Synthesis and luminescent properties of complexes of Eu(III) with 2-thienyltrifluoroacetonate, terephthalic acid and phenanthroline

Article abstract of DOI:10.1016/j.jpcs.2007.04.009

This work reports the synthesis and luminescent properties of complexes of europium(III) with 2-thienyltrifluoroacetonate (HTTA), terephthalic acid (TPA) and phenanthroline (Phen), in the solid state. The new complexes were characterized by elemental analysis, infrared (IR) spectroscopy, scanning electronic microscopy (SEM) and thermal stability analysis. Both binuclear complex Eu₂(TPA)(TTA)₄Phen₂ and polynuclear complex Eu(TPA)(TTA)Phen present better thermal stability than the mononuclear complex Eu(TTA)₃Phen does. The formation of the binuclear/polynuclear structure of the complexes appears to be responsible for the enhancement of the thermal stability. The emission spectra show narrow emission bands that arise from the ⁵D₀→⁷F_J (J=0-4) transition of the Eu³⁺ ion. The spectral data of the complexes Eu(TPA)(TTA)Phen and Eu₂(TPA)(TTA)₄Phen₂ present only one sharp peak in the region of the ⁵D₀→⁷F₀ transition indicating that only one Eu³⁺ ion species is present in each sample. In addition, the luminescence decay curves of the complexes Eu(TPA)(TTA)Phen and Eu₂(TPA)(TTA)₄Phen₂ fit a single-exponential decay law. The values of quantum efficiencies of the emitting ⁵D₀ level for the complexes Eu(TPA)(TTA)Phen and Eu₂(TPA)(TTA)₄Phen₂ are 29% and 28%, respectively.

Full text of DOI:10.1016/j.jpcs.2007.04.009

ARTICLE IN PRESS
Journal of Physics and Chemistry of Solids 68 (2007) 1674–1680
www.elsevier.com/locate/jpcs
Synthesis and luminescent properties of complexes of Eu(III) with
2-thienyltrifluoroacetonate, terephthalic acid and phenanthroline
Ã
X.H. Zhaoa,b, K.L. Huanga, , F.P. Jiaoa, S.Q. Liua, Z.G. Liub, S.Q. Hub
aCollege of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China
bKey Laboratory of Green Packaging and Application Biological Nanotechnology of Hunan Province,
Hunan University of Technology, Zhuzhou 412008, China
Received 10 March 2006; received in revised form 14 February 2007; accepted 6 April 2007
Abstract
This work reports the synthesis and luminescent properties of complexes of europium(III) with 2-thienyltrifluoroacetonate (HTTA),
terephthalic acid (TPA) and phenanthroline (Phen), in the solid state. The new complexes were characterized by elemental analysis,
infrared (IR) spectroscopy, scanning electronic microscopy (SEM) and thermal stability analysis. Both binuclear complex
Eu2(TPA)(TTA)4Phen2 and polynuclear complex Eu(TPA)(TTA)Phen present better thermal stability than the mononuclear complex
Eu(TTA)3Phen does. The formation of the binuclear/polynuclear structure of the complexes appears to be responsible for the
enhancement of the thermal stability. The emission spectra show narrow emission bands that arise from the 5D0-7FJ (J ¼ 0–4)
transition of the Eu3+ ion. The spectral data of the complexes Eu(TPA)(TTA)Phen and Eu2(TPA)(TTA)4Phen2 present only one sharp
5
peak in the region of the D0-7F0 transition indicating that only one Eu3+ ion species is present in each sample. In addition, the
luminescence decay curves of the complexes Eu(TPA)(TTA)Phen and Eu2(TPA)(TTA)4Phen2 fit a single-exponential decay law. The
values of quantum efficiencies of the emitting 5D0 level for the complexes Eu(TPA)(TTA)Phen and Eu2(TPA)(TTA)4Phen2 are 29% and
28%, respectively.
r 2007 Elsevier Ltd. All rights reserved.
Keywords: A. Rare earth complexes; B. Chemical synthesis; C. Thermal analysis; D. Luminescence
1. Introduction
pium(III) ions is very efficient. These result in the great
increase in luminescent intensity of europium(III) ions [3].
