Synthesis and electroluminescent property of ternary complexes Eu(TTA)3M

Article abstract of DOI:10.1016/j.jallcom.2009.11.020

Three kinds of rare earth ternary complexes of Eu³⁺ with HTTA and M (M = 5-NO₂Phen, 2,2′-Dipy and TPPO) have been synthesized and characterized using various spectral techniques such as elemental analysis, TGA-DTA, IR, UV and fluores

Full text of DOI:10.1016/j.jallcom.2009.11.020

Journal of Alloys and Compounds 492 (2010) 259–263
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Synthesis and electroluminescent property of ternary complexes Eu(TTA) M
3
a,∗
a
a
a
a
b
c
Yuguang Lv , Chunxiang Song , Yu Zhang , Jingquan Sha , Cuijuan Liu , Fujun Zhang , Lingxuan Wang
a
The Provincial Key Laboratory of Biomaterials, School of Pharmaceutical Sciences, Jiamusi University, Jiamusi 154007, China
Key Laboratory of Luminescence and Optical Information, Beijing Jiaotong University, Beijing 100044, China
Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China
b
c
a r t i c l e i n f o
a b s t r a c t
Three kinds ofrare earth ternary complexes of Eu3+ withHTTAandM (M = 5-NO Phen, 2,2 -Dipy andTPPO)
ꢀ
Article history:
Received 30 January 2009
Received in revised form 29 October 2009
Accepted 3 November 2009
Available online 11 November 2009
2
have been synthesized and characterized using various spectral techniques such as elemental analysis,
TGA-DTA, IR, UV and fluorescent. Results show that the complexes of Eu(III) emit strong red luminescence
when excited by UV light. The complex Eu(TTA)35NO2Phen posses the highest sensitized luminescent
efficiency and the longest lifetime in the studied complexes. TG curves indicate that Eu(TTA)35NO2Phen
is most stable. In device ITO/PVK/Eu(TTA)35NO2Phen/Al, Eu may be excited by intramolecular energy
transfer from ligands as observed by electroluminescence. The main emitting peak at 614 nm can be
3
+
Keywords:
Sol–gel synthesis
Luminescence
Electron emission spectroscopies
Thin films
5
7
3+
attributed to the transition of D0 → F2 of Eu ion, and this process results in the enhancement of red
emission from electroluminescence device.
© 2009 Elsevier B.V. All rights reserved.
1
. Introduction
The rare earth metals are unique elements, which fascinat-
efficiency but also are suitable to be thermally deposited. For this
reason, as a way to obtain pure red OLED devices and to use triplet
excited states, OLEDs based on tetrakis ␤-diketonate RE complexes
as electron transport and emitting layer were developed [16,17].
In this paper, we introduced three different second ligands for
the enhancement of luminescent properties, and three kinds of
Eu(III) rare-earth complexes with violet light absorption have been
designed and synthesized. The luminescence properties of the com-
plexes are influenced by the interaction among the different second
ligands. The result shows that electron transitions of lanthanides
can be manipulated by designing ligands. The luminescence of
lanthanide (III) complexes can be realized and enhanced by design-
ing ligands coordinate to lanthanide (III) ions. The intramolecular
ing luminescent properties lead to an outstanding role in light
conversion technologies. Stable complexes of luminescent triva-
lent lanthanide ions are of great interest owing to their broad
applications in biochemistry, material chemistry, medicine and
so forth [1–4]. Many rare-earth complexes have been developed
as the emitters in organic photoluminescence and electrolumi-
nescence devices [5–9]. The most useful lanthanide Eu3+ ion has
unusual spectroscopic characteristics, including millisecond life-
time, very sharp emission bands and large Stokes shifts. In this
regard, many research groups have extensively studied various
Eu(III) complexes for the purpose of achieving desirable lumines-
cent properties [10–14]. However, the quantum efficiency of most
of these lanthanide complexes is still low. Generally, the Eu3+ ion
shows very weak absorption in the visible region and often require
the application of strongly absorbing “antennae” for light harvest-
ing to obtain efficient photoluminescence. This may be mostly due
to inefficiency of the energy transfer, particularly, triplet–triplet
transfer in these lanthanide complexes. One of the most important
problems in this field is a selection of suitable ligands, which would
provide high efficiency of emission of the metal ions [15]. The rare-
earth ␤-diketonate complexes not only display a high luminescent
3
+
energy transfer efficient from organic ligands to Eu is the most
important factor which influencing the luminescence properties of
rare-earth complexes.
