Photophysical properties of ternary RE3+ (RE = Eu, Tb, Sm) hybrids with β-diketone functionalized linkages and 4-(4-nitrostyryl) pyridine though coordination bonding

Article abstract of DOI:10.1007/s10895-011-1008-y

In this paper, the organic ligands TTA and TAA are grafted onto the coupling agent to achieve the organic precursors (TTA-Si, TAA-Si) as first ligand and the organic 4-(4-nitrostyryl)pyridine (Nspy) is synthesized as the second ligand. Both of them are co

Full text of DOI:10.1007/s10895-011-1008-y

J Fluoresc (2012) 22:729–736
DOI 10.1007/s10895-011-1008-y
ORIGINAL PAPER
Photophysical Properties of Ternary RE3+ (RE = Eu, Tb, Sm)
Hybrids with β-Diketone Functionalized Linkages
and 4-(4-nitrostyryl)pyridine Though
Coordination Bonding
Yan-Yan Li & Bing Yan & Lei Guo
Received: 31 July 2011 /Accepted: 18 October 2011 /Published online: 29 October 2011
#
Springer Science+Business Media, LLC 2011
Abstract In this paper, the organic ligands TTA and TAA are
grafted onto the coupling agent to achieve the organic
precursors (TTA-Si, TAA-Si) as first ligand and the organic
4-(4-nitrostyryl)pyridine (Nspy) is synthesized as the second
ligand. Both of them are coordinated to the rare ions with the
carbonyl group and nitrogen atom respectively. After the
hydrolysis and copolycondensation between the teraethox-
ysilane (TEOS) and the ternary rare earth organic complex via
the sol–gel process, the chemical bonded hybrid materials are
constructed and characterized in detail. The obtained hybrid
materials present superior thermal stabilities and regular and
homogenous square blocks microstructure. Among the
hybrids Eu(TTA-Si)3Nspy shows a more strong characteristic
emission and longer lifetime than the hybrids Eu(TAA-
Si)3Nspy, while hybrids Tb(TAA-Si)3Nspy exhibits the
stronger characteristic emission and longer lifetime than the
hybrids Tb(TTA-Si)3Nspy. For Sm3+ hybrid materials, the
photoluminescence of Sm(TAA-Si)3Nspy is too weak to find
in the characteristic emission spectra, meanwhile, Sm(TTA-
Si)3Nspy has the excellent luminescent intensity.
biology, dyestuff, fluoroimmunoassays [1, 2], magnetic
resonance imaging (MRI), NIR-emitting probes and ampli-
fiers for optical communications [3–7]. A number of
investigations on the hybrid materials have been done in
the past decade. Generally speaking, the conventional
physical doping hybrid systems seem to be easily to occur
the quenching effect of the luminescent centers, leach of the
photoactive molecules and cluster of the emitting center
because of the weak interactions between the interfaces and
the high energy vibration by the surrounding hydroxyl
groups [8]. Therefore, in recent years, many studies have
focused their attention on the encapsulation of luminescent
rare earth complexes in silica-based matrices via strong
covalent bond, where the organic ligands can absorb the
enough energy and transfer it to the emitting metal to
sensitize them [9–11]. Moreover, embedding a rare earth
complex in an inorganic matrix via the strong covalent bond
in the process of sol–gel is beneficial for its thermal stability,
mechanic properties and luminescence output. More recently,
Binnemans has reviewed extensive research progress in the
field of rare earth-based luminescent hybrid systems [12]. In
view of the researches, the key procedure to construct
molecular-based materials is to design the “functional bridge
molecule” which could be obtained by the grafting reaction,
where it can both coordinates lanthanide ions and constitutes
the covalent Si–O network [8, 13–18].
.
.
Keywords Rare earth ion Hybrid materials
.
