Synthesis, characterization, and luminescence properties of the ternary europium complex covalently bonded to mesoporous SBA-15

Article abstract of DOI:10.1021/jp051984n

A novel mesoporous SBA-15 type of hybrid material (phen-SBA-15) covalently bonded with 1, 10-phenanthroline (phen) ligand was synthesized by co-condensation of tetraethoxysilane (TEOS) and the chelate ligand 5-[N,N-bis-3-(triethoxysilyl)propyl]ureyl-1,10-phenanthroline (phen-Si) in the presence of Pluronic P123 surfactant as a template. The preservation of the chelate ligand structure during the hydrothermal synthesis and the surfactant extraction process was confirmed by Fourier transform infrared (FTIR) and ²⁹Si MAS NMR spectroscopies. SBA-15 consisting of the highly luminescent ternary complex Eu(TTA)3phen (TTA = 2-thenoyltrifluoroacetone) covalently bonded to a silica-based network, which was designated as Eu-(TTA)₃phen-SBA-15, was obtained by introducing the Eu(TTA) ₃?·2H₂O complex into the hybrid materials via a ligand exchange reaction. XRD, TEM, and N₂ adsorption measurements were employed to characterize the mesostructure of Eu(TTA)₃phen-SBA- 15. For comparison, SBA-15 doped with Eu(TTA)₃?·2H₂O and Eu(TTA)₃phen complexes and SBA-15 covalently bonded with a binary europium complex with phen ligand were also synthesized, and were named SBA-15/Eu(TTA)₃, SBA-15/Eu(TTA)₃phen, and Eu-phen-SBA-15, respectively. The detailed luminescence studies on all the materials showed that, compared with the doping sample SBA-15/Eu(TTA)₃phen and binary europium complex functionalized sample Eu-phen-SBA-15, the Eu(TTA) ₃phen-SBA-15 mesoporous hybrid material exhibited higher luminescence intensity and emission quantum efficiency. Thermogravimetric analysis on Eu(TTA)₃phen-SBA-15 demonstrated that the thermal stability of the lanthanide complex was evidently improved as it was covalently bonded to the mesoporous SBA-15 matrix. ? 2005 American Chemical Society.

Full text of DOI:10.1021/jp051984n

15278
J. Phys. Chem. B 2005, 109, 15278-15287
Synthesis, Characterization, and Luminescence Properties of the Ternary Europium
Complex Covalently Bonded to Mesoporous SBA-15
†
,‡
,†
†
†
†
†
Chunyun Peng, Hongjie Zhang,* Jiangbo Yu, Qingguo Meng, Lianshe Fu, Huanrong Li,
Lining Sun,† and Xianmin Guo
,‡
†,‡
Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, 5625 Renmin Street, Changchun 130022, People’s Republic of China, and
Graduate School of the Chinese Academy of Sciences, Beijing, People’s Republic of China
ReceiVed: April 17, 2005; In Final Form: June 8, 2005
A novel mesoporous SBA-15 type of hybrid material (phen-SBA-15) covalently bonded with 1,10-
phenanthroline (phen) ligand was synthesized by co-condensation of tetraethoxysilane (TEOS) and the chelate
ligand 5-[N,N-bis-3-(triethoxysilyl)propyl]ureyl-1,10-phenanthroline (phen-Si) in the presence of Pluronic P123
surfactant as a template. The preservation of the chelate ligand structure during the hydrothermal synthesis
and the surfactant extraction process was confirmed by Fourier transform infrared (FTIR) and 29Si MAS
NMR spectroscopies. SBA-15 consisting of the highly luminescent ternary complex Eu(TTA)
-thenoyltrifluoroacetone) covalently bonded to a silica-based network, which was designated as Eu-
TTA) phen-SBA-15, was obtained by introducing the Eu(TTA) ‚2H O complex into the hybrid materials
via a ligand exchange reaction. XRD, TEM, and N adsorption measurements were employed to characterize
the mesostructure of Eu(TTA) phen-SBA-15. For comparison, SBA-15 doped with Eu(TTA) ‚2H O and
Eu(TTA) phen complexes and SBA-15 covalently bonded with a binary europium complex with phen ligand
were also synthesized, and were named SBA-15/Eu(TTA) , SBA-15/Eu(TTA) phen, and Eu-phen-SBA-
5, respectively. The detailed luminescence studies on all the materials showed that, compared with the doping
3
phen (TTA )
2
(
3
3
2
2
3
3
2
3
3
3
1
sample SBA-15/Eu(TTA) phen and binary europium complex functionalized sample Eu-phen-SBA-15, the
3
Eu(TTA)
3
phen-SBA-15 mesoporous hybrid material exhibited higher luminescence intensity and emission
phen-SBA-15 demonstrated that the thermal
quantum efficiency. Thermogravimetric analysis on Eu(TTA)
3
stability of the lanthanide complex was evidently improved as it was covalently bonded to the mesoporous
SBA-15 matrix.
1
. Introduction
distribution) are of great interest for adsorption, sensing,
catalysis, and other applications. Recently, one of particular
7
Lanthanide complexes have long been known to give sharp,
interest is the use of ordered mesoporous silica materials as a
intense emission lines upon ultraviolet light irradiation, because
of the effective intramolecular energy transfer from the coor-
dinated ligands to the luminescent central lanthanide ion, which
8
support for lanthanide complexes. For example, Xu et al.
reported that the lanthanide complex [C5H5NC16H33][Eu(TTA)4]
(TTA ) 2-thenoyltrifluoroacetone) was incorporated into the
in turn undergoes the corresponding radiative emitting process
1
surface-modified mesoporous molecular sieve Si-MCM-41 by
(the so-called “antenna effect”). Therefore, they are expected
the strong hydrogen bonding interactions between the rare-earth
to be promising luminescent dopants for the preparation of
hybrid phosphors and other optical sources. In recent years, the
luminescence properties of lanthanide complexes supported on
a solid matrix have been studied extensively because their
photophysical properties could be modified by interaction with
the host structure. For example, the incorporation of lanthanide
complexes with â-diketones, aromatic carboxylic acids, and
8
a,d
complex and the silylating agent.
Meng et al. reported on
the preparation of luminescent silica mesoporous molecular
sieves MCM-48 activated by the europium complex Eu(DBM)3‚
2
H2O (where DBM is dibenzoylmethane) by using a simple
8e
2
wet impregnation method. However, these investigations were
mainly focused on doping mesoporous silica materials with
lanthanide complexes, in which only weak physical interactions
(hydrogen bonding, van der Waals force, or weak static effect)
exist between the mesoporous silica materials and the lanthanide
complexes. This will give little control over the clustering of
emitting centers, inhomogeneous dispersion of both components,
and leaching of the photoactive molecules in the obtained
materials. Recently, our group has reported the synthesis of
mesoporous silica MCM-41 covalently bonded with a binary
europium complex with phen ligand (Eu-phen-MCM-41) via
3
4
5
heterocyclic ligands into sol-gel-derived host structures by
covalent bonds has been extensively investigated. These studies
indicate that the thermal stabilities and mechanical properties
of the lanthanide complexes were improved by the matrixes.
