Controllable preparation and fluorescence properties of Y3+ and Eu3+ co-doped mesoporous silica

Article abstract of DOI:10.1016/j.jssc.2010.04.013

The controllable preparation and forming mechanism of rare-earth Y³⁺ and Eu³⁺ chemically co-doped fluorescent mesoporous silica were studied in detail. Their structures, morphologies, chemical compositions and emission properties were characterized and evaluated by small angle X-ray scattering, nitrogen adsorption/desorption measurements, high resolution transmission electron microscopy, inductive coupled plasma-atomic emission, X-ray photoelectron spectra and fluorescent spectroscopy. The results show that chemical composition of the resultant mesoporous materials were significantly affected by solution acidity condition, and can be effectively adjusted by varying the feed ratio of raw materials at a suitable solution acidity condition. These materials with a well-ordered two-dimensional hexagonal mesoporous structure and high specific surface area exhibit significantly broadened emission band from 526 to 682 nm and the fluorescent emission mechanism and influence of materials structure on optical properties were investigated.

Full text of DOI:10.1016/j.jssc.2010.04.013

ARTICLE IN PRESS
Journal of Solid State Chemistry 183 (2010) 1409–1415
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Controllable preparation and fluorescence properties of Y3+ and Eu3+
co-doped mesoporous silica
ÃÃ
Chao Zhang a, Shanyi Guang b, , Hongyao Xu a,c,
Ã
a College of Material Science and Engineering & State Key Laboratory of Chemical Fibers and Polymeric Materials, Donghua University, Shanghai 201620, China
b College of Chemistry and Chemical Engineering & Biology Engineering, Donghua University, Shanghai 201620, China
c State Key laboratory of Crystal Material, Shandong University, Jinan 250100, China
a r t i c l e i n f o
a b s t r a c t
The controllable preparation and forming mechanism of rare-earth Y3+ and Eu3+ chemically co-doped
fluorescent mesoporous silica were studied in detail. Their structures, morphologies, chemical
compositions and emission properties were characterized and evaluated by small angle X-ray
scattering, nitrogen adsorption/desorption measurements, high resolution transmission electron
microscopy, inductive coupled plasma-atomic emission, X-ray photoelectron spectra and fluorescent
spectroscopy. The results show that chemical composition of the resultant mesoporous materials were
significantly affected by solution acidity condition, and can be effectively adjusted by varying the feed
ratio of raw materials at a suitable solution acidity condition. These materials with a well-ordered two-
dimensional hexagonal mesoporous structure and high specific surface area exhibit significantly
broadened emission band from 526 to 682 nm and the fluorescent emission mechanism and influence
of materials structure on optical properties were investigated.
Article history:
Received 20 November 2009
Received in revised form
26 February 2010
Accepted 10 April 2010
Keywords:
RE co-doped
Well ordered
Mesoporous silica
Fluorescence
& 2010 Elsevier Inc. All rights reserved.
1. Introduction
solution or sol containing RE ions to form RE oxides or salts
nanoparticles in porous channel.), this simple post-synthesis
method often leads to the jam or blockage of the partial porous
channel and the uneven distribution of nanometer RE oxides or
salts in the mesoporous materials, which results in destruction of
the pore structures and decreases the drug loading efficiency. The
direct incorporation or chemical doping of RE ions into mesopor-
ous materials will effectively overcome the defect. In the paper,
the hydrolytic condensation coprecipitation synthesis approach
was employed to directly prepare novel well-ordered Y3+ and
Eu3+ directly co-doped mesoporous silica (RE-SBA-15). The
controllable preparation, formation mechanism and relationship
between their structures and fluorescence properties were
investigated.
The generation of structure-controllable and detectable drug
delivery system has drawn considerable attention owing to the
vital significance in the human health care and biomedical
materials science [1–4]. Mesoporous silica such as M41S and
SBA-15 have been demonstrated strong ability in controlled-
release systems due to their features of the ordered pore network,
high pore volume and surface area with rich silanol group [5–15].
