Near-infrared luminescence from visible-light-sensitized hybrid materials covalently linked with tris(8-hydroxyquinolinate)-lanthanide [Er(III), Nd(III), and Yb(III)] derivatives

Article abstract of DOI:10.1021/jp1088993

A series of new near-infrared (NIR) luminescent lanthanide-quinolinate derivatives [Ln(Q-Si)₃] and xerogels (named as LnQSi-Gel, Ln = Er, Nd, Yb) covalently linked with the Ln(Q-Si)₃ by using the 8-hydroxyquinoline-functionalized alkoxysilane (Q-Si) have been synthesized. The obtained xerogel materials LnQSi-Gel are rigid and show homogeneous by field-emission scanning electron microscopy (FE-SEM) images. The Fourier-transform infrared (FT-IR), fluorescence spectra of Ln(Q-Si) ₃, and LnQSi-Gel were measured, and the corresponding luminescence decay analyses were recorded. Of importance here is that the excitation spectra of the Ln(Q-Si)₃ and LnQSi-Gel extend to the region of visible light (more than 500 nm). Upon ligand-mediated excitation with the visible light, the Ln(Q-Si)₃ and LnQSi-Gel show the characteristic NIR-luminescence of the corresponding lanthanide ions through the intramolecular energy transfer from the ligands to the lanthanide ions. The good luminescent performances enable these NIR-luminescent xerogel materials to have possible applications in medical diagnostics, laser systems, and optics, etc.

Full text of DOI:10.1021/jp1088993

J. Phys. Chem. B 2010, 114, 16393–16397
16393
Near-Infrared Luminescence from Visible-Light-Sensitized Hybrid Materials Covalently
Linked with Tris(8-hydroxyquinolinate)-lanthanide [Er(III), Nd(III), and Yb(III)]
Derivatives
,
†
‡
‡
‡
†
,‡
Lining Sun,* Song Dang, Jiangbo Yu, Jing Feng, Liyi Shi, and Hongjie Zhang*
Research Center of Nano Science and Technology, Shanghai UniVersity, Shanghai 200444, People’s Republic of China,
and State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Changchun 130022, People’s Republic of China
ReceiVed: September 17, 2010
A series of new near-infrared (NIR) luminescent lanthanide-quinolinate derivatives [Ln(Q-Si)
3
] and xerogels
(
named as LnQSi-Gel, Ln ) Er, Nd, Yb) covalently linked with the Ln(Q-Si) by using the 8-hydroxy-
3
quinoline-functionalized alkoxysilane (Q-Si) have been synthesized. The obtained xerogel materials
LnQSi-Gel are rigid and show homogeneous by field-emission scanning electron microscopy (FE-SEM)
images. The Fourier-transform infrared (FT-IR), fluorescence spectra of Ln(Q-Si)
measured, and the corresponding luminescence decay analyses were recorded. Of importance here is that the
excitation spectra of the Ln(Q-Si) and LnQSi-Gel extend to the region of visible light (more than 500
nm). Upon ligand-mediated excitation with the visible light, the Ln(Q-Si) and LnQSi-Gel show the
3
, and LnQSi-Gel were
3
3
characteristic NIR-luminescence of the corresponding lanthanide ions through the intramolecular energy transfer
from the ligands to the lanthanide ions. The good luminescent performances enable these NIR-luminescent
xerogel materials to have possible applications in medical diagnostics, laser systems, and optics, etc.
1
. Introduction
Materials incorporating lanthanide ions (e.g., Nd , Er ,
by using versatile sol-gel synthetic route allows these draw-
backs to be successfully circumvented.1
0,19
Sol-gel-derived
3+
3+
hybrid materials combine chemical and thermal stability, the
mechanical strength and the process flexibility of silica, together
3+
Yb ) are of great interest for a wide range of near-infrared
1
-3
(
NIR) optical applications, such as laser systems, amplifiers
20,21
with the functional characteristics of active organic molecules.
4
-6
for optical communication,
and fluorescent bimolecular
7
,8
Physical mixing of the lanthanide complexes into the sol-gel
materials is very easy to do; however, the interactions between
lanthanide complexes and silica moieties in such sol-gel hybrid
materials are so weak that the phase separation, inhomogeneous
labeling in bioassays. Lanthanide ions exhibit, however, low
luminescence intensity due to the fact that the 4f-4f transitions
are parity forbidden. One of the most useful strategies that has
been employed to overcome this drawback is the complexation
of the lanthanide ions through the coordination with organic
ligands acting as sensitizers, which is the so-called “antenna
22,23
dispersion, and optical quenching of the dopants may occur.