6
Since their discovery in the early 1990s, ordered mesoporous
materials with unique properties (e.g., high surface area, high
pore volume, controlled pore structure, and uniform pore size
*
To whom correspondence should be addressed. Fax: +86-431-
5
698041. E-mail: hongjie@ciac.jl.cn.
9
a co-condensation process. This approach enables a higher and
†
Changchun Institute of Applied Chemistry, Chinese Academy of
more homogeneous surface coverage of organosilane function-
alities and can effectively prevent the aggregation of lanthanide
Sciences.
‡
Graduate School of the Chinese Academy of Sciences.
1
0.1021/jp051984n CCC: $30.25 © 2005 American Chemical Society
Published on Web 07/23/2005

Europium Complex Bonded to Mesoporous SBA-15
J. Phys. Chem. B, Vol. 109, No. 32, 2005 15279
SCHEME 1: Synthesis Procedure and Predicted Structure of Eu(TTA)3phen-SBA-15
complexes. However, Eu-phen-MCM-41 shows relatively
weak red luminescence and poor color purity because the water
molecules in the first coordination sphere of europium(III)
chloride phenanthroline complexes can deactivate the excited
spectively. Detailed analyses of luminescent properties of all
these synthesized materials and the thermal stability of the
resulting Eu(TTA)3phen-SBA-15 were investigated in relation
to guest-host interactions between the organic complex and
the silica matrix.
3
+
state of Eu ion by means of energy transfer to the O-H
vibration manifold. It is well-known that â-diketone ligand
3+
2. Experimental Section
coordinating with the central Eu ion can effectively prevent
3+
Eu ion against the residual water molecules and silanol
2.1. Materials. Tetraethoxysilane (TEOS, Aldrich), 3-(tri-
ethoxysilyl)propyl isocyanate (Aldrich), Pluronic P123 (Aldrich),
and ethanol were used as received. The solvent chloroform
3
3
,10
groups.
In the presence of â-diketone ligand, phen can
successfully compete with the water molecules in the first
coordination sphere around the Eu3 ion. Moreover, as the first
+
(CHCl ) was used after desiccation with anhydrous calcium
3+
ligand, TTA transferred energy to Eu ion more efficiently
than phen ligand did.11 Therefore, improved luminescence
behavior can be expected via introduction of Eu(TTA)3‚2H2O
into the phen functionalized mesoporous silica matrix.
chloride. Europium chloride (EuCl ) and gadolinium chloride
3
(GdCl ) were obtained by dissolving Eu O (99.99%, Shanghai
3
2
3
Yuelong) and Gd O (99.99%, Shanghai Yuelong) in hydro-
2
3
chloric acid, respectively.
On the other hand, as a host material for lanthanide
complexes, SBA-15 appears to be more attractive than meso-
porous silicas M41S because of its much larger uniform pore
2.2. Synthesis. 2.2.1. Synthesis of Phen-Functionalized SBA-
15 Mesoporous Silica (phen-SBA-15). The starting reagent
5-amino-1,10-phenanthroline (denoted as phen-NH ) was pre-
2
1
2
size (up to 30 nm), thicker silica wall, and better stability.
pared by the method of ref 14. Phen-Si was synthesized by the
For example, the larger pores make it an attractive host for the
insertion of large amounts of bulky molecules with functional
properties, and better stability makes it very suitable for
immobilization of functional molecules. In particular, a few
studies on the coordination of lanthanide ions or transition metal
ions with organic ligands covalently bonded to SBA-15 meso-
porous silica have been reported.13 However, the synthesis and
luminescence properties of SBA-15 mesoporous materials
covalently bonded with organic lanthanide complexes have not
been explored to date.
reaction of phen-NH and 3-(triethoxysilyl)propyl isocyanate
2
in CHCl as described in ref 5a. Then 2.0 g of P123 was
3
dissolved in 15 g of deionized water and 60 g of a 2 M HCl
solution at 35 °C. A mixture of TEOS and phen-Si was added
to that solution, leading to a composition with a molar ratio of
X phen-Si:(1 - X) TEOS:0.0172 P123:6 HCl:208.33 H O, where
2
X ) 0, 0.02, 0.04, and 0.06. The mixture was stirred at 35 °C
for 24 h and transferred into a Teflon bottle sealed in an
antoclave, which was then heated to 100 °C for 2 days. The
solid product was recovered by filtration, washed thoroughly
with deionized water, and air-dried at room temperature.
Removal of copolymer surfactant P123 was conducted by
Soxhlet extration with ethanol for 24 h to give the sample
denoted as phen-SBA-15(X) (X ) 0, 0.02, 0.04, and 0.06),
where X is the phen-Si:(TEOS + phen-Si) molar ratio.
Herein, we report a direct synthesis of phen-functionalized
SBA-15 mesoporous hybrid material (phen-SBA-15), in which
phen was covalently bonded to the framework of SBA-15 by
co-condensation of the modified phenanthroline 5-[N,N-bis-3-
(triethoxysilyl)propyl]ureyl-1,10-phenanthroline (phen-Si) and
tetraethoxysilane (TEOS) by using the Pluronic P123 surfactant
as template. Highly luminescent complex Eu(TTA)3phen-
functionalized SBA-15 [denoted as Eu(TTA)3phen-SBA-15]
was obtained by introducing Eu(TTA)3‚2H2O into the phen-
SBA-15 hybrid materials with a ligand exchange reaction. Thus,
the ternary europium complex Eu(TTA)3phen was successfully
linked to the framework of SBA-15 via a covalently bonded
phen group. In addition, for comparison, SBA-15 doped with
Eu(TTA)3‚2H2O and Eu(TTA)3phen complexes and SBA-15
covalently bonded with a binary europium complex with phen
ligand were also synthesized, and are designated SBA-15/Eu-
2.2.2. Synthesis of SBA-15 Mesoporous Silica CoValently
Bonded with Ternary Complex Eu(TTA)3Phen [Eu(TTA)3phen-
SBA-15]. Eu(TTA)3‚2H2O was prepared by the methods de-
1
5
scribed in the literature. While being stirred, phen-SBA-
15(0.04) was soaked in an excess of an Eu(TTA)3‚2H2O ethanol
solution [2 equiv of Eu(TTA)3‚2H2O per phen moiety]. The
mixture was heated under reflux for 12 h, followed by filtration
and extensive washing with acetone for removal of the excess
of Eu(TTA)3‚2H2O. The resulting Eu(TTA)3phen-SBA-15 was
dried at 60 °C under vacuum overnight. The hybrid mesoporous
product Eu(TTA)3phen-SBA-15 was obtained as outlined in
Scheme 1.