However, europium(III) complexes with b-diketones
ligands for practical application in light conversion events
are very limited due to their poor thermal stability and low-
mechanical resistances [4,5]. In recent years, although the
solubility and fluorescent intensity of Eu(III)–carboxylates
is weaker than that of Eu(III)–b-diketones, they were used
as light conversion material still, due to their good stability
[6,7]. The reason why Eu(III)–carboxylates have good
stability is that they can form binuclear complex or one-,
two- and three-dimensional coordination polymers [8–10].
The design of complexes of trivalent rare earth ions is an
important subject in the field of supramolecular and
coordination polymers, because of the possibility to obtain
the complexes having good luminescent properties. An
important aspect of this research field is to optimize the
luminescent properties and thermal stability of complexes
Europium(III) complexes with b-diketones ligands hav-
ing good luminescent properties, which have been found
important application in light conversion events, are
primarily thought to be due to both the unique electronic
structure of Eu3+ and the antenna effect of the ligands
[1,2]. As light conversion materials, ultraviolet (UV) light is
firstly absorbed by b-diketones ligands, then the absorbed
energy is transferred to Eu3+ ions and make them send out
their characteristic light. b-diketones ligands have broad
absorption bands in the region of near UV, and the energy
level of the triplet state of b-diketones ligands matches well
with the emission energy level of rare earth europium(III),
so the energy transfer of b-diketones ligands to euro-
Ã
Corresponding author. Tel.: +86 733 2661498; fax: +86 733 2887011.
E-mail address: klhuang@mail.csc.edu.cn (K.L. Huang).
0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jpcs.2007.04.009

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X.H. Zhao et al. / Journal of Physics and Chemistry of Solids 68 (2007) 1674–1680
1675
by a suitable selection of ligands [1,11]. The architecture of
2.2. Synthesis of complexes
coordination polymers could be reliably predicted. The
reaction of a metal compound holding one/two vacant or
substitutable coordination sites with a bridging ligand is
the most common and effective way for synthesis of
binuclear and one-dimensional chain complexes.
Recently, syntheses and luminescent properties of the
mononuclear complexes of europium(III) with b-diketones
ligands (e.g. 2-thienyltrifluoroacetonate (HTTA), diben-
zoylmethide) and phenanthroline (Phen) or trioctylpho-
sphine oxide have been shown [12,13]. However, the studies
on syntheses and luminescent properties of europium(III)
complexes of HTTA with terephthalic acid (TPA) and
Phen have not been reported yet.
The aim of this study is to report the synthesis and
luminescent properties of the new binuclear complex
Eu2(TPA)(TTA)4(Phen)2 and chain polynuclear complex
Eu(TPA)(TTA )Phen, bridging ligand TPA being used to
link europium(III) ions to form binuclear or polynuclear
structure. In addition, infrared (IR) spectroscopy, thermal
stability and scanning electronic microscopy (SEM) for the
above-mentioned complexes were applied.
The complex Eu2(TPA)(TTA)4Phen2 was prepared in the
following steps. In the first step, standard solution
(1.0 ꢂ 10ꢀ1 mol Lꢀ1) of Eu3+ was prepared by dissolving
Eu2O3 in hot hydrochloric acid, evaporating up to syrup
and diluting with ethanol to a desired volume. HTTA, TPA
and Phen were dissolved separately in ethanol with molar
ratio of 4:1:2. Subsequently, EuCl3 and HTTA solutions
were mixed with molar ratio of 1:2, adjusting pH values to
5.0 with sodium ethanol, stirred and refluxed for 40 min
keeping temperature in waterbath. Then, according to
molar composition of formula Eu2(TPA)(TTA)4Phen2,
Phen and TPA solutions were added dropwise, keeping
pH values 6.5, stirred and refluxed until the appearance of
an orange precipitate. The solid product was filtered,
washed and recrystallized in ethanol.
The complex Eu(TPA)(TTA)Phen was prepared by the
similar process as Eu2(TPA)(TTA)4Phen2, except that the
product is a pale yellow precipitate.
The mononuclear complex Eu(TTA)3Phen was synthe-
sized by the similar process as described in the literature by
Ji et al. [15]. The product obtained is an orange precipitate.
