Europium (III) complex functionalized Si-MCM-41 hybrid materials with visible-light-excited luminescence

Article abstract of DOI:10.1016/j.ica.2013.09.008

The synthesis of organics 9-hydroxyphenalenone (HPO), 2-methyl-9- hydroxyphenalenone (MHPO), 6-hydroxybenz[de]anthracen-7-one (HBAO), 5-amino-1,10-phenanthroline (phen-NH₂) and its functionalized mesoporous MCM-41 by covalent band are reported, as well as those of Europium (III) hybrid mesoporous materials, EuL₃phen-MCM-41 (L = HPO, MHPO, HBAO). The photoluminescence and microstructural properties are characterized, and the XRD and BET results revealed that all of these hybrid materials have uniformity in the mesostructure. It is worth noting that the excitation spectra of these hybrid materials have a broad absorption, which occupies from UV to visible region (250-475 nm). Upon ligand-mediated excitation with the visible light, the low efficient energy transfer exhibit between the organic ligands and europium(III) ion under visible excitation, but the maximum wavelength (456 nm/457 nm/451 nm) located at blue light region, which is in consistent with the blue LED light, then might be a feasible alternative in producing time-resolved luminescence under LED-excitation.

Full text of DOI:10.1016/j.ica.2013.09.008

Inorganica Chimica Acta 408 (2013) 96–102
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Europium (III) complex functionalized Si-MCM-41 hybrid materials
with visible-light-excited luminescence
⇑
Yan-Jing Gu, Bing Yan
Department of Chemistry, Tongji University, Siping Road 1239, Shanghai 200092, China
State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 June 2013
Received in revised form 13 August 2013
Accepted 1 September 2013
Available online 8 September 2013
The synthesis of organics 9-hydroxyphenalenone (HPO), 2-methyl-9-hydroxyphenalenone (MHPO), 6-
hydroxybenz[de]anthracen-7-one (HBAO), 5-amino-1,10-phenanthroline (phen-NH2) and its functional-
ized mesoporous MCM-41 by covalent band are reported, as well as those of Europium (III) hybrid mes-
oporous materials, EuL3phen-MCM-41 (L = HPO, MHPO, HBAO). The photoluminescence and
microstructural properties are characterized, and the XRD and BET results revealed that all of these
hybrid materials have uniformity in the mesostructure. It is worth noting that the excitation spectra of
these hybrid materials have a broad absorption, which occupies from UV to visible region (250–
475 nm). Upon ligand-mediated excitation with the visible light, the low efficient energy transfer exhibit
between the organic ligands and europium(III) ion under visible excitation, but the maximum wave-
length (456 nm/457 nm/451 nm) located at blue light region, which is in consistent with the blue LED
light, then might be a feasible alternative in producing time-resolved luminescence under LED-excitation.
Ó 2013 Elsevier B.V. All rights reserved.
Keywords:
Mesoporous silica
Hybrid materials
Coordination bonding assembly
Luminescence
Europium ion
1. Introduction
One promising way of longer wavelength sensitization of Eu3+
emission is via the modification of the ligand molecules with a
Luminescent lanthanide complexes have become focus because
of their unique spectral and properties, such as long luminescence
lifetimes, large Stokes shifts and narrow-line emissions [1–5]. In
particular, organic/inorganic hybrids materials are attracting a
continuously growing attention for their possibility of molecular
engineering result to better performances and easy and cheap pro-
cessing, which is not feasible with inorganic materials. Because of
the strongly forbidden character of f–f transitions, the relative
luminescent intensity of pure lanthanide is low. To overcome this
drawback, it has been found that excitation of organic units intro-
duced in the first coordination sphere of lanthanide ions or in its
close vicinity can result in energy transfer from the organics to
the lanthanide. This process is so called ‘‘antenna effect’’ [6–9],
was proved by Weissmann for the excitation of Eu3+ with ligands
absorbing in the UV region [10].