(TTA)3, SBA-15/Eu(TTA)3phen, and Eu-phen-SBA-15, re-

15280 J. Phys. Chem. B, Vol. 109, No. 32, 2005
Peng et al.
2
.2.3. Synthesis of SBA-15 CoValently Bonded with the
Europium Complex with Phen Ligand (Eu-phen-SBA-15). The
synthesis procedure for Eu-phen-SBA-15 was similar to that
of Eu(TTA)3phen-SBA-15 except that Eu(TTA)3‚2H2O was
replaced by EuCl3.
2
.2.4. Synthesis of SBA-15 Doped with the Eu(TTA)3‚2H2O
Complex [SBA-15/Eu(TTA)3]. SBA-15 doped with Eu(TTA)3‚
H2O [SBA-15/Eu(TTA)3] was prepared in the same way as
described for Eu(TTA)3phen-SBA-15 except that phen-SBA-
5 was replaced by pure SBA-15.
.2.5. Synthesis of SBA-15 Doped with the Eu(TTA)3Phen
Complex [SBA-15/Eu(TTA)3phen]. The Eu(TTA)3phen complex
2
1
2
1
6
was synthesized following the literature procedure. The
synthesis procedure for SBA-15/Eu(TTA)3phen was also similar
to that of Eu(TTA)3phen-SBA-15 except that phen-SBA-15
and Eu(TTA)3‚2H2O were replaced by pure SBA-15 and the
Eu(TTA)3phen complex, respectively.
Figure 1. XRD patterns of phen-SBA-15(X), when X ) (a) 0, (b)
0
.02, (c) 0.04, and (d) 0.06.
2
.2.6. Synthesis of the Gd(Phen)3Cl2 Complex. At room
temperature, 3 mmol of phen was dissolved in 10 mL of ethanol.
Then 1 mmol of a GdCl3 ethanol solution was added under
stirring, and the solution was heated under reflux for 2 h. The
white powder was filtered and washed with ethanol. The
resulting Gd(phen)3Cl2 was dried at 60 °C under vacuum
overnight.
2
.3. Characterization. Small-angle X-ray diffraction patterns
XRD) were recorded with Rigaku-Dmax 2500 diffractometer
using Cu KR radiation (40 kV and 200 mA) at a step width of
.02°. Fourier transform infrared (FTIR) spectra were measured
(
0
-
1
within the 4000-400 cm wavenumber range using a Perkin-
Elmer model 580B IR spectrophotometer with the KBr pellet
technique. Solid-state 29Si MAS NMR spectra were recorded
at 79.46 MHz, using a Bruker Avance 400 spectrometer. The
mesostructure of the Eu(TTA)3phen-SBA-15 hybrid material
was proven with a transmission electron microscope (TEM,
JEM-100CX(II)). Nitrogen (N2) adsorption/desorption isotherms
were measured by using a Nova l000 analyzer with nitrogen.
The samples were outgassed for 4 h at 120 °C before the
measurements. Surface areas were calculated by the Brunauer-
Emmett-Teller (BET) method and pore sizes by the Barrett-
Figure 2. FTIR spectra for phen-Si (a), as-synthesized phen-SBA-
5(0.04) (b), and surfactant-extracted phen-SBA-15(0.04) (c).
1
resulting phen-SBA-15(X) (X ) 0, 0.02, 0.04, and 0.06). For
the samples synthesized with phen-Si:(phen-Si + TEOS) molar
ratios below 0.04, three well-resolved diffraction peaks [(100),
(110), and (200) reflections] in the 2θ range of 0.8-2°, typical
of hexagonal SBA-15, are observed. However, with the
concentration of phen-Si increasing, the intensity of the (100)
reflection decreases gradually and the higher-angle peak (110)
and (200) reflections diminish in relative intensity [disappearing
entirely for phen-SBA-15 (0.06)]. The reduction in diffraction
intensity with an increase in phen-Si concentration can be partly
assigned to a decrease in the mesoscopic order of the materials,
such as variations in the wall thickness, and may also be partly
due to the contrast matching between the amorphous silicate
framework and organic moieties inside the pore channels of
3
+
Joyner-Halenda (BJH) methods. The content of Eu ion was
obtained by inductively coupled plasma-atomic emission spec-
troscopy and mass spectroscopy (ICP-AES-MS) with a TJA-
POEMS spectrometer. The UV-vis absorption spectra were
recorded with a TU-1901 spectrophotometer. The fluorescence
excitation and emission spectra were obtained with a Hitachi
F-4500 spectrophotometer equipped with a 150 W xenon lamp
as the excitation source. Luminescence lifetimes were measured
with a Lecroy Wave Runner 6100 digital oscilloscope (1 GHz)
using different wavenumber lasers (pulse width of 4 ns) as the
excitation source (Continuum Sunlite OPO). All the measure-
ments were performed at room temperature. The low-temper-
1
7
the materials. The results described above show that the
formation and self-assembly of surfactants aggregates might be
perturbed during the co-condensation when the phen-Si:(phen-
Si + TEOS) molar ratio is g0.06, and an optimum molar ratio
[phen-Si:(phen-Si + TEOS) ) 0.04] can be employed to
synthesize phen-functionalized SBA-15 with a high loading of
functionality yet a good mesostructure. Hence phen-SBA-15-
ature phosphorescence spectrum of the Gd3+ complex was
measured on a Hitachi F-4500 spectrophotometer at liquid
nitrogen temperature (77 K). Thermogravimetric analysis (TGA)
was performed on a Perkin-Elmer Pyris Diamond thermal
analyzer up to 700 °C at a heating rate of 10 °C/min under N2.
(0.04) was selected as the candidate for the following preparation
of SBA-15 mesoporous silica covalently bonded with the Eu-
(
TTA)3phen complex [Eu(TTA)3phen-SBA-15].
The presence of the organic ligand covalently bonded to the
3
. Results and Discussion
.1. Phen-Functionalized Mesoporous Silica SBA-15. Me-
mesoporous SBA-15 was characterized by FTIR and 29Si MAS
NMR spectroscopy. The FTIR spectra of phen-Si (a), as-
synthesized phen-SBA-15(0.04) (b), and surfactant-extracted
phen-SBA-15(0.04) (c) are shown in Figure 2. In Figure 2a,
3
soporous silica containing phen groups was synthesized as
described in the Experimental Section. During the synthesis, a
series of phen-functionalized SBA-15 samples with different
concentrations of phen-Si in the initial mixture were obtained.