Luminescence Photophysical property
Introduction
In this paper, we select TTA and TAA as the organic
ligands, and they have been modified by the addition of the
3-(triethoxysilyl) propyl isocyanate (TEPIC) and obtained
the bridge molecules TTA-Si and TAA-Si. The 4-(4-
nitrostyryl) pyridine (Nspy) has been synthesized. We take
the bridge molecule as the organic ligand and the Nspy as
the second ligand to construct the better luminescent hybrid
systems. In these hybrid systems, the bridge molecule and
Nspy can coordinate to the RE3+ by the carbonyl groups
The rare earth based organic–inorganic hybrid materials have
a wide variety of potential applications such as fluorescent
:
:
Y.-Y. Li B. Yan (*) L. Guo
Department of Chemistry, Tongji University,
Siping Road 1239,
Shanghai 200092, China
e-mail: byan@tongji.edu.cn

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J Fluoresc (2012) 22:729–736
and nitrogen atom respectively, the Si–O network is formed
after the cohydrolysis and copolycondensation processes
between the bridge molecule and the tetraethoxysilane
(TEOS) [19–24]. The characteristics of the resulting
materials are analyzed and compared in details. Through
the comparison of the different organic ligands, it is
recognized that TTA is more favorable to sensitize the
photoluminescence of the Eu3+ materials and Sm3+ materi-
als than TAA, while TAA is more benefit to sensitize the
luminescent of the Tb3+ materials than TTA.
later the TEPIC (4 mmol, 0.990 g) is then put into the
refluxing solution by drops. Then, the mixture is heated at
65 °C and refluxed in a covered flask for 12 h at the
nitrogen atmosphere, finally, a yellow oiled liquid is
furnished after isolation and purification and characterized
by IR and NMR. IR: –(CH2)3– 2,975 cm−1, Si–O 1,167 cm−1,
–CONH– 1,628 cm−1. Anal. Calcd. For C25H47O10N2F3Si2
(648.82): C, 46.28; H, 7.30; N, 4.32. Found: C, 45.93; H,
1
7.04; N, 4.09%. H NMR (CDCl3): δ 0.64 (4H, t), δ 1.26
(18H, t), δ 5.60 (2H, t), δ 6.97 (1H, d), δ 7.35 (1H, d), δ 7.51
(1H, d), δ 1.58 (4H, t), δ 3.12 (4H, t), δ 3.83 (12H, m). The
synthesize procedure of bridge molecule TAA-Si is similar to
that of TTA-Si except that the TTA is replaced by TAA. The
precursor is characterized by IR and NMR. IR: –CONH–
1,080 cm−1, Si–O 1,167 cm−1, –(CH2)3– 2,976 cm−1. Anal.
Calcd. For C28H47O10F3N2Si2S (716.92): C, 46.91; H, 6.60;
Experiment Section
Materials Ln(NO3)3 (Ln = Eu, Tb, Sm) are obtained by
dissolving their respective oxides (Eu2O3, Tb4O7 and Sm2O3)
in concentrated nitric acid. 2-Thenoyltrifluoroacetone (TTA)
and trifluoroacetylacetone (TAA) are purchased from the
Aladdin, Tetraethoxysilane (TEOS) is distilled and stored
under a N2 atmosphere, 3-(triethoxysilyl)-propyl isocyanate
(TEPIC) is purchased from Lancaster Synthesis Ltd, The
solvent tetra-hydrofuran (THF) is used after desiccation with
anhydrous calcium chloride, All the reagents are analytically
pure, Other starting reagents are used as received.
1
N, 3.91. Found: C, 47.08; H, 6.46; N, 3.73%. H NMR
(CDCl3): δ 0.62 (4H, t), δ 1.23 (18H, t), δ 3.14 (4H, m), δ
3.75 (12H, q), δ 4.75 (2H, t), δ 1.61 (4H, m), δ 1.89(3H, s).
1
From the IR and H NMR dates of the bridge molecules
TTA-Si and TAA-Si, it is demonstrated that the TEPIC has
grafted onto the ligand TTA and TAA.