The advancement of smart drug delivery materials, from one spot,
requires the in-situ detection and trace technique in the biological
system [16–19]. As well known, fluorescent labeling is an
effective method applied in biomedical detection. Rare-earth
(RE) ions doped materials are ideal candidates for the fluorescent
detection due to their high luminescence stability and
non-toxicity compared with organic or hybrid phosphors
[20–23]. Therefore, a great deal of effort has been devoted to
prepare RE blended mesoporous materials [24,25]. Nevertheless,
so far these mesoporous materials are generally doped with RE
oxides or salts nanoparticles by post-synthesis method (This
method is putting synthesized mesoporous materials into the
2. Experimental
2.1. Chemicals
Tetraethyl orthosilicate (TEOS), yttrium oxide (Y2O3),
europium oxide (Eu2O3) and hydrochloric acid (HCl) were used
as the sources for silica, ion (III) and catalyst, all of which were
purchased from Shanghai Chemicals Ltd. Yttrium nitrate
(Y(NO3)3) and europium nitrate (Eu(NO3)3) were prepared by
the reaction of Y2O3 and Eu2O3 with nitric acid (HNO3) purchased
from Shanghai Chemicals Ltd. Triblock copolymer poly(ethylene
Ã
Corresponding author at: State Key Laboratory of Chemical Fibers and
Polymeric Materials, College of Material Science and Engineering, Donghua
University, North Renmin Road, Shanghai 201620, China. Fax: +86 21 67792874.
ÃÃ
Also Corresponding author.
E-mail addresses: syg@dhu.edu.cn (S. Guang), hongyaoxu@163.com (H. Xu).
0022-4596/$ - see front matter & 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2010.04.013

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glycol)-block-poly-(propylene glycol)-block-poly(ethylene glycol)
(Pluronic P123, molecular weight 5800, EO20PO70EO20) as the
structure-directing template was purchased from Aldrich.
detector, in which the X-ray tube was operated at 40 kV and
30 mA while the diffractograms were recorded in the 2 range
0.4–2.81 with a 2 step size of 0.01 and a step time of 10 s.
y
y
Transmission electron microscopy (TEM) images were recorded
using a JEOL 2010 instrument operated at 200 kV. For TEM
imaging, samples were dispersed in ethanol and deposited on
carbon-coated copper grids. High resolution solid state 29Si NMR
(nuclear magnetic resonance) spectra were obtained on a Bruker
AC 300 NMR spectrometer operating at resonance frequency of
79.38 MHz. X-ray photoelectron spectroscopy (XPS) measure-
ments were performed on an ECSALAB 250 using a nonmono-
2.2. Synthesis
A
series of Y3+ and Eu3+ co-doped mesoporous silica
(RE-SBA-15) with various nSi/nRE (fixed nY/nEu ratios) and nY/nEu
ratios (fixed nSi/nRE ratios) were prepared by hydrolytic
condensation coprecipitation/hydrothermal synthesis approach
[26–30]. In a typical synthesis of RE-SBA-15, 2.0 g of Pluronic P123
was dissolved in 30 mL water to get a clear solution. Thereafter,
the required amount of dilute HCl solution was added, and the
solution was again stirred for another 1 h to mix with the
hydronium ions of the alkylene oxide units. Then, 4.2 g of TEOS
and the required amount of Y(NO3)3 and Eu(NO3)3 solution were
added, and the resulting mixture was stirred for 24 h at 35 1C and
then reacted hydrothermally at 90 1C for another 48 h in static
condition. The product was filtered, washed with deionised water,
and dried at 70 1C. Finally, the as-synthesized RE-SBA-15 samples
were heated at 250 1C for 2 h and then at 500 1C for another 4 h to
obtain the calcined porous samples by removing Pluronic P123.
chromatized Al Ka radiation, at a working pressure lower than
10ꢀ9 mbar. Excitation and emission spectra at room (298 K)
temperature were collected at an angle of 22.5 (front face) in a
spectrofluorimeter (Jasco FP6600) with a 150 W xenon lamp as
excitation source; and excitation/emission slits are 5 and 6 nm,
respectively; otherwise the same mass of all the RE-SBA-15
samples were put in the solid sample cell for test. Particle size
distribution was measured on a Mastersizer 2000 laser particle
size analyzer.
