Novel amphiphilic rare earth precursor complexes with octadecyl cis-butene dicarboxylate to synthesize GdxY2-xO3:Eu3+ nanophosphors

Article abstract of DOI:10.1016/j.jallcom.2009.01.083

Maleic anhydride was modified by long chain 1-octadecanol to mono-octadecyl cis-butene dicarboxylate (MAO), which has both hydrophilic and lipophilic groups. Then, a novel sort of corresponding amphiphilc rare earth (Gd³⁺, Y³⁺, Eu

Full text of DOI:10.1016/j.jallcom.2009.01.083

Journal of Alloys and Compounds 479 (2009) L62–L65
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Letter
Novel amphiphilic rare earth precursor complexes with octadecyl cis-butene
dicarboxylate to synthesize GdxY2−xO3:Eu3+ nanophosphors
Bing Yan∗, Hongxia Zhu
Department of Chemistry, Tongji University, Siping Road 1239, Shanghai 200092, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 October 2008
Received in revised form 17 January 2009
Accepted 21 January 2009
Available online 5 February 2009
Maleic anhydride was modified by long chain 1-octadecanol to mono-octadecyl cis-butene dicarboxy-
late (MAO), which has both hydrophilic and lipophilic groups. Then, a novel sort of corresponding
amphiphilc rare earth (Gd3+, Y3+, Eu3+) complex with the as-derived MAO was synthesized. Then, nano-
sized GdxY2−xO3:Eu3+ (x = 0.2, 0.6, 1.0, 1.4, 1.8) was achieved using this novel amphiphilic rare earth
complex as precursor molecule which can form nanosized micelle-like aggregates by special self-
assembly. Scanning electronic microscope (SEM), transmission electron microscopic (TEM) and X-ray
diffraction (XRD) were used to characterize the morphology and particle size of this nanometer material,
which present the regular nanocrystal with particle size of 70 nm. Besides that, this nanometric material
exhibits an especially strong emission at 610 nm.
Keywords:
Phosphors
Chemical synthesis
Luminescence
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
face morphology [18,19]. Therefore, it has become a challenge to
limit the agglomeration of particles effectively and control the mor-
Rare earth ions are characterized by an incompletely filled 4f
shell, which can absorb the excitation energy to be at the excited
state and then return to the ground state, resulting in emitting
state in the visible region [1,2]. These feature transitions within
the 4fn configuration have found an important application in the
luminescent probes or labels for chemical or biological macro-
molecules [3], the active center for luminescent materials [4] and
electroluminescent devices [5]. During the past decade, a signifi-
cant success has been achieved in the synthesis of nanosized rare
earth phosphors by a variety of methods, such as spray pyrolysis
[6], colloidal reactions [7], combustion synthesis [8], so-called wet
or soft chemical technology [9–12] and so on. But in most cases,
the syntheses primarily focused on the high-temperature solid-
state reactions providing agglomerated powders, which can allow
to readily alter the structural characteristics of the solid powders
[13,14]. Y2O3 doped with Eu ion has gained much attention because
it is the most important and favorable phosphors for its unsur-
passed red emitting with high luminescence quantum efficiency
in fluorescence lamps and projection television tubes [15]. Cubic
Y2O3 for its chemical stability is an excellent host material for rare
earth ions especially for Eu ion [16]. Nanoscale Y2O3:Eu3+ pow-
ders were fabricated firstly by Li et al. through the polyacrylamide
gel method [17]. However, the degree of aggregation Y2O3:Eu3+ is
serious, not like YVO4:Eu3+and Y2SiO5:Eu3+ which have better sur-
phology and microstructures in order to improve the optical and
electronic properties of nanoscale Y2O3:Eu3+. Extensive research
has paid more attention to the design and assembly of precursors
with special organic ligands during these years. As well known,
amphiphilic molecules were employed in Langmuir–Blodgett films
due to their hydrophilic and lipophilic groups [20]. Here, we choose
amphiphilic molecules as the precursors to prepare rare earth lumi-
nescent materials. This is because that the amphiphilic molecules
could form nanosized micelle-like aggregates with various mor-
phologies in aqueous medium by special self-assembling and the
micellization can be viewed as a process that drives the packing of
all junction points into a high density array, and then influences the
shape, structure, epitaxy and property of the precursors [21]. More-
over, the organic groups can also serve as a fuel for the nanocrystal
formation and a dispersing medium in high-temperature process,
which can also limit the agglomeration of particles [22].
In this context, using maleic anhydride as staring material,
1-octadecanol was grafted in order to achieve a new type of
amphiphilic mono-octadecyl cis-butene dicarboxylate (MAO), with
carboxylic acids as the hydrophilic segments and organic long chain
as the amphiphilic segments. Then the corresponding rare earth
(Gd3+, Y3+, Eu3+) complexes with the as-derived MAO ligands were
synthesized. On the basis of this, we obtained GdxY2−xO3:Eu3+
(x = 0.2, 0.6, 1.0, 1.4, 1.8) nanometric material by selecting the rare
earth complexes as the precursors. And we expect that the spe-
cial amphiphilc molecular ligands of the rare earth complexes can
control the morphology and microstructures of GdxY2−xO3:Eu3+
nanometric materials. The nanometer size, morphology and
∗
Corresponding author. Tel.: +86 21 65984663; fax: +86 21 65982287.
E-mail address: byan@tongji.edu.cn (B. Yan).
0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2009.01.083

