Host Differential Sensitization toward Color/Lifetime-Tuned Lanthanide Coordination Polymers for Optical Multiplexing

Article abstract of DOI:10.1002/anie.202011559

Optical multiplexing based on luminescent materials with tunable color/lifetime has potential applications in information storage and security. However, the available tunable luminescent materials reported so far still suffer from several drawbacks of low efficiency or poor stability, thus restraining their further applications. Herein, we demonstrate a strategy to develop efficient and stable lanthanide coordination polymers (LCPs) with tunable luminescence as a new option for optical multiplexing. Their multicolor emission from green to red and naked-eye-sensitive green emission with tunable lifetime (from ca. 300 to ca. 600 μs) can be controlled by host differential sensitization and energy transfer between lanthanide ions. The quantum efficiencies of developed samples range from around 20 % to 46 % and the luminescence intensity/lifetime appear quite stable in polar solvents up to ten weeks. Furthermore, with the aid of inkjet printing and concepts of luminescence lifetime imaging and time-gated imaging, we illustrate their promising applications of information storage and security in spatial and temporal domains.

Full text of DOI:10.1002/anie.202011559

A Journal of the Gesellschaft Deutscher Chemiker
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International Edition Chemie
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Accepted Article
Title: Host Differential Sensitization toward Color/Lifetime-Tuned
Lanthanide Coordination Polymers for Optical Multiplexing
Authors: Yiyi Ou, Weijie Zhou, Zece Zhu, Fengkai Ma, Rongfu Zhou,
Fang Su, Lirong Zheng, Li Ma, and Hongbin Liang
This manuscript has been accepted after peer review and appears as an
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202011559
Link to VoR: https://doi.org/10.1002/anie.202011559

