Hybrid EuIII Coordination Luminophore Standing on Two Legs on Silica Nanoparticles for Enhanced Luminescence

Article abstract of DOI:10.1002/chem.202102156

In this study, we have demonstrated a two-legged, upright molecular design method for monochromatic and bright red luminescent Ln^III-silica nanomaterials. A novel Eu^III-silica hybrid nanoparticle was developed by using a doubly bindi

Full text of DOI:10.1002/chem.202102156

Accepted Article
Accepted Article
Title: Hybrid Eu(III) Coordination luminophore Standing on Silica
Nanoparticles By Two Legs for Enhanced Luminescence
Authors: Teng Zhang, Yuichi Kitagawa, Ryoma Moriake, Pedro
Paulo Ferreira da Rosa, Md Jahidul Islam, Tomoki Yoneda,
Yasuhide Inokuma, Koji Fushimi, and Yasuchika Hasegawa
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To be cited as: Chem. Eur. J. 10.1002/chem.202102156
Link to VoR: https://doi.org/10.1002/chem.202102156
01/2020

10.1002/chem.202102156
Chemistry - A European Journal
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Hybrid Eu(III) Coordination luminophore Standing on Silica
Nanoparticles By Two Legs for Enhanced Luminescence
Dr. Teng Zhang,[a] Dr. Yuichi Kitagawa,[a, b] Ryoma Moriake,[c] Pedro Paulo Ferreira da Rosa,[c] Dr. Md Jahidul
Islam,[a] Dr. Tomoki Yoneda,[b] Prof. Yasuhide Inokuma,[a, b] Dr. Koji Fushimi[b] and Prof. Yasuchika
Hasegawa*[a,b]
[a]
[b]
[c]
Institute for Chemical Reaction Design and Discovery (WPI-ICReDD), Hokkaido University, Sapporo, Hokkaido 001-0021, Japan.
Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan.
Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan.
E-mail: hasegaway@eng.hokudai.ac.jp
Abstract: In this study, we demonstrated a two-legs standing-up
molecular design method for mono-chromatic and bright red
luminescent Ln(III)-silica nanomaterials. A novel Eu(III)-silica hybrid
nanoparticle using double binding TPPO-Si(OEt)3 (TPPO: triphenyl
phosphine oxide) linker were developed. The TPPO-Si(OEt)3 was
determined by 1H, 31P, 29Si NMR spectroscopy and single-crystal X-
ray analysis. Luminescent Eu(hfa)3 and Eu(tfc)3 parts (hfa:
Here, we focus on the lanthanide(III)-coordinated
nanomaterial as bright luminophore. The Ln(III)-
coordinated based materials show characteristic
a
luminescence with sharp spectral shape (FWHM < 10 nm),
large stokes shift and long emission lifetime (> micro
seconds) originated from 4f-4f forbidden transtions.[10,26] In
the past decade, various types of Ln(III)-based materials
such as sol-gel materials, polymers, and mesoporous
materials have been developed.[27-30] Binnemans and
Gunnlaugsson reported on Ln(III) complex-based sol-gel and
polymer derived luminescent materials.[31,32] An Eu/Tb(III)
complex-based sol-gel material with reversible stimuli-
responsive properties was also achieved.[33] The Ln(III)-
modified mesoporous materials were obtained by grafting
Ln(III) complex onto a mesoporous matrix, for example,
immobilizing lanthanide β-diketone or pyridine complexes
onto the SBA-15, MCM-41, and silica hosts were fully
investigated.[30,34,35] Even though their thermal stability
hexafluoroacetylacetonate,
tfc:
3-
(trifluoromethylhydroxymethylene)camphorate) were fixed on the
TPPO-Si(OEt)3 modified silica nanoparticles, producing in
Eu(hfa)3(TPPO-Si)2-SiO2 and Eu(tfc)3(TPPO-Si)2-SiO2, respectively.
The Eu(hfa)3(TPPO-Si)2-SiO2 exhibited higher intrinsic luminescence
quantum yield (93%) and longer emission lifetime (0.98 ms), which is
much larger than those of previously reported Eu(III)-based hybrid
materials. Eu(tfc)3(TPPO-Si)2-SiO2 also showed extra-large intrinsic
emission quantum yield (54%), although the emission quantum yield
for the precursor Eu(tfc)3(TPPO-Si(OEt)3)2 was found to be 39%.