Synthesis of 4-(4-Nitrostyryl) Pyridine (Nspy)
Nspy is prepared according to the procedure reported in
previous literature [26] as following: 4-picoline (0.186 g,
2 mmol) and 4-nitrobenzaldehyde (0.302 g, 2 mmol) are
dissolved in a round bottom flask with 20 mL acetic
anhydride as solvent. The mixture is heated at 90 °C in a
covered flak and refluxed for approximately 18 h. After
isolation and recrystallization, the desired product is obtained.
IR: cis-C=C 1,762 cm−1, anti-C=C 969 cm−1; –CH–
3,019 cm−1. Anal. Calcd. For C13H10O2N2: 1H NMR
(CDCl3): δ 7.13 (1H, d), δ 7.32 (1H, d), δ 8.62 (2H, br d), δ
8.16–8.22 (2H, m), δ 7.60–7.65 (2H, m), δ 7.38–7.42 (2H, m).
Measurements
The ultraviolet spectroscopy is measured by the Agilent
8453 spectrophotometer at the room temperature. The FT-
IR spectra are obtained on the Nexus 912 AO446 FT-IR
spectrophotometer with KBr pellet as the blank, in the
range of 4,000–400 cm−1. We obtain the ultraviolet–visible
diffuse reflection spectra of the powder samples on the
BWS003 spectrophotometer. 1H NMR spectra are recorded
in deuterate DMSO by a Bruker AVANCE-500 spectrom-
eter with tetramethylsilane (TMS) as internal reference.
Scanning electronic microstructure (SEM) are also used to
give a comprehensive description of the hybrid materials
morphology on Philip XL30 at the room temperature. The
luminescent excitation and emission spectra are obtained on
a RF spectrophotometer. The luminescent decay properties
are recorded on an Edinburgh Analytical Instruments.
Synthesis of the Finally Hybrid Systems
The sol–gel-derived hybrid material is prepared as follows:
The organic cross-linking precursor TTA-Si is dissolved in N,
N-dimethylformamide (DMF) solvent, then RE(NO3)3 and
Nspy are dropwise added into the solution under stirring
respectively. The mixed solution is agitated magnetically for
several hours at room temperature, after the coordination
reaction had completed between the organic precursor TTA-
Si, the secondary organic Nspy and RE(NO3)3. Then, an
approximately TEOS, HCl and H2O are put into the mixed
solution by drops. The mixed solution is continued agitated
magnetically for approximately 18 h to obtain a single phase
in a covered Teflon beaker. After that, it is aged at 65 °C
until the onset of gelation in about 6 days. The gels ware
denoted as RE(TTA-Si)3Nspy and are ground into powdered
Synthesis
Synthesis of Precursor TTA-Si and TAA-Si
Following the literature procedure [19–25], the bridge
molecules TTA-Si and the TAA-Si are acquired. Firstly,
TTA (2 mmol, 0.444 g) is dissolved in 20 mL of dehydrate
THF and NaH is added into the solution with stirring, 2 h

J Fluoresc (2012) 22:729–736
731
material for the photophysical studies. The detail synthetic
procedure and the possible structure for RE(TTA-Si)3Nspy
are shown in Fig. 1. RE(TAA-Si)3Nspy is prepared in the
same way as described for RE(TTA-Si)3Nspy except that
TTA is replaced by TAA. The detail synthetic procedure and
the possible structure for RE(TAA-Si)3Nspy are the same
except for TTA is replaced by TAA. (Fig. 1)
vibration of the C=O and the bending vibration of –NH–
group in the –CONH– respectively, while for the TAA-Si
are 1,520 cm−1 and 1,644 cm−1. Furthermore, the absorp-
tion peaks at 2,250, 2,273 cm−1 for N=C=O of TEPIC
disappeared in the IR spectra of TTA-Si and TAA-Si [28].
Considering what have detailed described above, which
adequately illustrate the TEPIC has successfully grafted to
the TTA and TAA respectively.
The strong broadband located at 1,050–1,134 cm−1
indicates the asymmetric stretching vibration of Si–O–Si
in the hybrids systems in the Fig. 2c. Meanwhile, the peaks
have appeared at 790 and 460 cm−1 indicating the presence
of the symmetric stretching vibration and planar bending
vibration of the group Si–O–Si respectively in the resulting
materials. All these have strongly demonstrated that the Si–
O networks have been formed. Furthermore, the shape peak
Results and Discussion
The Nspy is synthesized as described in experimental
section, which is characterized by 1HNMR and IR.