In the three Eu(III) complexes, Eu(TTA) 5NO Phen has the high-
3
2
est sensitized luminescent efficiency and the longest lifetime. In
PVK/Eu(TTA) 5NO Phen blend, the red emission of europium com-
3
2
plex is enhanced and PVK emission is quenched. Therefore, EL
devices of high red light EL efficiency are obtained.
2. Experimental
2
.1. Synthesis of the complexes
Rare-earth complexes were prepared as follows: EuCL36H2O(1 mmol) and HTTA
(
3 mmol) were dissolved in 50 mL ethanol. The pH value of the solution was adjusted
∗ Corresponding author. Tel.: +86 0454 8679535; fax: +86 0454 8623422.
E-mail address: yuguanglv@163.com (Y. Lv).
to 6–7 by the addition triethylamine. Then, 5-NO2 Phenanthroline (or 2,2 -Dipy,
TPPO) in ethanol solution was added to the reaction mixture, the molar ratio of 5-
ꢀ
0
925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2009.11.020

2
60
Y. Lv et al. / Journal of Alloys and Compounds 492 (2010) 259–263
Table 1
DTA-TG peaks of complexes.
◦
◦
◦
Melting point Tm1 ( C)
Decomposetemperature ( C)Tm2 ( C)
RE2O3 (%)
Weight loss (%)
Weight loss (%)
Analytically found
(
calculated)
Eu(TTA)3Dipy
Eu(TTA)35NO2Phen
Eu(TTA)3(TPPO)2
223
242
220
0.00
0.00
0.00
496
501
482
65.8
79.7
70.1
17.8 (18.1)
17.1 (16.9)
13.1 (12.8)
NO2 Phenanthroline (2,2 -Dipy) to Eu ion being 1:1 (TPPO to Eu3+ ion being 2:1).
ꢀ
3+
Table 2
The results of analytical data of complexes.
◦
The mixture solution was stirred at 50 C for 5 h. The precipitate was filtered, washed
with water and ethanol, dried at room temperature, and then stored in a silica-gel
drier [18].
Complex
Eu (%)
Analytically found (calculated) (%)
C
H
N
2.2. Electroluminescence device preparation
Eu(TTA)3Dipy
15.59 (15.64) 42.05 (41.99) 2.11(2.06)
2.90 (2.88)
Eu(TTA)35NO2Phen 14.55 (14.60) 41.48 (41.51) 1.89 (1.83) 4.10 (4.04)
The device structure of the complex Eu(TTA)3M was fabricated according to
Eu(TTA)3(TPPO)2
11.10 (11.08) 52.53 (52.49) 3.10 (3.06)
the literature method [19]. Poly(N-vinylcar-bazole) (PVK) was dissolved in chlo-
roform with a concentration of 10 mg/ml. In order to improve the performance of
Eu(TTA)3M thin film, Eu(TTA)3M was doped into PVK at weight ratio of 1:3. The PVK:
Eu(TTA)3M 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 thermal evaporation at a rate of
about 0.3 Å/s under high vacuum of 2 × 10− Torr.
2
.3. Measurements
Elemental analyses were performed with a PerkinElmer 2400 elemental ana-
lyzer; Metal contents were determined by EDTA complexometry(previous version:
6
Fig. 1. (a) and (b) Infrared spectra of ligands and complexes (ꢀ = 400–4000 nm) (c) Chemical structures of the complexes with various neutral ligands.

Y. Lv et al. / Journal of Alloys and Compounds 492 (2010) 259–263
261
elemental analyses were performed on a PerkinElmer 240C analytical instrument);
DTA-TG curves were obtained on a TGA-DTA 1700- PerkinElmer with sample
amount of 3.6 ± 0.2 mg; Infrared spectra used to identify synthesized materials were
−
−
1
1
obtained with a prostige-21IR spectrophotometer in the range of 4000–400 cm
(
previous version: infrared spectra were recorded in the range of 4000–400 cm
by a prostige-21IR spectrophotometer in KBr flake); UV–vis spectra were performed
on a UV-2501PCS double spectrophotometer; The excitation and emission spec-
tra were recorded on a Shimadzu 5301 spectrofluorophotometer equipped with a
1
50 W xenon lamp as the excitation source. Spectra were recorded using monochro-
mator slit widths of 1.5 mm on both excitation and emission sides; lifetimes were
measured with a Spex 1934D phosphorimeter using a 450 W flash lamp as the exci-
tation 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 spectrometer.