These results confirmed that the TPPO-Si(OEt)3 linker is a promising
candidate for development of Eu(III)-based luminescent materials.
enhanced, the emission quantum yields of previous Ln(III)
-
coordinated materials are smaller than those of
corresponding pure Ln(III) complexes. In this context, novel
conceptual design for Ln(III)-based luminescent materials is
required.
Introduction
Luminescent molecular materials attract considerable
attention not only due to their practical applications in lamps,
lasers and displays,[1] but also widely used in biomedicine,
optoelectronic devices, and sensors.[2-5] Thus, various types
of luminescent molecular materials using organic dyes,[6,7]
transition metal compounds,[8,9] and lanthanide-based
complexes[10-12] have been developed in the field of material
chemistry. To improve physical properties and chemical
stabilities of the luminescent molecular materials, many
research efforts have focused on hybrid nanomaterials
decorated with luminescent molecules.[13-15] The hybrid
luminescent nanomaterial can combine both advantages of
the solid matrix (rigidity and thermal stability) and the
molecular compound (flexibility for molecular design). Their
physicochemical properties depend on nature of the
substrate (silica, zirconia and zinc oxide) and the surface
conditions. Nanomaterial attached with noble metals (gold,
silver, platinum, ruthenium, and/or iridium) represent a class
of hybrid luminescent material that have been well studied,[16-
In previously reported Ln(III)-based materials, the Ln(III)
complexes were functionalized on the inorganic matrix surface
with one binding site (Figure 1a: L2 joint),[36-38] in this case, the
flexible vibration of the organic ligands can decrease of Ln(III)
emission quantum yield. Here, we demonstrate a novel fixation
method, taking advantage of an Eu(III) complex with organic
ligand covalently bonded to the silica nanoparticles through two
binding sites as support (Figure 1b: L2ʹ joins). Fixation of Eu(III)
complex on the covalent rigid Si-O-Si polymeric network
structures of the silica nanoparticles surface with two binding sites,
can promote effective suppression of the vibrational relaxation
process of the excited organic ligand, resulting in enhanced
luminescence performance. As reported in our previous work, the
hfa has low vibrational frequency for decreasing the non-radiative
rate constant,[39] and TPPO can formation of antisymmetric
structure for increasing of the radiative rate constant[40,41]
.
Therefore, in this study, we synthesized a new triphenylphosphine
1
oxide compound TPPO-Si(OEt)3 and identified by H, 31P, 29Si
NMR spectroscopies and single-crystal X-ray analysis. Using
Eu(hfa)3 complex with TPPO-Si(OEt)3 ligand covalently bonded to
the silica nanoparticle through two binding sites, we developed a
nano-luminophore Eu(hfa)3(TPPO-Si)2-SiO2 (Figure 1c). It
exhibited higher intrinsic luminescence quantum yield (93%) and
longer emission lifetime (0.98 ms), which is much larger than
19]
and applied in probes, bioimaging, and catalysis.[20-22] In
addition, organic ligand-functionalized nanomaterials for
enhancing luminescence were also investigated recently,
such as upconversion nanoparticles, quantum dots, and the
nanoMOFs.[23-25]
1
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those of previous Eu(III)-based hybrid materials. Furthermore, the
synthesized Eu(tfc)3(TPPO-Si)2-SiO2 also showed extra-large
intrinsic emission quantum yield (54%), although for the precursor
Eu(tfc)3[TPPO-Si(OEt)3]2 was found to be 39%. In the present
work, conceptual two-legs standing-up molecular design for bright
luminescent Ln(III)-silica nanomaterials is demonstrated for the
first time.
and the TPPO-Si(OEt)3 coordination in Eu(III) can play a role in
double-binding sites on the SiO2 nanoparticles.
Concerning the synthesis of lanthanide complex functionalized
hybrid materials, two fixation processes were reported: route 1:
lanthanide complex with linker is directly attached on the solid
matrix; route 2: lanthanide complex is fixed on the linker-modified
solid matrix.[45,46] In this study, ethyl groups in the linker ligand
TPPO-Si(OEt)3 are easily removed under the coordination
reaction with Eu(III) complex in solution. From this reaction
condition, we selected the route 2: using Eu(III) complex
Eu(hfa)3(H2O)2 (1) fixed on the TPPO-Si(OEt)3 modified SiO2
nanoparticles in ethanol solution (Scheme S2). In addition,
complex Eu(hfa)3[TPPO-Si(OEt)3]2 (2) was also prepared
(Scheme S3) for comparison with the target nano-luminophore
Eu(hfa)3(TPPO-Si)2-SiO2 (3) (Figure 2).
