Fixed-component lanthanide-hybrid-fabricated full-color photoluminescent films as vapoluminescent sensors

Article abstract of DOI:10.1002/chem.201204061

Full-color lanthanide (Ln) photoluminescent materials have attracted considerable interest owing to their potential applications in display systems and lighting technologies. Herein, full-color photoluminescent films have been designed and fabricated faci

Full text of DOI:10.1002/chem.201204061

DOI: 10.1002/chem.201204061
Fixed-Component Lanthanide-Hybrid-Fabricated Full-Color
Photoluminescent Films as Vapoluminescent Sensors
[
a]
[b]
[c]
[a]
[a]
[a]
Jun Xu, Lei Jia, Nengzhi Jin, Yufei Ma, Xiao Liu, Wenyu Wu,
[
a]
[a]
[d]
Weisheng Liu, Yu Tang,* and Feng Zhou
Abstract: Full-color lanthanide (Ln)
photoluminescent materials have at-
tracted considerable interest owing to
their potential applications in display
systems and lighting technologies.
Herein, full-color photoluminescent
films have been designed and fabricat-
ed facilely with a fixed-component Ln-
based (Ln=Tb and Eu) polymer
hybrid doped with a proton-sensitive
amide-type b-diketonated photosensi-
tizer, N-(2-pyridinyl)benzoylacetamide
cence emissions of the films are ach-
ieved by changing the amounts of OH
tion of the excitation wavelength, and
white-light emission can be achieved
when the given film is excited at the
visible region (405 nm). The photo-
physical properties and the mecha-
nisms of the intra- and intermolecular
energy transfer before and after depro-
tonation have been investigated in
detail. Meanwhile, the films might find
application as vapoluminescent sensors
due to their good stability, sensitivity,
reversibility, and quick response when
triggered by a base–acid vapor.
ꢀ
in the hybrid rather than varying the
relative concentrations of the lantha-
nide ions and photosensitizers, thus
representing a new paradigm for full-
color displays. The emission color can
also be finely tuned through the varia-
Keywords: energy transfer · lantha-
nides · luminescence · sensors ·
white-light emission
(
HPBA). The tunable photolumines-
[
5]
Introduction
like emissions as well as their wide range of lifetimes. Ide-
ally, white-color emissions should consist of relative red,
green, and blue luminescent components with suitable inten-
Full-color photoluminescent materials, especially those with
white-color emissions, have attracted increased attention in
recent years because they are known for their potential ap-
plications in various important devices such as color-tunable
3
+
3+
sities. Therefore, doping Eu (red-light emission) and Tb
(green-light emission) complexes accompanied by an excess
amount of blue-light-emitting ligand in the materials results
in three primary colors and offers full-color photolumines-
[1]
[2]
phosphors, white-light-emitting devices, and multicolor
[3]
[6]
light-emitting diodes (LEDs). One of the promising com-
ponents in the design of full-color materials are lanthanide
cence, including white emission.
Known for more than one hundred years, b-diketones
continue to draw considerable interest because of their ef-
fectiveness in energy transfer to Ln ions. However, most
[4]
(
Ln)-based hybrids, which possess distinct advantages over
organic chromophores, such as their sharp and intense line-
[7]
b-diketones are not good ligands for sensitizing the lumines-
3
+
5
[
a] J. Xu, Y. Ma, X. Liu, W. Wu, Prof. W. Liu, Prof. Y. Tang
Key Laboratory of Nonferrous Metal Chemistry
and Resources Utilization of Gansu Province
State Key Laboratory of Applied Organic Chemistry
College of Chemistry and Chemical Engineering
Lanzhou University, Lanzhou 730000 (P.R. China)
Fax : (+86)931-891-2582
cence of Tb because of their triplet levels below the D
4
3
+ [5a]
resonance level of Tb
assembled functional amide-type b-diketone-based Ln inor-
ganic–organic hybrid materials. The introduction of an
amide group increases the triplet levels of the b-diketone ar-
.
