Enhanced magneto-optical properties of semiconductor EuS nanocrystals assisted by surface plasmon resonance of gold nanoparticles

Article abstract of DOI:10.1002/chem.201302259

Remarkable magneto-optical properties of a new isolator material, that is, europium sulfide nanocrystals with gold (EuS-Au nanosystem), has been demonstrated for a future photo-information technology. Attachment of gold particles that exhibit surface plasmon resonance leads to amplification of the magneto-optical properties of the EuS nanocrystals. To construct the EuS-Au nanosystems, cubic EuS and spherical Au nanocrystals have been joined by a variety of organic linkers, that is, 1,2-ethanedithiol (EDT), 1,6-hexanedithiol (HDT), 1,10-decanedithiol (DDT), 1,4-bisethanethionaphthalene (NpEDT), or 1,4-bisdecanethionaphthalene (NpDDT). Formation of these systems was observed by XRD, TEM, and absorption spectra measurements. The magneto-optical properties of the EuS-Au nanosystem have been characterized by using Faraday rotation spectroscopy. The Faraday rotation angle of the EuS-Au nanosystem is dependent on the Au particle size and interparticle distance between EuS and Au nanocrystals. Enhancement of the Faraday rotation of EuS-Au nanosystems was observed. The spin configuration in the excited state of the EuS-Au nanosystem was also investigated using photo-assisted electron paramagnetic resonance. Copyright

Full text of DOI:10.1002/chem.201302259

DOI: 10.1002/chem.201302259
Enhanced Magneto-optical Properties of Semiconductor EuS Nanocrystals
Assisted by Surface Plasmon Resonance of Gold Nanoparticles
Akira Kawashima,[a] Takayuki Nakanishi,[a] Tamaki Shibayama,[a] Seiichi Watanabe,[a]
Koji Fujita,[b] Katsuhisa Tanaka,[b] Hitoshi Koizumi,[a] Koji Fushimi,[a] and
Yasuchika Hasegawa*[a]
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Chem. Eur. J. 2013, 19, 14438 – 14445

FULL PAPER
Abstract: Remarkable magneto-optical
properties of a new isolator material,
that is, europium sulfide nanocrystals
with gold (EuS–Au nanosystem), has
been demonstrated for a future photo-
information technology. Attachment of
gold particles that exhibit surface plas-
mon resonance leads to amplification
of the magneto-optical properties of
the EuS nanocrystals. To construct the
EuS–Au nanosystems, cubic EuS and
spherical Au nanocrystals have been
joined by a variety of organic linkers,
that is, 1,2-ethanedithiol (EDT), 1,6-
hexanedithiol (HDT), 1,10-decanedi-
thiol (DDT), 1,4-bisethanethionaphtha-
lene (NpEDT), or 1,4-bisdecanethio-
naphthalene (NpDDT) . Formation of
these systems was observed by XRD,
TEM, and absorption spectra measure-
ments. The magneto-optical properties
of the EuS–Au nanosystem have been
characterized by using Faraday rotation
spectroscopy. The Faraday rotation
angle of the EuS–Au nanosystem is de-
pendent on the Au particle size and in-
terparticle distance between EuS and
Au nanocrystals. Enhancement of the
Faraday rotation of EuS–Au nanosys-
tems was observed. The spin configura-
tion in the excited state of the EuS–Au
nanosystem was also investigated using
photo-assisted electron paramagnetic
resonance.
Keywords: gold
· nanoparticles ·
semiconductors · surface plasmon
resonance
Introduction
ther progress in applications. Optical glass containing para-
magnetic TbIII ions, currently used in the visible region, ex-
hibits a small Faraday effect efficiency (7 8cmꢀ1 at 633 nm,
0.1 T).[9] Thus, effective new materials with a large Faraday
effect in the visible region are crucially required for future
photonic science and engineering.
A promising and important material for use in optical iso-
lators is europium sulfide (EuS) as a magnetic semiconduc-
tor with favourable magnetic and optical properties.[10] EuS
is characterized by degenerate 4f orbitals of EuII ions exist-
ing between the conduction band (5d orbitals of EuII) and
the valence band (3p orbitals of S2ꢀ); the 4f–5d electronic
transition and spin configuration lead to a large magneto-
optical (Faraday) effect, which makes this a promising
active material for future optical isolators.[11] In particular,
EuS nanocrystals are distinctly characterized by their ferro-
magnetic properties and large Faraday effect in the blue-
light region.[12]
Modern optical telecommunication systems are playing an
ever-increasing role in our information intensive society.[1]
In recent years, worldwide effort has been focused on re-
search on optical telecommunication devices, such as
lasers,[2] optical fibers,[3] and photonic devices.[4] In particu-
lar, the optical isolator is a key device that allows the trans-
mission of light in only one direction, for high-speed and
highly accurate optical information technology. The perfor-
mance of an optical isolator is based on the optical Faraday
effect, which causes rotation of the plane of polarized light
that is linearly proportional to the component of the mag-
netic field in the direction of propagation. Various types of
magneto-optical materials showing the Faraday effect have
been reported over the past few decades.[5] In particular, the
preparation of semiconductor materials with magnetic dop-
ants has been investigated for the development of optical
isolators; stochastic control of a number of magnetic dop-
ants in II–VI or III–V systems has also been investigated.[6]
At the present stage, fiber-optic communication systems in
the visible region are focused on telecommunications for
wavelength division multiplex technology (WDM) and opti-
cal sensors for medical equipment.[7] Previous semiconductor
CdTe:Hg nanocrystals show a large Faraday effect in the
visible region (150 8cmꢀ1 at 633 nm, 0.1 T);[8] however, toxic-
ity concerns regarding these materials have prevented fur-
In this study, a new optical isolator composed of the in-
trinsic magnetic semiconductor EuS nanocrystals and bril-
liant gold nanoparticles is focused. The brilliance of gold
materials is known to be due to localized surface plasmon
resonance (LSPR) that leads to unique and unusual photo-
physical enhancement,[13] and has recently been the main
focus in the areas of photophysics, materials chemistry, bio-
logical science and advanced photonics, for improvements in
properties such as enhanced luminescence and photo-cata-
lytic properties.[14] Artemyev and co-workers revealed that
excitation of the LSPR band of gold nanoparticles promotes
efficient luminescence of neighbouring CdSe nanopar-
[a] A. Kawashima, Prof. Dr. T. Nakanishi, Prof. Dr. T. Shibayama,
Prof. Dr. S. Watanabe, Prof. Dr. H. Koizumi, Prof. Dr. K. Fushimi,
Prof. Dr. Y. Hasegawa
AHCTUNGTRENNUNG
ticles.[14a] Small magneto-optical enhancements of Bi:YIG
and iron oxide crystals covered with a gold layer or a thin-
film have also reported.[15] However, direct evidence of am-
plification of Faraday effect assisted by LSPR is not clear at
the present stage. In order to analyse and estimate the mag-
neto-optical signal amplification by LSPR, precise control of
gold particle size and the distance between the gold and the
magnetic materials should be required on the nanoscale.