Figure 1. Ln(III) complexes immobilized on the solid matrix with a) one binding
site and b) two binding sites. c) Eu(hfa)3 complex with TPPO-Si(OEt)3 ligand
covalently bonded to the silica matrix via two binding sites.
Figure 3. X-ray crystal structure of the triphenylphosphine oxide compound
Ph2POC6H4CONH(CH2)3Si(OEt)3 (TPPO-Si(OEt)3).
Results and Discussion
Characterizations
Dynamic light scattering (DLS) detection showed average size
of the prepared silica nanoparticles is 36 nm (Figure 4a), which is
in agreement with previously reported result.[47] After modification
with Eu(III) complexes, the resulting nano-luminophore
3
displayed an average size of 53 nm (Figure 4b). To get a further
understanding of 3 at the nanometre scale, we performed the
transmission electron microscopy (TEM) investigation. TEM
images revealed particle size of the pure silica nanoparticles
(average size around 36 nm, Figure 4c) well-agrees with the DLS
result, and energy dispersive X-ray spectroscopy (EDS)
confirmed the presence of oxygen and silicon element in the
nanoparticles (Figure S3). Significantly different from the pure
silica nanoparticles, TEM images of nano-luminophore
3
Figure 2. Chemical structures of the compounds that used in this study.
contained numerous dark objects (Figure 4d). The objects with
large size attribute to the Eu(hfa)3(TPPO-Si)2 aggregates on the
SiO2 surface, the others are too small to see clearly belong to the
Eu(hfa)3(TPPO-Si)2 dispersion functionalized on the silica
nanoparticles (Figure S4). Compared with pure SiO2, EDS
showed the presence of additional europium, phosphorus and
fluorine element in the nano-luminophore 3 (Figure S5), indicated
it was constructed by both Eu(hfa)3(TPPO-Si)2 and silica
nanoparticles. In the EDS, europium exhibited different species,
due to the outer shell electron can come from different shells with
different energy. Furthermore, we measured X-ray photoelectron
spectroscopy (XPS) of nano-luminophore 3 (Figure S6). In the
XPS spectrum, the Eu 3d (5/2) bands corresponding to Eu(III)
were observed at 1135 and 1165 eV, which is similar to previously
reported simple Eu(III) compounds,[48] confirmed the Eu(hfa)3 is
one component of nano-luminophore 3, consistent with the EDS
result.
Preparation of nano-luminophore Eu(hfa)3(TPPO-Si)2-SiO2.
The linker ligand for fixation on the SiO2 nanoparticles,
triphenylphosphine oxide compound, TPPO-Si(OEt)3, was
synthesized according to the procedure in Scheme S1. We used
diphenyl(p-tolyl)phosphine as a starting compound and oxidized
it with potassium permanganate, the achieved 4-
(diphenylphosphino) benzoic acid can be isolated as white
crystals from ethanol solution (Figure S1). Then, reaction of 4-
(diphenylphosphino) benzoic acid in thionyl chloride with 3-
aminopropyl triethoxysilane results in the product of TPPO-
Si(OEt)3. The structure was characterized using 1H, 31P, and 29Si
NMR spectroscopies, respectively (Figure S2). Previous
organosilane compounds have been reported as yellow oils.[42-44]
We successfully removed the yellow impurities and obtained a
colorless single-crystals for X-ray analysis from the ethyl
acetate/hexane solution. The crystal of TPPO-Si(OEt)3 is in
monomeric form (Figure 3), which can attach with Eu(III) complex,
effectively. Generally, the Eu(hfa)3 binded with two TPPO units,[40]
2
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previously reported phosphine oxide Eu(III) complex.[51-53]
Furthermore, 1H NMR signals of the free ethyl groups come
from TPPO-Si(OEt)3 modified SiO2 nanoparticles in CD3OD
were also detected (Figure S8), consistent with the IR result
that showed disappearance of characteristic -CH3 vibrational
bands. Based on the TEM, IR and NMR results,
unambiguously indicate that Eu(hfa)3 units were tight-fixed
on the TPPO-Si-modified SiO2 nanoparticles.
