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Cite this: New J. Chem., 2014,
38, 2114

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Fabrication and optical characterization of
multimorphological nanostructured materials
containing Eu(III) in phosphate matrices for
biomedical applications
T. T. Huong,*a L.T. Vinh,ab T. K. Anh,a H. T. Khuyen,a H. T. Phuongac and
L. Q. Minhad
EuPO4ÁH2O nanorods/nanoparticles with a rhabdophane-type hexagonal form have been successfully
synthesized using microwave assisted co-precipitation. The effects of chemical composition and pH on
the size, shape, morphology and luminescence properties have been investigated by powder X-ray
diffraction, Field Emission Scanning Electron Microscopy (FESEM), and photoluminescence spectroscopy.
The mean size of the nanorods is about 15–30 nm in diameter and 200–400 nm in length and the size

Received (in Victoria, Australia)
7th October 2013,
Accepted 9th January 2014
DOI: 10.1039/c3nj01206a

of nanoparticles is 10–20 nm. A powdered sample of these EuPO4ÁH2O nanorods/nanoparticles emitted
yellow-green light with narrow bands at 594, 619, 652, and 697 nm under UV-vis excitation. The surface

b
Department of Chemistry, Hanoi University of Mining and Geology, Vietnam
c
Department of Chemistry, Hanoi Medical University, Vietnam
d
University of Engineering and Technology, National University Hanoi, Vietnam

2114 | New J. Chem., 2014, 38, 2114--2119

There are several kinds of nano-materials containing rare
earth ions with high luminescent efficiencies of up to and above
ten percent. Such as YVO4:Eu3+ nanoparticles,8,9 LnPO4ÁH2O:Eu,
Tb nanomaterials10–14 and ZrO2:Yb3+, Er3+ nanoparticles,15
which have been developed for agrobiological and medical
applications.4,5,16
In previous studies, we have been successful in synthesizing
nanorods/nanowires of EuPO4, and TbPO4.17,18 It was found
that the size and shape of the products have important effects
on their luminescent intensity. However, nano-sized materials
with high luminescent yields are still required for medical and
biological applications. Therefore, we are continuously trying
to achieve higher luminescent intensities from these nanomaterials containing the rare earth ion Eu3+ in these phosphate
matrices.
In this report, we focus on the fabrication and luminescent
characterization of EuPO4ÁH2O, a multimorphological nanostructured material (e.g. particles, rods). The EuPO4ÁH2O nanoparticles and nanorods were synthesized using microwave
assisted co-precipitation. The effects of chemical composition
and pH on the size, shape, morphology and luminescence
properties of the prepared materials were also investigated.
Then, we investigated the surface effects of the built core–shell
structure on the fluorescent properties, and the compatibility

We observed that the EuPO4ÁH2O nanorods were in fact rods of
connected particles, which then broke up into nanoparticles
with diameters of about 15–20 nm. Based on the FESEM results
in Fig. 1, we can primarily summarize that the shape (from rod
to particle) of the synthesized samples can be controlled by
adjusting the mole ratio of Eu3+ and PO43À. The results show
that at a mole ratio of Eu3+/PO43À = 1/15, a breaking up process
has started, and we start to see the formation of nanoparticles
in place of nanorods. So we chose this ratio to study the effects
of other factors such as pH, etc.
The investigation of the influence of a pH range between 2
and 12 on the morphology of the EuPO4ÁH2O nanomaterial was

Fig. 1 FESEM images of the EuPO4ÁH2O multimorphological nanostructured material with changes in the mole ratio of Eu3+ and PO43À, synthesized
at pH = 6: (a) Eu3+/PO43À = 1/1; (b) Eu3+/PO43À = 1/3; (c) Eu3+/PO43À = 1/5; (d) Eu3+/PO43À = 1/10; (e) Eu3+/PO43À = 1/15; (f) Eu3+/PO43À = 1/30.

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Fig. 2 FESEM images of the EuPO4ÁH2O multimorphological nanostructured materials with changing pH values: pH = 2 (a), pH = 4 (b), pH = 6 (c),

inhibited. Therefore, the formed nanorods/nanowires started to
break up, and started to form nanoparticles. This reconstruction
maybe due to a preferential ionic interaction, in which the

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hydroxide anions (OHÀ) compete with the phosphate anions. In
addition, the rapidly changing electric field of the microwave
reactor may result in a nanoscale sized slit in the microdomain
of the as formed nanorods/nanowires. In short it can be
summarized that with pH values between 8 and 12 the breaking
up process of the EuPO4ÁH2O nanorods/nanowires became
obvious. When the pH = 12 the formation of the nanoparticles
was nearly complete and the FESEM image clearly shows
individual EuPO4ÁH2O nanoparticles. Nevertheless we found
that when the pH was increased, the size of the EuPO4 particles
decreased and that the particle size was more uniform.
Phase and structure. XRD patterns of the prepared EuPO4Á
H2O nanomaterials show that a rhabdophane-type hexagonal
form (PDF card No. 20-1044) is the dominant phase (Fig. 3).
Qualitatively, as shown in Fig. 3 (lines 1–6), the changing of the
mole ratio of Eu3+ and PO43À causes no change in the crystalline phase composition or crystallinity of the prepared samples.
The X-ray diffraction analysis results show that the phase of the

393 nm.