Our group recently designed and
[8]
3
+
chitecture, and energy transfer to Tb was attempted. It is
well known that b-diketones coordinated to metal ions usu-
ally exist as an enol tautomer (deprotonated form). A pyri-
dine ring is condensed to the amide-type b-diketone block
because of its acceptance of the residual proton. This
amide-type b-diketone architecture N-(2-pyridinyl)benzoyla-
cetamide (HPBA) is assumed to possess the ability to trans-
fer energy to Tb under neutral conditions because of the
proton accepted by its own pyridyl nitrogen atom. In addi-
tion, when the proton is removed completely under alkaline
conditions, the negatively charged architecture might effi-
E-mail: tangyu@lzu.edu.cn
[
[
b] Dr. L. Jia
Department of Physics and Chemistry
Henan Polytechnic University
Jiaozuo 454000 (P.R. China)
[9]
[
c] N. Jin
Gansu Computing Center
Lanzhou 730030 (P.R. China)
3
+
d] Prof. F. Zhou
State Key Laboratory of Solid Lubrication
Lanzhou Institute of Chemical Physics
Chinese Academy of Sciences
Lanzhou 730000 (P.R. China)
3
+
ciently transfer energy to Eu , similar to classic b-diketone
ligands. This phenomenon offers a prerequisite for the re-
alization of multicolor photoluminescent materials. The in-
[5a]
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201204061.
4556
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Chem. Eur. J. 2013, 19, 4556 – 4562

FULL PAPER
corporation of Ln complexes within matrices should be the
megatrends for practical applications. Poly(vinyl pyrroli-
done) (PVP) polymer can firmly encapsulate Ln complexes
and is apparently a good candidate to increase the strength
of the hypersensitive transitions of Ln ions; therefore, PVP
could not be detected, which confirms that the complex mol-
ecules are homogeneously distributed in the PVP matrices.
Luminescence properties
[10]
is preferred for application in optical devices.
Photophysical properties of the multicolor photolumines-
ꢀ
We then designed novel full-color photoluminescent films
fabricated with the use of a new fixed-component specific
Ln-based (Ln=Tb and Eu) PVP hybrid (Scheme 1). The
cence polymer films: Interestingly, when the OH concentra-
tion in the hybrid was increased, the fabricated films display
the various color luminescent emissions under UV excitation
listed in Figure 1a (films A, E, F, G, H, and K); Figure 1b il-
lustrates the photoluminescence spectra of the correspond-
ing films at room temperature. To deduce whether deproto-
nation alters sensitization to Ln ions, the room-temperature
excitation and emission spectra of films A and K were ex-
amined (Figures S4 and S5 in the Supporting Information).
The excitation spectrum of film A displayed an intense and
broad band with a maximum at approximately 371 nm, and
a bathochromic shift was observed in film K. Upon optimal
excitation, film A only displayed emission peaks at 488, 545,
5
7
5
6
81, and 620 nm, which can be assigned to the D ! F (J=
4
J
3+
, 5, 4, 3, respectively) transitions of Tb . Upon excitation
at 387 nm, film K exhibited emissions at 579, 592, 611, 653,
5
7
and 703 nm, which can be attributed to the D ! F (J=0,
0
J
3
+
Scheme 1. Synthesis of multicolor emission polymer films.
1
, 2, 3, 4, respectively) transitions of Eu . These results in-
dicate that HPBA is an excellent antenna chromophore for
3
+
ꢀ
Tb . However, after deprotonation, PBA becomes a com-
3
+
films reported here realize tunable photoluminescence emis-
sions from green to red (from films A to K) depending on
the changes of OH concentrations in the hybrid, which is
paratively good organic chelator to transfer energy to Eu .
The films evidently exhibited distinct chromaticity coordi-
nates observed in the CIE chromaticity diagram (Fig-
ꢀ
[11]
5
7
more facile than the traditional methods that typically rely
ure 1c). The detailed integrated intensities of the D ! F
4
J
3
+
3+
5
7
3+
on tuning the ratios of Ln and organic ligands. The emis-
sion color can also be finely tuned through variation in the
excitation wavelength, and white-light emission can be ach-
ieved when the given film is excited at the visible region
(Tb ; 545 nm) and D ! F (Eu ; 611 nm) transitions of
0
J
the deprotonated films are shown in Figure S6 in the Sup-
ꢀ
porting Information. As the OH concentrations increase,
3
+
the emission intensity of Tb decreases, whereas that of
3
+
(
approximately 405 nm). To the best of our knowledge, it is
Eu increases, which is consistent with the above observa-
tion by the naked eye. The luminescence lifetimes and quan-
tum yields of the complexes and the films, which are two im-
portant parameters for the estimation of the luminescence
efficiency, have also been determined (Table S1 in the Sup-
porting Information). Films A and K have longer lumines-
cence lifetimes and higher overall quantum yields than the
corresponding Tb–HPBA and Eu–PBA complexes, thus in-
dicating that PVP chains could firmly encapsulate Ln com-
the first example of Ln-based materials that can emit full-
color photoluminescence, including white-color emission, as
ꢀ
a function of OH concentrations and excitation wave-
length. It is worth noting that the luminescence of the film
can efficiently transform from green to red even after sever-
al cycles when the film is exposed to base–acid vapor.