Recently, a challenge of lanthanide ions is to develop lumines-
cent complexes that can be sensitized by visible light, to reduce
the harm of UV excitation on living biological samples and meet
the demands of less harmful labeling reagents in the life sciences
[11–14]. Especially to develop luminescent Eu3+ complexes that
can be sensitized by visible light to satisfy the demand for less-
harmful labeling reagents in the life sciences and low-voltage-
driven pure-red emitters in optoelectronic technology [15–20].
suitable expanded p-conjugated system, which have a smaller
energy gap between the lowest singlet excited state (S1) and the
T1 state. And the excitation wavelength for Eu3+ complexes can
be extended into the visible region through the usual triplet
pathway has been demonstrated by several researchers [21–30].
In this article, we discuss the preparation and detailed studies of
the luminescence properties (upon excitation with visible light) of
europium complexes covalently grafted onto the surface of meso-
porous MCM-41. We have synthesized organic ligands, 2-methyl-
9-hydroxyphenalenone (MHPO), 9-hydroxyphenalenone (HPO)
and 6-hydroxybenz[de]anthracen-7-one (HBAO), first. In addition,
1,10-phenanthroline (phen) was functionalized with organosilane
(named as phen-Si), which not only coordinating with lanthanide
ions but also acting as an organosilane precursor to prepare the
mesoporous MCM-41 materials. Then we prepared ternary hybrids
materials EuL3phen-MCM-41 (L = HPO, MHPO, HBAO) via coordi-
nation reactions in ethanol solvent, which with low cost, low exci-
tation power instead of the UV lamp as excitation sources.
2. Experimental section
2.1. Chemicals
Cinnamoyl chloride,
a-methylcinnamic acid, 2-methoxynaph-
⇑
thalene, phosphorus pentachloride (PCl5), benzoyl chloride, alumi-
num chloride (AlCl3) and methylene chloride (CH2Cl2) were from
Corresponding author. Tel.: +86 21 65984663; fax: +86 21 65982287.
E-mail address: byan@tongji.edu.cn (B. Yan).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.09.008

Y.-J. Gu, B. Yan / Inorganica Chimica Acta 408 (2013) 96–102
97
Aladdin. 3-(Triethoxysilyl)-propylisocyanate (TEPIC) and cetrimo-
nium bromide (CTAB) were from Lancaster. Tetraethoxysilane
(TEOS) was from Aldrich. 1,10-Phenanthroline, hydrochloric acid
(HCl), concentrated sulfuric acid (H2SO4) and concentrated nitric
acid (HNO3) were purchased from Sinopharm chemical reagent,
Eu(NO3)3ꢀ6H2O were obtained by dissolving Eu2O3 in concentrated
nitric acid (HNO3). The solvents were ethanol, 1,2-dichloroethane.
of CHCl3 in a flask. The solution was stirred while 2 mL of TEPIC
was added dropwise. The chloroform was evaporated at atmo-
spheric pressure, and the resulting mixture was heated at 80 °C
in a covered flask for 12 h. Cold hexane was then added to precip-
itate the white powder. The powder was collected by filtration,
purified in methanol, and dried in a vacuum. 1H NMR (CDC13,
Me4Si): 0.56 (4H, m), 1.16 (18H, t), 1.62 (4H, m), 3.22 (4H, m), 3.71
(12H, q), 7.21 (2H, s), 7.68 (2H, m), 7.88 (1H, s), 8.24 (2H, m),
9.24 (2H, m). IR: CONH (1653, 1538 cmꢁ1), C–Si (1162 cmꢁ1),
Si–O (1090 cmꢁ1).
2.2. Synthetic procedures
2.2.1. Synthesis of 9-hydroxyphenalenone (HPO), 2-methyl-9-
hydroxyphenalenone (MHPO) and 6-hydroxybenz[de]anthracen-7-
one (HBAO)
2.2.4. Synthesis of phen-functionalized MCM-41 material (phen-MCM-
41)
HPO was synthesized according to the method in Refs. [31,32].
2-Methoxynaphthalene (1.58 g, 0.01 mol) and cinnamoyl chloride
(1.66 g, 0.01 mol) were dissolved in 100 mL of 1,2-dichloroethane.