To estimate the thermal stability of complex
luminophore , we performed the thermogravimetric analysis
(TGA). TGA curve showed the decomposition temperature of
complex was 191 °C (Figure S9). On the other hand,
decomposition temperature for the nano-luminophore was
2 and nano-
3
2
3
282 °C. Significant covalent rigid Si-O-Si polymeric network
structures between Eu(hfa)3(TPPO-Si)2 units and the silica
nanoparticles promote thermo-stable structure under heat-
treatment.[54]
Figure 4. Size distributions of a) pure SiO2 and b) Eu(hfa)3(TPPO-Si)2-SiO2 (3).
TEM images of c) pure SiO2 and d) Eu(hfa)3(TPPO-Si)2-SiO2 (3).
Photophysical Properties
Emission spectra of Eu(III) complex
1, 2 and nano-
To investigate the tight-binding between Eu(hfa)3 and
TPPO-Si(OEt)3 modified SiO2 nanoparticles, we carried out
IR measurements. The P=O stretching vibration bands of
luminophore were excited at 350 nm (Figure 6), which at
3
the end absorption of the hfa ligand (Figure S10), indicate
the hfa can transfer energy efficiently to the central Eu(III).
The emission bands observed at 579, 593, 614, 652, and 699
nm, attributed to the Eu(III) ion 5D0 → 7Fj (j = 0 - 4) transitions.
Emission spectra are normalized with respect to the
magnetic dipole transition intensities at 593 nm (Eu: 5D0-7F1),
which is known to be insensitive to the surrounding
environment of the lanthanide ions.[40] The characteristic of
Eu(III) red luminescence is corresponding to the strongest
TPPO-Si(OEt)3, Eu(III) complex
2 and nano-luminophore 3
are shown in Figure 5. Free organic ligand TPPO-Si(OEt)3
displays a P=O stretching vibration at 1184 cm-1 (Figure 5,
black line).[49] However, for complex
3
2
and nano-luminophore
the P=O bands were observed at 1142 cm-1 (Figure 5, red
and blue lines). The P=O stretching vibrational energy in
metal coordination compound is generally smaller than that
in non-coordinated organic ligand,[50] indicating the P=O
sharp emission band at 614 nm (5D0
→
7F2) due to the
group in nano-luminophore
3 is directly connected with the
electric dipole transition, and shape of this transition band is
generally affected by coordination environment of the central
Eu(III).[55] Relative emission intensity of nano-luminophore
is larger than the precursor Eu(III) complex
effective large transition band of nano-luminophore
Eu(hfa)3 unit. In addition, we observed the disappearance of
characteristic -CH3 vibrational bands at around 3000 cm-1 in
3
nano-luminophore
3 due to the elimination of ethyl groups for
1
and
2
. The
is
connection on SiO2 surface.
3
linked with a large radiative rate constant based on the
asymmetric coordination structure on the SiO2 surface.
According to the emission spectrum, the splitting shape of the
band at 614 nm for complex
2
is similar to nano-luminophore
, and the transition
3
,
but significantly different from complex 1
intensity is depended on the electric transition probability. Based
on these photophysical findings, we consider that in the nano-
luminophore
3 Eu(hfa)3 uints are attached by two TPPO units
linked with SiO2.
Emission lifetimes were determined from the slopes of
logarithmic plots of the decay profiles (Figure S11). The
lifetime corresponding to Eu(III) complex
luminophore in solid state were calculated to be 0.42, 0.74,
and 0.98 ms, respectively (Table S2). Two components of
emission lifetimes for nano-luminophore were estimated as
1, 2, and nano-
3
Figure 5. a) FT-IR spectra of TPPO-Si(OEt)3 (black line), Eu(hfa)3[TPPO-
Si(OEt)3]2 (2)(red line) and Eu(hfa)3(TPPO-Si)2-SiO2 (3) (blue line). b) Expanded
IR spectra for P=O vibrational frequencies.