Here, we report on the successful and remarkable magne-
to-optical properties of a new isolator material based on
Division of Materials Chemistry
Faculty School of Engineering Hokkaido University
North-13 West-8, Kita-ku, Sapporo Hokkaido 060-8628 (Japan)
Fax : (+81)11-706-7114
E-mail: hasegaway@eng.hokudai.ac.jp
[b] Prof. Dr. K. Fujita, Prof. Dr. K. Tanaka
Graduate School of Engineering
Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201302259.
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Y. Hasegawa et al.
EuS nanocrystals directly linked with gold nanocrystals
(EuS–Au nanosystems) through organic linkers. The dis-
tance between the EuS and Au nanocrystals is controlled by
use of different the organic molecules, that is, 1,2-ethanedi-
thiol (EDT), 1,6-hexanedithiol (HDT), 1,10-decanedithiol
(DDT), 1,4-bisethanethionaphthalene (NpEDT), or 1,4-bis-
decanethionaphthalene (NpDDT). The Faraday effect has
been estimated by using polymer thin films containing the
EuS–Au nanosystem (matrix: polymethylmethacrylate
(PMMA)). Efficient Faraday rotation results from a specific
spin configuration of the EuS–Au nanosystem under photo-
irradiation. The characteristic spin configuration was also in-
vestigated by using photon-assisted electron paramagnetic
resonance (EPR). The study and development of magneto-
optical enhancement of EuS assisted by LSPR is expected
to open up a new field of photophysics and photonic sci-
ence. Practical and scientific photo-signal amplification
using EuS–Au nanosystems controlled through the interpar-
ticle distance has been performed for the first time in this
study.
Results and Discussion
Preparation of EuS–Au nanosystems: Monodisperse EuS
and Au nanocrystals were synthesized by thermal reaction
of the tetraphenylphosphonium tetra
bamate)europium(III) complex ([PPh4][Eu
the chloro(triphenylphosphine)gold(I) complex ([PPh3-
uCl]) as single source precursors in oleylamine at 3008C
G
ACHUTGTNRENdNUG ithioACHTUNGTNERcNUGN ar-
Figure 1. Reaction schemes of a) cube-shaped EuS nanocrystals, b) spher-
ical Au nanoparticles and c) EuS–Au nanosystems. XRD spectra of
d) EuS nanocrystals and e) Au nanoparticles. Black lines in XRD spectra
(d and e) are based on the JCPDS data for EuS and Au crystals.
R
G
G
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
for 6 h and 1808C for 30 min under a N2 atmosphere, respec-
tively (Figure 1a and b). The prepared powders were sepa-
rated by centrifugation and washed with toluene. After
washing, purple and red powders of EuS and Au, respective-
ly, were obtained. X-ray diffraction (XRD) confirmed the
formation of crystalline EuS nanocrystals and Au nanoparti-
cles. In Figure 1d, the diffraction peaks at 2q=25.8, 29.8,
42.9, 50.9, 53.0, 62.4, 68.4, and 70.58 were assigned to the
(111), (200), (220), (311), (222), (400), (331), and (420)
planes of NaCl type EuS. From the X-ray pattern of the Au
particles, the diffraction peaks at 2q=38.3, 44.4, 64.4, 77.6,
and 81.6 were assigned to the (111), (200), (220), (311), and
(222) face-centred-cubic (fcc) planes of Au (Figure 1e). The
intensity ratios in the diffraction patterns agreed with those
for bulk EuS and Au. We evaluated the full-width at half
maximum (FWHM) of the 2q=29.8 and 38.3 peaks, which
correspond to Bragg diffraction from the EuS (200) and Au
(111) planes, respectively. The EuS and Au crystallite sizes
calculated from the Scherer equation from the XRD data
were found to be 16.2 and 16.4 nm, respectively.