Figure 2a depicts the IR spectra of Nspy. The peaks at
1,762 cm−1 and 969 cm−1 emerged in the IR spectra of
Nspy indicate the stretching vibration of cis-C=C and anti-
C=C. Furthermore the peaks at 1,598 cm−1, and 1,508 cm−1
suggesting the skeleton stretching vibration of benzene
ring. Given what have described above, the Nspy have been
synthesized successfully.
at 1,383 cm−1 is associated with the absorption of NO3 . In
−
addition, the presence of –CH2– can be clearly evidenced
by the peak at 2,929 cm−1. In a word, the resulting
materials have been obtained.
The IR spectra for the modified precursors (TTA-Si,
TAA-Si) are compared to the free β-diketone ligand TTA
and TAA, whose spectral band assignments are shown in
Fig. 2b. The characteristic absorption peaks (3,113,
3,058 cm−1) of –CH2– in the IR spectra of TTA and TAA
respectively had been replaced by a strong broad band
located at 2,975 cm−1 which derived from the three
methylene groups of (TEPIC [27]. Besides, new peaks at
1,520 cm−1 and 1,628 cm−1 are generated by the stretching
Figure 3a and b show the ultraviolet visible diffuse
reflectance spectra of different hybrid systems, where a
broad band ranging from 200 to 500 nm in near-UV region
is observed, which is due to the transition from the
modified organic ligand Si–O–Si compound host to the
first excited state owing to the π–π* transition of the
aromatic ring (TTA-Si or TAA-Si).we can see that the
ultraviolet visible diffuse reflection spectra of the selected
resulting materials all have the similar spectra. In addition,
Fig. 1 Selected scheme of the
synthesis process of the precur-
sor and the predicted structure of
the hybrid systems: RE(TTA-
NO2
O2N
C
C
C
C
Si)3Nspy (RE = Eu, Tb, Sm)
H2O
N
N
O
O
S
CONH(CH2)3
CONH(CH2)3
O
S
Si
O
O
RE3+
O
(H2C)3HNOC
Si
O
O
C
C
O
O
O
Si
O
(H2C)3HNOC
O
Si
O
CF3
O
O
F3C
C
F3C
S
Si
Si
O
O
O
O
O
RE = Eu, Tb, Sm

732
J Fluoresc (2012) 22:729–736
(A)
clearly seen from the emission spectra of the sample.
Meanwhile, we can see that the emission intensities of these
two kinds of materials are determined in orders: Eu(TTA-
Si)3Nspy > Eu(TAA-Si)3Nspy, which may be explained by
energy transfer degree. In addition, among the emission
peaks of these hybrid systems, the electronic dipole
transition 5D0→7F2 located at 613 nm is the strongest
emission, which indicates that the chemical environment of
Eu3+ is in low symmetry because the electronic dipole
transition 5D0→7F2 strongly varies with the local symmetry
of Eu3+, while the magnetic dipole transition 5D0→7F1
which is very independent of the environment of Eu3+ is
much weaker than the electronic dipole transition. Further-
more, we can also see that the intensities ratio of red
emission to orange emission is large which can also
indicates that the Eu3+ is in an anti-symmetric environment
TTA-Si
TTA
2975
1520
2975
TAA-Si
TAA
1520
4000 3500 3000 2500 2000 1500 1000
500
-1
Wavenumeber/cm
(B)
(A)
0.8
1383
1050-1134
792
Eu-TAA-Si-Nspy
2929
457
0.6
460
Tb-TAA-Si-Nspy
789
788
2935
Eu-TTA-Si-Nspy
0.4
462
2935
Eu-TTA-Si-Nspy
Eu-TAA-Si-Nspy
2928
0.2
456
788
Tb-TTA-Si-Nspy
2935
Sm-TTA-Si-Nspy
464
791
0.0
200 250 300 350 400 450 500 550 600 650 700
Wavelength / nm
4000 3500 3000 2500 2000 1500 1000
500
-1
Wavenumber / cm
(B)
Fig. 2 FTIR spectra of a beta-diketones and linkages; b the hybrid
systems: Eu(TTA-Si)3Nspy, Eu(TAA-Si)3Nspy, Tb(TTA-Si)3Nspy, Tb
(TAA-Si)3Nspy, Sm(TTA-Si)3Nspy
0.8
0.6
the UV-visible diffuse reflection spectrum is very similar to
the exaction of the Eu3+ hybrid systems.