Figure 1 depicts the variation of the XRD patterns for the
-
1
the spectrum of phen-Si is dominated by ν(C-Si,1193 cm )
-
1
and ν(Si-O,1079 cm ) absorption bands, characteristic of
trialkoxylsilyl functions. In panels b and c of Figure 2, the

Europium Complex Bonded to Mesoporous SBA-15
J. Phys. Chem. B, Vol. 109, No. 32, 2005 15281
Figure 5. TEM images of Eu(TTA)
the [100] (a) and [110] (b) zone axes. Both scale bars are 50 nm.
3
phen-SBA-15 recorded along
Figure 3. 29Si MAS NMR spectrum of the phen-SBA-15(0.04).
Figure 6. N
2
adsorption and desorption isotherms of SBA-15 (a, s),
phen-SBA-15 (c,
Figure 4. XRD patterns of phen-SBA-15(0.04) (a) and Eu(TTA)
SBA-15 (b).
3
phen-
phen-SBA-15(0.04) (b, - - -), and Eu(TTA)
3
-
- -).
formation of the Si-O-Si framework is evidenced by the bands
-
1
-1
located at 1088 and 1080 cm (νas, Si-O), 802 and 799 cm
2
°, which can be indexed as (100), (110), and (200) reflections
-
1
(
νs, Si-O), and 456 and 462 cm (δ, Si-O-Si) (ν represents
stretching, δ in-plane bending, s symmetric, and as asymmetric
of a two-dimensional hexagonal (p6mm) structure of SBA-15
material. The values of the corresponding unit cell parameter a
-1
vibrations). The peaks at 1652 and 1536 cm , originating from
the CONH group of phen-Si, can also be observed both in the
as-synthesized material and in the surfactant-extracted material,
which is consistent with the fact that the phen group in the
framework remains intact after both the hydrolysis-condensa-
tion reaction and the surfactant extraction procedure. In addition,
the surfactant-extracted phen-SBA-15 only exhibits weak
(
a ) 2d100/ 3) of phen-SBA-15(0.04) and Eu(TTA)3phen-
x
SBA-15 are 11.74 and 11.69 nm, respectively. Compared with
that of phen-SBA-15(0.04), the d100 spacing value of Eu-
(TTA)3phen-SBA-15 is nearly unchanged, indicating that the
framework hexagonal ordering has been retained very well upon
the introduction of Eu(TTA)3‚2H2O. The diffraction pattern of
phen-SBA-15(0.04) exhibits an intensity greater than that of
Eu(TTA)3phen-SBA-15. The reduction in diffraction intensity
upon the introduction of Eu(TTA)3‚2H2O into phen-SBA-15
may be assigned to the presence of Eu(TTA)3phen inside the
pore channels of Eu(TTA)3phen-SBA-15.
-
1
templete ν(C-H) vibrations at 2700-3000 cm and a disap-
-
1
pearance of δs(C-H) vibrations at 1375 cm , which confirms
that most of the surfactant has been removed.
2
9
Si MAS NMR spectroscopy results of the surfactant-
extracted phen-SBA-15(0.04) mesoporous silica sample are
The hexagonal symmetry of Eu(TTA)3phen-SBA-15 inferred
from XRD is also in agreement with the TEM investigation.
displayed in Figure 3. The peaks corresponding to the various
m
m
siloxane Q [Q ) Si(OSi)m(OH)4-m, m ) 2-4] and organosi-
n
n
TEM images of Eu(TTA) phen-SBA-15 are presented in Figure
loxane T [T ) RSi(OSi)nOH3-n, n ) 1-3] species can be
3
5
and confirm the suggested p6mm symmetry, indicating that
after the complexation process the mesostructure of the Eu-
TTA)3phen-SBA-15 sample can be substantially conserved.
identified clearly. The relative integrated intensities of the
1
2
3
organosiloxane T , T , and T NMR signals can be employed
(
to estimate the degree of hydrolysis-condensation of organic
1
2
The distance between the centers of the mesopores is estimated
to be 11 nm, in good agreement with the value determined from
the corresponding XRD data.
functional groups. Compared with T and T organosiloxane
3
3
3
2
1
centers, the predominance of T [the T :(T + T + T ) ratio is
.65] suggests that the hydrolysis and condensation of the organo
0
functionality (phen-Si) in the order structure is nearly complete,
indicating a strong linkage (three Si-O-Si covalent bonds)
between the organic ligand and the silica matrix.
The N2 adsorption/desorption isotherms of phen-SBA-15-
(0.04), Eu(TTA)3phen-SBA-15, and pure SBA-15 samples are
shown in Figure 6. The textural data of the materials are given
in Table 1. All these samples display type IV isotherm curves
with an H1 hysteresis at high relative pressure, characteristic
of highly ordered mesoporous materials according to the IUPAC
3
.2. Ternary Complex of Eu(TTA)3phen-Functionalized
Mesoporous Silica SBA-15. The power X-ray diffraction
analyses performed on phen-SBA-15(0.04) (a) and Eu-
1
8
(
TTA)3phen-SBA-15 (b) are compared in Figure 4. These
classification. It can be seen that capillary condensation of
N2 occurred over slightly wider P/P0 ranges in phen-SBA-15-
patterns feature distinct Bragg peaks in the 2θ range of 0.8-

15282 J. Phys. Chem. B, Vol. 109, No. 32, 2005
Peng et al.
TABLE 1: Textural Data of SBA-15, Phen-SBA-15, and
Eu(TTA)
phen-SBA-15a
3
d
100
a
0
S
BET
2
V
D
t
3
sample
(nm) (nm) (m /g) (cm /g) (nm) (nm)
SBA-15
phen-SBA-15
Eu(TTA) phen-SBA-15 10.12 11.69 872
10.76 12.42 1197
10.17 11.74 996
1.81 7.39 5.03
1.62 6.43 5.31
1.41 5.77 5.92
3
a
d
100 is the d(100) spacing, a
0
the cell parameter (a
0
) 2d100/x3),
S
BET the BET surface area, V the pore volume, D the pore diameter,
and t the wall thickness, calculated by a - D.
0
Figure 8. Emission spectrum of phen-SBA-15(0.04) (a, excited at
2
79 nm, s) and TTA (b, excited at 219 nm, - - -) as solids and
-
4
absorption spectrum of EuCl
spectra are normalized to a constant intensity at the maximum.
3
at 1 × 10 mM in ethanol (c, - - -). All
Figure 7. Absorption spectra of phen-Si (a, s) and TTA (b, - - -)
-
4
at 1 × 10 mM in ethanol. The excitation spectrum for Eu-
TTA) phen-SBA-15 as a solid (c, - - -) was monitored at 612 nm.
All spectra are normalized to a constant intensity at the maximum.
