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Synthesis, characterization and luminescent properties of Tb(III) doped Eu(III) complex
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2011 Adv. Nat. Sci: Nanosci. Nanotechnol. 2 025015
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ADVANCES IN NATURAL SCIENCES: NANOSCIENCE AND NANOTECHNOLOGY

Adv. Nat. Sci.: Nanosci. Nanotechnol. 2 (2011) 025015 (4pp)

doi:10.1088/2043-6262/2/2/025015

Synthesis, characterization and
luminescent properties of Tb(III) doped
Eu(III) complex nanoparticles
Thi Khuyen Hoang1 , Thanh Huong Nguyen1 , Thu Huong Tran1 ,

Kim Anh Tran1 , Thanh Binh Nguyen1 and Quoc Minh Le1,2
1

Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet
Road, Cau Giay Dist, Hanoi, Vietnam
2
University of Engineering and Technology, Vietnam National University, 144 Xuan Thuy Road,
Cau Giay Dist, Hanoi, Vietnam
E-mail:

Received 15 October 2010
Accepted for publication 19 April 2011
Published 10 June 2011
Online at stacks.iop.org/ANSN/2/025015
Abstract
In recent years, considerable effort has been devoted to the development of transition metal
complexes as novel luminescent materials that have potential application in the fluorescent
labels for chemistry or biology. Among them, the nanostructured lanthanide complexes have
been receiving much attention because of their excellent luminescence properties, which are
attributed to the intramolecular energy transfer between the ligands and chelated lanthanide
ions and their high solubility in water. This paper presents some results of the synthesis and
characterization of the nanoparticles of Eu(III) and Tb(III) complexes with naphthoyl
trifluoroacetone and tri-n-octylphosphineoxide. In addition, the influence of the dopant Tb(III)
on the photophysical properties of the system of lanthanide complexes of Eu(III) and Tb(III) is
also studied.
Keywords: lanthanide complexes, nanoparticles, luminescence, fluorescent labels
Classification number: 4.02

lifetime (sub-microsecond to millisecond range), sharply
spiky emission spectra (<10 nm full width at half-maximum,

FWHM), large Stockes shifts (>150 nm), and high quantum
yield (∼1) [9, 10]. In this study, the nanostructured Tb(III)
doped Eu(III) complexes with tri-n-octylphosphineoxide and
naphthoyl trifluoroacetone ligands were synthesized and their
characterization and spectral properties, such as fluorescence
intensity, emission spectrum and fluorescence lifetime, were
studied in detail.

1. Introduction
Various luminescent nanoparticle materials have recently
been fabricated and applied in diagnostics, high throughput
screening, and bioimaging [1–4]. The use of fluorescent
nanoparticle labels in highly sensitive assays is based on
their optical properties [5–8]. The lanthanide chelate labels in
biological studies contain typically an organic chromophore,
which sensitizes to absorb the excitation light and transfer
the excitation energy to the lanthanide ions. Consequently,
lanthanide chelates exhibit broad excitation spectra owing to
the organic ligands and narrow emission spectra resulting
from the lanthanide ions. Recently, their application to
biological labeling has attracted growing interest due to their
high photochemical stability and quantum yield, and their
good water solubility, and because they possess a reactive
group that allows covalent attachment to biomolecules.
The spectral characteristics include a long fluorescence
2043-6262/11/025015+04$33.00

2. Experimental
2.1. Materials
EuCl3 · 6H2 O (99,99%), TbCl3 · 6H2 O (99,99%), tri-n-octylphosphineoxide

(TOPO)
and
1-(2-naphthoyl)-3,3,
3-trifluoroacetone (NTA) were purchased from Sigma
Aldrich. Sodium dodecyl sulfate (SDS), dimethyl sulfoxide
1

© 2011 Vietnam Academy of Science & Technology

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Adv. Nat. Sci.: Nanosci. Nanotechnol. 2 (2011) 025015

T K Hoang et al

Table 1. The ratios of Eu(III) complex solution and Tb(III) complex
solution.
Sample

MEu

Ratio
Tb/Eu

100% Eu

(a)

MTbEu1a MTbEu2a MTbEu3a MTbEu4a
16/1

8/1

4/1

1/1

(b)

Figure 1. Structure of lanthanide chelates with NTA and TOPO
ligands.