3
. Results and discussion
3.1. DTA-TG analysis
In order to examine the thermal stability of the complexes, ther-
mal gravimetric (TG) and differential thermal analyses (DTA) are
◦
carried out between 30 and 900 C in the static atmosphere of air.
Fig. 2. UV spectra of complexes: (a) Eu(TTA)35NO2Phen, (b)Eu(TTA)3Dipy and (c)
Eu(TTA)3(TPPO)2.
DTA-TG plots of three complexes show significantly different pat-
terns. DTA-TG peaks of three complexes are listed in Table 1. Table 1
shows the complex Eu(TTA) 5NO Phen with an endothermic peak
3
2
Table 3
◦
◦
around 242 C and about weight 79.7% of loss at 348–850 C, in
which TG curve shows that Eu(TTA) 5NO Phen is more stable than
The luminescence properties of rare-earth complexes.
3
2
Matter
ꢀex (nm) Eu(TTA)3M
em (nm)
Relative intensities
(a.u.)
Lifetimes
(␮s)
Eu(TTA) Dipy and Eu(TTA) (TPPO) in the air. Therefore, the com-
3
3
2
ꢀ
plex is well suited for the use as the emission materials.
Eu(TTA)3Dipy
Eu(TTA)3(TPPO)2
Eu(TTA)35NO2Phen 385
386
383
614
614
614
802
653
968
612
436
865
3.2. IR spectra analysis
Infrared spectra of ligands and complexes are shown in Fig. 1. For
−
1
5
5
7
5
7
Eu(TTA) Dipy (in Fig. 1a), the bands at around 1506 and 759 cm
D0 → F3 and D0 → F4, respectively, the relative intensity of
3
7
are corresponded to stretching vibration of –N C and rC-H vibra-
D0 → F2 is stronger than other luminescence emissions. The
ꢀ
−1
tion of 2,2 -Dipy, respectively. The peak at about 520 cm reveals
the presence of O → RE, which cannot be observed in the ligands.
In addition, typical asymmetric vibrations of the carbonyl group
emission peak positions of Eu(TTA)35NO2Phen are basically same
as those of Eu(TTA)3Dipy and Eu(TTA)3(TPPO)2, indicating that
there is a typical Eu3+ luminescence emission. More importantly,
the Eu(TTA)35NO2Phen complex shows also the longest lifetime in
Table 3 (about 865 ␮s).
−
1
in HTTA are detected at about 1601 and 1539 cm . In the case
of Eu(TTA) 5NO Phen, the bands at wavenumber 1539, 2438and
30 cm are corresponded to stretching vibration of –N C, –N O,
3
2
−1
7
and rC-H vibration of 5NO -Phen, respectively. In addition, typical
3.4. Electroluminescence
2
asymmetric vibration of the carbonyl group in HTTA are detected
−1
at about 1605 and 1549 cm
In Fig. 1(b), Eu(TTA) (TPPO) typical vibration are listed: 1650(s,
.
Fig. 4 shows absorption spectra of PVK and PVK/Eu(TTA) Dipy.
3
3
2
Obviously, the emission of PVK in the PVK/Eu(TTA) Dipy blend
3
C
O), 1250 −1150(s, C F), 1125(s, P O). The elemental analy-
sis data of the europium complexes are listed in Table 2. The
results of elemental analysis indicate that the composition of
the complexes conforms to Eu(TTA) Dipy, Eu(TTA) 5NO Phen and
3
3
2
Eu(TTA)3 (TPPO) , respectively. Fig. 1(c) shows the chemical struc-
2
tures of the complexes with various neutral ligands.
3.3. UV absorption spectra and fluorescence properties
UV spectra of the complexes Eu(TTA) 5NO Phen and
3
2
Eu(TTA) Dipy are shown in Fig. 2. All of the complexes exhibit
3
absorption in the ultraviolet region with the maximal absorption
of Eu(TTA) 5NO Phen at 273 and 342 nm {Eu(TTA) Dipy at 305
3
2
3
and 335 nm}. For Eu(TTA) (TPPO) , the maximal absorption peaks
3
2
are located at 285 and 353 nm.