B. Yan, H. Zhu / Journal of Alloys and Compounds 479 (2009) L62–L65
L63
Fig. 1. Scheme of the synthesis of mono-octadecyl cis-butene dicarboxylate (MAO) by the modification of maleic anhydride (A) and rare earth complexes with long chain
MAO (B).
photoluminescence of this nanometer material were discussed in
detail.
and microstructure were characterized by scanning electronic microscope (SEM,
Philps XL-30), transmission electron microscopic (TEM, H-800). Excitation and mis-
sion spectra for solid powders of this phosphor were determined with PerkinElmer
LS-55 model fluorophotometer (excitation wavelength 613 nm, scan rate 1000 nm/s,
excitation slit width = 3 nm, emission slit width = 3 nm).
2. Experimental
2.1. Synthesis of mono-octadecyl cis-butene dicarboxylate (MAO) by the
modification of maleic anhydride
3. Results and discussion
The synthesis of MAO was adopted as the similar procedure in Ref. [23]. Maleic
anhydride (0.98 g/10 mmol) was mixed with equimolar amount of long chain 1-
eicosanol (2.98 g) in a flask. Then the solid mixtures were placed in an oil bath at the
temperature 110–115 ◦C and react for 16 h. Finally the samples were recrystallized
with n-hexane three times to afford the white powder MAO (Fig. 1A). Anal. Calcd.
for C22H40O4 (MAO, mp: 66 ◦C): C, 71.70; H, 10.94; Found: C, 671.47; H, 10.63.
Fig. 2 shows the XRD pattern of nanometer GdxY2−xO3:Eu3+
synthesized by rare earth complex with long chain MAO precur-
sors (the representative indices peaks have been indicated). All
the diffraction peaks of these samples are similar to those of
Y2O3 (JCPDS65-3178) except for the distinction of diffraction inten-
sity, which belongs to body-centered cubic structure. No apparent
diffraction peak can be checked, suggesting that the Eu3+ occupied
the lattice of Y3+ (or Gd3+) for their similar ion radius. The average
crystallite size was estimated from the full width at half maximum
of the diffraction peak by the Sherrer equation [10,11].
2.2. Synthesis of nanometer size GdxY2−xO3:Eu3+ (x = 0.2, 0.6, 1.0, 1.4, 1.8) by novel
rare earth complex with long chain MAO
The synthesis of nanometer size Y2O3:Eu3+ by rare earth complex with long chain
MAO was described in the following way. The rare earth oxides (Eu2O3, Y2O3:Eu3+
)
were converted to their nitrates by the treatment with concentrated nitric acid. The
corresponding rare earth complexes with this ligand (MAO) were prepared by homo-
geneous precipitation. Excess MAO (3.3 mmol) over rare earth nitrates was dissolved
into ethanol solution and its pH value was adjusted to be about 7.0 with ammonia
solution. Then mixed alcohol solutions of rare earth nitrates (Gd(NO3)3 + Y(NO3)3
(1 mmol) and Eu(NO3)3 (0.05 mmol)) with the molar ratio 1.00:0.05 were added
very slowly to the above solutions and mixed homogenously. After that, the above
mixed solutions were heated under 60 ◦C, whose pH value became alkalescence by
dipping in 1 mol% ammonia solution. After that, the temperature was increased to
100 ◦C to evaporate the excess solvent until the solution became viscous, dried and
the hybrid precursors, which are also served both as dispersing medium and fuel,
were achieved finally (Fig. 1B). At last, the samples were heat-treated at 1000 ◦C for
about 3 h in order to remove the organic components from rare earth coordination
polymeric systems and form the material. The typical scheme of the synthesis can
be shown as below:
kꢀ
Dh k l
=
(1)
ˇ(2ꢁ) cos ꢁ
0.5Gd(NO3)3 + 0.5Y(NO3)3 + 0.05Eu(NO3)3 + 3.10MAO + xNH3·H2O
→ [Ln(MAO)3]complex + xꢀNH3·H2O
→ GdxY2−xO3: Eu3+ + CO2↑ + H2O ↑ + NH3↑ + NO2↑
2.3. Physical measurements of GdxY2−xO3:Eu3+
Elemental analyses (C, H, N) of MAO were carried out by the Elementar Cario EL
elemental analyzer. Infrared spectroscopy of MAO with KBr pellets was performed
on a Nicolet Nexus 912 AO446 model spectrophotometer in the 4000∼400 cm−1
.
The nanometer particles were synthesized by means of X-ray powder diffraction
(XRD, 40 kV and 20 mA, Cu K␣, Philps PW1710, reflections peaks for 211, 220, 400,
420, 440 and 620 directions were used in our measurements). The morphology
Fig. 2. XRD of GdxY2−xO3:Eu3+ derived from rare earth complexes with MAO pre-
cursors: (a) x = 1.8, (b) x = 1.4, (c) x = 1.0, (d) x = 0.6, and (e) x = 0.2.

