Enhanced luminescence of novel rare earth complexes Eu(3,5-DNBA)3Phen in nano-TiO2

Article abstract of DOI:10.1016/j.saa.2008.07.003

Eu³⁺ (or Tb³⁺) of 3,5-dinitrobenzoic acid and 1,10-phenanthroline ternary rare earth complexes were synthesized and characterized by thermal analysis, infrared spectroscopy, elemental analysis and fluorescence spectroscopy. In this s

Full text of DOI:10.1016/j.saa.2008.07.003

Spectrochimica Acta Part A 72 (2009) 22–25
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Enhanced luminescence of novel rare earth complexes Eu(3,5-DNBA)3Phen in
nano-TiO2
Yuguang Lva,b, Jingchang Zhanga,∗, Weiliang Caoa, Yali Fua
a Institute of Modern Catalysis, Beijing University of Chemical Technology, State Key Laboratory of Chemical Resource Engineering, Beijing 100029, China
b College of Chemistry and Pharmacy, Jiamusi University, Jiamusi 154007, China
a r t i c l e i n f o
a b s t r a c t
Eu3+ (or Tb3+) of 3,5-dinitrobenzoic acid and 1,10-phenanthroline ternary rare earth complexes were syn-
thesizedandcharacterizedby thermalanalysis, infrared spectroscopy, elemental analysisandfluorescence
spectroscopy. In this study an organic–inorganic combined device indium tin oxide/poly(N-vinylcar-
bazole):RE(3,5-DNBA)3Phen:TiO2/Al was fabricated. The nano-TiO2 has been used in the luminescence
layer to change the electroluminescence property of RE(3,5-DNBA)3 Phen (RE = Eu3+or Tb3+).
© 2008 Published by Elsevier B.V.
Article history:
Received 7 September 2007
Received in revised form 1 July 2008
Accepted 3 July 2008
Keywords:
Ternary complexes
Nano-TiO2
Characteristics
Electroluminescence
1. Introduction
2. Experiments
Rare earth metal complexes have special characteristics, such as
extremely narrow emission bands and high internal quantum effi-
ciencies, which are suitable to be used as the emission materials
[1–4]. Therefore, many rare earth complexes have been synthe-
sized and used as organic electroluminescence devices [5–10].
Titanium dioxide (titania, TiO2) with the rutile-type structure is
transparent for light in the wide range of the visible spectrum. The
absence of light absorption, along with its high refractive index
(n ∼ 2.7), makes rutile-type TiO2 a fascinating material for photonic
applications in the visible regions. In spite of this advantage, lit-
tle attention has been paid to rare earth ternary complexes with
Eu3+ (or Tb3+), 3,5-dinitrobenzoic acid and 1,10-phenanthroline in
nano-TiO2.
The complexes of Eu(3,5-DNBA)3Phen and Tb(3,5-DNBA)3Phen
were synthesized, and nano-TiO2 was mixed with the rare earth
complex and poly(N-vinylcar-bazole) to form the luminescence
layer in the electroluminescence [11–16]. It was found that there
was an efficient energy transfer process between the complex and
nano-TiO2, when the device was operating at low voltages. It shows
that it is an effective method to improve the electroluminescence
intensity of lanthanide complex by using electronic characteristics
of inorganic semiconductor materials.
2.1. Materials
The purity of europium (terbium) oxides was 99.99%. Other
reagents were used in analytical grade.
2.2. Synthesis of materials RE(3,5-DNBA)3Phen
1 mmol mixture of EuCl3·6H2O (or TbCl3·6H2O), and 3 mmol
of 3,5-DNBA were dissolved in ethanol. The pH value of the
mixture was adjusted to 6–7 by adding 3 mmol ammonia. Then
1,10-phenanthroline in ethanol solution was added to the reaction
mixture, the molar ratio of 1,10-phenanthroline to RE3+ ion was 1:1.
The precipitate was filtered, washed with water and ethanol, dried
at room temperature, and then stored in a silica–gel drier. Nano-
TiO2 was prepared using the chemical vapor deposition (CVD) of
TiCl4 [17]. The compositions of the complexes were analyzed by IR
and elements analysis according to the ordinary methods, and its
chemical structure was shown in Fig. 1. Elemental analysis data of
complexes were listed in Table 1.
2.3. Measurements
Elemental analyses were performed on a PerkinElmer 240 C ana-
lytical instrument. DTA–TG curves were obtained with a TGA–DTA
1700-PerkinElmer (in N2). Infrared (IR) spectra were recorded in the
range of 4000–400 cm−1 by a prostige-21IR spectrophotometer in
KBr flake. The excitation and emission spectra measurements were
∗
Corresponding author. Tel.: +86 1 64434904; fax: +86 1 64434898.
E-mail address: zhangjc1@mail.buct.edu.cn (J. Zhang).
1386-1425/$ – see front matter © 2008 Published by Elsevier B.V.
doi:10.1016/j.saa.2008.07.003

