Study of the luminescence properties of a novel rare earth complex Tb(DPC)22H2O

Article abstract of DOI:10.1016/j.saa.2009.04.009

Rare earth complex Tb(DPC)₂2H₂O was synthesized by introducing Pyridine-2,6-dicarboxylic acid(H₂DPC) as the ligand and characterized by UV, fluorescent and infrared spectra as well as elemental analysis. The complex exhibi

Full text of DOI:10.1016/j.saa.2009.04.009

Spectrochimica Acta Part A 74 (2009) 26–29
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Study of the luminescence properties of a novel rare earth complex
Tb(DPC)22H2O
Yuguang Lva,∗, Qiuping Lia, Chunhui Shib, Hairan Liua, Fenghua Liua, Lili Wua,
Dongmei Wua, Hong Liua, Jie Xiec
a The Provincial Key Laboratory of Biomaterials, College of Chemistry and Pharmacy, Jiamusi University, Jiamusi 154007, China
b Clinic Medical College, Jiamusi University, Jiamusi 154002, China
c Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Rare earth complex Tb(DPC)22H2O was synthesized by introducing Pyridine-2,6-dicarboxylic
acid(H2DPC) as the ligand and characterized by UV, fluorescent and infrared spectra as well as elemen-
tal analysis. The complex exhibited ligand-sensitized green emission, and it has the higher sensitized
luminescent efficiency and longer lifetime. The effect and mechanism of the ligand (H2DPC) on the lumi-
nescence properties of terbium complex was discussed. In device ITO/PVK/Tb(DPC)22H2O/Al, Tb3+ may
be excited by intramolecular energy transfer from ligand as observed by electroluminescence. The main
Received 21 September 2008
Received in revised form 6 April 2009
Accepted 15 April 2009
Keywords:
Organic compound
Thin films
Electroluminescence
Energy transfer
7
emitting peak at 545 nm can be attributed to the transition of 5D4→ F5 of Tb3+ ion and this process results
in the enhancement of green emission from electroluminescence device.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
that the complex of Tb (III) emits strong green luminescence when
excited by UV light.
Recently, considerable of studies have been focused on the
design and assembly of fluorescent rare earth complexes [1–4]. Tb3+
ion, the complexes of which emit green light, is one of the rare
earth ions that show the best luminescence property. The ligands
are usually called “antennas” absorb and transfer energy to the rare
earth ions and consequently increase their luminescence intensity.
Many rare earth complexes have been developed as the emitters
in organic photoluminescence and electro-luminescence devices
[5–16]. In order to improve the luminescence properties of rare-
earth complexes, the choosing of ligands is very important. Though
much work has been done, the effect the ligands on the lumines-
cence properties of rare-earth complexes still needs to be further
studied. Pyridine-2,6-dicarboxylic acid (H2DPC) possess biological
active in the body of the animal and plant. Its derivatives and com-
plexes were extensively and deeply studied and were used to all
sorts of fields [17,18]. But very little discussions were reported in
organic photoluminescence and electroluminescence.
2. Experiments
2.1. Reagents and apparatus
Tb4O7 (99.99%), pyridine-2,6-dicarboxylic acid (H2DPC) and
other chemicals were analytical reagent grade and used without
further purification. TbCl3·6H2O was prepared by dissolving ter-
bium oxides in hot hydrochloric acid (and evaporating excess HCl
and water).
Elemental analyses were performed on a Perkin-Elmer 240C
analytical instrument. Infrared spectra were recorded in the range
of 4000–400 cm−1 by a prostige-21IR spectrophotometer in KBr
flake. UV–vis spectra were performed on a UV-2501PCS dou-
ble spectrophotometer. The excitation and emission spectra were
recorded on a Shimadzu 5301 spectrofluorophotometer equipped
with a 150W xenon lamp as the excitation source. Spectra were
recorded using monochromator slit widths of 1.5 nm on both exci-
tation and emission sides. Lifetimes were measured with a Spex
1934D phosphorimeter using a 450-w flash lamp as the excita-
tion source (pulse width = 3 ␮s). The 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.
In this paper, we have successfully synthesized rare earth com-
plex Tb(DPC)22H2O with remarkably sharp green emission bands.
In PVK/Tb(DPC)22H2O blend, the green emission of terbium com-
plex was enhanced and PVK emission was quenched. Results show
∗
Corresponding author. Tel.: +86 0454 6822098.
E-mail addresses: yuguanglv@163.com, lvyuguang@yahoo.cn (Y. Lv).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.04.009