(
3
(0.04) and Eu(TTA)3phen-SBA-15 than in the pure SBA-15
sample. Phen-SBA-15(0.04) exhibits a smaller specific area
and a slightly smaller pore size and pore volume in comparison
with those of pure SBA-15, which might be due to the presence
of both organic ligand phen on the pore surface and the co-
surfactant effect of phen-Si, which interacts with surfactant and
3 2
Figure 9. Emissiom spectrum of Gd(phen) Cl at 77 K (λex ) 298
-
4
reduces the diameter of the micelles.1 In addition, upon
introduction of Eu(TTA)3‚2H2O into the phen-SBA-15, the
specific area, pore size, and pore volume of Eu(TTA)3phen-
SBA-15 are smaller than those of phen-SBA-15. This also
confirmed the incorporation of the Eu(TTA)3phen complex in
the channels of SBA-15.
9
nm) at 5 × 10 M in methanol.
transfer in Eu(TTA)3phen-SBA-15 occurs mainly between
3
+
ligand TTA and the central Eu ion.
The efficient ligand-to-metal ion energy transfers in Eu-
(TTA)3phen-SBA-15 are also investigated by energy difference
3
.3. Luminescence Properties. 3.3.1. Antenna Effects and
between the triplet states of ligands and the resonance energy
level of the central lanthanide ion. The efficiency of the
intramolecular energy transfer was very sensitive to the energy
levels of the triplet state of the ligand. According to the
Luminescence. The excitation spectrum of the resulting Eu-
(
TTA)3phen-SBA-15 and the absorption spectra of the ligands
(TTA and phen-Si) are shown in Figure 7. The overlaps between
the excitation band of Eu(TTA)3phen-SBA-15 (Figure 7c) and
the absorption bands that came from ligands TTA (Figure 7b)
1
,22
luminescence theory of lanthanide complexes,
the require-
ment for an efficient intramolecular energy transfer is that the
energy difference between the triplet state of the ligand and the
and phen-Si (Figure 7a) can be observed clearly, which indicates
that the central Eu3+ ion in Eu(TTA)3phen-SBA-15 can be
3
+
resonance energy level of the central Eu ion be in the range
efficiently sensitized by the ligands (TTA and phen), an antenna
-1
3+
of 500-2500 cm . The triplet-state energy level of phen ligand
effect, and thus suggests that Eu ion is surrounded by TTA
and phen-Si.20 In addition, the F o¨ rster model,20a,21 which
is determined from the phosphorescence spectrum of the
3
+
1,22,23
respective Gd complex at 77 K under UV excitation.
considers the overlap between the emission spectrum of the
donor and the absorption spectrum of the acceptor, is essential
for energy transfer phenomena. As Figure 8 demonstrates, the
observed overlaps between the absorption spectrum of EuCl3
in ethanol and the emission spectra of TTA and phen-SBA-15
lead to the conclusion that both the phen group covalently
bonded to the SBA-15 and the ligand TTA can sensitize the
luminescence of the central Eu3 ion. Meanwhile, we observed
that the overlap between the absorption band of ligand TTA
and the excitation band is larger than that between the absorption
band of ligand phen-Si and the excitation band, suggesting that
TTA is a more efficient sensitizer than phen for the lumines-
cence of the central Eu3 ion and the intramolecular energy
Three phosphorescence bands are observed in the emission
spectrum of Gd(phen)3Cl2 (Figure 9, excited at 298 nm). The
triplet-state energy level of phen ligand was determined from
-
1
the shortest-wavelength phosphorescence band (22 173 cm )
due to the 0-0 transition of phen ligand. It has been reported
2
2c
that the triplet-state energy level of TTA ligand is 20 400
+
cm and the resonance energy level of Eu ion22a is 19 020
-1
3+
-
1
cm . Therefore, the energy differences between the triplet-
5
state energy levels of TTA and phen ligands and the D1 level
of Eu ion are 1380 and 3153 cm , respectively. According
to the luminescence theory of lanthanide complexes, the ligand
3
+
-1
+
3+
TTA can sensitize Eu ion luminescence efficiently and the

Europium Complex Bonded to Mesoporous SBA-15
J. Phys. Chem. B, Vol. 109, No. 32, 2005 15283
Figure 10. Excitation (- - -) and emission (s) spectra of Eu(TTA)
3
phen (a, λex ) 385 nm), Eu(TTA)
3
phen-SBA-15 (b, λex ) 352 nm), SBA-
phen (d, λex ) 350 nm), and
1
5/Eu(TTA)
3
(c, λex ) 341 nm) (- - -, the emission spectrum of SBA-15 excited at 350 nm), SBA-15/Eu(TTA)
3
Eu-phen-SBA-15 (e, λex ) 279 nm) [- - -, the emission spectrum of phen-SBA-15(0.04) excited at 279 nm] as solids. All the excitation spectra
3+
were obtained by monitoring the emission wavelength of the Eu ions at 612 nm. All spectra are normalized to a constant intensity at the maximum.
intramolecular energy transfer between TTA ligand and Eu3+
ion is more efficient than that between phen ligand and Eu
ion.
intra-4f 6 5D0 f FJ (J ) 0, 1, 2, 3, or 4) transitions of Eu
7
3+
3
+
ion; this energy transfer process seems to be very efficient for
the Eu(TTA)3phen complex. The observed number of Stark
5
7
Figure 10 presents the normalized excitation and emission
spectra for the Eu(TTA)3phen complex (a), Eu(TTA)3phen-
SBA-15 (b), SBA-15/Eu(TTA)3 (c), SBA-15/Eu(TTA)3phen (d),
and Eu-phen-SBA-15 (e) as solids at room temperature. The
excitation spectra of the materials were obtained by monitoring
the emission wavelength of the Eu3+ ions at 612 nm. As shown
in Figure 10a, the excitation spectrum of the pure Eu(TTA)3phen
complex exhibits a broad excitation band (BEB) between 200
and 500 nm (λmax ) 385 nm), which can be assigned to the
π-π* electron transition of the ligands.11,24 A peak at 467 nm
components for D0 f FJ (J ) 0, 1, and 2) transitions is 1, 3,
and 5, respectively. The other transitions are negligible since
their intensities are weak and their Stark components are not
completely resolved. The stark splitting reveals an ordered
“crystalline” rare-earth ion environment, rather than an amor-
8b
phous one. However, for Eu(TTA)3phen-SBA-15 (Figure
10b), the excitation spectrum become narrower than that of the
Eu(TTA)3phen complex and the maximum excitation shifted
from 385 to 352 nm. This pronounced blue shift of the excitation
band as the introduction of the europium complex into the SBA-
15 was attributed to a hypsochromic effect resulting from the
change in the polarity of the environment surrounding the
7
5
is observed due to the f-f absorption transition ( F0 f D2) of
3+
Eu ion. This transition is weaker than the absorption of the
organic ligands and overlapped by BEB, which proves that
luminescence sensitization via excitation of the ligands is much
8e
europium complex in the mesoporous silicas SBA-15. No f-f
3
+
transition of Eu ion could be observed in the spectrum,
3
+
3+
more efficient than the direct excitation of the Eu ion
absorption level. As no emission from the ligands is detected,
the emission spectrum (excited at 385 nm) displays only the
indicating that the energy transfer from the ligands to Eu ion
is more efficient in Eu(TTA)3phen-SBA-15 than in the pure
Eu(TTA)3phen complex. Excitation at 352 nm provides the

15284 J. Phys. Chem. B, Vol. 109, No. 32, 2005
Peng et al.