III
Results and Discussion
plexes and inhibit the vibration of the ligands around Ln
and intermolecular collisions of the complex.
[10]
Characterization of the multicolor photoluminescence poly-
mer films: The FTIR spectra of films A and K are similar to
those of pure PVP (Figure S1 in the Supporting Informa-
tion). A few small characteristic vibrational modes of pyri-
dine in the corresponding Tb–HPBA or Eu–PBA complex
Energy-transfer studies: To clarify the effect of deprotona-
tion of the photosensitizer HPBA on luminescence color
tunability, the mechanism of the most probable inter- and
intramolecular energy-transfer (ET) processes demonstrated
in Figure 2 were examined on the basis of experimental data
(Table S2 in the Supporting Information). The singlet
energy levels of the photosensitizers were estimated for sol-
utions in methanol with the use of their UV-visible absorb-
(
Figure S2 in the Supporting Information) emerge in the
spectra of film A or film K, thereby suggesting that PVP
can firmly encapsulate Ln complexes and confine the vibra-
tions of the ligands. The powder X-ray diffraction (PXRD)
patterns of the complex-doped PVP films (Figure S3 in the
Supporting Information) show only amorphous peaks of
PVP, and the crystalline peaks of the complex molecules
ance edges. The triplet excited energy level (T ) data of the
1
ligands were calculated by the low-temperature (77 K) phos-
3
+
phorescence spectra of the corresponding Gd complexes
Chem. Eur. J. 2013, 19, 4556 – 4562
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4557

Y. Tang et al.
3
+
3+
ꢀ
Figure 2. Energy-level diagram of the Tb :Eu :HPBA:PBA @PVP
hybrid. The dashed arrows represent nonradiative decays and the most
probable inter- and intramolecular energy-transfer processes.
ꢀ
1
proximately 7058 cm
(0.88 eV) higher than the corre-
5
sponding D level. Such a large energy gap resulted in the
0
nonradiative deactivation of the europium emitting state
and the quenching of the luminescence of the complex. By
ꢀ
contrast, the triplet excited energy level of PBA was ap-
ꢀ
1
proximately 3590 cm
(0.45 eV) higher than the corre-
5
3+
sponding D level of Eu , and only slightly higher than the
corresponding D level in Tb . Therefore, the efficient sen-
sitization of Eu was promoted. Therefore HPBA is a good
photosensitizer for Tb . After deprotonation, the triplet-
state energy levels T of PBA changed, thus resulting in the
efficient transfer of energy to Eu
0
5
3+
4
3
+
3
+
ꢀ
1
3
+
.
In addition, ET mechanisms might occur not only be-
tween organic photosensitizers and Ln ions, but also be-
3
+
3+
tween Tb and Eu . For all luminescence dopants incor-
porated in PVP, the distance between these molecules was
[
13]
short enough to promote intermolecular ET.
stand the mechanism of intermolecular ET, the average life-
To under-
5
3+
times of the excited state D (Tb ) of the films were moni-
tored in the presence and absence of Eu at different OH
4
3
+
ꢀ
concentrations (Figure 3), and the experimental data are
listed in Tables S3 and S4 in the Supporting Information.
5
The decreasing lifetime values of the D emitting level of
4
3
+
ꢀ
Tb were observed along with the increase of the OH
Figure 1. a) Fluorescence microscopy images and b) emission spectra of
films A, E, F, G, H, and K. c) CIE chromaticity diagram showing the (x,
y) photoluminescence emission color coordinates from films A to K with
3
+
concentrations both in the presence and absence of Eu
.
ꢀ
At the same OH concentration, the film doped with both
ꢀ
increasing OH concentrations from 0.0 to 1.0 equiv (the step increment
3+
3+
5
Tb and Eu exhibited a shorter D lifetime than that of
4
was 0.1 equiv) relative to the photosensitizer HPBA.
3+
the film doped only with Tb . This result indicates the
transfer of energy from Tb to Eu
3
+
3+ [14]
.