2. Experimental details
3. Result and discussion
2.1. Reagents and apparatus
3.1. Composition of complexes
About 99.99% Eu2O3 was purchased from Jiangxi South
Rare Earth Metals Institute in China. HTTA, TPA, Phen
and other reagents were all analytical grade and used
without further purification.
Analytical data of Eu(III), C, H and N percentages
(found/calculated) for Eu(TTA)3Phen are Eu(III): 15.10/
15.27; C: 43.64/43.40; H: 1.97/2.01; N: 2.40/2.81; for
Eu(TPA)(TTA)Phen are Eu(III): 22.01/21.18; C: 46.68/
46.84; H: 2.17/2.23; N: 3.77/3.90; and for the complex Eu2
(TPA)(TTA)4Phen2 are Eu(III): 17.15/17.74; C: 44.36/
44.84; H: 2.02/2.10; N: 3.58/3.27. The elemental analysis
data are similar to the calculated values.
C, H and N analyses were performed on 2400 II
CHNSLO elemental analyzer (American Perkin-Elmer).
The Eu(III) percentage was determined by complexometric
titration with EDTA, according to the method described
by Lyle and Rahman [14]. The IR spectra were measured at
room temperature on Nicolet-550 spectrophotometer
(American Perkin-Elmer) using KBr pellets in the spectral
range of 4000–400 cmꢀ1. The SEM was obtained in a
microscope JSM-5600LV along with the gold sputtering
technique. Differential thermoanalysis (DTA) was per-
formed in a SHDT-40 thermoanalyticmeter using alumi-
num crucibles with ꢁ18.40 mg of sample, under dynamic
synthetic air atmosphere (40 mL minꢀ1) and heating rate of
10 1C minꢀ1 in the temperature range of 30–600 1C. The
thermogravimetric (TG) curves were recorded with a
thermobalance model SHDT-40, using platinum crucibles
with ꢁ18.0 mg of sample, under the same conditions as for
DTA. A SPEX FL-2T2 spectrofluorometer was used to
record the excitation and emission spectra of the complexes
using a 450 W Xenon lamp as excitation source. This
apparatus was controlled by a DM3000F spectroscopic
computer. The lifetime measurements of the complexes
were carried out on a SPEX 1934D spectrophotometer at
room and liquid nitrogen temperatures. The decay curves
at 298 K were recorded under excitation and emission at
375 and 613 nm, respectively.
3.2. Characterization of complexes
Table 1 presents some results of IR spectra. The presence
of carboxylate groups is definitely confirmed by both
asymmetric stretching bands (uas) at 1552, 1556 cmꢀ1 and
symmetric stretching bands (us) at 1397, 1399 cmꢀ1 in the
Eu(III) complexes. According to Deacon, Taylor and
Musie’s studies [16–18], the coordination mode of carbox-
ylate groups with Na+ ions is mainly the bidentate
coordination in Na+ carboxylates. If the separation value
(D ¼ uasꢀus) in the rare earth carboxylate complex is lower
than that in the Na+ carboxylate, the coordination mode
of carboxylate groups with rare earth ions is mainly the
bidentate chelating, bidentate bridging or tridentate
chelating-bridging coordination. The separation values
between uas (COO) peaks and us (COO) peaks are 155
and 157 cmꢀ1 in the two Eu(III) complexes, respectively
(see Table 1), which are lower than that in Na2TPA
(D ¼ 168 cmꢀ1). Furthermore, owing to the great steric
hindrance from the ligands TTA and Phen in the

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1676
Table 1
The IR spectra of some compounds
Compounds
us (COO)/cmꢀ1
uas (COO)/cmꢀ1
D (uasꢀus)
u (CO)/cmꢀ1
u (CQN)/cmꢀ1
TTA
Na2TPA
Phen
1680
1395
1563
168
1596
1554
1559
1562
Eu (TTA)3Phen
Eu (TPA)(TTA)Phen
Eu2 (TPA)(TTA)4Phen2
1598
1604
1603
1399
1397
1556
1552
157
155
F
F
F
S
S
F
F
F
F
S
F
F
F
S
F
O
N
O
O
O
F
O
O
O
O
O
O
O
O
O
2
Eu
O
Eu
2
Eu
N
O
O
N
Eu
O
N
O
N
O
N
O
N
N
Scheme 1. Chemical structures of the complexes: (A) Eu2(TPA)(TTA)4Phen2 and (B) Eu(TPA)(TTA)Phen.