To overcome these shortages, the HQ was functionalized with
2
4
effect”.9,10 The ligands absorb UV or visible light and efficiently
transfer the energy to the central lanthanide ion (intramolecular
organosilane (the obtained alkoxysilane is named as Q-Si),
which can play double roles of not only coordinating with
lanthanide ions but also acting as an organosilane precursor to
synthesize the xerogel hybrid materials. The hydrolysis and
polycondensation processes of the multifunctional alkoxysilane
Q-Si and TEOS are easily controlled. Thus, the lanthanide
quinolinate derivatives can be covalently bonded to the xerogel
material, and the problems mentioned above (phase separation
and inhomogeneous dispersion between organic and inorganic
moieties) can be avoided effectively. To the best of our
knowledge, NIR-luminescence of the lanthanide complexes
covalently linked xerogel via excitation into visible region have
not been reported by other groups up until now.
energy transfer), ultimately resulting in sensitized Ln3+ ion
emission.
Most investigations have focused on organic ligands such as
2,11
diketones, quinolines, phenanthrolines, cryptands, etc. 8-Hy-
droxyquinoline (HQ) and its metalloquinolates possess superb
ability to chelate many metal ions and have been proved to be
a suitable complexing agent for trivalent lanthanide ions.1
2,13
NIR-emitting lanthanide chelates based on HQ and its metal-
loquinolates have appeared frequently in recent literature,
because they are promising candidates for active components
1
4-16
in NIR-luminescent optical devices.
However, the practical applications of the NIR-luminescent
lanthanide complexes are limited to a large extent, essentially
due to their poor thermal stabilities and low mechanical
strength.1 In the past few years, it has been recognized that
the combination of the lanthanide complexes and inorganic
networks with favorable thermal and mechanical characteristics
Normally, the materials containing the lanthanide derivatives
can be excited by ultraviolet light; however, materials excited
with visible light are advantageous over ultraviolet-excitable
materials for the reasons that (i) the long-wave excitation
strongly reduces the background fluorescence, and (ii) the visible
excitation is less prone to the interferences by inner filter effects
due to the absorption of light, etc.2 In the present work, the
new lanthanide-quinolinate derivatives [Ln(Q-Si) ] and xe-
3
rogel materials covalently linked with lanthanide-quinolinate
derivatives [LnQSi-Gel, Ln ) Er, Nd, Yb] by 8-hydroxyquino-
7,18
5,26
*
To whom correspondence should be addressed. E-mail: lnsun@shu.edu.cn
(
L.-N.S.); hongjie@ciac.jl.cn (H.-J.Z.).
†
Shanghai University.
‡
Changchun Institute of Applied Chemistry.
1
0.1021/jp1088993  2010 American Chemical Society
Published on Web 11/22/2010

1
6394 J. Phys. Chem. B, Vol. 114, No. 49, 2010
Sun et al.
line-functionalized alkoxysilane (Q-Si) were synthesized. The
xerogel materials were very rigid, and no cracks were observed.
Upon excitation with the visible light, both the derivatives and
the xerogel materials show the characteristic NIR-luminescence
of the corresponding lanthanide ions. The NIR-luminescence
behavior has been investigated in detail.
lanthanide-quinolinate derivatives were supposed to be synthe-
sized during the corresponding sol-to-xerogel conversion ac-
companied with the evaporation of HCl, respectively. For the
luminescence and SEM measurements, the xerogel samples were
ground to powders. The powders were then washed with water
and ethanol for removal of the surplus Ln3 ions; thus, all of
the complexes in the materials were attached to the matrix by
the Q-Si. Before the fluorescence measurements were operated,
the materials were dried under a vacuum at 80 °C for 24 h.
+
2
. Experimental Section
.1. Materials. Tetraethoxysilane (TEOS, Aldrich), (3-ami-
2
2
.5. Characterization. All measurements were carried out
nopropyl)triethoxysilane (APTES, Aldrich), sodium hydroxide,
chloroform, and light petroleum were used as received. 8-Hy-
droxyquinoline (HQ, C. P.) was bought from Beijing Fine
at room temperature. Scanning electron micrographs (SEM)
were obtained using a JSM-6700F microscope operating at 10.0
-1
kV. FT-IR spectra were measured within a 4000-400 cm
Chemical Co. (Beijing, China). Ytterbium oxide (Yb
9.99%), neodymium oxide (Nd , 99.99%), and erbium oxide
Er , 99.99%) were purchased from Yue Long Chemical Plant
Shanghai, China).