Theoretically, the
in 1:1 methanol/ethanol mixture (Figure S7 in the Support-
ing Information). From the experimentally observed triplet
energy, the sensitizing properties of the ligands were readily
ET efficiency (E) between the donor and the acceptor can
be determined by Equation (1):
[14]
[12]
evaluated in terms of the so-called energy-gap law. The
triplet excited energy level of HPBA was located approxi-
t
da
E ¼ 1ꢀ
ð1Þ
t
d
ꢀ
1
5
mately 3858 cm (0.48 eV) higher than the D4 level of
3
+
5
Tb . Therefore, efficient intramolecular energy transfer
was facilitated. For Eu , the energy level of HPBA was ap-
in which tda and t are the D lifetimes of the films in the
d
4
3
+
3+
presence and absence of Eu , respectively. The ET efficien-
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Chem. Eur. J. 2013, 19, 4556 – 4562

Full-Color Photoluminescent Films
FULL PAPER
Figure 4. The optimized geometries and calculated spatial distributions
(
DFT, B3LYP/6-31G*, Gaussian 03) of HOMOs and LUMOs of the pho-
ꢀ
tosensitizers HPBA and PBA .
the change of the excitation wavelength. Upon selective ex-
citations, tunable luminescence emission is then achieved.
For film G, the broad-band emission with a maximum at ap-
proximately 490 nm emerged when the film was excited at
3
90 nm. To determine the source of this broad band, the
emission spectra of the ligands and the complexes were ex-
6
3+
amined. The first excited level ( P ) of Gd was far above
7
/2
the T state of the ligands; therefore, the emission spectra of
1
3
+
the Gd complexes provided information on the energy
[18]
levels of the ligands. Consequently, the emission spectra
of Gd–HPBA, Gd–PBA, Tb–HPBA, and Eu–PBA in the
solid state were determined (Figure 5a). The broad band at
approximately 490 nm of film G is attributed to the emission
ꢀ
of PBA (Figure 5a). When the excitation wavelength was
ꢀ
altered from 390 to 430 nm, the emission of PBA increased
steadily, thus indicating a lower and less efficient energy
3
+
transfer from the ligand to Ln (Figure S9 in the Support-
ing Information). When film G was excited at 405 nm, the
CIE chromaticity diagram established white-light chromatic-
ity coordinates at (0.351, 0.380) (Figure 5b). This white-color
emission (the white line in Figure 5a) consists of relative red
5
Figure 3. a) The average excited-state
D
4
lifetimes for films D to H.
5
ꢀ
b) The
D
4
lifetimes for Tb-based PVP films with varying OH concen-
trations from 0.3 to 0.7 equiv (the step is 0.1 equiv) of the hybrid.
3
+
3+
ꢀ
(Eu ), green (Tb ), and blue (PBA ) luminescent compo-
nents with suitable intensities. The detailed emission spectra
and the CIE chromaticity diagrams of films A, E, F, H, and
K through the change of the excitation wavelength are illus-
trated in Figures S10 to S14 in the Supporting Information.
To research the possibility of practical applications, the
stabilities of the films and absolute complexes were investi-
gated. To compare photoluminescence stability, kinetic scans
of the luminescence induced by light in the different sam-
ples were performed (Figure 6). Less fluorescence quench-
ing was noted in all the films, and this result implies a better
photostability than that of the Tb–HPBA complex. It is ob-
served that Eu–PBA did not show a clear fluorescence de-
crease, thus indicating that the ligand becomes more effec-
tive in protecting europium ions from photobleaching after
deprotonation. The TG curves of films A and K demon-
strate profiles similar to that of PVP (Figure S15 in the Sup-
porting Information). However, absolute Tb–HPBA and
Eu–PBA generally begin thermal decomposition at around
3
+
3+
cy of Tb to Eu displays a stable enhancement with an
ꢀ
increase in OH concentrations (Figure S8 in the Supporting
Information). The detailed ET mechanism might be mainly
supported by the phonon-assisted Fçrster transfer mecha-
[15]
nism.
To further understand the effect after deprotonation, the
molecular geometry and the highest-occupied molecular or-
bital (HOMO) and the lowest-unoccupied molecular orbital
LUMO) energy levels of the free ligands HPBA and PBA
were optimized with density functional theory (DFT) at the
ꢀ
(
[16]
B3LYP/6-31G* level by Gaussian 03 (Figure 4). The esti-
mated S !S transition (E ) can be calculated principally by
0
1
g
a HOMO!LUMO excitation. The energy levels of the
lowest triplet excited state can be calculated with the time-
dependent DFT approach (Table S5 in the Supporting Infor-
[17]
mation), which matched well with the above experimental
data.