After the reaction flask was cooled in an ice bath, aluminum chlo-
ride (1.35 g, 0.01 mol) was slowly added to the flask with stirring.
After the reaction had come to room temperature, a further 7.3 g of
aluminum chloride was added to the solution and refluxed for 3 h.
The reaction mixture was quenched with ice hydrochloric acid and
extracted with methylene chloride. All the organic extracts were
combined, dried over anhydrous sodium sulfate. The solution
was treated with rotary evaporator to remove the solvent and
gained a yellow solid. The compound was purified by sublimations
from ethanol to yield yellow flakes, which IR information was
Phen-functionalized MCM-41 mesoporous material was pre-
pared under acidic mixture as the following molar composition
0.03phen-Si: 0.97TEOS: 0.139CTAB: 3.76NH3ꢀH2O: 66.57H2OꢀCTAB
(1.65 g) was dissolved in deionized water (39 g) and concentrated
ammonia (18 ml), stirred and heated to 35 °C. A mixture of phen-Si
and TEOS was added into the above solution by drops at 35 °C with
stirring for 24 h and transferred into a Teflon bottle sealed in an
autoclave to react at 100 °C for 48 h. Then filtrated out the solid
product, and washed with adequate deionized water, and air-dried
for 12 h at 65 °C. Extraction with ethanol under reflux by Soxhlet
for 2 days to remove copolymer surfactant CTAB and received the
sample denoted as phen-MCM-41.
showed in Fig. 2(A). IR: –OH 3050 cmꢁ1, C@O 1633 cmꢁ1 1H
;
NMR (CDCl3, Me4Si): d 7.18 (2H, d), d 8.10 (2H, d), d 8.03 (2H, d),
d 7.61 (1H, t), d 16.06 (1H, s, OH).
2.2.5. Synthesis of MCM-41 mesoporous material covalently bonded
with Eu3+ complexes (denoted as EuL3phen-MCM-41, L = HPO, MHPO,
HBAO)
The precursors phen-MCM-41 and L (L = HPO, MHPO, HBAO)
were dissolved in ethanol, and a right amount of Eu(NO3)3ꢀ6H2O
was added into the solution while stirring (the molar ratio of Eu3+:-
L:phen-MCM-41 = 1:3:1). The mixture was stirred at room temper-
ature for 12 h, followed by filtration and extensive washing with
EtOH. The resulting material EuL3phen-MCM-41 was dried over-
night at 60 °C. The whole synthesis scheme was shown in Fig. 1.
According to the Ref. [23], we had taken similar method to syn-
thesize MHPO and HBAO, which IR information was showed in
Fig. 2(A). MHPO: 1H NMR: (CDC13, Me4Si): d 16.27 (H, s, OH), d
8.01 (H, d), d 7.90 (H, d) d 7.85 (H, d), d 7.82 (H, s), d 7.51 (H, t), d
7.13 (H, d), d 2.36 (3H, s, CH3). 13C NMR: (CDC13, Me4Si): d 15.8
(CH3), d 77.1 (CH3CC@O), d 110.3, d 122.8, d 123.9, d 125.2, d
125.4, d 125.8, d 131.6, d 131.8, d 132.8, d 139.1, d 140.5
(O@CC@COH), d 177.1 (COH), d 180.6 (C@O). HBAO: 1H NMR:
(CDC13, Me4Si): d 15.73 (H, s, OH), d 7.20–8.70 (m, 9H). 13C NMR:
(CDC13, Me4Si): d 109.1–140, d 169.9 (COH), d 185.9 (C@O). These
data demonstrate the organics had been synthesized successfully.