prominent emission line for the EuPO4ÁH2O nanomaterials at
pH = 2, 4, 6, 8, 9, 10, 11, 12. These fluorescence properties of
EuPO4ÁH2O have attracted a great deal of attention in biology
and medicine.
To use EuPO4ÁH2O products in the study of biomedical
processes, the first step is the need to functionalize the nanomaterials, i.e. to connect its surface to a number of functional
groups (organic), such as OH, NH2, SH. . ..1,7 We have studied the
appropriate chemical reactions for functionalizing luminescent
nanomaterials such as EuPO4ÁH2O using sol–gel technology.18
We present here the effect of shells and organic functionalization on the photoluminescent characterization of EuPO4Á
H2O nanomaterials. Due to the large surface-to-volume ratio
of nanophosphores their surface plays an important role in
their optical properties. Therefore the modification of their
surface by sol–gel coating technology can bring about a large
change in emission intensity of these nanophosphores. The
conditions used in the sol–gel deposition were chosen to
optimize the fabrication of an outer layer that contained the
chosen functional group so as to maintain the emission properties as much as possible. PL spectra of EuPO4ÁH2O synthesized
at pH = 2 and the core–shell nanophosphores of EuPO4Á
H2O@silica–NH2 under excitation at lex = 393 nm are presented
in Fig. 5. The results reveal that the luminescent intensity was
substantially changed after the EuPO4ÁH2O nanoparticles had
been coated with a shell layer, which was linked with an amine
group (NH2) (Fig. 5).
These luminescent experimental results indicate that the
NH2 group in the shell effectively quenches the luminescent
intensity of EuPO4ÁH2O. However, the influence of the sol–gel
shell layer on the structure of the fluorescent spectra is negligible,

one of the key products of the Industrial Centre for Investigation
and Production of Vaccine and Biologicals (POLYVAC-centre).
Application as a fluorescent immunoassay (FIA) of viruses/vaccines
We applied a comparative analysis method and used the conjugated
IgG-linked nanomaterials, as well as a commercial product as the
reference, in the cell incubation procedure of the POLYVAC-centre.18
We have experimentally researched the conjugated product IgG–
EuPO4ÁH2O in an incubation process with vaccine fabricates. The
images obtained from fluorescent microscopic measurements are
shown in Fig. 6. In Fig. 6(a), one can see the image of a commercial
conjugate incubated with standard Vero cells from the vaccine
production processing line of the POLYVAC-centre. Fig. 6(b), shows
the image of Vero cells infected with the measles virus, and the
commercial conjugate. Fig. 6(c) shows the image of measles virus

infected Vero cells and EuPO4ÁH2O@silica–NH2–IgG. Incubation
processing with an exposure procedure of the conjugate in the
POLYVAC-centre was used for the preparation of the tested specimens. The obtained fluorescent images in the Fig. 6(b) and (c) show
clearly the locations of the products of the immune reactions
between the antibody of the MP commercial conjugate and the
EuPO4ÁH2O@silica–NH2–IgG conjugate and the antigen of the
measles virus in the vaccine. The results indicate that the fabricated
conjugates could be used for the detection and recognition of the
measles virus, and for controlling the quality of the fabrication
process. The performance of EuPO4ÁH2O@silica–NH2 linked with
IgG for fluorescence immunoassay (FIA) analysis using a fluorescent
optical microscope may be comparable with the commercial conjugate (label) for reference. Nevertheless, the prepared EuPO4Á
H2O@silica–NH2–IgG conjugates have shown a strong, stable, yellow
green fluorescence emission and a reproducible intensity in a broad
range of pH values, and in the biological microenvironments of


2118 | New J. Chem., 2014, 38, 2114--2119

EuPO4ÁH2O nanostructured materials were prepared using a
microwave assisted method combined with co-precipitation
using Eu(NO3)3Á5H2O (Sigma-Aldrich, 99.9%), and NH4H2PO4
(Merck, 99%) as starting materials. The reaction solution was
magnetically stirred for 120 min and the pH of this solution
was adjusted in the range of 2–12 by adding 10 mol LÀ1 NaOH.
After that, at each selected pH value, this reacting solution was
irradiated using a MAS-II microwave synthesis extraction workstation (Sineo Co.) for 15 minutes with the microwave power
adjusted from 300 to 900 W. The mole ratio of Eu3+ and PO43À

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was changed as follows: Eu3+/PO43À = 1/1; 1/3; 1/5; 1/10; 1/15; 1/30.
The final products were collected, centrifuged at 5900 rpm, and
cleaned several times using ethanol and distilled water.
The primary silicate shell as a protecting layer and functionalization with NH2 was fabricated as following: 10 ml of
tetraethylorthosilicated (TEOS) (1/2) in absolute ethanol and
10 ml of as-synthesized EuPO4ÁH2O solution was mixed with a
magnetic stirrer at room temperature (24 hours). The pH of
this solution was adjusted to the range of 11–12 by adding

luminescence spectrum photometer system, Horiba Jobin Yvon
IHR 320 (USA). The excitation wavelength was 393 nm. The
microsized images of the virus infected cells exposed to the
nanomaterial conjugates were viewed using fluorescent microscopic equipment, an Olympus BX-40 (Japan), and pictured
using a digital camera, Nikon D5000, with a resolution of 12.30,
f/3.5–5.6 G VR.

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Acknowledgements
This work was supported by Vietnam’s National Foundation for
Science and Technology Development (NAFOSTED), project
code: 103.06-2012.72 and implemented in the framework of
long-term Research Topics of Rare Earth Nanoluminophores
and Application, and partly supported by the National Key Lab
of Electronic Materials and Devices in Institute of Materials
Science, Vietnam Academy of Science and Technology.

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