2
008C (Figure S16 in the Supporting Information), thus indi-
A potential white-light-emitting device: Furthermore, the
tuning of photoluminescence color can also be obtained by
cating that the films were stable relative to absolute Tb–
HPBA and Eu–PBA. These good luminescent properties
Chem. Eur. J. 2013, 19, 4556 – 4562
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4559

Y. Tang et al.
Figure 6. Photoluminescence stabilities of Tb–HPBA, film A, film E (nor-
5
7
malized intensities of the D
4
! F
5
transition as a function of time); and
5
7
Eu–PBA, film H, film K (normalized intensities of the D! F
2
transition
as a function of time).
that the photoluminescence of the film could be changed
from green to red and back to green when the film was ex-
posed to a base–acid vapor. To present this characteristic
graphically, film A that contained laser-etched Olympic five-
ringed flags was used (Figure 7). As expected, the exposure
Figure 5. a) Emission spectra of Gd–HPBA (blue line), Gd–PBA (cyan
line), Tb–HPBA (green line), Eu–PBA (red line), and film G excited at
Figure 7. Fluorescence microscopy images of the laser micropatterned
film A: a) as obtained on a silicon slice, b) upon brief exposure with
Et N, c) treated with continuous-flow Et N, and d) upon treatment with
3 3
4
05 nm (white line) in the solid state at room temperature. b) CIE chro-
maticity diagram showing the (x, y) emission color coordinates of Tb–
HPBA (dot a), Eu–PBA (dot b), Gd–HPBA (dot c), Gd–PBA (dot d),
and film G excited from 390 to 430 nm (dashed arrow, the step is 10 nm)
and irradiated at 405 nm (dot e). Inset: white emission behavior of
film G coated on clean quartz glass irradiated at 405 nm by a laser
source.
HCl vapor shifting the luminescence back to the pristine one.
of the film to Et N vapor resulted in an intensification of
3
the red emission, which could serve as a signal. The lumines-
cence of the film shifted back to the green emission when
treated with HCl gas (see Movie S1 in the Supporting Infor-
mation). Such a mixed Ln-based film exhibited higher sensi-
tivity than the single Tb-based luminescent switch, as dem-
onstrated in its larger slope of the luminescence decay rate
(Figure S17 in the Supporting Information). From the stand-
point of device applications, the reversibility and the re-
sponse time of the sensor are also important. The spectral
changes at 545 and 612 nm of the films were monitored over
several base–acid vapor cycles (Figure 8). The films exhibit-
and stabilities enable the films to be used in potential opti-
cal applications.
Application of the film as a vapoluminescent sensor: The
color-tunable mechanism can also be applied to a vapolumi-
nescent sensor. Some reports have described the vapolumi-
nescent switch of materials triggered by the presence of
[19]
base–acid vapors, but such reports are scarce for vapolu-
minescent color-tunable materials. Interestingly, we found
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Chem. Eur. J. 2013, 19, 4556 – 4562

Full-Color Photoluminescent Films
FULL PAPER
successive fuming to remove excess amounts of acid. PVP K-30 and 2-
aminopyridine were purchased from Alfa Aesar. Ethyl benzoylacetate
was purchased from Lanzhou Aihua Corporation.
Synthesis of HPBA: The photosensitizer N-(2-pyridinyl)benzoylaceta-
mide (HPBA) was prepared by the reaction of 2-aminopyridine with
[
21]
1
ethyl benzoylacetate. Yield: 70%; m.p. 104–1088C; H NMR (CDCl
00 MHz): d=4.21 (s, 2H), 7.23 (t, 1H), 7.71 (t, 1H), 8.26 (d, 1H), 8.61
d, 1H), 7.46 (t, 2H), 7.50 (t, 1H), 8.17 (d, 2H), 9.99 ppm (s, 1H); ele-
3
,
4
(
12 2 2
mental analysis calcd (%) for C14H N O : C 69.79, H 4.68, N 11.38;
found: C 69.99, H 5.03, N 11.66.