2.2.2. Synthesis of 5-amino-1,10-phenanthroline
2.3. Physical characterization
5-Amino-1,10-phenanthroline (denoted as phen-NH2) was pre-
pared as described in Ref. [33]. 10 g 1,10-phenanthroline was
added to a three-necked flask, then added 15 ml of concentrated
sulfuric acid, mixing, continue stirring and heating, slowly drop-
ping a mixture of 60 ml of concentrated sulfuric acid and concen-
trated nitric acid (VH2SO4:VHNO3 = 1:1), control the heated
temperature does not exceed 170 °C, refluxed for 3 h, cooled to
room temperature, the reaction solution was poured into ice-
water, adjust the pH to about 6.0 with a 10% NaOH solution, that
yellow solid precipitation, filtration, washing, drying, recrystallized
from ethanol and dried to give a pale yellow solid 5-nitro-1,10-
phenanthroline morpholine. Hydrazine hydrate (1 mL) diluted in
ethanol (20 mL) was added dropwise to a suspension of 5-nitro-
1,10-phenanthroline (1 g) with 5% Pd/C (200 mg) in ethanol. The
mixture was stirred at 70 °C for 5 h. After filtration, the solution
was concentrated until the formation of a green-yellow precipitate.
The yellow solid was filtered off and washed with water. IR: 3470,
3416, 3250, 3059, 1643, 1618, 1587, 1562, 1504, 1493, 1446, 1420,
1H NMR spectra were recorded in CDCl3 on a BRUKER ARX400
spectrometer with tetramethylsilane (TMS) as inter reference. FTIR
spectra were measured within the 4000–400 cmꢁ1 region on an
infrared spectrophotometer using KBr pellet technique. The X-ray
diffraction (XRD) measurements of the powder samples were de-
tected on a BRUKER D8 diffractometer (40 mA, 40 kV) using mono-
chromated Cu Ka radiation (k = 1.54 Å) in a 2h range from 0.6° to
6°. Nitrogen adsorption/desorption isotherms were carried out by
a Nova 1000 analyzer at the liquid nitrogen temperature. The sur-
face areas were calculated by Brunauer–Emmett–Teller (BET)
method, meanwhile the Barrett–Joyner–Halenda (BJH) model was
used to evaluate the pore size distributions from the desorption
branches of the nitrogen isotherms. Transmission electron micro-
scope (TEM) experiments were conducted on a JEOL2011 micro-
scope operated at 200 kV or on
a JEM-4000EX microscope
operated at 400 kV to exhibit the final mesoporous materials’
structure. Thermogravimetry (TG) data were measured on Netzsch
STA 409C under nitrogen atmosphere by heating/cooling at the
rate of 15 °C/min with the crucibles of Al2O3. The luminescent exci-
tation and emission spectra and luminescence lifetime were ac-
quired on an Edinburgh FLS920 phosphorimeter, while
luminescence lifetime was gained for using a 450 W xenon lamp
as excitation source.
1384, 1344, 1217, 1141, 1092, 853, 735, 724, 709, 624 cmꢁ1
.
2.2.3. Synthesis of 5-amino-1,10-phenanthroline-Si (denoted as phen-
Si)
Phen-Si was synthesized by using phen-NH2 as the starting re-
agent [34–37]. phen-NH2 (0.212 g, 1 mmol) was dissolved in 20 mL

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Y.-J. Gu, B. Yan / Inorganica Chimica Acta 408 (2013) 96–102
Fig. 1. Scheme of synthesis of EuL3phen-MCM-41 (L = HPO, MHPO, HBAO).
The IR spectra of Eu(PHO)3phen-MCM-41(NO3)3, Eu(MPHO)3
3. Results and discussion
phen-MCM-41(NO3)3 and Eu(HBAO)3 phen-MCM-41(NO3)3 are
shown in Fig. 2(B). The evident bands appear at 1091 cmꢁ1 are re-
sult from asymmetric Si–O stretching vibration modes, and the
band at 801 cmꢁ1 belongs to the symmetric Si–O stretching vibra-
tion. The Si–O–Si bending vibration is at 467 cmꢁ1, and the band at
962 cmꢁ1 is associated with silanol (Si–OH) stretching vibrations of
surface groups [38]. In addition, the presence of hydroxyl can be
clearly evidenced by the band at 3422 cmꢁ1. Compared with pure
MCM-41, hybrid mesoporous material not only has a skeleton
characteristic peaks of mesoporous molecular, but also appeared
in the 1340–1700 cmꢁ1 rang attributable to the –CONH– group
of phen-Si, which indicates that the phen-Si successfully grafted
to the MCM-41 mesoporous matrix.