nanoparticles are composed of a single fcc EuS and metallic
Au crystals, respectively. The prepared EuS nanocrystals
were attached to the Au nanocrystals by using a self-assem-
bly technique (Figure 1c). First, as a pre-treatment, the sur-
faces of the EuS nanocrystals were covered with alkanedi-
thiols, 1,2-ethanedithiol (EDT), 1,6-hexanedithiol (HDT),
1,10-decanedithiol (DDT), 1,4-bisethanethionaphthalene
(NpEDT), or 1,4-bisdecanethionaphthalene (NpDDT), as
linker molecules. In order to confirm that the dithiols were
attached to the EuS surface, we carried out IR mea-
AHCTUNGTREGsNNNU urements. Characteristic IR absorption bands of dithiol-
capped EuS nanocrystals (EuS–NpDDT) after centrifuga-
ꢀ1
ꢀ
tion process are observed at 2670 (s, S H) and 1470 cm
(Ar) and the shapes of these band are significantly different
from those of pure NpDDT molecules. These different
shapes and wavenumber shifts might be due to stacking of
naphthalene units on the EuS surface (see Supporting Infor-
mation, Figure S2). We consider that NpDDT is attached on
the EuS surface. After pre-treatment with linker molecules,
the surface-modified EuS nanocrystals were attached to the
Au nanocrystals in a chloroform solution as shown in Fig-
ure 1c. High-resolution TEM (HR-TEM) images of the pre-
pared EuS–Au nanosystems are shown in Figure 2. We ob-
served cubic EuS nanocrystals attached to spherical Au
nanocrystals with clear lattice fringes. In the HR-TEM
Transmission electron microscopy (TEM) observations
showed that the EuS and Au particles had typically cubic
and spherical shapes, respectively (see Supporting Informa-
tion, Figure S1), and both had an average particle size of
18.5 nm. These average sizes are similar to the size deter-
mined from the XRD data. From these results, it was sur-
mised that the cubic EuS nanocrystals and spherical Au
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Magneto-optical Properties of Nanomaterials
FULL PAPER
Figure 2. a),b) TEM images of EuS–Au nanosystems. c),d) High-resolu-
tion TEM images of EuS–Au nanosystems.
image, the crystallinity was clear and well-resolved, and lat-
tice planes of EuS (0.21 nm (220)) and Au (0.24 nm (111))
were observed. The average distance between EuS and Au
in EuS–EDT–Au, EuS–HDT–Au, EuS–DDT–Au, EuS–
NpEDT–Au, and EuS–NpDDT–Au determined by TEM
observations was estimated to be 0.97, 1.54, 1.91, 1.81, and
3.52 nm, respectively (see Supporting Information, Fig-
ure S3). We thus successfully prepared EuS–Au nanosystems
with various distances between the EuS and Au nanocrys-
tals.
To evaluate the optical properties of EuS–Au nanosys-
tems, polymer thin films were prepared by casting EuS–Au
nanosystems with polymethylmethacrylate (PMMA) in
chloroform. The thickness of the resulting thin films, ob-
tained by using a surface profiler, was found to be 10 mm. A
photograph and the absorption spectra of the PMMA thin
films containing EuS–Au nanosystems are shown in Fig-
ure 3a. The broad absorption band at 513 nm is assigned to
the 4f–5d transition in the EuS nanocrystals. We also found
a specific absorption band around 700 nm, which is much
different from the wavelength of the LSPR band of the pre-
pared Au nanocrystals. Such a red-shift of the LSPR band is
observed under dielectronic environments.[4b] The specific
absorption band at 700 nm might be caused by the LSPR
band of the Au linked to large dielectric EuS nanocrystals.
We have also found the distance between EuS and Au is de-
pendent of the length of dithiols. The characteristic red-
shifts of LSPR and distance depended on the thiol moiety
suggest that Au nanoparticles are directly linked with di-
thiol-covered EuS nanocrystals.
Figure 3. a) UV/Vis absorption spectra of EuS nanocrystals (blue) and
EuS–Au nanosystems (red). Inset show a photograph of the PMMA thin
films containing EuS–Au nanosystems. b) The calculated MFM constants
of polymer thin films containing EuS nanocrystals (blue) and EuS–DDT–
Au nanosystems (red) under an external magnetic field of 15000 Oe.
rotation spectrum at room temperature under an external
magnetic field of 15000 Oe had clear positive and negative
peaks, which could have contributed to the 4f–5d transition
in the EuS nanocrystals. The Verdet constant, which indi-
cates the strength of the Faraday rotation, was calculated by
using Equation (1), in which q, H, and l are the Faraday ro-
tation angle, the external magnetic field and the thickness of
the thin film, respectively.
V ¼ q=ðH ꢁ lÞ
ð1Þ
In order to estimate the Faraday rotation efficiency of the
EuS–Au nanosystems, we consider that the Verdet constant
should be normalized by the photon-absorption ability of
the EuS–Au nanosystems, which contains information on
the absorption coefficient e of EuS, plasmon band of Au,
concentration of EuS–Au, and optical-pass length l. The
magneto-optical figure of merit (MFM) is given by Equa-
tion (2), in which A is the absorbance of the PMMA thin
films containing the EuS–Au nanosystems.