3. Results and discussion
2.3. Design of samples
3.1. The controllable preparation and forming mechanism
The first set of samples were prepared at a fixed nSi/nRE ratio of
5 and nY/nEu ratio of 4 by changing the acidity of the solution (HCl
concentration: c¼0.15, 0.30, 0.45 and 0.60 mol/L). The second set
of RE-SBA-15 samples were prepared at a fixed nY/nEu molar ratio
of 4 and substance concentration of HCl of 0.45 mol/L by varying
the nSi/nRE ratios (nSi/nRE¼2.0, 5.0, 10, 20 and 40). The third set of
The chemical component contents of these resultant
RE-SBA-15 samples were determined by ICP method and the
results were summarized in Table 1. It can be seen from Table 1
that at relative low and high solution acidity the component
contents in resulting products significantly deviate from the feed
ratio (nSi/nRE). For example, the nSi/nRE ratio changes from original
feed ratio 5:1 to practical 11.82:1 in the resulting materials
obtained in a solution acidity of 0.15 M HCl (Table 1, no. 1), and
5:1 to 46.72:1 in a solution acidity of 0.60 M HCl (Table 1, no. 4).
However, the component contents (nSi/nRE ratio) of the resultant
products are close to the feed ratios at 0.45 M HCl concentration
(Table 1, no. 3), suggesting that the acidity of reaction system
significantly affects the component contents in resultant
materials and a suitable solution acidity in the reaction system
(0.45 M HCl) will play a key role to actualize the effective control
of chemical component contents of these mesoporous silica.
To investigate the deviation reason of component contents at
relatively low or high solution acidity and the influence mechan-
ism of solution acidity, we used the aqueous ammonia to
neutralize the clear filtrate of each sample to pH values 10.0.
The white flocculent precipitates were observed in the clear
filtrate with HCl concentration of 0.30, 0.15, or 0.60 M (Table 1,
no. 1, 2, 4), which were confirmed to be RE ions hydroxide. The
precipitate amount significantly increases with the increment of
deviation value in the resulting materials. However, almost no
significant precipitate was observed in the filtrate with HCl
concentration of 0.45 M, hinting that the rare-earth elements
were almost completely incorporated into the resultant mesopor-
ous materials. The solid precipitate in other three samples were
samples were obtained at
a fixed nSi/nRE ratio of 5 and
concentration of HCl of 0.45 mol/L (0.45 mol/L HCl) by changing
the nY/nEu ratios (nY/nEu¼9.0, 5.7, 4.0, 3.0 and 2.3).
2.4. Preparation of RE-doped nanoparticles (RE-NPs)
For comparison, the Y3+ and Eu3+ co-doped nanoparticle SiO2
were prepared by sol–gel method, which consisted of the nSi/nRE
ratio of 5.15 and nY/nEu ratios of 3.94. In the specific procedure,
1.72 g Y(NO3)3 and 0.53 g Eu(NO3)3 were dissolved in 25 mL of
water to get a clear solution, thereafter, 8.4 g TEOS and 5 mL HCl
solution (3 mol/L) were added, and the resulting mixture was
stirred for 2 h at 60 1C and then transferred into closed vessel in
static condition to form gel. The gel was heated at 500 1C for 4 h to
obtain the calcined samples.
