Luminescence of a europium (III) complex containing 4-n-octyloxydibenzoylmethane ligands doped poly(methylmethacrylate)

Article abstract of DOI:10.1016/j.physb.2009.03.016

A europium (III) complex containing 4-n-octyloxydibenzoylmethane (ODBM) ligands doped poly(methylmethacrylate) (PMMA) was synthesized. Its luminescence properties have been investigated by fluorescence emission spectra and lifetime measurements. According

Full text of DOI:10.1016/j.physb.2009.03.016

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Physica B 404 (2009) 1957–1960
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Physica B
journal homepage: www.elsevier.com/locate/physb
Luminescence of a europium (III) complex containing
4-n-octyloxydibenzoylmethane ligands doped poly(methylmethacrylate)
Ã
Hao Liang a, , Fang Xie a, Jie Xu b, Biao Chen c, Shi Bian d
a Department of Chemical Engineering, Huizhou University, Guangdong 516007, China
b Key Lab of Green Processing and Functional Textiles of New Textile Materials, Ministry of Education, Wuhan University of Science and Engineering, Hubei 430073, China
c Department of History of Science and Technology and Archaeometry, University of Science and Technology of China, Anhui 230026, China
d School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangdong 510275, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A europium (III) complex containing 4-n-octyloxydibenzoylmethane (ODBM) ligands doped poly
(methylmethacrylate) (PMMA) was synthesized. Its luminescence properties have been investigated by
fluorescence emission spectra and lifetime measurements. According to the fluorescence emission
Received 9 February 2009
Received in revised form
6 March 2009
spectra, the Judd–Ofelt parameters O2, O4 of Eu(ODBM)3Phen doped PMMA have been calculated and
Accepted 14 March 2009
the radiative properties were presented also. It showed that the long alkyloxy in ligand in the ODBM
ligand can improve the radiative properties. The evaluation of the radiative properties showed that
Eu(ODBM)3Phen doped PMMA has potential to be used for applications in amplifiers and lasers.
& 2009 Elsevier B.V. All rights reserved.
Keywords:
Polymers
Luminescence
Europium
Complex
1. Introduction
fluorescent quantum efficiency, pure luminescent color and good
stability [7].
In this paper, a europium
b-diketone complex, Eu(ODBM)3-
There has been much interest in lanthanides complexes doped
polymer optical waveguide for applications in amplifiers and
lasers [1–4]. Polymers are promising host candidates for these
applications because of their excellent properties such as high
Phen, in which the central ligand is 4-n-octyloxydibenzoyl
methane and the neutral ligand is 1,10-phenanthroline (Phen),
has been incorporated into PMMA. The luminescence properties
of Eu(ODBM)3Phen doped PMMA were studied in comparison to
that of Eu(DBM)3Phen (DBM: dibenzoylmethane) doped PMMA
system.
transparency, low cost and easy fabrication. As
a polymer
material, poly(methylmethacryate) (PMMA) attracted particular
interest for its low optical absorption, simple synthesis and low
cost. The PMMA matrices have substantial influence on the
spectral shift of luminescent maxima, in particularly for the
organic compounds, and the electron-phonon (vibronic) interac-
tions may play here principal role. These effects may also
substantially modify all the transfer kinetic processes between
the RE Eu centers and the surrounding organic ligands [5].
Lanthanide complexes have long been known to give sharp,
intense emission lines upon ultraviolet light irradiation, because
of the effective intramolecular energy transfer from the coordi-
nated ligands to the luminescent central lanthanide ions, which in
turn undergo the corresponding radiative emitting process (the
so-called antenna effect) [6]. From all lanthanides complexes,
2. Experimental
The ligand, 4-n-octyloxydibenzoylmethane, was synthesized
by the Claisen condensation [8]. Eu(III)
Eu(ODBM)3Phen were synthesized according to the following
procedure. To solution of 4-n-octyloxydibenzoylmethane
b-diketone chelates,
a
(3 mmol) and 1,10-phenanthroline (1 mmol) in 20 ml THF, 1N
solution of NaOH (3 mmol) was added followed by the addition of
an aqueous solution of EuCl3 (1 mmol). The reaction mixture was
heated at 60 1C for 3 h. The precipitate was collected and washed
with water and ethanol for three times, and dried under vacuum.
The product was recrystallized using anhydrous ethanol. Ele-
mental analysis calculated for EuC81H89O9N2: C, 69.27%; H, 6.21%;
N, 1.99%. Found: C, 68.95%; H, 6.29%; N, 2.01%. The molecular
structure of Eu(ODBM)3Phen is shown in Fig. 1. The central Eu3+
ion is bound to three ODBM ligands with long alkyloxy group
(ꢀOC8H17), Phen acts as a synergic shielding ligand, which can
europium
b-diketone complexes are famous for their lumines-
cence properties. As red-emitting material, they have high
Ã
Corresponding author. Tel.: +86 752 2435190.
E-mail address: lianghao@ustc.edu (H. Liang).
0921-4526/$ - see front matter & 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.physb.2009.03.016