complexes Eu(TPA)(TTA)Phen and Eu2(TPA)(TTA)4
Phen2, the bidentate bridging and tridentate chelating-
bridging coordination of carboxylate groups with Eu(III)
ions becomes more difficult than the bidentate chelating
coordination does. Thus, the coordination mode of
carboxylate groups with rare earth ions is mainly the
bidentate chelating coordination mode in the complexes
Eu(TPA)(TTA)Phen and Eu2(TPA)(TTA)4Phen2, and
their possible chemical structures proposed are given in
Scheme 1. In addition, the IR spectra also show a
360 1C; Eu2(TPA)(TTA)4Phen2 melts at ꢁ241 1C and
decomposes approximately from 364 to 410 1C; and
Eu(TPA)(TTA)Phen melts at ꢁ259 1C and decomposes
approximately from 385 to 445 1C. So, the thermal stability
for the above-mentioned Eu(III) complexes decreases in the
following order: the polynuclear complex Eu(TPA)(TTA)-
Phen 4 the binuclear complex Eu2(TPA)(TTA)4Phen2 4
the mononuclear complex Eu(TTA)3Phen. Moreover, the
TG curves (Fig. 2A–C) do not present any event relative to
water loss, in the interval 50–200 1C, indicating that three
complexes are in anhydrous form. This is corroborated
by IR spectroscopy and elemental analysis. The TG curves
of the complex Eu(TPA)(TTA)Phen presents the weight
loss in higher temperature range than the mononuclear
complex Eu(TTA)3Phen as well as the binuclear complex
Eu2(TPA)(TTA)4Phen2 does, which suggests the formation
of the chain structure of the Eu(TPA)(TTA)Phen.
displacement of u (CQO) stretching from ꢁ1680 cmꢀ1
,
in free TTA ligand, to approximately 1603 cmꢀ1 in the
complexes, and a displacement of u (CQN) stretching
from 1596 cmꢀ1, in free Phen ligand, to approximately
1559 cmꢀ1 in the complexes, indicating that Eu(III) ion is
coordinated by the oxygen or nitrogen atoms [19].
The SEM photographs of the complexes Eu2(TPA)
(TTA)4Phen2 and Eu(TPA)(TTA)Phen are shown in Fig. 1.
For the binuclear complex Eu2(TPA)(TTA)4Phen2, the
formation of the agglomerated structure can be obtained
by intermolecular force, and for the polynuclear com-
plex Eu(TPA)(TTA)Phen, the needle/stripe-shaped struc-
ture can be obtained by chain conglomeration, which
suggests the formation of the chain structure of Eu
(TPA)(TTA)Phen.
The DTA and TG curves of Eu(TTA)3Phen, Eu
(TPA)(TTA)Phen and Eu2(TPA)(TTA)4Phen2 are shown
in Fig. 2 in the temperature range from 50 to 600 1C. From
the DTA curves shown in Fig. 2, we can observe that the
complex Eu(TTA)3Phen melts at ꢁ183 1C and decomposes
approximately in the temperature range from 260 to
3.3. Luminescent properties of the complexes
The excitation spectra of the Eu(III) complexes,
recorded in the spectral range of 220–450 nm by monitor-
5
ing the emission at the hypersensitive D0-7F2 transition,
are shown in Fig. 3. The excitation spectrum of Eu2
(TPA)(TTA)4Phen2 consists of a weak band at ꢁ307 nm
and a strong broadband at ꢁ378 nm, corresponding to the
absorber of the ligands TPA and TTA. The excitation
spectrun of Eu(TPA)(TTA)Phen presents also two bands at
ꢁ308 and ꢁ372 nm attributed to the ligands TAP and
TTA. Furthermore, compared with Eu2(TPA)(TTA)4Phen2,
the excitation band of Eu(TPA)(TTA)Phen shows a peak

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1677
(b)
(a)
100
200
300
400
500
600
Temperature
(b)
(a)
100
200
300
400
500
600
Temperature
(b)
Fig. 1. SEM photographs of the complexes: (A) Eu2(TPA)(TTA)4Phen2
and (B) Eu(TPA)(TTA)Phen.