MFM ¼ q=ðH ꢁ AÞ
ð2Þ
Magneto-optical properties: The wavelength dependence of
the Faraday rotation angle was measured for the PMMA
thin films containing the EuS–Au nanosystems. The Faraday
The refractive index of PMMA is 1.48, which is much
smaller than that of EuS materials (n=2.43). The circular
Chem. Eur. J. 2013, 19, 14438 – 14445
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14441

Y. Hasegawa et al.
birefringence of the matrix PMMA is also smaller than the
Faraday rotation of the EuS nanocrystals. Double refraction
in the PMMA thin films does not affect the Faraday rotation
of the EuS nanocrystals in the measurement of circular bire-
fringence. The calculated MFM constants are shown in Fig-
ure 3b and Table 1. First, we observed that the Faraday rota-
Table 1. Molecular length (d) and magneto-optical properties of EuS
nanocrystals and EuS–Au nanosystems linked with EDT, HDT, DDT,
NpEDT and NpDDT.
d [nm]
MFM peak
position lmax [nm]
MFMpeak
[10ꢀ6 8Oeꢀ1 absꢀ1
]
EuS
–
563
565
565
567
567
572
14.8
8.29
11.1
18.1
14.4
10.0
EuS–EDT–Au
EuS–HDT–Au
EuS–DDT–Au
EuS–NpEDT–Au
EuS–NpDDT–Au
0.407
0.937
1.469
1.356
3.155
tion angle is dependent on the interparticle distance be-
tween the EuS and Au nanocrystals. Remarkable enhance-
ment of the Faraday rotation angle of the polymer thin film
with the EuS–DDT–Au nanosystem was observed, although
EuS–Au nanosystems with shorter interparticle distance
(EuS–EDT–Au and EuS–HDT–Au) yield a smaller Faraday
rotation angle compared with the EuS–DDT–Au systems.
We also confirmed that the MFM constant for polymer thin
films with mixtures of EuS and Au nanocrystals (non-linked
particles) is very similar to that for polymer thin films with
EuS nanocrystals (see Supporting Information, Figure S4).
Amplification of the Faraday rotation angle assisted by the
Au nanocrystals might be directly linked to the distance be-
tween the EuS and Au nanocrystals. Generally, the electric
field associated with LSPR is affected by the interparticle
distance between gold and functional materials, such as
a semiconductors, luminescent dyes, and photochromic mol-
ecules. A small interparticle distance promotes quenching of
the excited state of functional materials, resulting in a de-
crease in the luminescent and photocatalytic efficiency. In
contrast, the electric field of LSPR does not affect materials
with long interparticle distances.[16] We observed the small
MFM constants of EuS–NpDDT–Au nanosystems with
a longer distance between EuS and Au (Table 1). We con-
clude that amplification of the Faraday rotation angle is also
dependent on interparticle distance. The amplification of
the Faraday effect of EuS–Au nanosystems is also depen-
dent on the Au particle size (Figure 4). Au nanoparticles
with diameters of 18.5 nm show a larger amplification of the
Faraday effect compared to those with diameters of 8 and
73 nm. For the size dependence of the plasmon absorption,
El-Sayed reported that the plasmon bandwidth of gold
nanoparticles increases with decreasing size in the intrinsic
size region (mean diameter smaller than 25 nm), and in-
creases with increasing size in the extrinsic size region
(mean diameter longer than 25 nm).[17] The broadening of
the plasmon band is caused by transformation of the excita-
tion energy into adsorbate levels located above the Fermi
Figure 4. a) The calculated MFM constants of polymer thin films contain-
ing EuS–DDT–Au nanosystems consisted of same EuS nanocrystals (par-
ticle size : 18.5 nm), but different particle size of Au nanoparticles, 8 nm
(green), 18.5 nm (red), and 73 nm (blue). b)–d) TEM images of EuS-
DDT-Au nanosystems consisted of different particle size of Au nanopar-
ticles: b) 8, c) 18.5, and d) 73 nm.
level. Therefore, effective LSPR is achieved by using gold
nanoparticles with a smaller plasmon band and diameter
around 25 nm. We propose that the observed amplification
of the Faraday effect of EuS–DDT–Au nanosystems con-
taining 18.5 nm Au nanoparticles might be caused by LSPR
on Au nanoparticles with a smaller plasmon bandwidth.
Estimation of spin configuration under photo-irradiation: To
estimate the spin configuration in the excited state of the
EuS–Au nanosystems, we carried out EPR measurements in
the dark and under irradiation with a halogen lamp (150 W,
l=520 nm; FWHM=10 nm using a band-pass filter). The
dark EPR spectra are shown in Figure 5a. The signals at
around 350 and 870 mT were caused by the characteristic
spin configuration of EuII. The observed EPR signal from
the EuS–Au nanosystems is larger than that from the corre-
sponding EuS nanocrystals. The enhancement of the EPR
signal in EuS–Au nanosystems might be due to specific 4f–
5d spin interactions on the EuS surface attached to Au
nanoparticles. Figure 5b shows the difference between the
EPR spectra under dark and light conditions. For the EuS–
DDT–Au nanosystem, large and small enhancements of the
peaks at 350 and 870 mT are observed, respectively. On the
other hand, for EuS nanocrystals, only a small enhancement
of the EuII signal at 350 mT is observed. The signal enhance-
ment for the EuS–Au nanosystem is directly linked to an in-
crease in the magnetic spin polarization under irradiation.
Recently, we reported that enhanced spin polarization in
EuS nanoscale aggregates leads to an increase in Faraday
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Magneto-optical Properties of Nanomaterials
FULL PAPER
band of the Au nanoparticles was confirmed by photo-assist-
ed EPR spectroscopy. These new nanosystems provide am-
plification of Faraday rotation under irradiation at the plas-
mon band of gold. By control of irradiation at the plasmon
band, we can tune the Faraday rotation angle of EuS–Au
nanosystems, finely. The photo-switching system of the Fara-
day rotation angle would make a new high-speed photonic
router for future photo information technology. The EuS–
Au nanosystem is anticipated, based on this work, to open
up future fields of innovative photo-information science and
technology.