Hydrated LnCl
dissolving Ln
surplus HCl by evaporation.
.2. Synthesisof8-Hydroxyquinoline-FunctionalizedAlkoxy-
2 3
O ,
region on an American BIO-RAD Co. model FTS135 infrared
spectrophotometer with the KBr pellet technique. The CHN
elemental analyses were carried out on a VarioEL analyzer. The
excitation and emission spectra were recorded by a HORIBA
Jobin Yvon FluoroLog-3 spectrofluorometer equipped with a
9
2 3
O
(
(
2 3
O
3
salts (Ln ) Er, Nd, Yb) were obtained by
3
O in hydrochloric acid (HCl) and removing the
2
4
50 W Xe-lamp as an excitation source and a monochromator
iHR320 equipped with a liquid-nitrogen-cooled R5509-72 PMT
as the detector. The time-resolved measurements were done by
using the third harmonic (355 nm) of a Spectra-physics Nd:
YAG laser with a 5 ns pulse width and 5 mJ of energy per
pulse as the source, and the NIR emission lines were dispersed
by a HORIBA Jobin Yvon emission monochromator iHR320
equipped with liquid-nitrogen-cooled R5509-72 PMT, and the
data were analyzed with a LeCroy WaveRunner 6100 1 GHz
Oscilloscope.
2
23
silane (Q-Si).. The method used for the synthesis of Q-Si
was according to the reported procedure. The synthesis of
-formyl-8-hydroxyquinoline was according to the literature and
2
2
5
2
7
was characterized by the reported procedure. The ethanol in
this procedure was used after desiccation. The 5-formyl-8-
hydroxyquinoline was dissolved in a suitable volume of
anhydrous ethanol, and APTES was added with a molar ratio
of 1:1 (APTES to 5-formyl-8-hydroxyquinoline), then refluxed
for 12 h under stirring in a nitrogen atmosphere. Next, the
solvent was distilled off under reduced pressure, yielding the
3
. Results and Discussion
8
-hydroxyquinoline-functionalized alkoxysilanes, Q-Si: a deep
orange oil-like liquid (Q-Si). Anal Calcd for C19 Si:
C, 60.61%; H, 7.50%; N, 7.44%. Found: C, 60.12%; H, 7.62%;
N, 7.84%. NMR (CDCl ): δ 9.76 (1H, d); 8.80 (1H, d); 8.59
1H, s); 7.68 (1H, d); 7.53 (1H, q); 7.18 (1H, d); 3.84 (6H, q);
To obtain stable lanthanide complexes with good optical
H
28
N
2
O
4
properties, the ligands are designed to provide enough coordina-
tion sites to bind the central ion, to shield it from the surrounding
matrix, and also to act as “antenna chromophores” to transfer
excitation energy to the central ion.28 Figure S1 shows the
3
(
3
.66 (2H, t); 1.89 (2H, m); 1.23 (9H, t); 0.75 (2H, t).
.3. Synthesis of Lanthanide Quinolinate Derivatives
Ln(Q-Si) , Ln ) Er, Nd, Yb]. The Q-Si was dissolved in
3
structures of the Ln(Q-Si) , which was predicted on the basis
2
of the experimental process and the complex structure derived
from HQ.2
9,30
[
3
a suitable volume of anhydrous ethanol. A stoichiometric
amount of lanthanide chloride ethanol solution was then added
dropwise to the solution under stirring. The molar ratio of Ln3
ion:Q-Si was 1:3. The orange-yellow precipitates (the colors
are a little different depending on the lanthanide ions) appeared
immediately. After being stirred for 4 h, they were collected
by filtration and dried at 70 °C under vacuum overnight. Next,
the precipitates were washed with anhydrous ethanol three times.
In silica-based sol-gel hybrid materials, there are numerous
hydroxyl groups (in Si-OH and H O) that act as nonradiative
2
+
channels for the excited states of the lanthanide ions and have
strong quenching properties toward the luminescence of lan-
thanide complexes. In this case, the co-condensation of TEOS
and Q-Si is able to induce some -OH groups to be substituted
by organic groups; thus, the increased hydrophilicity of the
modified materials can be achieved. Therefore, the Q-Si plays
three roles during the sol-gel process: one is as an organosilane
precursor to occur the cohydrolysis and copolycondensation with
TEOS, the second is acting as a ligand to coordinate with the
central lanthanide ions, and the third is acting a silylation agent
for the precursor in the sol-gel process. In this way, the
lanthanide quinolinate derivatives were supposed to be synthe-
sized and coupled to the silica backbone.31 The proposed
structure of the LnQSi-Gel hybrid material is displayed in
Scheme 1.