In view of organic ligand phen-NH2 and phen-Si, the –NH2
vibration is located in the vicinity of 3416 cmꢁ1 disappears in the
functional precursor phen-Si, and the silane coupling agent is lo-
cated in the 2287–2385 cmꢁ1 of the N@C@O absorption peak has
completely disappeared. Meanwhile, phen-Si located in 2931 and
2857 cmꢁ1 belonging to the vibration of the coupling agents in
the three methylene absorption peak. In addition, located at
1162 cmꢁ1 derived from the vibration of Si–C group in the vicinity
of an absorption peak, and 1090 cmꢁ1 due to the absorption peak
of the Si–O vibration generating also appears in the infrared spec-
tra of the phen-Si, these data described coupling agent TEPIC suc-
cessfully grafted onto the organic ligand phen-NH2.

Y.-J. Gu, B. Yan / Inorganica Chimica Acta 408 (2013) 96–102
99
Fig. 3. SAXRD patterns of Eu(PHO)3phen-MCM-41(NO3)3, Eu(MPHO)3phen-MCM-
41(NO3)3 and Eu(HBAO)3phen-MCM-41(NO3)3.
high relative pressures according to the IUPAC classification, which
show characteristic of mesoporous materials with highly uniform
size distributions [40–44]. The specific area and pore size
have been calculated using Brunauer–Emmett–Teller (BET) and
Barrett–Joyner–Halenda (BJH) methods, respectively. Table 1 sum-
marized the structure data of all these mesoporous materials (BET
surface area, total pore volume, and pore size, etc.). After function-
alized with phen and introduced Eu3+ ions and HPO/MHPO/HBAO,
the result material exhibits a smaller surface area and a slightly
smaller pore size and pore volume in comparison with pure
MCM-41, which may be owe to the lanthanide complexes graft
on the pore surface [45]. Furthermore, it can be infered that the
deposition of lanthanide complexes has not destroyed the meso-
porous structure, which coincides with the XRD results.
The hexagonal mesostructures of Eu(HBAO)3phen-MCM-
41(NO3)3 are further demonstrated by a HRTEM images in Fig. 5.
From the figure, we can clearly observed the regular hexagonal ar-
ray of uniform channels characteristic of Eu(HBAO)3phen-MCM-
41(NO3)3 mesoporous material, which reveals Eu(HBAO)3phen-
MCM-41(NO3)3 maintain its mesoporous structure well after the
organic modified process. The distance between the centers of
the mesopore is estimated to be about 4.2 nm, which is consistent
with the result of XRD data (see Table 1).
Fig. 6 shows the selected TGA curve of Eu(MPHO)3phen-MCM-
41(NO3)3 hybrids, which shows three main degradation steps.
The first step of weight loss about 6.2% for from 50 to 140 °C could
be attributed to the desorption of physically absorbed water and
residual solvent. The second weight loss is about 14.5% weight loss
is observed for the second range between 150 and 390 °C, corre-
sponding to the loss of the thermal degradation of the phen-
MCM-41 framework and possible incompletely removed surfac-
tants. After that, the further weight loss (about 12.1%) of MPHO ap-
pears at more than 400 °C.
The excitation and emission spectra of the resulting hybrid
mesoporous materials containing Eu3+ are reported on Fig. 7. The
excitation spectrum was obtained by monitoring the emission of
Eu3+ ions at 614 nm and are dominated by a series of broad bands
in the region about 250–475 nm. The band with the maximum at
350 nm is due to HPO(MHPO, HBAO), then the bands at 250–
300 nm and visible region of 375–475 nm are owe to phenanthro-
line moieties and the ligands HPO/MHPO/HBAO, respectively,
which enables photoexcitation of these hybrids materials both by
ultraviolet and visible sources. We take 456, 457 and 451 nm as
Fig. 2. The IR spectra of HPO, MHPO, HBAO (A), and Eu(PHO)3phen-MCM-41(NO3)3,
Eu(MPHO)3phen-MCM-41(NO3)3 and Eu(HBAO)3phen-MCM-41(NO3)3 (B).