Experimental Section
Materials: Europium
sodium N,N-diethyldithiocarbamate trihydrate (Na
were purchased from Kanto Chemical Co. Inc. TetrachloroaurateACHTUNGTRENNUNG
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
rahydrate (HAuCl4·4H2O), tetraphenylphosphonium bromide (BrPPh4),
triphenylphosphine (PPh3), 1,6-hexanedithiol (HDT) and chloroform
were purchased from Wako Pure Chemical Industry, Ltd. Oleylamine
(OA), 1,2-ethanedithiol (EDT) and 1,10-decanedithiol (DDT), 1,4-dihy-
droxynaphthalene and p-toluenesulfonic acid were obtained from Tokyo
Chemical Industry Co., Ltd. All other chemicals and solvents were re-
agent grade and were used without further purification.
Apparatus: Infrared spectra were recorded on a JASCO FT/IR-350 spec-
trometer. 1H NMR data were measured by on
a JEOL AL-300
(300 MHz) spectrometer. 1H NMR chemical shifts were determined by
using tetramethylsilane (TMS) as an internal standard. Elemental analy-
ses were performed with a Yanaco CHN corder MT-6. XRD spectra
were characterized by a RIGAKU X-ray diffractometer RINT 2200.
High-resolution images of the EuS–Au nanosystems were obtained with
a TEM, JEOL 2010 FASTEM (200 kV), and high-resolution TEM (HR-
TEM), JEM-ARM1300. UV/Vis absorption spectra were measured on
a JASCO V-570 spectrophotometer at room temperature. The thickness
of the PMMA thin films containing the EuS–Au nanosystem were ob-
tained by using a surface profiler (KLA Tencor ALPHA-STEP IQ). Elec-
tron spin resonance spectra of EuS–Au nanosystems were measured
using a JEOL JES-TE200 ESR spectrometer.
Figure 5. a) EPR spectra of EuS nanocrystals (blue) and EuS-DDT-Au
nanosystems (red). b) The difference between the EPR spectra under
dark and light condition with
a halogen lamp (150 W, l=520 nm;
FWHM=10 nm using a band-pass filter) of EuS nanocrystals (blue) and
EuS–DDT–Au nanosystems (red). The microwave frequency is
9.39 GHz, and the incident microwave power is 2.0 mW at room tempera-
ture.
rotation signals.[12] We consider that large spin polarization
in EuS nanocrystals provides strong magneto-optical proper-
ties. The spin polarization of EuS nanocrystals in the elec-
tronic transition state can be estimated from the EPR spec-
tra under irradiation.[18] The increase in the EPR signal due
to irradiation may be one of the most important pieces of
evidence of an enhanced Faraday effect for EuS assisted by
gold, observed for the first time in the present work.
Synthesis of tetraphenylphosphonum tetrakis(diethyldithiocar
ACHTUNGTRENNUNGbamate)-
A
E
N
ACHTUNGTRENNUNG
(9.00 g, 39.9 mmol) in methanol (32 mL) was added to EuCl3·6H2O
(2.80 g, 7.64 mmol) dissolved in methanol (32 mL), and the reaction was
stirred for 3 h. The reaction mixture was then filtered and a solution of
BrPPh4 (16.04 g, 38.26 mmol) in methanol (20 mL) was added to the fil-
trate and stirred for 1 h. The resulting precipitate was separated by filtra-
tion and washed twice with ethanol. 1H NMR (300 MHz, CDCl3, 258C,
TMS): d=7.91–7.70 (m, 20H; Ar-H), 3.17 (m, 16H; CH2), 1.61 ppm (q,
3
ꢀ
ꢀ
J (H,H)=7 Hz, 24H; CH3); IR (KBr): n˜ =1485–1482 (C N), 1442 (P
Phenyl), 1007 cmꢀ1 (C S); elemental analysis calcd (%) for
C44H60EuN4PS8: C 48.73, H 5.58, N 5.17, S 23.65; found: C 48.55, H 5.51,
N 5.00, S 23.41.
ꢀ
Conclusion
Synthesis of cube-shaped EuS nanocrystals: Under an N2 atmosphere,
[PPh4][EuACHTNUGRTENUNG(S2CNEt2)4] (1.91 g, 1.76 mmol) was dissolved into oleylamine
Gold materials have attracted the attention of many re-
searchers because of their brilliance as a result of LSPR.
This study suggests that brilliant gold can accelerate optical
telecommunication systems for the first time. Here, we suc-
cessfully prepared cubic EuS nanocrystals attached to spher-
ical Au nanoparticles to produce EuS–Au nanosystems. The
magneto-optical properties of these EuS–Au nanosystems
are dependent on the interparticle distance between EuS
and Au and the Au nanoparticle size. The enhanced spin-po-
larization of the EuS–Au nanosystems excited at the LSPR
(10 mL, 30.4 mmol), and the mixture was heated at 1808C and stirred for
20 min. Then the reaction mixture was heated to 3008C and stirred for
6 h, after which the purple liquid was centrifuged at 4000 rpm for 10 min.
The resulting precipitate was added to chloroform (10 mL) and centri-
fuged at 4000 rpm for 15 min, and the clear purple liquid of oleylamine-
capped EuS nanocrystals was obtained.