The solid complexes have characteristics line emission of f–f
transition of metal ions when they are excited by UV light. The
fluorescence characteristics of the complexes in liquid state are
listed in Table 3. Fluorescent spectra are recorded by monitoring
3
+
the Eu luminescence at 614 nm. Fluorescence emission spectrum
of the Eu(TTA) 5NO Phen complex is shown in Fig. 3. Five typi-
3
2
3
+
cal Eu luminescence peaks appear at 583.0, 593.5, 614.0, 656.0
and 707.5 nm, which are due to D → F , D → F , D → F ,
5
7
5
7
5
7
0
0
0
1
0
2
Fig. 3. Typical emission spectra of Eu(TTA)35NO2Phen complex excited at 385 nm.

2
62
Y. Lv et al. / Journal of Alloys and Compounds 492 (2010) 259–263
Fig. 6. EL spectra of complexes Eu(TTA)3Dipy at a driving voltage of 12 V.
Fig. 4. Absorption spectra of PVK and PVK/Eu(TTA)3Dipy blend.
Fig.
6 is electroluminescent spectrum of the complex
Eu(TTA) Dipy at a driving voltage of 12 V. The electrolumines-
3
is stronger than that of PVK alone. Moreover, the Eu3+ emission
in the PVK/Eu(TTA) Dipy blend is also stronger than that of the
cence intensity dependence on the driving voltage is obtained by
using the time-base spectra. In the structural device, electrolu-
minescence intensity sharply increases when the driving voltage
of 12 V.
3
Eu(TTA) Dipy complex.
3
Fig.
5
shows
electroluminescence
spectrum
of
PVK/Eu(TTA) 5NO Phen and PVK/Eu(TTA) Dipy(at
a
driving
3
2
3
Fig.
7
is current–voltage curves for the complex
voltage of 14 V). The intensity of the red emission at 614 nm in
Eu(TTA) 5NO Phen of structure devices at 8 V. It is found that
3
2
device I{ITO/PVK/Eu(TTA) 5NO Phen/Al} is stronger than the
3
2
the Eu(TTA) 5NO Phen structural device effectively improves
3 2
device II{ITO/PVK/Eu(TTA) Dipy/Al}.The intensity of the device
3
the electroluminescence intensity of lanthanide ions. As shown
in Fig. 7, the electron current in the Eu(TTA) 5NO Phen device
III{ITO/PVK/Eu(TTA) -(TPPO) /Al}is almost invisible in the elec-
3
2
3
2
troluminescence spectrum. The emission peaks are observed
around 579, 590, 614, 653, and 699 nm, which are assigned to the
sharply increases when the driving voltage goes beyond 16 V.
The luminescence properties of the complexes are influenced
by the interaction among the ligands. Electron transitions of
lanthanides can be manipulated by designing ligands. The lumines-
cence of lanthanide (III) complexes can be realized and enhanced by
designing ligands coordinate to lanthanide (III) ions. In this paper,
we introduced different ligands for the enhancement of the lumi-
5
7
4
f transitions of Eu(III) ( D → F : i = 0; 1; 2; 3; 4), respectively.
0
i
The most intense peaks corresponding to the electronic dipole
5
7
3+
transition ( D → F of Eu ion) were observed at 614 nm. The
0
2
electroluminescence starts at forward bias of 12 V, the brightness
of the device is strengthened with the increase of the bias voltage.
Fig. 5. EL spectra of complexes Eu(TTA)35NO2Phen and Eu(TTA)3Dipy in device I
Fig. 7. Current–voltage curves for the complex Eu(TTA)35NO2Phen at various driv-
and device II (at a driving voltage of 12 V).
ing voltages.

Y. Lv et al. / Journal of Alloys and Compounds 492 (2010) 259–263
263
nescent properties. In conclusion, we designed and synthesized
three kinds of rare-earth complexes with violet light absorption.
The intramolecular energy transfer effectively from organic lig-
mission of Hei Long Jiang Province(11541362), Commission of Hei
Long Jiang Province(B200917), China National Funds for Young Sci-
entists(20901031), Key Laboratory of Photochemistry, Institute of
Chemistry, Chinese Academy of Sciences and Key Laboratory of
Luminescence and Optical Information, Beijing Jiaotong University.