(a)
position blue shift. These facts show the presence of the
different coordination environments around of Eu(III) ion
in different complexes, corresponding to the formation of
the Eu(III) complexes.
The emission spectra were recorded in the range of
560–710 nm with the maximum excitation wavelengths, at
77 K, as shown in Fig. 4. It can be seen from Fig. 4 that the
emission spectra of the complexes Eu2(TPA)(TTA)4Phen2
and Eu(TPA)(TTA)Phen present only one sharp peak in
100
200
300
400
500
600
Temperature
Fig. 2. (a) DTA and (b) TG curves of the complexes: (A) Eu(TTA)3Phen,
(B) Eu2(TPA)(TTA)4Phen2 and (C) Eu(TPA)(TTA)Phen.
5
the region of the D0-7F0 transition indicating that only
one Eu(III) ion species is present in each sample, since the
band is unsplit by the ligand field effect. In addition, in the
emission spectra, the forced electric dipole transition
(5D0-7F2), which is sensitive to changes in the chemical
environment around the Eu(III) ion, is the strongest
transition, indicating that Eu(III) ion is in a site without
a center of inversion [20,21].
Fig. 5 presents the luminescence decay curve of Eu2
(TPA)(TTA)4Phen2, at liquid nitrogen temperature. This

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X.H. Zhao et al. / Journal of Physics and Chemistry of Solids 68 (2007) 1674–1680
1678
(b)
(a)
250
300
350
400
450
0.000
0.001
0.002
0.003
t / s
0.004
0.005
Wavelength (nm)
Fig. 3. Excitation spectra of the complexes: (a) Eu(TPA)(TTA)Phen and
(b) Eu2(TPA)(TTA)4Phen2, with emission monitored at 613 nm, at room
temperature.
Fig. 5. Luminescence decay curve of Eu2(TPA)(TTA)4Phen2, at liquid
nitrogen temperature by monitoring the 5D0-7F2 transition.
(TTA)4Phen2, the lifetime values are concerned with both
the absence of H2O molecule and the structure of the
complexes. The lifetime value for Eu(TPA)(TTA)Phen is
longer than that for Eu2(TPA)(TTA)4Phen2 is mainly
ascribed to the formation of polynuclear structure of the
complex, which results in a rigid polymeric chain structure.
In Table 2 the lifetime (t) of the emitting state 5D0, non-
radiative (Anrad), radiative (Arad) and tot-radiative rates
(Atot) can be related through the following equation:
Atot ¼ Arad þ Anrad ¼ 1=t. (1)
The radiative (Arad) rates were obtained by summing
over the radiative rates A0J for each 5D0–7Fj transition
P
(b)
(a)
(
JA0J) and A0J is obtained according to the relation
A0J ¼ A01ðI0J=I01Þðn01=n0JÞ, (2)
where I01 and I0J are the integrated intensities of the
560
580
600
620
640
660
680
700
5
5D0-7F1 and D0-7FJ transitions (J ¼ 2 and 4), n01 and
Wavelength (nm)
n0J being the respective energy barycenters of these
5
transitions. The magnetic dipole allowed D0-7F1 transi-
Fig. 4. Emission spectra of the complexes: (a) Eu(TPA)(TTA)Phen and
(b) Eu2(TPA)(TTA)4Phen2, at 77 K under excitation at 375 nm.
tion which is not influenced by the chemical environment
was taken as the reference [23], the coefficient of
spontaneous emission, A0l is given by the expression
A0l ¼ 0.31 ꢂ 10ꢀ11 n3 (n01)3, and its value is estimated to
be ꢁ50 sꢀ1 [11]. And the evaluation values of Arad are 568.0
and 448.0 for the Eu2(TPA)(TTA)4Phen2 and Eu(TPA)
(TTA)Phen, respectively.
curve fits a first-order exponential decay law, which reveals
that only one symmetry site is occupied by the Eu(III) ion.