Synthesis of chloro(triphenylphosphine)gold(I) ([PPh3AuCl]): A solution
of HAuCl4 (10.0 g, 24.3 mmol) in ethanol (150 mL) was added, with stir-
ring, to PPh3 (12.7 g, 48.6 mmol) dissolved in ethanol (100 mL); the reac-
tion mixture was then heated under reflux for several hours, and cooled
to room temperature. The resulting precipitate was separated by filtra-
Chem. Eur. J. 2013, 19, 14438 – 14445
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Y. Hasegawa et al.
tion and washed twice with ethanol. Recrystallization from hexane gave
white crystals of [PPh3AuCl]. 1H NMR (300 MHz, CDCl3, 258C, TMS):
[1] N. Stafford, Nature 2010, 467, S19–S21.
d=7.50 ppm (m, 15H, Ar-H); IR (KBr): n˜ =1407 cmꢀ1 (P Phenyl); ele-
ꢀ
[2] a) S. Nakamura, Science 1998, 281, 956–961; b) S. J. Pearton, J. C.
Zolper, R. J. Shul, F. Ren, J. Appl. Phys. 1999, 86, 1–78; c) M. S.
Gudiksen, L. J. Lauhon, J. Wang, D. C. Smith, C. M. Lieber, Nature
2002, 415, 617–620.
[3] a) J. C. Knight, J. Broeng, T. A. Birks, P. S. J. Russel, Science 1998,
282, 1476–1478; b) P. Russell, Science 2003, 299, 358–362.
[4] a) T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, P. A. Wolff,
Nature 1998, 391, 667–669; b) W. L. Barnes, A. Dereux, T. W. Ebbe-
sen, Nature 2003, 424, 824–830.
mental analysis calcd (%) for C18H15AuCl: C 43.70, H 3.06, N 0; found:
C 43.58, H 3.02, N 0.
Synthesis of Au nanoparticles: Under an N2 atmosphere, [PPh3AuCl]
(0.50 g, 1.01 mmol) was dissolved into oleylamine (30 mL, 91.2 mmol),
and the mixture was heated at 1808C and stirred for 30 min. The solution
was then cooled to room temperature and the red liquid was centrifuged
at 4000 rpm for 10 min. The precipitate was added to chloroform (20 mL)
and centrifuged at 4000 rpm for 15 min, and the clear red liquid of oleyla-
mine-capped Au nanoparticles was obtained.
[5] a) J. A. Gaj, J. Ginter, R. R. Gała˛zka, Phys. Status Solidi B 1978, 89,
655–662; b) Y. Wang, N. Herron, K. Moller, T. Bein, Solid State
Commun. 1991, 77, 33–38; c) H. Ohno, A. Shen, F. Matsukura, A.
Oiwa, A. Endo, S. Katsumoto, Y. Iye, Appl. Phys. Lett. 1996, 69,
363–365; d) J. M. Kikkawa, D. D. Awschalom, Nature 1999, 397,
139–141; e) T. Jungwirth, W. A. Atkinson, B. H. Lee, A. H. Mac-
Donald, Phys. Rev. B 1999, 59, 9818–9821; f) D. J. Norris, N. Yao,
F. T. Charnock, T. A. Kennedy, Nano Lett. 2001, 1, 3–7; g) K. Ando,
H. Saito, Z. W. Jin, T. Fukumura, M. Kawasaki, Y. Matsumoto, H.
Koinuma, Appl. Phys. Lett. 2001, 78, 2700–2702; h) Y.-w. Jun, Y.-y.
Jung, J. Cheon, J. Am. Chem. Soc. 2002, 124, 615–619; i) H. Kato, T.
Matsushita, A. Takayama, M. Egawa, K. Nishimura, M. Inoue, J.
Appl. Phys. 2003, 93, 3906–3911; j) N. S. Norberg, K. R. Kittilstved,
J. E. Amonette, R. K. Kukkadapu, D. A. Schwartz, D. R. Gamelin, J.
Am. Chem. Soc. 2004, 126, 9387–9398; k) S. C. Erwin, L. Zu, M. I.
Haftel, A. L. Efros, T. A. Kennedy, D. J. Norris, Nature 2005, 436,
91–94.
[6] a) H. Akinaga, S. Miyanishi, K. Tanaka, W. Van Roy, K. Onodera,
Appl. Phys. Lett. 2000, 76, 97–99; b) K. Ando, H. Saito, Z. Jin, T.
Fukumura, M. Kawasaki, Y. Matsumoto, H. Koinuma, J. Appl. Phys.
2001, 89, 7284–7286; c) M. Inoue, R. Fujikawa, A. Baryshev, A.
Khanikaev, P. B. Lim, H. Uchida, O. Aktsipetrov, A. Fedyanin, T.
Murzina, A. Granovsky, J. Phys. D 2006, 39, R151.
[7] a) J. Kido, Y. Okamoto, Chem. Rev. 2002, 102, 2357–2368; b) J.-
C. G. Bꢁnzli, S. Comby, A.-S. Chauvin, C. D. B. Vandevyver, J. Rare
Earths 2007, 25, 257–274; c) S. V. Eliseeva, J.-C. G. Bunzli, Chem.
Soc. Rev. 2010, 39, 189–227.
Synthesis of 1,4-bisalkanethionaphthalene: 1,4-Bisalkanethionaphtalene
(1,4-bisethanethionaphtalene (NpEDT) or 1,4-bisdecanethionaphtalene
(NpDDT)) were prepared by previously reported.[19] Under an N2 atmos-
phere, 1,4-dihydroxynaphthalene (0.81 g, 5.0 mmol), p-toluenesulfonic
acid (0.48 g, 2.5 mmol) and alkanedithiol (1,2-ethanedithiol (EDT) or
1,10-decanedithiol (DDT), 46 mmol) were dissolved in benzene (50 mL),
and the mixture was heated at reflux (808C) for 1 h. After aqueous
workup, the product was purified by column chromatography on silica
gel by using ethyl acetate as an eluent. The collected product was crystal-
lized from a mixture of ethyl acetate and n-hexane to give NpEDT or
NpDDT as a white solid, respectively.