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B. Yan, H. Zhu / Journal of Alloys and Compounds 479 (2009) L62–L65
Fig. 4. Selected excitation spectra of Gd1.0
complex with MAO precursor.
Y
1.0 O3:Eu3+ derived from the rare earth
ture of Gd1.0 Y1.0 O3:Eu3+ samples is further characterized by TEM
(Fig. 3B), which shows that the particles have a size distribution
in the range of 80–150 nm, which are correlated with SEM and the
XRD value.
By selecting maleic anhydride as staring material, 1-octadecanol
was grafted to achieve amphiphilc MAO ligand and the corre-
sponding rare earth (Gd3+, Y3+, Eu3+) complexes was synthesized
in situ sol–gel synthesis. Then under heating at 1000 ◦C, we used
this amphiphilc rare earth complex as the precursor, which was
also served as dispersing medium to form nanometer size mate-
rial, to prepare the nanometer size GdxY2−xO3:Eu3+ material. We
supposed that in sol–gel process, amphiphilc molecule has special
self-assembling: the hydrophobic segments of the copolymer form
the core of the micelle while the hydrophilic segments form the
corona or outer shell. The hydrophobic micelle core can serve as a
microenvironment for the growth of the rare earth complex, while
the corona shell serves as a stabilizing layer between the hydropho-
bic core and the external medium. We further hypothesized that the
same organization would occur if a particle were a junction point
of many hydrophobic and hydrophilic arms. The incompatible flex-
ible arms can undergo spatial separation by wrapping around the
metallic core. The resulting multi-arm hybrid amphiphile would be
driven to aggregate in order to minimize the entropically unfavor-
able contacts with water molecules. In all, the MAO ligand molecule,
with carboxylic acids as the hydrophilic segments and organic long
chains as the amphiphilic segments, could form nanosized micelle-
like aggregates with various morphologies in aqueous medium
by self-assembling, so the morphology of GdxY2−xO3:Eu3+ nano-
Fig. 3. Selected SEM (A) and TEM (B) of Gd1.0 Y1.0 O3:Eu3+ derived from rare earth
complexes with MAO precursors.
where ˇ(2ꢁ) is the width of the pure diffraction profile in radi-
ans, k is 0.89, ꢀ is the wavelength of the X-rays (0.154056 nm), ꢁ is
the diffraction angle, and Dh k l is the average diameter of the crys-
tallite. From the estimated data, the nanometer GdxY2−xO3:Eu3+
materials for rare earth complex with (MAO) precursors obtained
were phase pure, and have a size distribution in the range of 70 nm
[23,24]. The thermal decomposition temperature was increased for
rare earth coordination polymers in place of rare earth nitrates. As
a result, the particle size was larger than that reported in Ref. [25].
Of course, the higher temperature and the larger size are also nec-
essary and important to obtain the higher luminescence intensity.
All the resultant products were indexed to be body-centered cubic
phase of complex oxides GdxY2−xO3 for the thermal decomposition
temperature below 1200 ◦C [26].
materials can be controlled by their amphiphilc rare earth (Gd3+
,
Y3+, Eu3+) complexes as precursor molecules. This preparation
technology used amphiphile molecules as a control to synthesize
solid-state nanometer material, which can be expected to be a can-
didate technology for the synthesis of luminescent materials by
different rare earth complex precursors.
Surface morphology and particle distribution of GdxY2−xO3:Eu3+
samples derived from the rare earth complex with MAO precursors
are investigated by scanning electron microscopy (SEM) (as shown
in Fig. 3A for the selected SEM of Gd1.0 Y1.0 O3:Eu3+). It can be seen
that the products mainly consist of granules, which exist with a lit-
tle conglomeration in the SEM for the higher temperature 1000 ◦C
of thermal decomposition, but most of which are uniform. It is rea-
sonable that, the special ligand of the rare earth complex precursors
synthesized by ourselves may influence the surface morphology
by providing a better condition for growth of the grains, for it has
both hydrophilic and lipophilic groups. We can also predict approx-
imately that the material particle size is around 100 nm, which is in
agreement with the data from the XRD estimation. The microstruc-
The excitation spectra of the red luminescence (ꢀem = 613 nm)
show asymmetric band for nanometer GdxY2−xO3:Eu3+ derived
from the rare earth complex precursors. Three excitation peaks
were observed 256, 323 and 397 nm, and the other peaks were not
apparent (as shown in Fig. 4 for the selected excitation spectrum of
Gd1.0 Y1.0 O3:Eu3+)AQ for change. The strong broad excitation band
3−
centered at 250 nm corresponds to the VO4
group absorption
and Eu3+–O2− charge transfer state (CTS), which is ascribed to be
the charge transfer band between O2− and central Eu3+ ion. The
wide strong excitation band of host absorption and CTS is favorable
for the energy transfer and luminescence of Eu3+ ion. Besides,
there exist some narrow excitation bands in the long wavelength