The excitation and emission spectra of the resulting
europium hybrid materials are shown in Fig. 4a and b. A
high baseline is observed in the emission spectra of Eu
(TAA-Si)3Nspy, which indicates the energy transfer effi-
ciency between TAA and Eu3+ is low, while for Eu(TTA-
Si)3Nspy, the base line is very low. The emission lines of
hybrid material Eu(TTA-Si)3Nspy are assigned to 5D0→7FJ
transitions located at around 576, 587, 613, 648, and
695 nm, for J=0, 1, 2, 3, and 4, respectively, while in
hybrid Eu(TAA-Si)3Nspy, only 5D0→7FJ (J=0, 1, 2)
transitions at 576, 587 and 613 nm are obtained, the
5D0→7F0 and 5D0→7F4 transitions are too weak to be
0.4
0.2
0.0
Tb-TTA-Si-Nspy
Tb-TAA-Si-Nspy
200 250 300 350 400 450 500 550 600 605 700
Wavelength / nm
Fig. 3 Ultraviolet–visible diffuse reflection absorption spectra of a Eu
(TTA-Si)3Nspy and Eu(TAA-Si)3Nspy; b Tb(TTA-Si)3Nspy and Tb
(TAA-Si)3Nspy

J Fluoresc (2012) 22:729–736
733
emission lines assigned to the 5D4→7FJ transitions are located
at 490, 543, and 586 nm, for J=6, 5, and 4 respectively.
Among all these emission peaks, the most striking green
luminescence (5D4→7F5) is observed due to the fact that this
emission is the most intense one in the emission spectra.
Besides, the more smooth baseline of the characteristic
emission of the Tb(TAA-Si)3Nspy indicates the more
effective energy transfer between the ligand TTA-Si and the
Rare earth ion, compared to that of Tb(TTA-Si)3Nspy. What
have discussed in the front may indicate that the TTA may be
more favorable for the luminescence of the Tb3+, which may
be explained by the energy degree. Of course, other factors
such as relatively rigid structure of silica gel which can limit
the vibration of ligand of Tb3+ and prohibit nonradiative
transitions may also contribute to the striking green emission.
(A)
Eu-TAA-Si-Nspy
Eu-TTA-Si-Nspy
=614nm
em
250
275
300
325
350
375
400
Wavelength / nm
(A)
(B)
Tb-TAA-Si-Nspy
7
5
F
D0
2
=545
em
Eu-TTA-Si-Nspy
nm
Tb-TTA-Si-Nspy
Eu-TAA-Si-Nspy
nm
ex
ex
5
7
D
F
0
1
7
5
F
3
D
0
7
5
7
5
F
D
F
D
0
0
0
4
225
250
275
300
325
350
375
450
500
550
600
650
700
750
Wavelength / nm
Wavelength / nm
Fig. 4 Excitation spectra (a) and emission spectra (b) of europium
hybrids (Eu(TTA-Si)3Nspy, Eu(TAA-Si)3Nspy)
(B)
7
5
F
D4
[29]. A prominent feature that may be noted in these spectra is
the low intensity ratios of I(5D0→7F2)/I(5D0→7F1). The
intensity (the integration of the luminescent band) ratio of
the 5D0→7F2 transition to 5D0→7F1 transition has been
widely used as an indicator of Eu3+ site symmetry [30].