(DMSO), dimethyl formamide (DMF) and polyvinylpyrrolidone (PVP) (M = 40 000 g mol−1 ) were from Merck.
Deionised water was used for the preparation of nanoparticle
solutions. All other chemicals were of analytical grade.

Figure 2. FESEM images of the fluorescent nanoparticles of
(a) Tb(III) doped Eu(III): NTA.TOPO and (b) Tb(III) doped Eu(III):
NTA.TOPO@PVP.

2.2. Synthesis

spectrophotometer system (Horiba Jobin Yvon IHR 550).
Fourier transform infrared (FTIR) spectra of the nanoparticles
were measured by using an IMPACT 410-Nicolet (FTIR)
spectrometer.

Eu(III) complex solution was prepared from 50 mg

EuCl3 · 6H2 O, 135 mg TOPO and 125 mg NTA in 40 ml
DMSO. Tb(III) complex solution was formed from 60 mg
TbCl3 · 6H2 O, 160 mg TOPO and 125 mg NTA in 40 ml
DMSO. Eu(III) complex and Tb(III) complex solutions were
mixed with the ratios in table 1.
The fabrication of the nanostructured particles of
lanthanide complexes was carried out using a vortex mixer
(Labinco L46, Netherlands). The reaction tube containing
5 ml of water was stirred at 500 rpm and a mixture of
0.25 ml Tb(III) doped Eu(III) complex solution and 0.1 ml
SDS 10 mM was rapidly added to the tube using a
maximum vortex mixing speed of 2500 rpm. The reactions
were carried out at room temperature. A colloidal solution
of Tb(III) doped Eu(III) nanoparticles was produced by
agglomerating hydrophobic chelates in aqueous solution.
After agglomeration, 0.1 ml PVP was added into the solution.
A PVP shell was subsequently grown onto the agglomerated
nanoparticles (figure 1).
The morphology and size of the nanoparticles were
determined by using a field emission scanning electron
microscope (FESEM, Hitachi, S-4800). The emission
(fluorescence) spectra were recorded on a luminescence

3. Results and discussion
In this research, uniform fluorescent nanoparticles were
synthesized in one step at room temperature. Figure 2 shows
FESEM images of synthesized nanoparticles of Tb(III) doped
Eu(III) chelate with TOPO and NTA ligands. Aggregation
of nanoparticles is not observed. The obtained nanosized
particles were uniform with a mean diameter of 25 nm ± 5 nm

and shell thickness of 10 nm.
The FTIR spectra of the synthesized nanoparticles of
Tb(III) doped Eu(III) chelates are given in figure 3. A broad
band at wavenumber of 3444 cm−1 is attributed to the H2 O
molecule, and the band at 1650 cm−1 is related to the C = O
group of the ligand. The complexation between Eu(III) and
Tb(III) with NTA.TOPO ligands is evidenced by a narrow
band located at 1388 cm−1 , which appeared to prove that
Eu(III) or Tb(III) ions may be coordinated to two oxygen
atoms of ligands.

2


Adv. Nat. Sci.: Nanosci. Nanotechnol. 2 (2011) 025015

T K Hoang et al

1.0
3444.64

Tbeu3a_01
Date : Fri Sep 2010
Scans : 32
Resolution : 4000

Absorbance

0.8

0.6
1649.92

0.4
493.15
1107.97

0.2

1018.95
1434.21
1388.37
1253.55

768.18
671.11
598.31

0.0
4000

3500

3000

2500

2000

1500

1000

500

-1

wavenumbers (cm )

Figure 3. The Fourier transform infrared (FTIR) spectra of nanoparticles of Tb(III) doped Eu(III): NTA.TOPO@PVP.
6000

250

616nm
MEu

5000

5

7

D 0- F 2

MEu
MTbEu4a
MTbEu3a

200

MTbEu3a

Intensity (au)

Intensity

4000

3000

2000
5

5

0

MEu

100

MTbEu4a

7

D 0- F 1

1000

150

5
5

7

D0- F0

7

D0- F3

50

7

D0- F4

0
500

550

600

650

700

750

800

850

wavelength (nm)

0

1

2

3

4

5

Time (ms)

Figure 4. Fluorescent spectra of nanoparticles of Eu(III):
NTA.TOPO@PVP at λexc = 370 nm.