ARTICLE IN PRESS
1958
H. Liang et al. / Physica B 404 (2009) 1957–1960
5D0-7F2
OC8H17
1.0
0.8
0.6
0.4
0.2
0.0
N
N
O
O
Eu
5D0-7F1
5D0-7F0
3
5D0-7F4
5D0-7F3
Fig. 1. Chemical structure of Eu(ODBM)3Phen.
550
600
650
700
750
800
reduce the rate of nonradiative decays and enhance the
fluorescence intensity of the complex strongly [9].
Wavelength (nm)
Eu(ODBM)3Phen doped PMMA was made by bulk polymeriza-
tion. First, Eu(ODBM)3Phen was dissolved in the purified MMA
(the concentration of Eu3+ is 1000 ppmwt). Then, 0.01 mol/L of 2,
2-Azoisobutyronitrile (AIBN) as an initiator was added to the
above solution and mixed in a vessel. To avoid autoacceleration
(also referred to as Trommsdor effect) that takes place during the
polymerization, prepolymerization of the above solution was
carried out in order to get a syrup of partially polymerized MMA.
The obtained syrup was injected into a model, and then the
thermal polymerization of the filled model was carried out in an
oven at 45 1C for 48 h under air condition and additionally heated
at 90 1C until solidification was fulfilled. The solid samples were
cut to 2 mm thickness and polished for fluorescence measure-
ments.
Fig. 2. Fluorescence emission spectrum of Eu(ODBM)3Phen doped PMMA.
1
0.1
Elemental analyses were performed using a Perkin-Elmer
2400CHN elemental analyzer. The fluorescence emission spectra
of Eu(ODBM)3Phen doped PMMA were recorded on a Shimadzu
RF-5301PC spectrofluorophotometer. The measurement of the
fluorescence decay curves was performed at room temperature.
The third harmonic (355 nm) of a Nd:YAG laser was used as a
pump source. The emission at the 5D0-7F2 transition of Eu3+ was
monitored and recorded as a function of time. Data were acquired
using a Tektronix TDS 5000 digital oscilloscope and analyzed
using a computational program ORIGINs6.1.
0.0
0.5
1.0
1.5
2.0
Time (ms)
Fig. 3. Decay curve of Eu(ODBM)3Phen doped PMMA (the concentration of Eu-ion
is 1000 ppmwt).
The 5D0-7F1 transition is usually used as a reference because
it is allowed by magnetic dipole and its intensity is independent of
the environment. Because the variation of the relative intensity
ratio (R) of 5D0-7F2 to 5D0-7F1 transition is very sensitive to the
structural change in the vicinity of Eu3+ ions, it can be used to
reflect the local structure and asymmetry in the vicinity of
europium ions [11]. The calculated R value of Eu(ODBM)3Phen
doped PMMA is 12.1, which is higher than that of Eu(DBM)3Phen
doped PMMA (R ¼ 10.1) [12]. It indicated that the incorporation
of the long alkyloxy group in ODBM ligand makes Eu(ODBM)3
3. Results and discussion
3.1. Fluorescence emission spectra Eu(ODBM)3Phen doped PMMA
The fluorescence emission spectra of Eu(ODBM)3Phen doped
PMMA are shown in Fig. 2. The concentration of Eu3+ ion is
1000 ppmwt.
The emission spectrum was recorded from 550 to 750 nm
under the excitation at 396 nm. It can be found five emission
peaks corresponding to 5D0-7F0,1,2,3,4 can be clearly distinguished
for Eu(ODBM)3Phen doped PMMA. The presence of only one
5D0-7F0 line for the above three doped polymers indicates that
the Eu3+ ion occupies only a single site and a single chemical
environment exists around it. The 5D0-7F2 transition dominates
all other transitions and emission intensity of this transition
strongly depends on the chemical environment where the Eu3+
ion is located. The much stronger intensity of 5D0-7F2 than those
of other transitions indicates the ligand field surrounding the Eu3+
ion is highly polarizable [10]. It also indicated that Eu(ODBM)3-
Phen doped PMMA has good color purity and the Eu3+ ion is in a
site without a center of inversion.
Phen presents
Eu(DBM)3Phen.
a more asymmetric structure than that of
3.2. Metastable state lifetime of the Eu(ODBM)3Phen doped PMMA
The metastable state lifetime of the Eu(ODBM)3Phen doped
PMMA was obtained from the decay curve. The decay curve of
Eu(ODBM)3Phen doped PMMA is shown in Fig. 3.
In a semi-logarithmic plot a single-exponential decay function
results in a straight line. It can be found in Fig. 3, the decay curve
can be fit with a single exponential, which is also indicating that
there is only one site symmetry from the Eu3+ ion [9]. The
metastable state lifetime of Eu(ODBM)3Phen doped PMMA is