Y. Lv et al. / Spectrochimica Acta Part A 74 (2009) 26–29
27
Fig. 2. UV spectra of ligand and complex Tb(DPC)22H2O.
Fig. 1. Infrared spectra of the complex Tb(DPC)22H2O (ꢀ = 400–4000 nm) (1, DPC; 2,
Eu(DPC)22H2O; 3, Tb(DPC)22H2O)
2.2. Electroluminescence device preparation
The device structure of the complex Tb(DPC)22H2O was
fabricated according to the literature method [19,20]. Poly(N-
vinylcar-bazole) (PVK) was dissolved in chloroform with
a
concentration of 10 mg/ml. In order to improve the performance
of Tb(DPC)22H2O thin film, Tb(DPC)22H2O was doped into PVK
at weight ratio of 1:5. The PVK:Tb(DPC)22H2O thin film was
fabricated on the top of cleaned ITO coated glass substrate by spin-
coating method. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline
(BCP) and aluminum quinoline (Alq3) films were fabricated by ther-
mal evaporation at a rate of about 0.3 Å/s under high vacuum of
2 × 10−6 Torr.
2.3. Synthesis of the complexes
The Tb (III) complex was synthesized by mixing the TbCl3·6H2O
and the ligand (H2DPC) in ratio 1:2 in ethanol under stirring. The
precipitation produced by adding ammonia. The precipitation was
then filtered, washed with water and ethanol and dried, then stored
in a silica-gel drier.
Fig. 3. Typical emission spectra of the complex Tb(DPC)22H2O excited at 330 nm.
3.2. UV absorption spectra analysis
UV absorption spectra of ligand and complex in DMF solution
(5 × 10−5 mol/L) are shown in Fig. 2. They all exhibit domain absorp-
tion peaks in the ultraviolet region (200–400 nm). The results show
that UV spectra of the Tb (III) complex with the ligand are similar.
3. Results and discussion
3.1. IR spectra analysis
The spectra for the ligand H2DPC and the corresponding Tb3+
complex are shown in Fig. 1. The spectra of the Tb3+ complex with
the ligand are not similar. The characteristic absorption bands for
H2DPC at 1661 cm−1(ꢁC O) and 3200–2500 cm−1 (ꢁ-OH) disap-
peared in the Tb3+ complexes. The presence of carboxylate groups in
the various complexes was definitely confirmed by both the asym-
metric stretching bands (ꢁasCOO–) at about 1585 cm-1 and the
symmetric stretching (ꢁsCOO–) at about 1420 cm−1. The elemental
analysis data of the terbium complex were listed in Table 1.
3.3. Luminescent properties of the complex
The excitation spectra for the complex Tb(DPC)22H2O were
recorded by monitoring the Tb3+ luminescence at 545 nm in the
range of 200–450 nm. The emission spectra were recorded in the
rangeof400–700 nmbymonitoringthemaximumexcitationwave-
length (in Fig. 3). The results show that Tb(DPC)22H2O emits the
typical sharp emission bands corresponding to the transitions of
7
7
7
7
the Tb3+ ion 5D4→ F6, 5D4→ F5, 5D4→ F4 and 5D4→ F3, respec-
Table 1
The results of analytical data of complexes.
Complex
Tb (%)
Analytically found (calculated) (%)
C
H
N
O
Tb(DPC) 22H2O
30.27(30.29)
32.12(32.09)
1.89(1.91)
5.35(5.33)
30.46(30.48)

28
Y. Lv et al. / Spectrochimica Acta Part A 74 (2009) 26–29
Table 2
stant depend on the energy differences between the triplet level of
the ligands and the resonant emissive energy level of RE3+
The luminescence properties of rare earth complex.
.
To the complex Tb(DPC)22H2O, the fact of steric hindrance
effect and the fact of the energy transfer both increase the energy
transfer efficiency between the ligand and the Tb3+. The complex
Tb(DPC)22H2O exhibits strong luminescence intensity.
Matter
ꢀex (nm) ꢀem (nm) Relative intensities (a.u.) Lifetimes (␮s)
330 545 1025 885
Tb(DPC) 22H2O
3.4. Electroluminescence
Fig.
4 is electroluminescent spectrum of the complex
Tb(DPC)22H2O at a driving voltage of 8 V. The electrolumi-
nescence intensity dependence on the driving voltage is obtained
by using the time-base spectra. In the structural device, electro
-luminescence intensity sharply increases when the driving volt-
age goes beyond 12 V. This process resulted in the enhancement
of green emission from electroluminescent device, which is made
from metal complexes.
Fig. 5 is power–voltage curves for the complex Tb(DPC)22H2O of
structure devices at 8 V. The electron current in the Tb(DPC)22H2O
device sharply increases when the driving voltage goes beyond
10 V. It is found that the Tb(DPC)22H2O structural device effectively
improves the electroluminescence intensity of lanthanide ions.
Fig. 4. EL spectra of the complex Tb(DPC)22H2O at various driving voltages.
4. Conclusion
In summary, it is concluded that by using a chemical copre-
cipitation method, the novel terbium complex Tb(DPC)22H2O has
successfully been synthesized and characterized for it structural
and photoluminescence and electroluminescence properties. The
complex has higher sensitized luminescent efficiency and longer
lifetime. The present study shows great promise for the design of a
new type electroluminescence device configuration.
7
tively. The relative intensity of the emission at 5D4→ F5 is stronger
than other luminescence emissions. Moreover, the emission peak
positions of the complex indicated that there is a typical Tb3+ lumi-
nescence emission. More importantly, the complex Tb(DPC)22H2O
shows also long lifetime in Table 2 (about 885 ␮s).
The results show that the ligand absorbs and transfers energy
to Tb3+[21,22]. The luminescence properties of the complex are
influenced by the interaction between the ligands. It indicates
that luminescence properties of the complex depend on the lig-
and. The intramolecular energy transfer efficiency from organic
ligands to RE3+ is the most important factor which influencing
the luminescence properties of rare-earth complexes. According to
the intramolecular energy mechanism, the intramolecular energy
transfer efficiency depends chiefly on two energy transfer pro-
cesses: the first one comes from the triplet level of ligands to the
emissive energy level of the RE3+ by Dexter’s resonant energy trans-
fer interaction; the second one is just an inverse energy transfer by
a thermal deactivation mechanism. Both energy transfer rate con-
Acknowledgments
This work was supported by emphasis research fund for Jiamusi
University (Szj2008-018, 2008-017), research fund for the Provin-
cial Key Laboratory of Biomaterials Jiamusi University (E08050204,
E08050207), Education Commission of Hei Long Jiang Province
(10541221, 11521288) and Key Laboratory of Photochemistry, Insti-
tute of Chemistry, Chinese Academy of Sciences.
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