Elemental Analysis. Anal. Calcd for Er(Q-Si)
H, 6.27%; N, 6.50%. Found: C, 52.05%; H, 6.02%; N, 6.29%.
Anal. Calcd for Nd(Q-Si) : C, 53.87%; H, 6.38%; N, 6.62%.
Found: C, 52.97%; H, 6.10%; N, 6.38%. Anal. Calcd for
Yb(Q-Si) : C, 52.68%; H, 6.24%; N, 6.47%. Found: C,
1.89%; H, 6.09%; N, 6.21%.
.4. Synthesis of the Xerogel Materials Covalently Linked
with Lanthanide Quinolinate Derivatives [LnQSi-Gel, Ln
3
: C, 52.91%;
3
3
5
2
)
Er, Nd, Yb]. Q-Si was dissolved in anhydrous ethanol, and
then TEOS and deionized water (acidified with HCl, pH ) 2)
3.1. Fourier Transform Infrared Spectra (FT-IR). The FT-
were added under stirring. After 2 h, an appropriate amount of
IR spectra of the Ln(Q-Si) and LnQSi-Gel hybrid materials
3
LnCl
3
ethanol solution was introduced into the above solution.
have been measured and exhibit very similar results depending
on different lanthanide ions, respectively. Figure 1 displays the
3+
The molar ratio of Q-Si:TEOS:H
2
O:Ln was 3:75:300:1. The
mixed solution was stirred for about 5 h at room temperature
to ensure homogeneous mixing and achieve one single phase,
and then placed into a cuvette. The precursor solution converted
to a wet gel after several days of gelation at 40 °C and then
was continuously dried to obtain a transparent xerogel. The
representative patterns of Nd(Q-Si) and NdQSi-Gel. The band
3
-
1
at 1641 cm assigned to the CdN bond can be observed in
Figure 1a and b, which suggests the retaining of the imine
2
2
groups in the Nd(Q-Si)
3
and NdQSi-Gel. After lanthanide-
quinolinate derivatives are covalently linked to the sol-gel,

NIR Luminescence from Visible-Light-Sensitized Materials
J. Phys. Chem. B, Vol. 114, No. 49, 2010 16395
SCHEME 1: Proposed Structure of the LnQSi-Gel, Ln
)
Er, Nd, Yb
Figure 2. SEM images of NdQSi-Gel with a magnification of 35 000.
Figure 1b shows a different pattern from Figure 1a due to the
hydrolysis/condensation of TEOS and Q-Si. In Figure 1b, the
peak at 1080 cm- corresponds to the Si-O symmetric
1
-1
stretching vibration, and the band at 450 cm can be attributed
to the bending vibration of Si-O-Si band, which indicates the
formation of the Si-O-Si framework in NdQSi-Gel.
3.2. Scanning Electron Microscopy (SEM). The LnQSi-Gel
materials were transparent and rigid, and no cracks were
observed. The SEM images of LnQSi-Gel (Ln ) Er, Nd, and
Yb) are very similar to each other, as shown by the representa-
tive pattern of the NdQSi-Gel. As shown in Figure 2, it can
be observed that the NdQSi-Gel appears very homogeneous
and no sign of any phase separation was observed even if the
magnification was increased to 35 000. This can be explained
by the strong covalent-bond bridge between the inorganic and
organic phases.1 As a result, the material is composed quite
uniformly and is one-component organic-inorganic hybrid
material.33
Figure 3. Excitation (λem ) 980 nm) and emission (λex ) 401 nm)
spectra for the YbQSi-Gel material.
from 240 to 650 nm, which is due to the light absorption by
the organosilane Q-Si ligand. These broad bands extend to the
visible range, which enables photoexcitation of Yb(Q-Si) and
3
YbQSi-Gel by visible sources. After ligand-mediated excitation
8,32
at 401 nm, both the emission spectra of the Yb(Q-Si) and
3
+
3
YbQSi-Gel show the characteristic emission of the Yb ion,
a band in the 910-1180 nm range with the main and strongest
3
.3. Photoluminescence Studies. Yb3+ ion is a very unusual
case of the lanthanide ions, as it has only one single excited
2
5/2 7/2
peak at 980 nm. This is assigned to the F f F transition
2
of the Yb3 ion.