ARTICLE IN PRESS
H. Liang et al. / Physica B 404 (2009) 1957–1960
1959
0.553 ms, which is higher than that of Eu(DBM)3Phen doped
Table 1
O2 O4 parameters of Eu(ODBM)3Phen doped PMMA and Eu(DBM)3Phen doped
PMMA.
,
system (0.469 ms) [12]. This indicated that the energy transfer to
the Eu3+ from the ODBM ligand is more efficient than that from
the DBM ligand. According to the molecular structures showed in
Fig. 1, we suggest that the main reason might be that the
incorporation of the long alkyloxy group in OBDM. The long octyl
chain structure of OBDM ligand can form a sheath around the Eu3+
ions, which can reduce the nonradiative decays caused by the host
of polymer.
O2 (10ꢀ20 cm2)
O4 (10ꢀ20 cm2)
Eu(ODBM)3Phen doped PMMA
Eu(DBM)3Phen doped PMMA
19.31
18.90
0.621
0.311
Table 2
3.3. Judd–Ofelt analysis of Eu(ODBM)3Phen doped PMMA
Radiative properties of Eu(ODBM)3Phen doped PMMA.
(cmꢀ1
)
Aed (sꢀ1
)
Amd (sꢀ1
)
A (sꢀ1
)
B (%) s
(10ꢀ22 cm2)
It is well known that due to selection rules, the 5D0-7F2,4,6
transitions of Eu3+ are allowed by induced electric dipole
mechanisms. According to the Judd–Ofelt theory, the spontaneous
emission probability of an electric dipole transition between
initial J manifold jðS; LÞJito terminal manifold jðS0; L0ÞjJ0i is given by
[13,14]
Emission transition
n
5D0-7F0
5D0-7F1
5D0-7F2
5D0-7F3
5D0-7F4
17271
16906
16223
15320
14225
0
0
0
0
0
0
51.90
51.90 7.72 2.96
611.38 90.92 53.31
611.38
0
0
0
0
0
0
0
9.13
9.13
1.36 0.39
AT (sꢀ1
)
672.41
2
4e2n3 nðn2 þ 2Þ
ꢀ
ꢁ
64
p
Aed ¼ A ðS; LÞJ; ðS0; L0ÞJ0
¼
Sed
Radiative lifetime trad (ms) ¼ 1.487
3hð2J þ 1Þ
9
2
X
64
p
4e2n3 nðn2 þ 2Þ
0
0
0
2
¼
OtjhðS; LÞJjjUðtÞjjðS ; L ÞJ i
3hð2J þ 1Þ
9
t¼2;4;6
where h is Planck’s constant, m is the mass of the electron, c is the
velocity of light, n is the refractive index of the medium, is the
is the total angular
Once the intensity parameters Ot is determined, they can be
used to calculate the radiative properties. The total transition
emission probability AT is calculated using [13,14]
n
wavenumber of the transition and
J
momentum of the ground state, the jjUðtÞjj are the squared
reduced matrix elements of the rank t ¼ 2, 4, 6 and their values do
2
X
AT
¼
A½ðS; LÞJ; ðS0; L0ÞJ0ꢁ
not change with the host for Ln3+ ions. The three coefficients O2
,
S;L;J
O4
, O6 contain implicitly the odd-symmetry crystal field terms,
where A½ðS; LÞJ; ðS0; L0ÞJ0ꢁ is the spontaneous emission probability of
radial integrals and perturbation denominators.
a
transition between initial
J
manifold jðS; LÞJi to terminal
The 5D0-7F1 of Eu3+ ion is a magnetic dipole transition which
is independent of the environment and can be used as a reference.
The spontaneous emission probability of magnetic dipole transi-
tion Amd is [15]
ꢂ
0ꢃ
0
0
ꢂ
manifold ðS ; L ÞJ
.
The fluorescence branching ratio is obtained from [13,14]
A½ðS; LÞJ; ðS0; L0ÞJ0ꢁ
0
0
0
P
b
½ðS; LÞJ; ðS ; L ÞJ ꢁ ¼
S;L;JA½ðS; LÞJ; ðS0; L0ÞJ0ꢁ
64p4n3
n3Smd
Amd
¼
The radiative lifetime of the transition involved is an important
3hð2J þ 1Þ
parameter in consideration of the pumping requirement for the
threshold of laser action and can be calculated as [13,14]
Smd refers to the strength of the magnetic dipole line strength of
the 5D0-7F1 transition, which is a constant and independent of
the medium.
1
P
trad½ðS; LÞJꢁ ¼
The jjUðtÞjj values of Eu3+ ion are taken from Carnall et al. [16].
S;L;JA½ðS; LÞJ; ðS0; L0ÞJ0ꢁ
2
The spontaneous emission probability of an electric dipole
Another important radiative property is the stimulated emis-
sion cross section of the measured fluorescence [13,14]:
transition Aed depends on jjUðtÞjj . The Ot can be determined from
2
the ratios of intensities of 5D0-7F2,4,6 transitions to the intensity
of 5D0-7F1 transition as follows:
lp4
cn2Dleff
s
½ðS; LÞJ; ðS0; L0ÞJ0ꢁ ¼
A½ðS; LÞJ; ðS0; L0ÞJ0ꢁ
R
8p
nJ3
2
e2
ðn2 þ 2Þ
IJð
n
Þ d
n
AJ
2
R
¼ ¼
Amd Smd
OtjjUðtÞjj
n3md
9n2
where lp is the peak position of the emission line, Dleff is the
effective band width of the emission transition.
Imd
ðn
Þ dn
Table 1 presents O2
,
O4 parameters of Eu(ODBM)3Phen doped
With the measured lifetime
tm, together with the above
PMMA and Eu(DBM)3Phen doped PMMA.
calculated radiatve lifetime rad, the luminescence quantum yield
t
It has been well established that the parameter
O2 is structure-
Z
Z
can be calculated:
sensitive and associated to the covalency and asymmetry of the
rare earth sites [17,18]. It can be found in Table that
tm
¼
1
trad
Eu(ODBM)3Phen doped PMMA presents a higher O2 value, which
indicates the long alkyloxy group in ODBM ligand can increase the
covalency and asymmetry of Eu3+ ion, while the increase of the O4
intensity parameter of Eu(ODBM)3Phen doped PMMA can be due
to the steric factors. Compared with DBM ligands, the relative
bigger ODBM ligands can prevent the Phen ligand from getting
The obtained spontaneous transition probability of electric
dipole transition Aed and magnetic dipole transition Amd, the total
transition probability AT, the fluorescence branching ratio , the
and the radiative lifetime trad
b
stimulated emission cross section
are presented in Table 2.
s
closer to the Eu3+ ion, thus decreasing the
O4 intensity parameter.
From Table 2, the transition 5D0-7F2 showed a high
b
value. It
value
near 50% becomes a potential laser emission transition [19]. The
luminescence quantum yield of Eu(ODBM)3Phen doped PMMA
The O6 intensity parameter was not determined because the
5D0-7F6 transition could not be experimentally detected. This
indicated that the O6 is not important here.
has been already established that an emission level with b
Z