When the interactions of the rare-earth complex with its local
chemical environment are stronger, the complex becomes
more nonsymmetrical and the intensity of the electric-dipolar
transitions becomes more intense. As a result, 5D0→7F1
transition (magnetic-dipolar transitions) decreased and
5D0→7F2 transition (electric-dipolar transitions) increased.
In this situation, the intensity ratios are approximately 2.3
which mean that the matrix didn’t disturb the coordination
between the organic groups and lanthanide ions.
5
Tb-TAA-Si-Nspy
Tb-TAA-Si-Nspy
=306nm
ex
=361nm
ex
7
5
F
D
6
4
5
7
F
D
4
4
450
475
500
525
550
575
600
Wavelength / nm
The luminescence properties of Tb(TTA-Si)3Nspy and Tb
(TAA-Si)3Nspy are shown in Fig. 5a and b respectively. The
Fig. 5 Excitation spectra (a) and emission spectra (b) of terbium
hybrids (Tb(TTA-Si)3Nspy, Tb(TAA-Si)3Nspy)

734
J Fluoresc (2012) 22:729–736
For Sm(TTA-Si)3Nspy hybrid material, a broad excitation
clustering of the emitting could be avoided and a better
photoluminescence of hybrid material is obtained.
band centered at around 367 nm is observed in Fig. 6a. With
the 367 nm as the exaction wavelength, the peaks at 560 nm,
5
The emission quantum efficiency (η) of the D0 excited
4
595 nm, and 644 nm assigned to the G5/2→6HJ transitions
state can be determined on the basis of the emission
spectrum and the lifetime of the Eu3+ firstly excited level
(τ, 5D0). Assuming that only nonradiative and radiative
processes are essentially involved in the depopulation of the
5D0 state, the experimental luminescence lifetime can be
calculated by the equation [31–37].
for J=5/2, 7/2, and 9/2 respectively are viewed in Fig. 6b
and the most intense emission is located at 644 nm.
Moreover, a broad emission band is observed which
indicates that the ligand TTA has not effectively transferred
the energy to the Sm3+. The low energy transfer efficiency
may be prevented by selecting the energy-matching ligand.
While for Sm(TAA-Si)3Nspy, the intensities of its emission
spectra are so weak that cannot be seen from the emission
spectra. Accordingly, we may also expect that through this
efficient way, the leaching of the photoactive molecules and
texp ¼ ðAr þ AnrÞꢀ1
ð1Þ
The Ar and Anr represent the radiative transition rates
and nonradiative transition rates respectively. The quantum
efficiency of the luminescence, which can be defined as the
possession ratio of the radiative transition to the total
transition, is calculated by the following equation.
(A)
h ¼ Ar=ðAr þ AnrÞ
ð2Þ
According to the Eqs. 1 and 2, the η which can be
described as the product of the radiative transition and the
luminescence decay time, the equation as the followed.
=594nm
em
h ¼ Artexp
ð3Þ
Sm-TTA-Si-Nspy
Here, Ar is achieved by summing over the radiative rates
5
A0J for each D0→7FJ transitions of Eu3+.
X
Ar ¼
A0J ¼ A00 þ A01 þ A02 þ A03 þ A04
ð4Þ
Considering the magnetic dipole D0→7F1 transition is
independent of Eu3+ chemical environment, so it is
available as the internal reference for the whole spectrum.
The other experimental coefficients of spontaneous emis-
sion, A0J can be calculated according to the equation.