3
+
ands to Eu is the most important factor which influencing the
luminescence properties of rare-earth complexes. The intramolec-
ular energy transfer effectively depends chiefly on two energy
transfer processes: the first one comes from the triplet level of lig-
ands to the emissive energy level of the Eu3+ by Dexter’s resonant
energy transfer interaction; the second one is just an inverse energy
transfer by a thermal deactivation mechanism. Both energy trans-
fer rate constant depend on the energy differences between the
triplet level of the ligands and the resonant emissive energy level of
References
[
[
[
1] Q.M. Wang, B. Yan, X.H. Zhang, J. Photochem. Photobiol. A Chem. 174 (2005)
119.
2] M. Hasegawa, A. Ishii, S. Kishi, J. Photochem. Photobiol. A Chem. 178 (2006)
220.
3] S. Ma, M. Gao, R. Li, H.G. Pan, Y.Q. Lei, J. Alloys Compd. 457 (2008) 457.
3+
Eu
.
[4] Y. Hasegawa, H. Kawai, K. Nakamura, N. Yasuda, Y. Wada, S. Yanagida, J. Alloys
Compd. 408 (2006) 669.
[
5] K. Takato, N. Gokan, M. Kaneko, J. Photochem. Photobiol. A: Chem. 169 (2005)
09.
4
. Conclusions
1
[
[
6] Y. Liu, C.F. Ye, G.D. Qian, J.R. Qiu, J. Lumin. 118 (2006) 158.
7] Y. Hasegawa, Y. Wada, S. Yanagida, J. Photochem. Photobiol. C: Photochem. Rev.
According to the data and discussion above, we have success-
5
(2004) 183.
fully prepared three kinds of Eu(III) complexes by using the UV
absorption reagents as ligands. TG curve prove the complexes are
[
8] K. Nakamura, Y. Hasegawa, H. Kawai, N. Yasuda, Y. Wada, S. Yanagida, J. Alloys
Compd. 408 (2006) 771.
◦
[9] K. Manseki, Y. Hasegawa, Y. Wada b, S. Yanagida, J. Alloys Compd. 408 (2006)
05.
10] K. Manseki, Y. Hasegawa, Y. Wada, S. Yanagida, J. Lumin. 111 (2005) 183.
[11] X. Jiang, Y. Wu, C. He, Mater. Lett. 62 (2) (2008) 286.
12] V. Tsaryuk, K. Zhuravlev, V. Kudryashova, V. Zolin, J. Legendziewicz, I. Pekareva,
P. Gawryszewska, J. Photochem. Photobiol. A: Chem. 197 (2008) 190.
13] K. Zhuravlev, V. Tsaryuk, V. Kudryashova, V. Zolin, Yu. Yakovlev, J. Leg-
endziewicz, Spectrochim. Acta Part A 72 (2009) 1020.
stable, ranging from ambient temperature to 200 C in air. The study
8
of luminescence properties shows that the complex Eu(TTA) 5NO2
3
[
Phen has the highest sensitized luminescent efficiency and the
longest lifetime than Eu(TTA) Dipy and Eu(TTA) (TPPO) . The
[
3
3
2
present study shows great promise for the design of a new type
electroluminescence device configuration.
[
[
[
[
14] S.L. Liu, C.L. Wen, C. Chen, S.S. Qi, E.X. Liang, Mater. Res. Bull. 43 (2008) 2397.
15] W. Wang, Y. Huang, N. Tang, Spectrochim. Acta Part A 66 (2007) 1058.
16] M.A. Katkova, V.A. Ilichev, A.N. Konev, I.I. Pestova, G.K. Fukin, M.N. Bochkarev,
Org. Electron. 10 (2009) 623.
Acknowledgments
This work was supported by emphasis research fund for Jia-
musi University (Szj2008-018), research fund for the Provincial Key
Laboratory of Biomaterials Jiamusi University (E08050204), Health
Commission of Hei Long Jiang Province(2009-360), Education Com-
[17] W.G. Quirino, C. Legnani, R.M.B. dos Santos, K.C. Teixeira, M. Cremona, M.A.
Guedes, Thin Solid Films 517 (2008) 1096.
[
[
18] Y.G. Lv, J.C. Zhang, W.L. Cao, Y.L. Fu, J. Alloys Compd. 462 (2008) 153.
19] Y.G. Lv, J.C. Zhang, W.L. Cao, F.J. Zhang, Z. Xu, J. Photochem. Photobiol. A: Chem.
188 (2007) 155.