The lifetime values (in Table 2) of the emitting 5D0 level are
obtained from the luminescence decay curves of Eu2
(TPA)(TTA)4Phen2, Eu(TPA)(TTA)Phen and Eu(TTA)3
Phen (the lifetime value reported for Eu(TTA)3Phen is
0.673 ms in Ref. [22]), at room temperature. Table 2 shows
that the luminescence lifetimes of the emitting 5D0 level for
the complexes obtained are longer than that reported for
the Eu(TTA)3(H2O)2 complex [19]. The rathe long lifetime
value for Eu(TTA)3Phen is mainly ascribed to the
substitution of the water molecules by the Phen, consider-
ing that an efficient non-radiative decay rate in the
hydrated compound takes place via strong vibronic
coupling with vibrational states of the O–H oscillators
[1]. However, for Eu(TPA)(TTA)Phen and Eu2(TPA)
The quantum efficiencies (Z) of the emitting 5D0 level can
be obtained from the following equation:
Z ¼ Arad=Atot ¼ Arad ꢂ t. (3)
For the complexes Eu2(TPA)(TTA)4Phen2, Eu(TPA)
(TTA)Phen and Eu(TTA)3Phen, their values are,
ꢁ0.28(568.0 ꢂ 0.486 ꢂ 10ꢀ3), ꢁ0.29(448.0 ꢂ 0.654 ꢂ 10ꢀ3
)
and ꢁ0.48(698.5 ꢂ 0.687 ꢂ 10ꢀ3), respectively. The quan-
tum efficiency for the Eu(TTA)3Phen complex is higher
than that for the Eu(TTA)3(H2O)2 complex, and this fact is
due to luminescence quenching produced by OH vibration

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X.H. Zhao et al. / Journal of Physics and Chemistry of Solids 68 (2007) 1674–1680
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Table 2
Luminescence data of complexes in solid state
Complexes
t (ms)
298 K
Arad (sꢀ1
)
Atot (sꢀ1
)
Anrad (sꢀ1
)
Z (%)
O2
O4
(10ꢀ20 cm2)
(10ꢀ20 cm2)
Eu(TTA)3(H2O)2 [19]
[Eu(TTA)3Phen]a
0.260
0.687
0.654
0.486
1110
3846
1456
1529
2058
2736
757.5
1081
1490
29
48
29
28
33.0
26.3
20.7
22.3
4.6
5.7
3.4
5.2
698.5
448.0
568.0
Eu(TPA)(TTA)Phen
Eu2(TPA)(TTA)4Phen2
aThe lifetime value (0.687 ms) determined for Eu(TTA)3Phen is close to that (0.673 ms) reported in Ref. [22].
in the Eu(TTA)3(H2O)2. However, for Eu(TPA)(TTA)-
Phen and Eu2(TPA)(TTA)4Phen2, the quantum efficiencies
are lower than that for the Eu(TTA)3Phen complex, and
quite close to as reported for the Eu(TTA)3(H2O)2 complex
Eu(TPA)(TTA)Phen are smaller that those for Eu2(TPA)
(TTA)4Phen2, indicating a further decrease in the covalent
character of the Eu(III) ion–oxygen atoms interaction, and
a further perturbation on the chelate effect of the TTA
ligand by the steric factors from the TPA ligands (see
Scheme 1).
[19], the reason being their very low-radiative rates Arad
.
The chelate effect of the bidentate TTA ligand in the
complexes Eu(TPA)(TTA)Phen and Eu2(TPA)(TTA)4
Phen2 is perturbed by the addition of TPA molecule,
which results in a decrease of the Eu(III) luminescence
under ꢁ375 nm excitation wavelength (a increase of the
Eu(III) luminescence under ꢁ307 nm excitation wave-
length). Moreover, a different coordination environment
together with symmetry around Eu(III) is also a possible
reason for the differences in Atot as well as Arad of the
above-mentioned complexes.
4. Conclusions
The two new complexes of europium(III) with HTTA,
TPA and Phen have been synthesized. Compositions of
these complexes are revealed to be Eu(TPA)(TTA)Phen
and Eu2(TPA)(TTA)4Phen2.