3
0.74 and 1.15 ms, the two emission centers should originate
from luminescence of the single- and aggregate-Eu(III)
complex units on the SiO2 surface. Emission lifetime for
Further NMR spectroscopy also reveals the evidence for
connection between Eu(hfa)3 unit and the TPPO-Si(OEt)3
modified SiO2 nanoparticles. In deuterated chloroform, the
free TPPO-Si(OEt)3 displayed a sharp 31P NMR signal at
29.4 ppm (Figure S6). However, after it reacted with the
nano-luminophore
complex and Eu(III)-based singly anchoring hybrid
materials (Table S3).[34,38,46] Furthermore, to compare with
the nano-luminophore we prepared a control sample of
3 is much larger than the corresponding
1, 2
dehydrated Eu(hfa)3(H2O)2, the resulting Eu(III) complex
2
exhibited one broad 31P NMR signal at -90.5 ppm (Figure S7),
due to the NMR signal is strongly affected by the
paramagnetism of the central Eu(III), consistent with
3
,
SiO2@Eu(hfa)3(TPPO)2 (mixture of SiO2 nanoparticles and
Eu(hfa)3(TPPO)2 complex).
3
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Table 1. Photophysical properties of Eu(III) complexes in solid.
τobs a / ms
kr / s-1
knr / s-1
Φff b / %
Φtot c/ %
ηsens d / %
Samples
Eu(hfa)3(H2O)2
(
1
)
0.42
0.74
0.98
0.16
0.42
0.50
5.9 × 102
1.8 × 103
25
9
36
Eu(hfa)3(TPPO-Si(OEt)3)2
Eu(hfa)3(TPPO-Si)2-SiO2
Eu(tfc)3(H2O)2
(
2
)
7.8 × 102
9.5 × 102
5.93 ×102
9.40×102
1.07×103
5.8 × 102
6.9 × 10
5.78×103
1.46×103
9.20×102
58
93
9
31
27
53
29
-
(3)
e
(
4
)
-
Eu(tfc)3[TPPO-Si(OEt)3]2
Eu(tfc)3(TPPO-Si)2-SiO2
(
5
)
39
54
9
5
23
9
(
6
)
[a] λex = 356 nm. [b] Caclulation method is shown in exprimental section. [c] λex = 320 nm. [d] The photosensitized energy transfer efficiency ηsens
Φtot / Φff. [e] The value is too low to collect.
=
based materials such as Eu(III)-SBA-15 (29%),[34] Eu(III)-
MCM-41 (81%),[35] Dpdp-ePMO-Eu(tta)3 (7.5%)[37] and even
larger than the pure Eu(III) complex with phosphine oxide
and pyridine ligand[41,61-63]. In addition, the photosensitized
energy transfer efficiency ηsens for nano-luminophore
estimated to be 29%, which is smaller than Eu(III) complex
and . The ηsens might be related to excited triplet-state
lifetime. To get a further understanding of the energy transfer
efficiency observed for complex and , we investigated
3 was
1
2
2
3
lifetime of the corresponding gadolinium complex at 90K
(Table S5). The average triplet-state lifetime of hfa ligand in
Gd(hfa)3(TPPO-Si)2-SiO2 is 15 ms, which is smaller than
those of in the Gd(hfa)3[TPPO-Si(OEt)3]2 (47 ms), in
Figure 6. Emission spectra of Eu(hfa)3(H2O)2 (1) (black line), Eu(hfa)3[TPPO-
Si(OEt)3]2 (2) (red line) and Eu(hfa)3(TPPO-Si)2-SiO2 (3) (blue line), which were
excited at 350 nm in solid state at room temperature.
agreement with their energy transfer efficiency in complex
and nano-luminophore
Using organic ligand TPPO-Si(OEt)3 as support, we
developed a nano-luminophore , which shows larger
emission quantum yield than those of previous reported
Eu(III)-coordinated materials, suggesting TPPO-Si(OEt)3 is a
promising candidate for the development of Eu(III)-based
luminescent nanomaterials. To verify this supposition, we
2
3
.