TABLE 2: Photoluminescent Data of Eu(TTA)
3
phen, Eu(TTA)
3
phen-SBA-15, SBA-15/Eu(TTA)
3
, SBA-15/Eu(TTA)
3
phen, and
Eu-phen-SBA-15 as Solidsa
Eu(TTA)
3
phen
Eu(TTA)
3
phen-SBA-15
SBA-15/Eu(TTA)
3
SBA-15/Eu(TTA)
3
phen
Eu-phen-SBA-15
-
-
-
-
-
1
1
1
1
1
ν
ν
ν
ν
ν
00 (cm
01 (cm
02 (cm
03 (cm
04 (cm
)
)
)
)
)
17271
16978
16393
15361
14245
137.72
17301
16978
16367
15361
14286
22.36
283.84
0.97
17301
16949
16340
15385
14327
1.72
17301
16978
16340
15385
14265
4.88
17301
16978
16340
15361
14327
8.07
I
01
I
02
1133.25
100
9.75
1.25
44.61
0.15
48.03
1.51
C
Eu (mol %)
I
I
Ω
Ω
τ (ms)
τ
A
A
02/CEu
02/I01
11.33
8.23
13.87
0.33
0.70
1429
298.33
13.19
22.38
0.52
0.49
2041
7.80
5.67
9.66
0.43
0.30
3333
362
2971
297.40
14.23
17.24
0.57
0.32
3125
30.23
5.95
10.16
0.54
0.39
2564
-
20
2
2
(×10 cm )
-
20
2
4
(×10 cm )
exp (s-1)
-
1
0
-4
(s-1
(s-1
)
)
436
993
768
1273
604
2521
374
2190
rad
0
-4
nrad
ηlnt (%)
30.51
37.61
10.86
19.33
14.60
a
5
f 7F
5
f 7F
5
f 7F
The energies of the D
0
J
transitions (ν0J), the emission intensity of the D
0
1
transition (I01) and the D
0
2
transition (I02), the
3
+
5
7
contents of the Eu (CEu), the emission intensity of the D
the D
decay rates (Anrad), and the emission quantum efficiency (η) of the D
0
f F
2
transition divided by the contents of the Eu (I02/CEu), the intensity ratios between
5
7
5
7
0
f F
2
and D
0
f F
1
transitions (I02/I01), experimental intensity parameters (Ω ), lifetimes (τ), radiative decay rates (Arad), nonradiative
λ
5
3+
0
Eu excited state were obtained at room temperature.
typical luminescence lines of Eu3+ ion at 578, 590, 611, 651,
ligand is more complete. The emission from the contribution
of phen moiety in the blue region is too weak to be observed in
5
7
and 700 nm, corresponding to D0 f FJ transitions (J ) 0, 1,
, 3, and 4, respectively). In comparison with the pure
2
Eu(TTA) phen-SBA-15. Therefore, the presence of â-diketone
3
Eu(TTA)3phen complex, the broadened emission lines and
decreased number of Stark components suggest less ordered
ligand TTA in the mesoporous matrix improved the lumines-
cence properities of our prepared Eu(TTA) phen-SBA-15.
3
3+
crystalline environments of Eu ion in Eu(TTA)3phen-SBA-
3
.3.2. Luminescent Intensities. According to the literature
8b,25
15.
Moreover, no emission from the triplet state of the phen
8d
5
reported previously, the luminescent intensities of the D0 f
F2 transition for all materials were compared. The contents of
the Eu
or TTA ligands (no broad band emission in the blue and green
spectral regions) is detected, indicating that the efficient energy
7
3+
ion in molar percentage [CEu (mol %)] in the
3+
transfer from the ligands to Eu ion takes place. The difference
in the excitation and emission spectra of Eu(TTA)3phen and
Eu(TTA)3phen-SBA-15 shows that in the Eu(TTA)3phen-
SBA-15 mesoporous silica, the environment of ligands and the
siloxo part of the structure affect the energy transfer.
Eu(TTA)3phen complex, Eu(TTA)3phen-SBA-15, SBA-15/Eu-
TTA)3, SBA-15/Eu(TTA)3phen, and Eu-phen-SBA-15 and
their relative luminescent intensities (integrated intensities) of
(
5
7
the D0 f F2 transition (I02) are listed in Table 2. It can be
clearly seen that the I02/CEu (the intensity divided by the contents
In the case of SBA-15/Eu(TTA)3 (Figure 10c) and SBA-15/
Eu(TTA)3phen (Figure 10d), the maximum absorptions of their
excitation spectra shift to 341 and 350 nm, respectively, which
are similar to the observed blue shift in Eu(TTA)3phen-SBA-
3
+
of the Eu ion) in Eu(TTA)3phen-SBA-15 is the highest in
these samples. Compared with Eu(TTA)3phen, when the com-
plex is covalently bonded to mesoporous silica SBA-15, the
I02/CEu of Eu(TTA)3phen-SBA-15 increases 25 times, which
suggests that in the Eu(TTA)3phen complex a quenching of the
europium luminescence can be induced by the concentration
effect and/or the electron-phonon couplings with the third
vibrational overtone of the close-lying OH oscillator. This
behavior shows that SBA-15 is an excellent host for the
luminescent complex Eu(TTA)3phen because the luminescence
1
5. However, in the corresponding emission spectra of SBA-
1
)
5/Eu(TTA)3 (λex ) 341 nm) and SBA-15/Eu(TTA)3phen (λex
3
+
350 nm), in addition to the typical emissions of Eu ion,
two weak peaks at 412 and 407 nm are observable, which are
consistent with the emissions of the their host SBA-15 (see the
short dashed line in Figure 10c, excited at 350 nm). The presence
of the emissions of host SBA-15 suggests that in the above two
samples the ligand-to-Eu3 energy transfer is less efficient than
in Eu(TTA)3phen and Eu(TTA)3phen-SBA-15. It is worth noting
3+
quenching of Eu ion can be effectively decreased in this host.