2.5. Characterization
XRD patterns were recorded by a Philip X’pert Pro diffract-
ometer with Cu K
a radiation and operated at 40 mA and 45 kV in
the 2 range 10–601. The nitrogen adsorption–desorption mea-
y
surements of the mesoporous materials were performed on a
Micromeritics ASAP 2020M+C Surface Area and Porosimetry
Analyzer, in which the samples were outgased at 300 1C for 8 h
under vacuum (10ꢀ3 Torr) in the degas port of the adsorption
analyzer. The surface area was calculated by the Brunauer–
Emmett–Teller (BET) method, and pore size distribution was
derived from the adsorption branches of the isotherms using the
Barrett–Joyner–Halenda (BJH) method. Element component con-
tents in resulting materials were determined by a Leeman Prodigy
ICP-AES (Thermo Electro, IRIS Intrepid II) after the samples were
dissolved in a HF solution. Small-angle X-ray scattering (SAXS)
Table 1
Elemental analysis on RE-SBA-15 samples at different concentration of HCl.
Samples
cHCl (mol/L)
Feed ratio
Y/nEu
ICP-AES
n
nSi/nRE
nY/nEu
nSi/nRE
1
2
3
4
0.15
0.30
0.45
0.60
4.0
4.0
4.0
4.0
5.0
5.0
5.0
5.0
3.92
3.94
3.94
3.96
11.82
7.69
5.15
patterns were recorded on a Bruker Nanostar U diffractometer
˚
46.72
using Cu Ka radiation (1.54 A) with a distance 107 cm of sample to

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collected by centrifuging the precipitated solution for 5 min at
6000 r/min, then calcined at 1000 1C for 4 h and weighted to be
33.9%, 56.8% and 88.3% of the mass of the added raw rare-earth
ions oxide. They are almost consistent with the amount that is not
incorporated into the resultant product; further confirming that
the acidity of reaction system significantly affects the component
contents in the products. This kind of deviation effect may come
from the different hydrolysis rate between the RE ions and TEOS
in corresponding acidity solutions. Only when hydrolysis rate of
the RE ions matches with that of TEOS, the chemical component
can be effectively controlled by varying the feed ratio of raw
materials, such as 0.45 M HCl concentration in the system,
suggesting that adjusting acidity of the medium is available for
quantitative RE ions incorporation into the silica pore walls. The
similar phenomenon was also observed in metal-doped SBA-15
[26,29].
In addition, it is also found that the nY/nEu ratio in resulting
products is rarely affected by the acidity of the synthetic system,
which may be owing to the similar ion radius of Y3+ and Eu3+, and
almost equal hydrolysis rate under the same condition. On the
basis of the above studies, we fixed the overall HCl concentration
of 0.45 M in the solution and added different feed ratios of nSi/nRE
or nY/nEu in the preparations. It can be seen from Table 2 that the
component contents are almost completely consistent with the
feed ratio although the feed ratio of nSi/nRE varys from 2.0 to 40.0
(Table 2, no. 1–5) or feed ratio of nY/nEu from 9.0 to 2.3 (Table 2,
no. 6–9), further supporting that the component contents in the
RE-doped mesoporous silica can be precisely adjusted by varying
the feed ratio of raw materials at a suitable solution acidity in
current system.
sharper stage by stage, suggesting that orderliness reduces with
the increase of doped RE ions content. However, a clear (100)
diffraction peak still remains even at the highest RE content
(nSi/nRE¼2.05).
Based on Bragg equation, the strongest (100) diffraction peak
significantly shifts in the d-spacing range from 7.92 to 8.67 nm,
which corresponds the unit cell parameters (a) varying from 9.15
pffiffiffi
to 10.01 nm as calculated from the formula a ¼ 2d100
= 3 (Table 2,
no. 1–5). Additionally, it is noted that the wall thicknesses
(Wt¼aꢀdp) of the RE-SBA-15 samples increase from 3.56 to
4.43 nm (Table 2, no. 1–5 Wt) with the increasing RE content due
to the larger ionic radius of Y3+ and Eu3+ than Si, and longer bond
length of RE–O than Si–O bond. Similar results have also been
reported in the metal-substituted mesoporous materials [29,30].