+
16,18,23
It should also be noted that the Yb ion
3+
2
-1
2
state, F5/2, whose energy level is 10 200 cm above the F7/2
ground state. Figure S2 and Figure 3 show the excitation and
emission band is not a single sharp band but a shoulder peak
arising at long wavelength than the primary 980 nm peak.
Similar splitting has been reported previously, and this may be
emission spectra of Yb(Q-Si) and YbQSi-Gel, respectively.
3
3
+
The two excitation spectra both monitored at 980 nm are
composed of a broad band in the ultraviolet/visible spectral range
due to the splitting of the energy levels of the Yb ion as a
34
consequence of ligand field effects. It was reported that the
3+
Yb ion has some advantages for laser emission because of its
1
8,35
very simple f-f energy level structure mentioned above.
In
addition, the relative transparency of human tissue at ap-
proximately 1000 nm suggests that in vivo luminescent probes
operating at this wavelength (Yb3 ion-based emission) could
have diagnostic value. Thus, the visible-light-sensitized
+
Yb(Q-Si) and YbQSi-Gel have potential application in laser
3
systems and medical diagnostic.
The fluorescence spectra of Nd(Q-Si) and NdQSi-Gel are
3
shown in Figure S3 and Figure 4, respectively. The excitation
spectra were obtained by monitoring the strongest emission of
the Nd3 ion at 1064 nm. For Nd(Q-Si)
+
and NdQSi-Gel, the
3
broad bands ranging from 227 to 643 nm and from 237 to 605
nm of the excitation spectra can be observed, respectively, which
is assigned to the absorption of the Q-Si ligand, superimposed
with the excitation band (at 581 nm) originating from the
4
2
3+
characteristic absorption transition I9/2 f G17/2 of the Nd
ion. It should be noted that the absorption transition at 581 nm
Figure 1. FT-IR spectra of (a) Nd(Q-Si) and (b) NdQSi-Gel.
3

1
6396 J. Phys. Chem. B, Vol. 114, No. 49, 2010
Sun et al.
and
other Er-doped materials, the fwhms of Er(Q-Si)
3
ErQSi-Gel are quite broad, which is necessary for getting a
wide gain bandwidth for optical amplification.1
8,38,39
As described above, the characteristic NIR-emission of Ln3
+
ion was obtained in the corresponding Ln(Q-Si) and LnQSi-
3
Gel (Ln ) Er, Nd, Yb) material by exciting the visible-light-
absorption of the organic ligands, respectively. The observed
NIR emissions do arise by the sensitization of the lanthanide
ions from the organic ligands moiety, because no absorption of
the lanthanide ions occurs at the corresponding excitation
wavelengths. Thus, it is obvious that the intramolecular energy
transfer does happen between the organic ligands and the
lanthanide ions. Therefore, it is reasonable to conclude that the
lanthanide complexes are synthesized and covalently linked to
the silica network in the LnQSi-Gel (Scheme 1). The triplet-
state energy level of Q-Si ligand is determined to be 21 090
Figure 4. Excitation (λem ) 1064 nm) and emission (λex ) 401 nm)
spectra for the NdQSi-Gel material.
-
1
cm from the phosphorescence spectrum of the corresponding
2
4
40
Gd complex at 77 K. According to Dexter’s theory, the Q-Si
3+
ligand can match well with the 4f levels of the Ln ions, and
the efficient NIR luminescence of the Ln3 ions can be obtained
+
in the corresponding Ln(Q-Si) and LnQSi-Gel (Ln ) Er, Nd,
3
Yb) materials, respectively.
The lifetime measurement of Ln(Q-Si)
3
and LnQSi-Gel (Ln
)
Er, Nd, Yb) was investigated by using an excitation
wavelength of 355 nm and monitored around the strongest
emission line of their corresponding emission spectra. The
decays of Ln(Q-Si)
3
are single-exponential, and the corre-
2
2
sponding lifetimes of the
F
5/2
f
F7/2 transition of
4
4
4
Yb(Q-Si)
3
, F3/2 f I11/2 transition of Nd(Q-Si)
15/2 transition of Er(Q-Si) complexes are 1.9, 0.14, and 0.48
µs, respectively. The decay curve for NdQSi-Gel is singly
3
, and I13/2 f
Figure 5. Excitation (λem ) 1531 nm) and emission (λex ) 415 nm)
spectra for the ErQSi-Gel material.