Y. Lv et al. / Spectrochimica Acta Part A 72 (2009) 22–25
23
Fig. 1. Chemical structure of ternary complexes of RE(3,5-DNBA)3Phen.
Table 1
Elemental analysis.
Complex
RE%
Analytically found (calculated)%
C
H
N
Eu(3,5-DNBTA)3Phen
Tb(3,5-DNBTA)3Phen
15.72 (15.74)
16.37 (16.35)
41.03 (41.01)
40.70 (40.72)
1.78 (1.76)
1.76 (1.75)
11.62 (11.60)
11.51 (11.52)
performed on a Shimadzu 5301 spectrofluorophotometer equipped
with a 150 W xenon lamp as the excitation source. Spectra were
recorded using monochromator slit widths of 1.5 nm on both exci-
tation and emission sides. The PL and EL spectra were measured on
a fluorolog-3 Spectrophotometer of the American SPEX Company.
The luminance was measured by PR-650 spectra-scan spectrome-
ter.
3.3. Photoluminescence properties
All excitation spectra were recorded by monitoring the lumines-
cence at 614 nm for Eu3+ and 545 nm for Tb3+ in Fig. 4. For ligand
(3,5-DNBA) and RE(3,5-DNBA)3Phen, the excitation spectrum con-
sists of a broad band ranging from 260 to 400 nm, and their ꢀex
are 312 and 315 nm, respectively in Fig. 4(a). Fig. 4(b) shows the
emission spectra of ligand and RE(3,5-DNBA)3Phen, which were
obtained by exciting these complexes with ultraviolet. It can be
observed that the spectra are the typical ligand centered transitions
in 414 nm. The experiment results prove that the RE3+ absorbs the
3. Results and discussion
3.1. DTA–TG analysis
DTA–TG plots of Eu(3,5-DNBA)3Phen are shown in Fig. 2.
DTA–TG plots of complex Tb(3,5-DNBA)3Phen showed similar
curve patterns. For DTA plots of Eu(3,5-DNBA)3Phen, exothermic
peak at 245 and 410 ◦C, the gross weight loss is 75%. RE(3,5-
DNBA)3Phen decompose in two steps, ranging from 450 to 700 ◦C,
TG curves prove that the complexes are stable.
3.2. IR spectra analysis of the complexes
FTIR absorption spectra of complexes are shown in Fig. 3. It is
noted that similar results are obtained from Eu(3,5-DNBA)3Phen
and Tb(3,5-DNBA)3Phen complexes. The band in the spectra of
complexes at about 525 cm−1 (which cannot be observed in the
ligands) reveals the presence of O → RE. The band at wave number
1560 cm−1 is due to stretching vibration of –N C, while at 721 cm−1
is corresponding to rC–H vibration of 1,10-phenanthroline. In addi-
tion, typical asymmetric vibration of VC group bands is detected
O
at about 1608 and 1531 cm−1
.
Fig. 2. DTA–TG plots of Eu(3,5-DNBA)3Phen.

24
Y. Lv et al. / Spectrochimica Acta Part A 72 (2009) 22–25
Fig. 3. (a) Infrared spectra of RE(3,5-DNBA)3Phen in the range 4000–400 cm−1. (b)
Infrared spectra of RE(3,5-DNBA)3Phen in the range 2800–400 cm−1
Fig. 4. (a) Typical excitation spectra of ligands and complex RE(3,5-DNBA)3Phen.
(b) Typical emission spectra of ligands and complex RE(3,5-DNBA)3Phen.
.
energy and transferred it to the ligands, and then the ligands emit
typically blue luminescence.
3.4. Electroluminescence properties
Two electroluminescence devices with different structures were
fabricated, which were denoted as A and B, respectively. Their struc-
ture can be abbreviated as ITO/PVK:RE(3,5-DNBA)3Phen:TiO2/Al
for A and ITO/PVK:RE(3,5-DNBA)3Phen/Al for B. In device A,
nanometer material of TiO2 was used as a function layer for the
transportation and acceleration of electron.
In this experiment, no electroluminescence for device B with
the pure organic structure. Fig. 5 shows a typical EL spectrum of
Eu(3,5-DNBA)3Phen in device A, the characteristic emissions of
europium ions are obtained at a driving voltage of 11 V. The emis-
sion peak at 594 nm is corresponding to the energy level transitions
of 5D0–7F1 of europium ion (Eu3+), the 5D0–7F1 has strong orange
luminescence emission. Compared to device B, the luminescence
property of Eu3+ complex changed obviously in device A. Under the
same conditions, no emission band was observed for the complex
Tb(3,5-DNBA)3Phen. Semiconductor TiO2 thin film acts as electron
function layer and hole blocking layer according to its electronic
characteristics and energy level [18–20]. Therefore, the EL property
of Eu(3,5-DNBA)3Phen has been greatly changed.
Fig. 5. EL spectrum of Eu(3,5-DNBA)3Phen at a driving voltage of 11 V.

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4. Conclusion
412) and the emphasis research fund for Jiamusi University
(Szj2008-018).
Eu3+ and Tb3+ of 3,5-dinitrobenzoic acid and 1,10-phenanthro-
line ternary complexes had been synthesized and characterized.
The experiment results showed that the RE3+ absorbs the energy
and the energy was transferred to ligands, then the ligands emit
typical blue luminescence.
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Acknowledgments
This work was supported by research fund for the Doctoral
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