Synthesis of the films: PVP K-30 powder (1 g) was dissolved in DMF
(
40 mL) that contained distilled water (10 mL), followed by the addition
3
+
of the constant amount of photosensitizer HPBA (1 mmol) and Ln
(
Ln=Eu, Tb) ions to acquire the hybrid. The molar ratio of HPBA/Eu-
A
H
U
G
R
N
U
G
3
)
3
2
A
H
U
T
E
N
G
3
)
3
2
spin-coated on clean quartz glasses and finally dried at 808C under
vacuum for 8 h. The polymer film was obtained after the total evapora-
tion of the solvent. The tunable photoluminescence films (A–K) were
ꢀ
fabricated after the addition of the varied OH (NaOH) concentrations
from 0.0 to 1.0 equiv (the step is 0.1 equiv) relative to the photosensitizer
into the hybrid.
Figure 8. Responses of luminescence intensities at 545 nm (squares) and
6
12 nm (triangles) of film A during acid–base vapor exposure cycles.
Measurements: NMR spectra were recorded using a Bruker 400 MHz
spectrometer. Chemical shifts (d) are given in parts per million. The com-
positions of HPBA, 1, and 2 were determined by CHN elemental analy-
ses using an Elementar Vario EL analyzer. Mass spectra were recorded
using a Bruker UHR-TOF maXis 4G mass spectrometer. FTIR spectra
ed good reversibility even after eight cycles. In addition, the
response time of the film was also rapid. After exposure to
ꢀ
1
of the materials were conducted within the 4000–400 cm wavenumber
range by using a Nicolet 360 FTIR spectrometer with the KBr pellet
technique. PXRD were determined using a Rigaku-Dmax 2400 diffrac-
tometer with CuKa radiation over the 2q range of 3–608. Thermogravi-
metric analyses (TGA) were performed using a Perkin–Elmer thermal
Et N vapor for 10 s, the red emission appeared completely.
3
After exposure to HCl gas for approximately 10 s, the green
emission reappeared (see Movie S1 in the Supporting Infor-
mation). The films also maintained their luminescence for a
few weeks without any degradation. Therefore, such a color-
tunable solid-state luminescence sensor by external stimuli
ꢀ
1
analyzer up to 8008C at a heating rate of 108Cmin under a nitrogen at-
mosphere. The phosphorescence spectra of Gd–HPBA and Gd–PBA
were measured at 77 K in a methanol/ethanol mixture (1:1 v/v) using a
Hitachi F-4500 spectrophotometer. The steady-state luminescence spectra
and the lifetime measurements were measured using an Edinburgh In-
struments FSL920 fluorescence spectrometer with a 450 W Xe arc lamp
as the steady-state excitation source and an Nd-pumped OPOlette laser
as the excitation source for lifetime measurements. In the experiments of
photoluminescence stability, the 450 W Xe arc lamp was used as the irra-
diation source, with a slit of 0.4 nm and a shutter opening after 10 s for
800 s. The overall quantum yields of the samples were determined by an
[20]
would be of importance in a variety of applications.
Conclusion
In conclusion, we have demonstrated for the first time the
realization of tunable photoluminescence films by changing
[
22]
absolute method with an integrating sphere (150 mm diameter, BaSO
4
ꢀ
coating) using an Edinburgh Instrument FLS920. Three parallel measure-
ments were carried out for each sample, so that the presented value cor-
responds to the arithmetic mean value. The errors in the quantum-yield
values associated with this technique were estimated to be within
OH concentrations of a designed fixed-component Ln-
based hybrid. The emission color of the films can also be
finely tuned by varying the excitation wavelength, and
white-light emission can be achieved in the visible region.
This novel approach to tuning emission color is a promising
strategy in the development of lanthanide-based full-color
photoluminescent displays. At the same time, base–acid
vapor-responsive luminescent films with good stability, sensi-
tivity, reversibility, and quick response might provide access
to sensor materials. The results of this work might have
great theoretical and practical significance for the design of
multifunctional materials. Further investigations of these
materials and other candidates are still ongoing in our lab.
[
23]
10%. The micropatterned films were prepared by laser micromachin-
ing using a LUCE laser source (l=1064 nm, Bright Solution, Italy).
Acknowledgements
The research leading to these results has received funding from the Na-
tional Natural Science Foundation of China (projects 21071068,
20931003) and the Fundamental Research Funds for the Central Univer-
sities (project lzujbky-2011-17).
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Materials: All reagents and solvents were obtained from commercial
sources and used without further purification. Terbium (Tb
and europium nitrates (Eu(NO ·6H O) were obtained by dissolving
Tb and Eu (99.99%, Shanghai Yuelong) in nitric acid followed by
3 3 2
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