The small-angle X-ray diffraction (SAXRD) pattern as a popular
and efficient method was used to characterize highly ordered mes-
oporous material with hexagonal symmetry of the space group
P6mm. The SAXRD patterns of Eu(PHO)3phen-MCM-41(NO3)3,
Eu(MPHO)3phen-MCM-41(NO3)3 and Eu(HBAO)3 phen-MCM-
41(NO3)3 are shown in Fig. 3. As shown in the figure, all samples
display three well-resolved diffraction bands in the 2h range of
0.6–6°, which are indexed as the (100), (110), and (200) diffrac-
tions, which confirm a well-ordered MCM-41 type mesoporous
structures. The (110) and (200) diffraction peak intensity are de-
creased, indicating that the degree of ordering of the mesoporous,
which may be the result of the interaction of the skeleton structure
of the mesoporous pore organic group, but it still maintained cor-
responding diffraction peak, the introduction of europium com-
plexes of the mesoporous crystalline form did not have much
impact, the samples remain ordered hexagonal structure of
MCM-41 [39]. The structure data are shown in Table 1 of all the
samples.
The characterization of the nitrogen adsorption–desorption was
used to further investigate the channel structure of these materials.
The corresponding isotherms are showed in Fig. 4. They all exhibit
typical type IV isotherms with distinct H1-type hysteresis loops at

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Y.-J. Gu, B. Yan / Inorganica Chimica Acta 408 (2013) 96–102
Table 1
Structural Parameters of Eu(PHO)3phen-MCM-41(NO3)3, Eu(MPHO)3phen-MCM-41(NO3)3 and Eu(HBAN)3phen-MCM-41(NO3)3.a
Sample
d100 (nm)
a0 (nm)
SBET (m2/g)
V (cm3/g)
D (nm)
t (nm)
Eu(PHO)3phen-MCM-41(NO3)3
Eu(MPHO)3phen-MCM-41(NO3)3
Eu(HBAN)3phen-MCM-41(NO3)3
4.23
4.29
4.21
4.88
4.95
4.86
233
177
164
0.16
0.12
0.12
2.67
2.77
2.93
2.21
2.18
1.93
p
a
d100 is the d(100) spacing, a0 the cell parameter (a0 = 2 d100
thickness, calculated by a0 ꢁ D.
/ 3), SBET the BET surface area, V the total pore volume, DBJH the average pore diameter, and t the wall
Fig. 6. The selected TG-DSC curves of Eu(MPHO)3phen-MCM-41(NO3)3.
Fig. 4. N2 adsorption-desoption isotherms of EuL3phen-MCM-41(NO3)3, (L = PHO,
MHPO, HBAO).
strongly varies; with the local symmetry of Eu3+
, then the
5D0 ? 7F1 transition corresponds to a parity-allowed magnetic di-
pole transition, which is independent of the host matrix. So the
emission spectra indicate that the Eu3+ site is located in an envi-
ronment without inversion symmetry, and it demonstrates that
the effective energy transfer occurred between the precursors
and the chelated europium (III) ions [46–48]. Additional, the exci-
tation wavelength between 450 and 490 nm can compatible with
blue LED for europium (III) ions, which can be exploited in electro-
luminescent devices and many other applications [49–52].