The 2D SAXS patterns of the RE-SBA-15 samples with various
nY/nEu ratios (nY/nEu¼2.29, 2.98, 3.94, 5.73 and 8.96) (Table 2, no.
6–9) are shown in Fig. 1(B). It can be observed from Fig. 1(B) that
three diffraction peaks of all samples with different nY/nEu ratios
are indexed to the (100), (110) and (200) diffractions of the
3.2. Structure analysis
The porous structure reflected by 2D SAXS patterns (Fig. 1)
manifests that all RE-SBA-15 samples exhibit three well-resolved
diffraction peaks indexed as the (100), (110) and (200) reflections
in the XRD diffraction pattern, which are contributed to P6mm
hexagonal space group and are in good agreements with the XRD
pattern of pure hexagonally ordered SBA-15 material reported by
Zhao et al. [31] indicating that the RE-doped mesoporous silica
possess
a well-ordered two-dimensional hexagonal porous
Fig. 1. SAXS patterns of RE-SBA-15 samples (A) at a fixed nY/nEu ratios (ca. 3.95)
and different nSi/nRE ratios: (a) 2.05, (b) 5.15, (c) 10.39, (d) 20.53 and (e) 40.66, and
(B) at a fixed nSi/nRE ratios (ca. 5.2) and different nY/nEu ratios: (a) 2.29, (b) 2.98,
(c) 3.94, (d) 5.73 and (e) 8.96.
structure. With the increase of nSi/nRE ratios (nSi/nRE¼2.05, 5.15,
10.39, 20.53 and 40.66) (Fig. 1(A)) (Table 2, no. 1–5), the
diffraction peak (110) and (200) in the XRD profiles become
Table 2
Textural properties of RE-SBA-15 samples.
aa (nm)
ABET (m2/g)
dp (nm)
Vp (cm3/g)
d
Wte (nm)
b
c
Samples
Feed ratio
Y/nEu
ICP-AES
n
nSi/nRE
nY/nEu
nSi/nRE
1
4.0
4.0
4.0
4.0
4.0
9.0
5.7
3.0
2.3
3.94
2.0
5.0
3.96
3.94
3.98
3.94
3.95
8.96
5.73
2.98
2.29
–
2.05
5.15
10.39
20.53
40.66
5.19
5.15
5.21
5.17
–
10.01
9.63
9.40
9.27
9.15
9.64
9.59
9.58
9.60
–
805
905
934
1010
1065
909
912
913
907
28
5.58
5.61
5.55
5.63
5.59
5.59
5.60
5.61
5.58
–
0.884
1.047
1.101
1.213
1.279
1.046
1.051
1.053
1.045
–
4.43
4.02
3.85
3.64
3.56
4.05
3.99
3.97
4.02
–
2
3
10.0
20.0
40.0
5.0
4
5
6
7
5.0
8
5.0
9
5.0
RE-NPs
5.2
a
The unit cell parameters were calculated from the (100) peaks of the SAXS patterns.
b
c
The specific surface areas were obtained from the multiple-point Brunauer–Emmett–Teller (BET) method.
Pore sizes were determined from the N2 desorption branch by the BJH method with Halsey equation.
The pore volumes were calculated at a relative pressure of 0.97.
d
e
Pore wall thicknesses were calculated as a difference between the unit cell parameters, a, and the BJH pore sizes, dp.