We found that SBA-15/Eu(TTA)3phen exhibited relative a high
I02/CEu compared with Eu(TTA)3phen-SBA-15. However, the
I02 of SBA-15/Eu(TTA)3phen is much lower than that of Eu-
+
that the emission spectrum for Eu-phen-SBA-15 (λex ) 279 nm,
Figure 10e) contains not only the emission of Eu3+ ion but also
(
TTA)3phen-SBA-15 because of the concentration limitation
a broad emission band in the blue spectral region peaking around
3
+
of Eu ion in SBA-15/Eu(TTA)3phen. For the SBA-15/Eu-
4
52 nm. The broad emission band is mainly attributed to the
8b,9
(TTA)3 sample, the lowest I02/CEu is probably related to the
π*-π relaxation of the free phen moiety, which is not able
to completely transfer the absorbed energy to the central Eu
ion (see the short dashed line in Figure 10e, excited at 279 nm),
3
+
3
+
presence of water molecules coordinated to Eu ion, which
3+
induces luminescence quenching of Eu ion via OH vibrations.
3
+
5
7
while for Eu(TTA)3phen-SBA-15, only the emission of Eu
ion is observed. Upon illumination of the Eu(TTA)3phen-SBA-
5 and Eu-phen-SBA-15 with a UV lamp (λ ) 365 nm), the
In addition, since the D0 f F1 transition does not depend
3
+
on the chemical environments around the Eu ion due to its
magnetic dipole nature, it can be used as a reference to compare
luminescent intensities of different Eu -based materials. The
1
3
+
resulting Eu(TTA)3phen-SBA-15 shows a pure red light and
much stronger luminescence, which is in agreement with their
emission spectra. As discussed above, compared with phen, TTA
is a more efficient sensitizer for the luminescence of central
5
7
relative luminescent intensities of the D0 f F1 transition (I01)
5
7
5
7
and the D0 f F2: D0 f F1 intensity ratios (I02/I01) for all
materials are also listed in Table 2. By comparison, it can be
seen that the I02/I01 values for Eu(TTA)3phen-SBA-15 and
3+
Eu ion and the intramolecular energy transfer from TTA

Europium Complex Bonded to Mesoporous SBA-15
J. Phys. Chem. B, Vol. 109, No. 32, 2005 15285
SBA-15/Eu(TTA)3phen are higher than for the other three
materials, which is in agreement with the I02/CEu results.
ν01
4
I0J
Arad ) A01
)
A0J
(4)
∑
∑
J
I01J)0ν0J
3
.3.3. Luminescence Decay Times. The luminescence decay
profiles relative to the five materials could be fitted with single
exponentials, from which the room temperature (RT) fluores-
cence lifetimes were calculated to confirm that all the Eu ions
detect the same average environment. The resulting lifetimes
Assuming that only nonradiative and radiative processes are
essentially involved in the depopulation of the D0 state, η can
be expressed as
5
3+
(
shown in Table 2) are on the same order of magnitude for all
Arad
samples. However, it appears that the lifetimes in hybrid
materials are lower than that in the Eu(TTA)3phen complex.
This can be attributed to a possible quenching by OH or silanol
groups in hybrid materials. Note that the fluorescence lifetime
η )
(5)
Arad + Anrad
When eqs 1-5 are applied, the parameters Arad and Anrad and
the quantum efficiency values, η, for the D Eu ion excited
state in the five samples can be obtained, as shown in Table 2.
As one can see, the quantum efficiencies of Eu(TTA) phen (η
30.51) and Eu(TTA)3phen-SBA-15 (η ) 37.61) are higher
than those of the other three materials. In addition, the quantum
efficiency of Eu(TTA)3phen-SBA-15 is higher than that of Eu-
TTA)3phen. This clearly demonstrates the modifications in the
5
3+
3
+
of Eu ion in SBA-15/Eu(TTA)3 (0.30 ms) is much shorter
0
than that in Eu(TTA)3phen-SBA-15 (0.49 ms). This, together
with much lower I02/CEu for the Eu3 ion in SBA-15/Eu(TTA)3,
+
3
)
can be ascribed to a quenching effect by the OH group (from
the coordinated H2O) in SBA-15/Eu(TTA)3,3 while in Eu-
,5a
(
TTA)3phen-SBA-15, the replacement of the water molecule
(
in the first coordination sphere by the second ligand phen
3
+
3+
Eu ion local environment as Eu(TTA) phen is covalently
bonded to SBA-15 mesoporous material. The lowest quantum
efficiently shields Eu ion from the coordinated H2O and better
3
sensitizes Eu3+ ion luminescence, which results in stronger
efficiency (η ) 10.86) in SBA-15/Eu(TTA)3 reflects the high
emission and a longer luminescence lifetime. It is evident from
-
1
3
+
nonradiative rate (Anrad ) 2971 s ) arising from the lumines-
the above results that in Eu(TTA)3phen-SBA-15, Eu ion is
mostly present as Eu(TTA)3phen which is covalently bonded
to the network, instead of as the Eu(TTA)3‚2H2O complex.
5
cence quenching of the D0 emitting level by OH oscillators of
the water molecules in the first coordination sphere, which
proves Eu ion is covalently bonded to the silica network in
Eu(TTA)3phen-SBA-15. The low quantum efficiency (η )
9.33) for SBA-15/Eu(TTA)3phen suggests that nonradiative
processes are operative possibly due to vibronic coupling with
the vibration of OH or silanol, which considerably quench the
luminescence of Eu ion, while in Eu(TTA)3phen-SBA-15,
we observed the higher emission quantum efficiency of the D0
Eu ion excited state due to the lower nonradiative transition
rate. This can be ascribed to the substitution of the silanol with
covalently bonded phen groups in the pore channel of meso-
porous SBA-15, which results in the decrease in the level of
nonradiative multiphonon relaxation by coupling to -OH
vibrations and nonradiative transition rate. The results described
3
+
3
.3.4. Emission Quantum Efficiencies (η). On the basis of
5
the emission spectra and lifetimes of the D0 emitting level, the
emission quantum efficiency (η) of the D0 europium ion excited
state can be determined. First, the emission intensity, I, taken
as integrated intensity S of the D0 f F0-4 emission curves,
1
5
5
7
3
+
can be defined as
5
3
+
Ii-j ) pω A N ≈ S
(1)
i-j i-j
i
i-j
5
7
where i and j are the initial ( D0) and final levels ( F0-4),
respectively, pωi-j is the transition energy, Ai-j is the Einstein’s
coefficient of spontaneous emission, and Ni is the population
5
26
5
of the D0 emitting level. The branching ratio for the D0 f
above further confirm that Eu(TTA) phen is successfully
covalently bonded to the SBA-15 network and organometallic
3
7
5
7
F5 and D0 f F6 transitions must be neglected as they are not
detected experimentally. Therefore, we can ignore their influence
complexes covalently bonding to the silica backbone might
provide an effective approach to synthesizing lanthanide complex-
functionalized mesoporous silica. Furthermore, Eu-phen-SBA-
15 (η ) 14.60) exhibits much lower emission quantum
efficiency than Eu(TTA)3phen-SBA-15, which shows that the
introduced TTA ligand in Eu(TTA)3phen-SBA-15 can ef-
5
27
in the depopulation of the D0 excited state. Since the magnetic
5
7
dipole D0 f F1 transition is relatively insensitive to the
chemical environments around the Eu3 ion, and thus can be
considered as a reference for the whole spectrum, the experi-
mental coefficients of spontaneous emission, A0J, were calculated
according to the relation28
+
3+
ficiently activate the luminescence of Eu ion.