When the SiO2@Eu(hfa)3(TPPO)2 was washed four times with
diethyl ether, resulting in non-emissive powders without
Eu(hfa)3(TPPO)2 (Table S4). These results clearly revealed that
3
the lifetime enhancement of nano-luminophore
3 due to the
Eu(hfa)3(TPPO-Si)2 complex covalently bonded to the silica
matrix.
prepared the Eu(III) complex Eu(tfc)3(H2O)2
(
4
),
) and hybrid nano-luminophore
) (Figure 2). The relative emission
is
(Figure S13), in
agreement with their observed luminescence lifetimes (Table
S6). Furthermore, the nano-luminophore provides larger
Φff (54%) than complex (39%) and (9%) (Table 1). This
Eu(tfc)3[TPPO-Si(OEt)3]2
Eu(tfc)3(TPPO-Si)2-SiO2 (
(5
6
Emission lifetimes, emission quantum yields, radiative and
non-radiative rate constants were summarized in Table 1.[56]
intensity of the 5D0 → 7F2 transition for nano-luminophore
6
The nano-luminophore
emission quantum yield (Φff, 93%), higher than the precursor
Eu(III) complex and . This Φff is based on a large radiative
3 exhibits an extra-large intrinsic
higher than Eu(III) complex
4 and 5
1
2
6
rate constant (kr, 9.5×102 s-1) and an extremely small non-
radiative rate constant (knr, 6.9×10 s-1). The knr is smaller than
those previously reported Eu(III) complex with phosphine
oxide, naphthalene, and pyridine ligands (102 s-1).[57-59] The
5
4
large Φff is also based on a higher radiative rate constant (kr,
1.07 × 103 s-1) and a lower non-radiative rate constant (knr,
9.20 × 102 s-1). Compare with complex
5
, the nano-luminophore
6 has a lower photosensitized energy transfer efficiency. The low
ηsens for nano-luminophore (9%) and (29%) might be
large kr for nano-luminophore
3 should be due to tight and
antisymmetric aggregations of the Eu(hfa)3(TPPO-Si)2 units
on the silica nanospheres (Scheme S5). Suppression of knr
6
3
related to the stabilization of the excited triplet states of tfc
and hfa ligand. Depending on the phosphorescence lifetime
of Gd(hfa)3(TPPO-Si)2-SiO2 (ave. lifetime = 15 ms) is smaller
than that of Gd(hfa)3[TPPO-Si(OEt)3]2 (ave. lifetime = 47 ms),
we consider that the unstable excited-triplet state of hfa and
of nano-luminophore
3 is achieved using the TPPO-Si(OEt)3
ligand bonded on the silica nanoparticles. It can be attributed
to the following reasons: (i) the organic ligand TPPO-Si(OEt)3
has
promotes faster radiative rate and suppresses non-radiative
rate; (ii) in the nano-luminophore , the covalent rigid Si-O-
a three-dimensional antisymmetric structure that
tfc ligand in nano-luminophore
3 and 6 promote their lower
3
photosensitized energy transfer efficiency.
Si polymeric network structures restrict the thermal-
vibrations of TPPO-Si(O)3 ligand.[54] The Φff of nano-
According to the above results, the triphenylphosphine
oxide compound TPPO-Si(OEt)3 can act as a support
covalent on the silica nanoparticles. In the case of hfa and tfc
as photosensitization ligand, the achieved Eu(III)
luminophore
3 is significantly higher than previously reported
Eu@Si-OH (38%)[60] (which is the Eu(TPPO)2 with one
bidentate anchored on the silica nanoparticles), and Eu(III)-
coordinated nano-luminophore
3 and 6 exhibit large intrinsic
4
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was synthesized for fixation of Eu(III) complex on the nano-
silica surface. Using Eu(hfa)3 complex with TPPO-Si(OEt)3
ligand covalently bonded to the silica nanoparticles through
two binding sites, we developed a nano-luminophore
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luminescence quantum yield and long emission lifetime, due
to the covalent rigid Si-O-Si polymeric network structure that
formed on the silica nanoparticles surface restricts the
vibration of the organic ligand. The emission quantum yield
of doubly anchoring Eu(hfa)3(TPPO-Si)2-SiO2 is much larger
than those of singly anchoring Eu(III) compounds on SiO2
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Entry for the Table of Contents
A novel method for development of lanthanide-based hybrid nanomaterials, taking advantage of an Eu(III) complex with organic ligand
covalently bonded to the silica nanoparticles through two binding sites as support was demonstrated. The developed hybrid nano-
luminophore exhibited higher intrinsic luminescence quantum yield (93%) and longer emission lifetime (0.98 ms), which is much larger
than those of previous Eu(III)-based hybrid materials.
7
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