Ligand exchange reactions: Dithiol-capped EuS nanocrystals were ob-
tained by adding EuS nanocrystals (0.08 g) dissolved in chloroform
(20 mL) to a solution of dithiol ligand (0.01–0.03 mol equiv; 1,2-ethanedi-
thiol (EDT), 1,6-hexanedithiol (HDT), 1,10-decanedithiol (DDT), 1,4-bi-
sethanethionaphthalene (NpEDT), or 1,4-bisdecanethionaphthalene
(NpDDT)) in chloroform (10 mL). The reaction mixture was stirred for
5 h at room temperature and the resulting solution was centrifuged at
4000 rpm for 10 min. The precipitate was dispersed in chloroform
(20 mL), and a liquid containing dithiol-capped EuS nanocrystals (EuS-
EDT, -HDT, -DDT, -NpEDT, or -NpDDT) was obtained.
Synthesis of EuS–Au nanosystems: The EuS–Au nanosystems were
formed by adding the solution of Au nanoparticles (0.08 g) in chloroform
(10 mL) to the solution of alkanedithiol-capped EuS nanocrystals (0.08 g)
in chloroform (20 mL), and then the mixture was stirred for 5 h at room
temperature. The solution was added to 1-dodecanethiol (1 mL), which
keeps EuS nanocrystals from aggregating, and stirred for 1 h. Thus solu-
tions of EuS–dithiol–Au nanosystems (dithiol: EDT, HDT, DDT,
NpEDT, or NpDDT) in chloroform were obtained.
[8] a) C. Buss, R. Pankoke, P. Leisching, J. Cibert, R. Frey, C. Flytzanis,
Phys. Rev. Lett. 1997, 78, 4123–4126; b) A. M. Shuvaev, G. V. Asta-
khov, A. Pimenov, C. Brꢁne, H. Buhmann, L. W. Molenkamp, Phys.
Rev. Lett. 2011, 106, 107404.
[9] a) S. Ganschow, D. Klimm, P. Reiche, R. Uecker, Cryst. Res. Tech-
nol. 1999, 34, 615–619; b) V. I. Chani, A. Yoshikawa, H. Machida,
T. Fukuda, Mater. Sci. Eng. B 2000, 75, 53–60.
Synthesis of EuS–Au nanosystems with different sizes of Au nanoparti-
cle: Au nanoparticles with different grain size were prepared by changing
the reaction times. Reaction times of 10, 30, and 60 min resulted in Au
particle sizes were of about 8, 18.5, and 73 nm, respectively, by TEM
measurements. The EuS–DDT–Au nanosystems were prepared by
method given above.
[10] a) P. Wachter, CRC Crit. Rev. Solid State Sci. 1972, 3, 189–241; b) P.
Wachter, in Handbook on the Physics and Chemistry of Rare Earths,
Vol. 2 (Eds.: Karl A. Gschneidner, Jr., E. LeRoy), Elsevier, 1979,
pp. 507–574; c) D. Gçrlitz, J. Kçtzler, Eur. Phys. J. B 1998, 5, 37–
43; d) T. Kasuya, J. Magn. Magn. Mater. 1999, 195, 141–147;
e) U. K. Sakalle, P. K. Jha, S. P. Sanyal, Bull. Mater. Sci. 2000, 23,
233–235; f) J. Kunes, W. Ku, W. E. Pickett, J. Phys. Soc. Jpn. 2005,
74, 1408–1411.
[11] a) J. C. Suits, B. E. Argyle, M. J. Freiser, J. Appl. Phys. 1966, 37,
1391–1397; b) Y. Hasegawa, S. Thongchant, Y. Wada, H. Tanaka, T.
Kawai, T. Sakata, H. Mori, S. Yanagida, Angew. Chem. 2002, 114,
2177–2179; Angew. Chem. Int. Ed. 2002, 41, 2073–2075; c) S.
Thongchant, Y. Hasegawa, Y. Wada, S. Yanagida, J. Phys. Chem. B
2003, 107, 2193–2196; d) F. Zhao, H. L. Sun, S. Gao, G. Su, J. Mater.
Chem. 2005, 15, 4209–4214; e) T. Mirkovic, M. A. Hines, P. S. Nair,
G. D. Scholes, Chem. Mater. 2005, 17, 3451–3456; f) T. Kataoka, Y.
Tsukahara, Y. Hasegawa, Y. Wada, Chem. Commun. 2005, 6038–
6040; g) Y. Hasegawa, M. Afzaal, P. OꢂBrien, Y. Wada, S. Yanagida,
Chem. Commun. 2005, 0, 242–243; h) M. D. Regulacio, N. Tomson,
S. L. Stoll, Chem. Mater. 2005, 17, 3114–3121; i) Y. Hasegawa, Y.
Okada, T. Kataoka, T. Sakata, H. Mori, Y. Wada, J. Phys. Chem. B
2006, 110, 9008–9011; j) M. D. Regulacio, K. Bussmann, B. Lewis,
S. L. Stoll, J. Am. Chem. Soc. 2006, 128, 11173–11179; k) F. Zhao,
H.-L. Sun, G. Su, S. Gao, Small 2006, 2, 244–248; l) M. L. Redꢃgolo,
Preparation of polymer thin films containing EuS–Au nanosystems and
Faraday rotation measurements: The obtained EuS–Au nanosystems
(2 mg) were added to a solution of polymethylmethacrylate (PMMA)
(2.0 g) in chloroform (8 mL) and dispersed well under ultrasonic treat-
ment, giving a colloidal suspension. The PMMA thin films were prepared
on a glass substrate from the colloidal suspension by means of a casting
method for the Faraday rotation measurements.