B. Yan, H. Zhu / Journal of Alloys and Compounds 479 (2009) L62–L65
L65
Then according to the design and assembly of molecules, the cor-
responding amphiphilc rare earth (Gd3+, Y3+, Eu3+) complex has
been prepared in situ sol–gel synthesis. After that, by using this
rare earth complex as precursor, for the special self-assembling of
amphiphilc molecules can influence the shape, structure, and epi-
taxy of the precursor, we obtained GdxY2−xO3:Eu3+ nanophosphors
under 1000 ◦C. The particles of this nanometer material exhibit uni-
form size in the range of 70–100 nm according to the results of
SEM, TEM and XRD. The luminescent properties show it exhibits
the characteristic emission of Eu3+ ion and band shift to 610 nm, all
of which indicate that amphiphilc rare earth complex with MAO can
influence the morphology and microstructures of GdxY2−xO3:Eu3+
material. Besides that, it can be found that it is a candidate technol-
ogy for the synthesis of nanometer rare earth oxides.
Acknowledgements
The work was supported by the Science Fund of Shanghai Uni-
versity for Excellent Youth Scientists.
Fig. 5. Selected emission spectra of Gd1.0 Y
1.0 O3:Eu3+ derived from the rare earth
complex with MAO precursor.
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4. Conclusion
In summary, amphiphilic MAO has been synthesized by the
modification of maleic anhydride with long chain 1-octadecanol.