the excitation wavelength to measure the emission spectra of
Eu(PHO)3phen-MCM-41(NO3)3, Eu(MPHO)3phen-MCM-41(NO3)3
and Eu(HBAO)3phen-MCM-41(NO3)3. As seen in the emission spec-
tra, the red luminescence was observed in their emission spectra,
which proves that the effective energy transfer took place and con-
jugated systems formed between the ligands and the chelated lan-
thanide ions in these hybrids. The emission bands of these hybrids
material were assigned to the 5D0 ? 7FJ (J = 0–4) transitions, for
Eu(PHO)3phen-MCM-41(NO3)3 was at 579, 591, 612, 651,
705 nm, Eu(MPHO)3phen-MCM-41(NO3)3 was at 579, 592, 612,
652, 704 nm, Eu(HBAO)3phen-MCM-41(NO3)3 was at 579, 592,
612, 652, 703 nm. In the emission spectra, the 5D0 ? 7F2 at about
612 nm shows the strongest emission among the transitions of
the materials containing Eu3+. To the best of our knowledge, the
5D0 ? 7F2 transition is a typical electric dipole transition and
The typical decay curves of the Eu3+ hybrid mesoporous materi-
als were detected at room temperature, and they can be described
as a single exponential in the form Ln[S(t)/S0] = ꢁk1t = ꢁt/
s, indi-
cating that all Eu3+ ions occupy the same average coordination
environment. The resulting lifetimes of Eu3+ hybrids were shown
in Table 2. On the basis of the emission spectra and lifetimes of
the 5D0 emitting level of Eu3+ hybrids and four main equations
according to Refs. [53–57], the emission quantum efficiencies of
Fig. 5. Selected HRTEM images of Eu(HBAO)3phen-MCM-41(NO3)3.

Y.-J. Gu, B. Yan / Inorganica Chimica Acta 408 (2013) 96–102
101
Atot ¼ 1=
s
¼ Ar þ Anr
ð4Þ
A0J is the experimental coefficients of spontaneous emissions.
The 5D0 ? 7F1 transition does not depend on the local ligand field
and thus may be used as a reference for the whole spectrum, in
vacuum A0–1 = 14.65 sꢁ1. An effective refractive index of 1.5 is used
leading to A (5D0 ? 7F1) about 50 sꢁ1. A0J was calculated by the
above equations. I01 and I0J are the integrated intensities of the
5D0 ? 7F1 and 5D0 ? 7FJ transitions (J = 0–4) with v01 and v0J
(v0J = 1/kJ) energy centers, respectively. The emission intensity
and can be taken as the integrated intensity of the 5D0 ? 7FJ emis-
sion bands [58,59]. v0J presents the energy barrier and can be
determined from the emission bands of Eu3+’s 5D0 ? 7FJ emission
transitions. Ar and Anr are the radiative transition rate and non-
radiative transition rate, respectively, among Ar can be determined
from the summation of A0J (Eq. (2)). Based on the above discussion,
the luminescence quantum efficiency can be calculated from the
luminescent lifetime, radiative, and non-radiative transition rate.
All
the
hybrid
materials
Eu(PHO)3phen-MCM-41(NO3)3,
and Eu(HBAO)3phen-MCM-
Eu(MPHO)3phen-MCM-41(NO3)3
41(NO3)3 possess the low quantum efficiency for 35.8%, 25.2%
and 22.2%, respectively, which suggesting the unsuitable energy
match and ineffective energy transfer in this hybrids system.
4. Conclusions
In this work, we have prepared europium (III) luminescent mes-
oporous hybrid materials, which took HPO, MHPO and HBAO as the
ligand to coordinate to Eu3+, and then introduced into phen-func-
tioned mesoporous MCM-41matrix. All the resulting materials
present their mesoscopically ordered MCM-41 structures and
highly uniform pore size distributions. Following by the visible-
light excitation, the hybrids of Eu(PHO)3phen-MCM-41(NO3)3,
Eu(MPHO)3phen-MCM-41(NO3)3
and
Eu(HBAO)3phen-MCM-
41(NO3)3 win red luminescence but low quantum efficiency
(1.69%, 0.62% and 1.25%, respectively), which show low energy
match between Eu3+ and HPO/MHPO/HBAO ligands. However,
the visible-light (456, 457 and 451 nm) excitation wavelength is
compatible with blue LED, which can be exploited in electrolumi-
nescent devices and many other applications.
Acknowledgments
Fig. 7. Excitation and emission spectra of the hybrid materials: EuL3phen-MCM-
41(NO3)3, (L = PHO, MHPO, HBAO).
This work is supported by the National Natural Science Founda-
tion of China (20971100, 91122003) and Program for New Century
Excellent Talents in University (NCET-08-0398).
the 5D0 europium ions excited state have been selectively deter-
mined. The detailed principles and methods adopted from Ref.
[55] and corresponding data were shown in Table 2:
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