ARTICLE IN PRESS
1960
H. Liang et al. / Physica B 404 (2009) 1957–1960
is about 37.2%, while the
about 29.4% [12]. The higher luminescence quantum yield
Z
of Eu(DBM)3Phen doped PMMA is
Acknowledgments
Z
revealed the higher intramolecular energy transfer efficiency in
Eu(ODBM)3Phen. The incorporation of the long alkyloxy group in
OBDM can form a sheath around the Eu3+ ions, which can reduce
the high vibrational energy C–H bonds of PMMA, making the
energy transfer from the ligand to the central Eu3+ ion more
efficient than that from the DBM ligand. In addition to that,
Eu(ODBM)3Phen doped PMMA also showed a larger stimulated
This work was supported by the Natural Science Foundation of
Guangdong Province, China (no. 8151601501000010), the Science
and Technology Planning Project of Huizhou, China (no. 2007P48),
the Key Project of Science and Technology Research of Ministry of
Education (no. 208089) and the Natural Science Foundation of
Hubei Province (no. 2008CDB261).
emission cross section
s
of 5D0-7F2 transition than that of
Reference
Eu(DBM)3Phen doped PMMA (43.79 ꢂ10ꢀ20 cm2) [12]. It is
obvious that the incorporation of the long alkyloxy group in
OBDM can also improve the radiative properties.
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4. Conclusion
In conclusion, europium (III) complex containing 4-n-octylox-
ydibenzoylmethane (ODBM) ligands doped poly(methylmetha-
crylate) was synthesized and its luminescence properties have
been studied. The sensitivity of the observed fluorescence to
the different polarizabilities of the organic ligands confirms the
principal role of the electron-vibration interactions, including
the anharmonic ones in the kinetic of the processes. The
Judd–Ofelt phenomenological parameters, O2 and O4, obtained
from the fluorescence emission spectrum, are 19.31 ꢂ10ꢀ20
and 0.621 ꢂ10ꢀ20 cm2, respectively. Radiative properties of
Eu(ODBM)3Phen doped PMMA were also presented. The result
showed that the long alkyloxy in ligand in the ODBM ligand can
improve the radiative properties.
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