5
225
250
275
300
325
350
375
400
Wavelength / nm
A0J ¼ A01ðI0J =I01Þðu01=u0J Þ
ð5Þ
(B)
In this equation, A0J is the experimental coefficients of
6
4
4
6
H
G
5/2
G
H
5/2
5/2
9/2
spontaneous emission, where J is representative for 0, 1, 2,
5
5
3 and 4 respectively. The D0→7F5 and D0→7F6 can be
4
6
G
H
5/2
7/2
neglected for the truth that their influence can be ignored in
5
the depopulation of the D0 excited state. The A01 is the
=367nm
ex
Einstein’s coefficient of spontaneous emission of the
5D0→7F1. In vacuum, the value of A01 can be determined
Table 1 Luminescence decay times (τ) and emission quantum
efficiency (η)
Sm-TTA-Si-Nspy
System
Eu-TTA-Si-Nspy
Eu-TAA-Si-Nspy
a
τ (μs)
426
505
22
355
288
11
Arad (s−1
)
450
500
550
600
650
700
η (%)
Wavelength / nm
I02/I01
6.25
4.5
Fig. 6 Excitation and emission spectra (a) and (b) of samarium
hybrids (Sm(TTA-Si)3Nspy)
a The luminescence decay times of 5 D0→7 F2 transitions

J Fluoresc (2012) 22:729–736
735
(A)
doping hybrid materials which generally experience the
phase separation phenomena, in this paper the inorganic
and organic phases can exhibit their distinct properties
together in the hybrid materials containing covalent bonds
[38]. The selected scanning electron micrographs of
systems are shown in the Fig. 7a and b respectively. The
micrograph of Eu(TTA-Si)3Nspy is made up of a lot of
single, ordered rectangular parallelepiped (see Fig. 7a)
which indicate the regular, homogeneous hybrid material
has been obtained. Meanwhile, the micrograph of Tb(TAA-
Si)3Nspy is made up of a great deal of regular square blocks
(see Fig. 7b). Considering the ligand TTA or TAA has the
multidimensional β-diketone with the thiophene ring or a
methylic, two carbonyl groups, and a trifluoromethyl group,
so its derivative TTA-Si or TAA-Si is prone to form a two-
dimensional layer-like or three-dimensional network-like
microstructure, and its corresponding complex may also
keep this trend. So this regular three-dimensional structure
we obtained may be due to the fact that the specific β-
diketone ligand acts as a functional bridge combining
inorganic matrices and organic components together.
(B)
Conclusions
In summary, the covalent linkage (TTA-Si or TAA-Si) is
obtained and the organic Nspy is synthesized, which are
both used to assemble the ternary rare earth (Eu3+, Tb3+,
Sm3+) hybrid system. The homogeneous microstructures
and morphologies of these hybrid systems show the
occurrence of self-assembly between the inorganic network
and organic chain. Besides, the luminescence properties of
these systems indicate that the ternary systems have a
longer time and higher quantum efficiency than the binary
systems. Moreover, we can see that the hybrids Eu(TTA-
Si)3Nspy shows a better luminescence than the hybrids Eu
(TAA-Si)3Nspy. While the hybrids Tb(TAA-Si)3Nspy
exhibits a better luminescence than the hybrids Tb(TTA-
Si)3Nspy. In addition, the hybrids Sm(TTA-Si)3Nspy
presents apparent photoluminescence of Sm3+, while the
hybrids Sm (TAA-Si)3Nspy does not.
Fig. 7 Scanning electron micrographs of a Eu(TTA-Si)3Nspy; b Tb
(TAA-Si)3Nspy
to be 50 s−1 approximately (A01=n3A01 (vacuum)). [32,
35], I is the emission intensity which can be taken as the
5
integrated intensity of the D0→7FJ emission bands [36,
37], υ0J refers to the energy barycenter and can be
5
determined from the emission bands of Eu3+’s D0→7FJ
emission transitions. According to the above discussion, it
can be seen there are two mainly factors contributing to the
value η, one factor is lifetime and the other is I02/I01 (red/
orange ratio). If the lifetimes and red/orange ratio are both
large, the quantum efficiency must be high. The quantum
efficiencies of the two kinds of europium hybrid systems
are described in Table 1, it can be seen in this order Eu-
TTA-Si-Nspy > Eu-TAA-Si-Nspy. The conclusion can be
drawn that the organic ligand TTA is more favorable for
luminescence of the Eu3+ hybrid material than the organic
ligand TAA.
Acknowledgments This work is supported by the National Natural
Science Foundation of China (20971100) and program for New
Century Excellent Talents in University (NCET-08-0398).
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