4
I
3
4
4
of the Nd3+ ion is much weaker than that of the ligand, which
exponential, and the corresponding lifetime of the F3/2 f I11/2
transition is 75 ns. The decay curves for YbQSi-Gel and
ErQSi-Gel can be fitted by the double-exponential function.
shows that the luminescence sensitization via exciting the ligand
is much more efficient than directly exciting the absorption level
2
2
3+
3+
The lifetimes of the F5/2 f F7/2 transition of Yb ion are 1.20
of the Nd ion. Following the photoexcitation at 401 nm, the
4
characteristic Nd3+ ion emissions were obtained for Nd(Q-Si)
µs (56.5%) and 0.36 µs (43.5%). The lifetimes of the I13/2
f
3
4
3+
I
15/2 transition of Er ion are 0.11 µs (48.1%) and 0.62 µs
and NdQSi-Gel. Both of the two emission spectra consist of
three bands, peaking at 904, 1064, and 1338 nm for Nd(Q-Si)
and peaking at 905, 1064, and 1336 nm for NdQSi-Gel. They
(
51.9%).
3
,
4
4
4
can be attributed to the f-f transitions of F3/2 f I9/2, F3/2
f
4
. Conclusions
4
4
4
I
11/2, and F3/2 f I13/2, respectively. Among the three emission
3
The lanthanide quinolinate derivatives Ln(Q-Si) have been
bands of the two emission spectra, the band centered at 1064
nm shows the strongest intensity, which is potentially applicable
synthesized and covalently bonded to xerogel by using the
8-hydroxyquinoline-functionalized alkoxysilane Q-Si success-
fully. The xerogels LnQSi-Gel (Ln ) Er, Nd, Yb) appear very
homogeneous with no sign of any phase separation as shown
by SEM image. Following the visible-light excitation, the
for the laser system.3
6,37
Figure S4 and Figure 5 display the excitation and emission
spectra of Er(Q-Si) and ErQSi-Gel, respectively. The broad
3
bands extending to more than 600 nm of the two excitation
spectra are due to the absorption of the organosilane Q-Si.
Upon excitation of the ligand absorption at 401 and 415 nm,
3
characteristic NIR-luminescence properties of Ln(Q-Si) and
LnQSi-Gel (Ln ) Er, Nd, Yb) show that the ligands shield
the lanthanide ions well from their surroundings and efficiently
transfer energy from their triplet states to the lanthanide ions.
The good NIR-luminescent properties of the LnQSi-Gel hybrid
materials upon excitation with the visible light provide an access
to multicomposite in optical applications, such as in medical
diagnostic probe, lasers, and optical amplifications.
the emission spectra of Er(Q-Si) and ErQSi-Gel were
3
obtained, centered at 1533 and 1531 nm, respectively. The
emission bands cover large spectrum ranges, and extend from
1
425 to 1660 nm for Er(Q-Si)
3
and from 1430 to 1700 nm for
ErQSi-Gel, respectively, which are attributed to the transition
4
4
from the first excited state to the ground state ( I13/2 f I15/2) of
the Er3 ion. For a long time, the erbium-doped materials have
attracted much attention in the field of optical amplification
because the transition around 1.54 µm matches one of the fiber
low-loss windows well and is in the right position of the third
telecommunication window. To enable a wide gain bandwidth
for optical amplification, a broad emission band of this transition
+
Acknowledgment. We are grateful for the financial support
from the National Natural Science Foundation of China (Grant
Nos. 21001072 and 20771099) and the MOST of China (Grant
No. 2006CB601103, 2006DFA42610), the Innovative Founda-
tion of Shanghai University (A.10-0110-09-906), the Key
Subject of the Municipal Educational Commission of Shanghai
(project J50102), and the Special Project for Nanotechnology
Shanghai (1052 nm03400).
6
is desirable. In this case, the full width at half-maximum (fwhm)
values of the 4
I
f
4
I
13/2
3
15/2 transition for Er(Q-Si) and
ErQSi-Gel are 82 and 81 nm, respectively. In comparison with

NIR Luminescence from Visible-Light-Sensitized Materials
J. Phys. Chem. B, Vol. 114, No. 49, 2010 16397
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3
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3
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1
5, 1969.
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