCs or quantum dots (QDs)
can form sols in suitable solvents (colloidal QDs). During recent
decades, the preparation and characterization of doped QDs have
provided new advances in not only the theoretical understanding
of the fundamental mechanisms that control doping but also the
fabrication of novel materials.2 Doping mechanisms and methods
for the incorporation of impurities into NCs have been widely
discussed.3–6
The optical properties of Group II–IV compounds are strongly
influenced by doping with nickel.7 The Ni impurity is important
as a luminescence centre and charge compensation, as well as
an electron trap, because it forms deep levels within the band gap
of the host material;8 this is of interest for the application of
Niii-doped compounds as phosphors and laser materials.
Here we report the synthesis of Ni-doped CdSe and CdSe(S)
nanoparticles capped by oleic and pelargic acids and their charac-
terization by transmission electron microscopy (TEM), optical
spectroscopy and inductively coupled plasma atomic emission
spectroscopy (ICP-AES).
Table 1 Experimental conditions, composition, form and size of the syn-
thesized nanoparticles.
Sample T/°C Cd:Ni/Se:S (at%) Nanoparticle shape and size
A
180
98.7:1.3/40.4:59.6 spherical, average diameter
of 3.2 nm
B
C
D
220
220
180
92.3:7.7/4.8:95.2
98.6:1.4/24.5:75.5
99.4:0.6/100:0
cubic, average length of 5.7 nm
tetrapodal, average length
and diameter of tetrapod rays
of 7.5 and 2.1 nm, respectively
E
220
98.7:1.3/100:0
rods, length distribution 10–20 nm,
average diameter of 3.2 nm
A comparison of the compositions and shapes of the nano-
particles allowed us to define general differences in the two
synthetic procedures. Using [(C5H11)2NC(S)S]2Ni as a Niii pre-
cursor results in a significant amount of sulfur impurity in nano-
particles. Furthermore, it leads to the preparation of QDs, which
have a cubic form unusual for CdSe and CdS QDs [Figure 1(b)].
In another series of experiments, Cd(AcO)2·2H2O (0.5 mmol), Ni(AcO)2·2H2O
The synthesis was based on a published procedure9 for the
preparation of pure CdSe QDs.† Table 1 summarizes the experi-
mental conditions and the composition, shape and size of the
synthesizednanoparticles.Synthesizedsampleswereinvestigated
by TEM, optical spectroscopy and ICP-AES.‡
(0.2 mmol) and an organic acid (oleic or pelargic in the synthesis of
samples D and E, respectively) (2.4 mmol) were dissolved in diphenyl
ether (5 ml). The mixture was heated at 150°C for 1 h in a continuous
argon stream to remove water and acetic acid. Then, the temperature was
stabilized at 180 or 220°C and 1 m TOPSe solution in TOP (0.5 ml)
was injected into the reaction mixture with vigorous stirring. After the
injection, the particle growth was carried out at the same temperature
during 5 min and the reaction mixture was cooled to room temperature.
The procedure of receiving pure samples was made as previously.
†
Cadmium oleate used as a cadmium precursor in the synthesis of QDs
was prepared by a published method.9 Cd(AcO)2·2H2O (0.5 mmol) and
oleic acid (2 mmol) were dissolved in diphenyl ether (5 ml). The mixture
was heated at 140°C for 1 h in a continuous argon stream to remove
water and acetic acid; then, the mixture was cooled to room temperature.
A 1 m trioctylphosphine selenide (TOPSe) solution in trioctylphosphine
(TOP) was prepared by dissolving elementary Se in TOP.
‡
TEM analysis was performed on a Leo Omega 912 electron microscope.
Size measurements were obtained on a statistical subset of QDs by the
manual calculation of QD images obtained by digitizing the micrograph
negatives. The optical absorption spectra were measured with a Varian
Carry 50 spectrophotometer (UV-VIS). The photoluminescence (PL)
experiments were measured on an Ocean Optics USB 4000 spectrometer
(excitation by a 30 mW laser at 405 nm). All measurements were taken
at room temperature.
ICP-AES (Optima 4300DV) for elemental analysis was performed on
the Ni-doped CdSe and CdSe(S) QDs samples. All samples were dis-
solved in conc. HNO3 with adding a few drops of a 30% H2O2 aqueous
solution. Then, the mixture was heated at 300°C, dissolved in 4% HNO3
distilled water solution with adding of H2O2 and the Cd, Ni, Se, and S
concentrations were measured against known Cd, Ni, Se and S standards.
The Cd emission was monitored at 226.502 and 214.440 nm, the Ni
emission was monitored at 232.003 and 341.476 nm, the Se emission was
monitored at 196.026 and 203.985 nm, and the S emission was monitored
at 181.975 and 180.669 nm. The reported doping concentrations are the
average values of three to five runs with an error of 1–2%.
For a typical synthesis, cadmium oleate (0.5 mmol) dissolved in a non-
polar high-boiling solvent (diphenyl ether) and [(C5H11)2NC(S)S]2Ni
[100 mg (0.19 mmol) in the synthesis of samplesA and B, 30 mg (0.06 mmol)
in the synthesis of sample C] used as a Ni2+ precursor were combined and
heated at 30–60 °C under Ar (to dissolve the nickel precursor). Then, the
temperature was stabilized at 180 or 220°C and 1 m TOPSe solution in
TOP (0.5 ml) was injected into the reaction mixture with vigorous stirring.
After the injection, the particle growth was carried out at the same tem-
perature during 5 min; then, the reaction mixture was cooled to room
temperature. An equal volume of acetone was added for the precipitation
of nanocrystals. Coagulated nanocrystals were separated by centrifugation,
dissolved in a non-polar solvent (hexane or octane), again precipitated
by acetone, separated and dissolved in the solvent (this procedure was
repeated twice to remove reagents and different reaction products).
© 2012 Mendeleev Communications. All rights reserved.
– 292 –
Dotsenko, Anna S.