3
.3.5. Judd-Ofelt Parameters. The experimental intensity
A ) A (I /I )(ν /ν )
(2)
parameters (Ωλ, λ ) 2 and 4) were determined from the
emission spectra for Eu ion in Figure 9 based on the D0 f
F2 and D0 f F4 transitions and the D0 f F1 magnetic
dipole-allowed transition as the reference, and they are estimated
according to the equation
0J
01 0J 01
01 0J
3
+
5
7
5
7
5
7
5
7
where ν01 and ν0J are the energy baricenters of the D0 f F1
5
7
28
and D0 f FJ transitions, respectively. A01 is the Einstein’s
2
6,28,30
5
7
coefficient of spontaneous emission between the D0 and F1
levels. Since in vacuo, (A0-1)vac ) 14.65 s , when an average
index of refraction n equal to 1.506 was considered, the value
-
1
2
3
4
e ω
1
5
(λ)
7
2
A )
ø
Ω 〈 D ||U || F 〉
(6)
3
-1 29
∑
λ
0
J
of A0-1 ) n (A0-1)vac ≈ 50 s . Lifetime, radiative (Arad), and
3
2
pc
J + 1
λ
3
nonradiative (Anrad) transition rates are related through the
2
7
following equation
where A0λ is the coefficient of spontaneous emission, e is the
electronic charge, ω is the angular frequency of the transition,
p is Planck’s constant over 2π, c is the velocity of light, ø is
1
τ
Atot
)
) Arad + Anrad
(3)
2
2
the Lorentz local field correction that is given by n(n + 2) /9
2
6
5
(λ)
7
2
with the refraction index n ) 1.5, and 〈 D0||U || FJ〉 values
where Arad can be obtained by summing over the radiative rates
A0J for each D0 f FJ transition
are the square reduced matrix elements whose values are 0.0032
and 0.0023 for J ) 2 and 4, respectively. The Ω6 parameter
5
7
31

15286 J. Phys. Chem. B, Vol. 109, No. 32, 2005
Peng et al.
red light. These conclusions were quantitatively stressed by
calculating emission quantum efficiency η and experimental
intensity parameters Ω2 and Ω4. The interactions between the
organic complex and the silica matrix however need to be
fundamentally investigated further.
Acknowledgment. This work is financially supported by the
National Natural Science Foundation of China (Grant 20372060),
the Key National Natural Science Foundation of China (Grant
20131010), the Important National Natural Science Foundation
of China (Grant 20490210), the “863” National Foundation for
High Technology Development and Programming (Grant
2002AA302105, 2002AA324080), and the Foreign Communion
&
Cooperation of the National Natural Science Foundation of
Figure 11. TGA (s) and DrTGA (- - -) curves of Eu(TTA)
SBA-15.
3
phen-
China (Grant 20340420326).
References and Notes
5
7
was not determined since the D0 f F6 transition could not be
experimentally detected.
(
1) Sato, S.; Wada, M. Bull. Chem. Soc. Jpn. 1970, 43, 1955-1962.
(
2) Serra, O. A.; Rosa, I. L. V.; Medeiros, C. L.; Zaniquell, M. E. D.
J. Lumin. 1994, 60-61, 112-114.
3) Binnemans, K.; Lenaerts, P.; Driesen, K.; G o¨ rller-Walrand, C. J.
Mater. Chem. 2004, 14, 191-195.
4) (a) Liu, F. Y.; Fu, L. S.; Wang, J.; Liu, Z.; Li, H. R.; Zhang, H. J.
The Ω2 and Ω4 intensity parameters for the five hybrid
materials are presented in Table 2. A point to be noted in these
results is the relatively high value of the Ω2 intensity parameter
for Eu(TTA)3phen-SBA-15. This might be interpreted as being
(
(
Thin Solid Films 2002, 419, 178-182. (b) Dong, D. W.; Jiang, S. C.; Men,
5
7
Y. F.; Ji, X. L.; Jiang, B. Z. AdV. Mater. 2000, 12, 646-649.
a consequence of the hypersensitive behavior of the D0 f F2
transition. The dynamic coupling mechanism is, therefore,
dominant, indicating that the Eu3+ ion is in a highly polarizable
chemical environment and suggesting an improvement of the
luminescence in Eu(TTA)3phen-SBA-15 when compared with
that exhibited by the Eu(TTA)3phen complex.2
(5) (a) Li, H. R.; Lin, J.; Zhang, H. J.; Fu, L. S.; Meng, Q. G.; Wang,
S. B. Chem. Mater. 2002, 14, 3651-3655. (b) Franville, A. C.; Zambon,
D.; Mahiou, R. Chem. Mater. 2000, 12, 428-435. (c) Embert, F.; Mehdi,
A.; Rey e´ , C.; Corriu, R. J. P. Chem. Mater. 2001, 13, 4542-4549.
(6) (a) Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.;
Beck, J. S. Nature 1992, 359, 710-712. (b) Beck, J. S.; Vartuli, J. C.;
Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.; Schmitt, K. D.; Chu, C.
T.-W.; Olson, D. H.; Sheppard, E. W.; McCullen, S. B.; Higgins, J. B.;
Schlenker, J. L. J. Am. Chem. Soc. 1992, 114, 10834-10843.
6,30a,32
3
.4. ThermograVimetric Analysis. The thermal stability of Eu-
(
TTA)3phen-SBA-15 was demonstrated by TGA measurement.
(7) (a) De Vos, D. E.; Dams, M.; Sels, B. F.; Jacobs, P. A. Chem.
Figure 11 shows the thermogravimetric weight loss curve (TGA)
and derivative weight loss (DrTGA) curve of Eu(TTA)3phen-
SBA-15. Three main weight loss peaks can be seen from the
DrTGA curve. The first weight loss (approximately 5%) peak
observed at ∼62 °C is due to physically adsorbed water. This
is followed by a weight loss (approximately 12%) peak at ∼340
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1
pure Eu(TTA)3phen complex was reported to be at ∼340 °C,
(
suggesting that the thermal stability of the lanthanide complex
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(
1
(
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4
. Conclusions
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2
005, 17, 1561-1569.
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5
7
5
7
5
transition, and in the D0 lifetimes among all the synthesized
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