Figure 6. Emission lifetime of nanoparticles of Tb(III) doped
Eu(III): NTA.TOPO@PVP at λexc = 325 nm.

7000

MTbEu4a
MTb
MTbEu1a
MTbEu2a
MTbEu3a
MTbEu4a
MEu

6000

5000

Intensity

4000

Emission spectra of nanostructured Eu(III) chelates and
Tb(III) doped Eu(III) chelates in aqueous solution were
measured under excitation of λexc = 325 nm and λexc =
370 nm. It can be seen that the nanoparticle complexes
exhibit the characteristic narrow emission peaks of trivalent
lanthanide ions. The Eu(III) nanoparticles showed a
maximum emission at 616 nm (figure 4). The emission spectra
consist of four main peaks at 593, 616, 652 and 702 nm,
which correspond to the 5 D0 →7 Fn (n = 1, 2, 3, 4) transitions
of Eu(III) (5 D0 →7F1 at 593 nm, 5 D0 →7F2 at 616 nm,
5
D0 →7F3 at 652 nm and 5 D4 →7F4 at 702 nm).
The influence of the dopant to optical properties of
the nanoparticle complexes of Tb(III) doped Eu(III) was

investigated. The shape of the spectra of samples of
nanoparticle Tb(III) doped Eu(III) chelates is similar in the
case of Eu(III) nanoparticles and the emission maximum is not

MEu
MTbEu3a
MTbEu2a

3000

MTbEu1a

2000

MTb

1000

0
350

400

450

500

550

600

650

700

750

800

wavelength(nm)

Figure 5. Fluorescent spectra of nanoparticles of Tb(III) doped
Eu(III): NTA.TOPO@PVP at λexc = 325 nm.

3


Adv. Nat. Sci.: Nanosci. Nanotechnol. 2 (2011) 025015

T K Hoang et al

shifted. However, the fluorescent intensity of nanoparticles in
aqueous solution depends strongly on the ratio of Tb(III) in
Eu(III) chelates (figure 5).
In the studied range of ratios, the intensity at the peak of
616 nm of sample MTbEu4a with ratio (1 : 1) is higher than
that of MEu. The fluorescence lifetime of nanosized complex
samples MTbEu4a, MEu, and MTbEu3a was found to be 587,
566 and 431 µs, respectively (figure 6).

Acknowledgments
This work was supported by the Vietnam Basic Research
Programming for application, project 2/2/742/2009/HÐÐTÐL, Vietnam’s National Foundation for Science and
Technology Development (NAFOSTED), project code:
103.06.46.09 and The Key Lab of Electronic Materials
and Devices. The authors acknowledge all the members of
FESEM and PL groups for their technical assistance.

4. Conclusions
References
The nanostructured particles of Tb(III) doped Eu(III) chelate
with TOPO and NTA ligands were successfully synthesized.
The uniform nanoparticles can be synthesized at room
temperature without rigorous experimental conditions. These
nanoparticles Tb(III) doped Eu(III) chelates are stable in
aqueous solution, which was obtained by adsorbing PVP
on their surface. The aggregation of the nanoparticles is
prevented, which is a result of the presence of a protective
polymer layer. A nanoparticle size of 25 nm ± 5 nm and a
shell thickness of 10 nm were obtained. The nanoparticle
complexes exhibit the characteristic narrow emission peaks
and maximum emission at 616 nm. The fluorescent intensity
of nanoparticles in aqueous solution depends on the ratio
of Tb(III) in Eu(III) chelates. The fluorescence lifetime of
synthesized nanoparticle chelates was approximately 550 µs.

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