The experimental intensity parameters, O2 and O4, are
sensitive to the changes in the chemical environment
around the Eu(III) ion. A higher value of O2 suggests the
Both binuclear complex Eu2(TPA)(TTA)4Phen2 and
chain polynuclear complex Eu(TPA)(TTA)Phen show
better thermal stability than the mononuclear complex
Eu(TTA)3Phen does. The formation of the binuclear/
polynuclear structure of the complexes appears to be
responsible for the enhancement of the thermal stability of
the complexes.
5
higher hypersensitive behavior of the D0-7F2 transition
[19]. They were determined from the emission spectra
5
5
(Fig. 4) based on the D0-7F2 and D0-7F4 electronic
transitions of the Eu(III) ion, and their values can be
estimated according to the following equation [19]:
The emission spectral data of the complexes Eu(TPA)
(TTA)Phen and Eu2(TPA)(TTA)4Phen2 show only one
sharp peak for the 5D0-7F0 transition indicating the
presence of a single chemical environment around the
Eu(III) ion in each sample. The values of the experimental
intensity parameters (OJ) indicate that the Eu(III) ion in
the two new complexes is in a site of very low symmetry.
However, as compared with the Eu(TTA)3(H2O)2 complex,
the Eu(III) ion in the two new complexes is still in a
less polarizable chemical environment. In addition, the
luminescence decay curve of the complexes Eu(TPA)
(TTA)Phen and Eu2(TPA)(TTA)4Phen2 fit a single-expo-
ꢀ
ꢀ
ꢀ
ꢀ
ꢁ
ꢂ
2
7
ð2Þ
O2 ¼ 3_c3A02=4e2o3w F2
U
5D0
,
(4)
where w is the Lorentz local field correction term that is
2
given by w ¼ nðn2 þ 2Þ =9 with a refraction index n ¼ 1.5,
ꢀ
ꢀ
ꢁ
ꢂ
2
D0 is a squared reduced matrix elements
ð2Þ
5
and 7F2
U
ꢀ
ꢀ
whose values are 0.0032. The O4 can also be obtained in a
ꢀ
ꢀ
ꢀ
ꢀ
ꢁ
ꢂ
2
D0 is 0.0023 [19].
ð4Þ
similar way, and 7F4
U
5
The values of O2 and O4 for the Eu(III) complexes
are shown in Table 2. It is noted that Eu(TTA)3(H2O)2
and Eu(TTA)3Phen have higher values of O2 than
those determined for both Eu2(TPA)(TTA)4Phen2 and
Eu(TPA)(TTA)Phen, suggesting the smaller hypersensitive
5
nential decay law. The longer lifetime of the D0 level in
complexes Eu(TPA)(TTA)Phen and Eu2(TPA)(TTA)4Phen2
is associated with the absence of water molecules.
The values of quantum efficiencies for the complexes
Eu(TPA)(TTA)Phen and Eu2(TPA)(TTA)4Phen2 are 29%
and 28%, respectively, and They are quite close to the
value for the Eu(TTA)3(H2O)2 complex. Based on these
luminescence characteristics and the good thermal stability
for two new complexes, we believe that they would be a
promising candidate as a very luminescent material for
photoluminescent applications.
behavior of the D0-7F2 transition and a lower covalent
5
character of the interaction between the Eu(III) ion and the
oxygen liganding atoms in the two new complexes. As a
consequence, this might also suggest that the chelate effect
of the bidentate TTA is perturbed by the addition of TPA
molecule in the first coordination sphere of the Eu(III) ion,
conferring a smaller electric dipole character to the
5D0-7F2 transition. From Table 2, it can also be seen
that the values of the parameters, O2 and O4, for

ARTICLE IN PRESS
X.H. Zhao et al. / Journal of Physics and Chemistry of Solids 68 (2007) 1674–1680
1680
Acknowledgments
[11] G.F. de Sa, O.L. Malta, C.M. Donega, A.M. Simas, R.L. Longo,
´ ´
P.A. Santa-Cruz, E.F. da Silva Jr., Coord. Chem. Rev. 196 (2000)
165–171.
The authors acknowledge the financial supports
from National Natural Scientific Foundation of China
(No. 20576142) and Funds of Hunan Education Bureau for
young scholars (No. 05B075).
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