The Faraday effect measurements were performed by using a measure-
ment system for Faraday and Kerr effects (JASCO, Model K-250). A Xe
lamp was used as the light source. The external magnetic field was
15000 Oe.
Acknowledgements
This work was partly supported by the Ministry of Education, Culture,
Sports, Science and Tech (MEXT), Japan through Grants-in-Aid for Sci-
entific Research on Innovative Areas of “Emergent chemistry of nano-
scale molecular systems” and New Polymeric Materials Based on Ele-
ment-Blocks (No.2401)“ (24102012).
14444
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ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 14438 – 14445

Magneto-optical Properties of Nanomaterials
FULL PAPER
D. S. Koktysh, S. J. Rosenthal, J. H. Dickerson, Phys. Status Solidi C
2007, 4, 406–408; m) Y. Hasegawa, T.-a. Adachi, A. Tanaka, M.
Afzaal, P. OꢂBrien, T. Doi, Y. Hinatsu, K. Fujita, K. Tanaka, T.
Kawai, J. Am. Chem. Soc. 2008, 130, 5710–5715; n) A. S. Pereira, P.
Rauwel, M. S. Reis, N. J. Oliveira Silva, A. Barros-Timmons, T. Trin-
dade, J. Mater. Chem. 2008, 18, 4572–4578; o) M. D. Regulacio, S.
Kar, E. Zuniga, G. Wang, N. R. Dollahon, G. T. Yee, S. L. Stoll,
Chem. Mater. 2008, 20, 3368–3376; p) V. M. Huxter, T. Mirkovic,
P. S. Nair, G. D. Scholes, Adv. Mater. 2008, 20, 2439–2443; q) R. S.
Selinsky, D. J. Keavney, M. J. Bierman, S. Jin, Appl. Phys. Lett. 2009,
95, 202501–202503; r) S. Kar, W. L. Boncher, D. Olszewski, N. Dol-
lahon, R. Ash, S. L. Stoll, J. Am. Chem. Soc. 2010, 132, 13960–
13962; s) R. S. Selinsky, J. H. Han, E. A. Morales Pꢄrez, I. A. Guzei,
S. Jin, J. Am. Chem. Soc. 2010, 132, 15997–16005; t) W. He, J. H.
Dickerson, Appl. Phys. Lett. 2011, 98, 081914–081913; u) S. Kar,
N. R. Dollahon, S. L. Stoll, J. Solid State Chem. 2011, 184, 1324–
1327; v) Y. Hasegawa, Chem. Lett. 2013, 42, 2–7.
6235; Angew. Chem. Int. Ed. 2004, 43, 6042–6108; c) J. Lee, A. O.
Govorov, J. Dulka, N. A. Kotov, Nano Lett. 2004, 4, 2323–2330;
d) Y. Tian, T. Tatsuma, J. Am. Chem. Soc. 2005, 127, 7632–7637.
[15] a) Y. Li, Q. Zhang, A. V. Nurmikko, S. Sun, Nano Lett. 2005, 5,
1689–1692; b) R. Fujikawa, A. V. Baryshev, J. Kim, H. Uchida, M.
Inoue, J. Appl. Phys. 2008, 103, 07D301–303; c) S. Ozaki, H. Kura,
H. Maki, T. Sato, J. Appl. Phys. 2009, 106, 123530–123533; d) P. K.
Jain, Y. Xiao, R. Walsworth, A. E. Cohen, Nano Lett. 2009, 9, 1644–
1650; e) L. Wang, C. s. Clavero, Z. Huba, K. J. Carroll, E. E. Car-
penter, D. Gu, R. A. Lukaszew, Nano Lett. 2011, 11, 1237–1240.
[16] a) S. L. McCall, P. M. Platzman, P. A. Wolff, Phys. Lett. A 1980, 77,
381–383; b) G. W. Ford, W. H. Weber, Phys. Rep. 1984, 113, 195–
287; c) B. N. J. Persson, Surf. Sci. 1993, 281, 153–162; d) J. R. Lako-
wicz, Anal. Biochem. 2001, 298, 1–24; e) T. L. Jennings, M. P. Singh,
G. F. Strouse, J. Am. Chem. Soc. 2006, 128, 5462–5467.
[17] S. Link, M. A. El-Sayed, J. Phys. Chem. B 1999, 103, 4212–4217.
[18] Y. Hasegawa, Y. Wada, S. Yanagida, J. Alloys Compd. 2006, 408–
412, 207–211.
[19] P. Charoonniyomporn, T. Thongpanchang, S. Witayakran, Y. Thebt-
aranonth, K. E. S. Phillips, T. J. Katz, Tetrahedron Lett. 2004, 45,
457–459.
[12] Y. Hasegawa, M. Kumagai, A. Kawashima, T. Nakanishi, K. Fujita,
K. Tanaka, K. Fushimi, J. Phys. Chem. C 2012, 116, 19590–19596.
[13] A. V. Zayats, I. I. Smolyaninov, A. A. Maradudin, Phys. Rep. 2005,
408, 131–314.
[14] a) O. Kulakovich, N. Strekal, A. Yaroshevich, S. Maskevich, S. Ga-
ponenko, I. Nabiev, U. Woggon, M. Artemyev, Nano Lett. 2002, 2,
1449–1452; b) E. Katz, I. Willner, Angew. Chem. 2004, 116, 6166–
Received: June 14, 2013
Published online: September 18, 2013
Chem. Eur. J. 2013, 19, 14438 – 14445
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14445