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hexagonal space group of P6mm and their intensities and peak
values are almost the same. The unit cell constants (a) are
calculated to be 9.64, 9.59, 9.63, 9.58 and 9.60 nm for the nY/nEu
ratios of 2.29, 2.98, 3.94, 5.73 and 8.96 (Table 2, no. 2, 6–9),
respectively. In addition, the results show their wall thicknesses
(Wt) are approximate at ca. 4.0 nm (Table 2, no. 2, 6–9). The unit
cell constant and wall thickness of the RE-SBA-15 samples with
different nY/nEu at fixed nSi/nRE (ca. 5.2) are near to each other,
suggesting that the nY/nEu ratios hardly affect the unit
cell constant and wall thickness of the resulting RE-SBA-15
samples, which are originated from the similar ions radii of doped
the relative pressure increases (p/p040.6), all isotherms exhibit
narrow step characteristic of capillary condensation of nitrogen
and the position of the capillary condensation step of relative
pressure scarcely shifts with varying nSi/nRE ratios. Additionally, it
is also found that the specific surface area and pore volume of the
RE-SBA-15 samples are significantly affected by nSi/nRE ratios (nSi/
nRE¼2.05, 5.15, 10.39, 20.53 and 40.66 are presented in Fig. 2A).
The pore volumes decrease from 1.028 to 0.884 cm3/g and the
specific surface areas decline from 1065 to 805 m2/g with
increasing rare-earth content (Table 2, no. 1–5). However, varying
nY/nEu ratios (nY/nEu¼2.29, 2.98, 3.94, 5.73 and 8.96) has little
effect on the specific surface area and pore volume of the RE-SBA-
15 samples (Table 2, no. 2, 6–9).
Fig. 2(B) shows that all the pore sizes for RE-SBA-15 samples
obtained from the adsorption branch by the BJH method
calculated with Halsey equation are nearly 5.6 nm (Table 2, no.
1–9), indicating the diameters of the RE-SBA-15 samples are
hardly influenced by nY/nEu ratios. However, the pore size
distribution is apparently broaden at relative high RE ions content
(nSi/nRE increasing to 2.05) (Table 2, no. 1), which agrees with the
SAXS patterns well. Similar to that of pore volumes and size,
various nY/nEu ratios have almost no obvious affection on pore size
distribution of the RE-SBA-15 samples.
Y3+ and Eu3+
.
The specific surface area and pore volume of the RE-SBA-15
samples are shown in Fig. 2A. All isotherms are of type IV
according to the IUPAC classification, and exhibit an H1 type
hysteresis loop, which is typical of mesoporous solids [31,32]. As
Fig. 3 shows the transmission electron microscopy (TEM)
images of RE-SBA-15 (Table 2, no. 2), which are, respectively,
viewed along the direction of the pore axis (Fig. 3(a)) and the
direction perpendicular to the pore axis (Fig. 3(b)). The
well-ordered hexagonal arrays of mesoporous channels further
confirm that RE-SBA-15 has a 2D p6mm hexagonal structure.
Simultaneously, there are no nanoparticles observed in the porous
channels, implying that the Y3+ and Eu3+ ions are not self-
aggregation. Based on the TEM images, the average distance
between two consecutive centers of hexagonal pores is estimated
to be ca. 9.6 nm and the average thickness of the wall is ca. 4.0 nm,
and its pore diameter is around 5.6 nm, which are in agreement
with the results obtained from the N2 adsorption measurements.
The wall structure analysis was carried out by employing solid
state 29Si NMR spectra. Fig. 4 shows the solid state 29Si NMR
spectrum of RE-SBA-15 (Table 2, no. 2). For comparison, the solid
state 29Si NMR spectrum of RE-NPs is also given. The chemical
shifts of ꢀ90, ꢀ101 and ꢀ110 ppm are attributed to silica peak of
Si(OSi(RE))x(OH)4ꢀx framework units where x¼2 (peak area Q2 in
29Si NMR spectra), x¼3 (Q3), and x¼4 (Q4), respectively [31].
In general, bulk silica materials mainly exhibit cross-linked Q4
framework unit peak ([(Q3+Q2)/Q4]o1) while RE-NPs samples
often possess a high fraction of incompletely cross-linked Q2 and
Q3 framework unit peaks ([(Q3+Q2)/Q4]41). Here, the RE-SBA-15
(Table 2, no. 2) exhibits higher fraction of incompletely cross-
linked Q2 and Q3 framework unit ([(Q3+Q2)/Q4]ffi5.26 than the
RE-NPs (ꢁ1.85) with a particle size distribution of 30–50 nm and
specific surface area of 28 m2/g (Table 2), implying that the RE
doping mesoporous materials exist more non-bridging oxygen
bonds of Si–OH or Si(OH)2, which is in accordance with its high
specific surface area of 905 m2/g.
Fig. 5 displays the XRD patterns of RE-SBA-15 (Table 2, no. 2)
and RE-NPs. Both XRD patterns show a diffraction peak with
2
y¼221 being assigning to amorphous SiO2 without any typical
characteristic diffraction peaks of Y2O3 (or Eu2O3) (JCPDS
29-0085), hinting that the Y3+ and Eu3+ ions do not produce
self-aggregation, but rather uniformly disperse in either wall of
mesoporous silica or nanometer silica particles.
Fig. 2. (A) Nitrogen adsorption isotherm (adsorption: closed symbols; desorption:
open symbols) of RE-SBA-15 samples with fixed nY/nEu ratios (ca. 3.95) and
different nSi/nRE ratios: (’) 2.05, (K) 5.15, (~) 10.39, (m) 20.53 and (.) 40.66. The
isotherms have been offset for clarity (the values of volume adsorbed are 0, 240,
540, 850 and 1170 for nSi/nRE ratios: 2.05, 5.15, 10.39, 20.53 and 40.66,
respectively.) (B) BJH Desorption pore size distributions for RE-SBA-15 samples
with fixed nY/nEu ratios (ca. 3.95) and different nSi/nRE ratios.
Fig. 6 shows the XPS survey spectra of RE-SBA-15 (no. 2) and
RE-NPs samples. The XPS spectra revealed the emission peaks
correspond to Si, Y, O, C, and Eu in the synthesized samples
[33,34]. The calibration of the energy scale was done by using the
C1s peak at 284.8 eV as a reference. The peaks at about 158.3 and

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Fig. 3. TEM images of RE-SBA-15 (no. 2) viewed along (a) the direction of the pore axis and (b) the direction perpendicular to the pore axis.
Fig. 6. XPS survey spectra of (a) RE-SBA-15 (no. 2) and (b) RE-NPs both calcined
at 500 1C.
Fig. 4. Solid state 29Si NMR spectra of (a) RE-SBA-15 (no. 2) and (b) RE-NPs both
calcined at 500 1C.
Table 3
Surface composition of RE-SBA-15 (no. 2) and RE-NPs estimated through XPS
analysis.
Samples Si (atom %) O (atom %) Y (atom %) Eu (atom %) nY/nEu nSi/nRE
2
26.24
68.35
66.74
4.36
4.51
1.04
1.10
4.17
4.10
4.86
4.93
RE-NPs 27.65
1134.6 eV show the binding energies of the 3d5/2 orbital of Y3+
and Eu3+ in the corresponding RE-SBA-15 (no. 2) and RE-NPs
products. Based on the XPS spectrum, the surface composition of
RE-SBA-15 (no. 2) and RE-NPs are estimated and the results are
shown in Table 3. It can be seen in Table 3, the nY/nEu and nSi/nRE
ratios in the surface of mesoporous wall or nanoparticles is close
to that of ICP-AES results, further confirming that Y and Eu
homogeneously are distributed into the walls of mesoporous
silica or nanometer silica particles.
3.3. Photoluminescence properties
Fig. 7 reveals the excitation and emission spectra of RE-SBA-15
(Table 2, no. 2) and RE-NPs (for comparison). In the excitation
Fig. 5. XRD powder patterns of (a) RE-SBA-15 (no. 2) and (b) RE-NPs both calcined
at 500 1C.

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Fig. 7. Room-temperature excitation and emission spectra for (a) RE-SBA-15
(no. 2) (lex¼250 nm, lem¼588 nm) and (b) RE-NPs (lex¼231 nm, lem¼616 nm)
both calcined at 500 1C. All spectra are normalized to a constant intensity at the
maximum.
Fig. 8. Room-temperature emission spectra of RE-SBA-15 samples with fixed
nSi/nRE ratios (ca. 5.2) and different nY/nEu ratios.
spectra, the charge transfer band (CTB) of RE-NPs is located at
231 nm while CTB of RE-SBA-15 significantly red-shifts to 250 nm.
The absorption band at 390 nm arising from the 4f to 4f transition
of inner-shell Eu3+ is significantly weakened owing to the
decrease of the cross-linked Q4 framework unit. Simultaneously,
a new strong absorption shoulder peak at 272 nm is found in the
excited spectrum of RE-SBA-15, which is assigned to higher non-
bridging oxygen coordinated Eu3+content in the mesopore. This is
consistent with that of 29Si NMR spectra. [20,35,36].
controllably prepared. Their chemical component contents can be
effectively adjusted by varying raw feed ratio in a suitable acidity
condition. These mesoporous materials possess unobstructed
porous channel, ca. 4 nm of wall thickness and high specific ratio
area from 805 to 1065 m2/g. These Y3+ and Eu3+ co-doped
mesoporous silica show a widened emission band with the main
peak located at 588 nm corresponding to the 5D0–7F1 transitions
and other four shoulder peaks, this broadening 4f–4f transition
emission may mainly come from the nanometer amorphous wall
of RE-SBA-15 with high specific surface area and a large amount
of non-bridging oxygen around Eu3+ ions also plays important
contribution, which enhances the relative intensity of magnetic-
dipole 5D0–7F1 transition of Eu3+ in RE-SBA-15. The work will
pave a new method for preparation of detectable drug/gene
carriers with high capacity.
In the emission spectra, RE-NPs show the strongest sharp
emission peak at 615 nm and four weak emission band at 542,
590, 650 and 700 nm, which are attributed to the transition
5D0–7F2 (615 nm), 5D1–7F1 (542 nm), 5D0–7F1 (590 nm), 5D0–7F3
(650 nm) and 5D0–7F4 (700 nm) transitions of Eu3+ in the resulting
RE-NPs sample, respectively [20,35]. However, RE-SBA-15 shows
a significantly broadened emission band in the region from 526 to
682 nm with the main peak located at 588 nm corresponding to
the 5D0–7F1 transitions and four shoulder peaks located at 540,
562, 612 and 654 nm corresponding to 5D1–7F1, 5D0–7F0, 5D0–7F2
and 5D0–7F3 transitions of Eu3+ in the resulting samples,
respectively. Such a broad emission profile is originated from
the amorphous wall of RE-SBA-15 with high specific surface area.
In addition, these large amount of non-bridging oxygen around
Eu3+ ions also benefit to enhance the relative intensity of
magnetic-dipole 5D0–7F1 of Eu3+ in RE-SBA-15 [32,37], which is
consistent with the result XRD solid and state 29Si NMR spectra.
The emission spectra of the RE-SBA-15 samples with different
nY/nEu ratios excited with 250 nm UV irradiation are shown in
Fig. 8. Their emission spectral profiles are identical to each other,
indicating that the relative intensity of 5D1–7F1, 5D0–7F0, 5D0–7F1,
5D0–7F2 and 5D0–7F3 transitions are hardly affected by different
nY/nEu. However, the emission intensity is affected by nY/nEu ratio
and the strongest emission band shows at nY/nEu ratio 3.94 with
fixed nSi/nRE ratios (ca. 5.2). Similar result was also found in Y3+
and Eu3+ co-doped nanoparticles in our previous work [23].
Acknowledgments
This research was financially supported by the National
Natural Science Fund of China (Grant nos. 20971021 and
20974018), Ph.D. Program Foundation of Ministry of Education
of China (No. 20070255012), Shanghai Leading Academic Disci-
pline Project (No. B603) and Open Project of the State Key
Laboratory of Crystal Materials (KF0809), the Program of
Introducing Talents of Discipline to Universities (No. 111-2-04).
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