Angewandte Chemie International Edition
10.1002/anie.202011559
RESEARCH ARTICLE
Host Differential Sensitization toward Color/Lifetime-Tuned
Lanthanide Coordination Polymers for Optical Multiplexing
[
a]+
[a]+
[b]
[a]
[a]
[a]
[c]
Yiyi Ou, Weijie Zhou, Zece Zhu, Fengkai Ma, Rongfu Zhou, Fang Su, Lirong Zheng, Li
[
d]
[a]
Ma, and Hongbin Liang*
[
[
a]
b]
Y. Ou, Dr. W. Zhou, Dr. F. Ma, Dr. R. Zhou, F. Su, Prof. H. Liang
MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, KLGHEI of Environment and Energy Chemistry, School of Chemistry, Sun Yat-sen
University, Guangzhou 510275, China
E-mail: cesbin@mail.sysu.edu.cn
Dr. Z. Zhu
Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan
430074, China
[
[
[
c]
d]
+]
Dr. L. Zheng
Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039, China
Prof. L. Ma
Department of Physics, Georgia Southern University, Statesboro, Georgia 30460, United States
These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of the document.
Abstract: Optical multiplexing based on luminescent materials with
tunable color/lifetime holds potential applications in information
storage and security. However, the available tunable luminescent
materials reported so far still suffer from several drawbacks of low
efficiency or poor stability, thus restraining their further applications.
Here, we demonstrate a strategy to develop the efficient and stable
lanthanide coordination polymers (LCPs) with tunable luminescence
as a new option for optical multiplexing. Their multicolor emission from
green to red and naked-eye-sensitive green emission with tunable
lifetime (from ~ 300 to ~ 600 μs) can be controlled by host differential
sensitization and energy transfer between lanthanide ions. The
environment and high toxicity of QDs, and tedious synthesis.
Therefore, it is urgently desired to further expand the alternative
luminescent materials to meet the demand of optical multiplexing
technology innovation.
Lanthanide coordination polymers (LCPs) including lanthanide
metal-organic frameworks (Ln-MOFs), constructed with
lanthanide-ion nodes and organic linkers, have drawn much
attention in the applications of chemical sensing, visible and near
infrared light-emitting devices, and so on.[17-21] With the merits of
lanthanide 4f-4f sharp emission with μs lifetime, antenna effect of
organic ligands [22, 23] and robust structure framework, the efficient
quantum efficiencies of developed samples range from ~ 20% to ~ 46% and stable LCPs are also endowed with the large potential to be
and the luminescence intensity/lifetime appear quite stable in polar
solvents up to ten weeks. Furthermore, with the aids of inkjet printing
and concepts of luminescence lifetime imaging and time-gated
imaging, we also illustrate their inspiring and promising applications
of information storage and security in spatial and temporal domains.
These results will open up an avenue to the efficient and stable LCPs
with tunable luminescence toward optical multiplexing applications.
the candidate for optical multiplexing applications. Recently,
substantial efforts have been devoted to the achievement of large-
scale color tunability in spatial domain in some Ln-MOF systems.
For example, a series of Ln-MOF hierarchical single crystals with
different lanthanide ions were designed to possess domain- and
orientation-controlled multicolor luminescence, which gives
possibility for multiplexed coding capability in a 3D way.[24]
A
heteroepitaxial growth of multiblock Ln-BTC microrods were also
developed for multicolor and thermally-responsive barcodes.[25, 26]
Further, a layer-by-layer approach was proposed to construct Ln-
surface-anchored MOFs (Ln-SURMOFs) to achieve tunable
Introduction
emission while suppressing the unwanted energy transfer
Optical multiplexing has attracted tremendous interests owing
to its potential applications in biodetection, information storage
and security, and so on.[1-4] The ever-increasing demand for the
superior multiplexing mode, i. e. the stable and high-degree
multiplexing in both spatial and temporal domains, calls for
luminescent materials with small size in nano/micrometer range,
excellent physicochemical stability, tunable emission with sharp
peaks, tunable lifetime in microsecond (μs) range, and high
luminous efficiency.[5-7] Hitherto, a range of promising materials
including the lanthanide-doped upconversion nanoparticles [8-10],
inorganic perovskite quantum dots (QDs) [11, 12], and inorganic-
organic hybrid composites [13-16] have been rationally designed
and played the significant roles in promoting the multiplexing
technologies. However, these state-of-the-art materials also
suffer from several drawbacks, such as low efficiency of
upconversion emission, poor resistance to polar solvent
between lanthanide ions.[27] However, to pursue the superior
multiplexing applications, only tunable color or multicolor in spatial
distribution is not enough, the color/intensity evolution in temporal
dimension based on the tunable lifetime of materials is much more
requisite.[1, 28] Unfortunately, there is still an absence of good
experience and feasible strategy in finely tailoring the lifetime of
LCPs emission. Furthermore, manipulating the emission color
and lifetime individually in one LCP system also becomes an open
question.
In this work, we demonstrate a strategy to design the
color/lifetime-tuned LCPs for optical multiplexing applications via
energy transfer (ET) manipulation based on host differential
sensitization, as schematically illustrated in Scheme 1. In our
3+
3+
strategy, several possible lanthanide (Ln) ions (such as Pr , Sm ,
3+
3+
3+
3+
3+
3+
Eu , Tb , Dy , Ho , Er , and Tm ) with different characteristic
emissions can be selected, among which the inter-ionic ET could
1
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
intensity/lifetime appear quite stable in polar solvents up to ten
weeks (the emission intensities keep at least ~ 79% of pristine
samples and the lifetime values have small relative standard
deviations < 0.5%). Basically, the crystal structure, local bonding
properties and ET dynamics of synthesized samples are studied
in depth by applying Rietveld refinement, X-ray absorption
spectroscopy (XAS) and statistical ET theory, respectively, to
elucidate their structure-property relationship. Finally, these
efficient and stable color/lifetime-tuned LCPs are used to fabricate
the colorless security inks. With the aids of inkjet printing
technique and concepts of luminescence lifetime imaging and
time-gated imaging, some interesting and enlightening
prototypical application patterns are demonstrated, implying that
these LCPs have decent performance in information storage and
security in both spatial and temporal domains.
Results and Discussion
Crystal Structure and Bonding Properties. The crystal
structures of synthesized samples were studied via powder X-ray
diffraction (XRD) technique at room temperature (RT), and the
corresponding Rietveld refinement was performed by using the
Scheme 1. (a) Schematic illustration of the design strategy for color/lifetime-
tuned LCPs. (b) Coordination environment of the lanthanide ions in Y-BTC host
and the energy transfer between lanthanide ions and organic ligands. (c)
Jablonski diagram with detailed energy levels and energy transfer processes in
color/lifetime-tuned lanthanide-ions-activated Y-BTC.
La(BTC)(H
model.[30] Typically, the refined pattern of Y-BTC host compound
in Figure 1a shows a good fitting quality (Rwp = 2.47%, R = 1.58%,
= 0.93%) and no other impurity phase is found, indicating the
2 6
O) (CCDC number: 290771) structure as an initial
p
R
b
successful synthesis of Y-BTC single phase. The refined
structural parameters are given in Table S1. The Y-BTC host
crystallizes in a monoclinic structure with space group Cc (9) and
occur. More importantly, the LCPs host should exhibit a so-called
differential sensitization effect for lanthanide emissions.
Specifically, the lanthanide ions that are efficiently sensitized by
cell parameters a = 11.32(1) Å, b = 17.79(2) Å, c = 7.12(1) Å, β =
3
1
19.2(5)°, V = 1252 Å , and Z = 4. There is only one yttrium site
(as illustrated red and blue balls in Scheme 1a) can exhibit the
surrounded by nine oxygen ions with and average distance of ~
.14 Å, in which the oxygen ions are originated from six water
molecules and three carboxyl groups of H BTC ligands, forming
large-scale color tunability under the excitation of hosts. Moreover,
by combining the sounding (blue ball) as ET donor and silent ions
2
3
(
orange ball) as ET acceptor with ligands, the developed LCPs
can achieve the lifetime tunability of sounding ions.
As proof-of-concept experiment, we designed and
synthesized a series of Tb -, Eu -, Sm -activated Y(BTC)(H
BTC=1,3,5-benzenetricarboxylic acid) (abbreviated as Y-BTC
hereafter) LCPs by a facile solvothermal method as shown in
a tricapped trigonal prismatic geometry. The distance between
adjacent Y3+ ions is ~ 5.81 Å. Furthermore, the π-π stacking
a
3+
3+
3+
2
O)
6
(H
3
3+
3+
Scheme 1b. In this system, the lanthanide ions Tb , Eu and
Sm3+ can exhibit the characteristic green, red and orange
emissions, respectively. They also have the resonant electronic
energy levels, permitting the inter-ionic ET to happen (Scheme
1
c).[29] The Y-BTC host compound has a simple crystal structure
with only one yttrium core and provides a single coordination
environment for lanthanide ions, which is isomorphic to La-BTC
compound.[30] It also possesses a suitable lowest triplet level (T
1
3
-1
at ~ 23.1×10 cm ) speculated from the low-temperature (10 K)
emission spectrum [31] (Figure S1, Supporting Information),
3+
3+
which allows that the sounding ions (Tb , Eu ) and silent ion
Sm3+ can be sensitized differentially as discussed below
(
Scheme 1c). Experimentally, the sounding ions Tb3+ and Eu3+
co-activated Y-BTC host (denoted as Tb Eu -BTC) are found to
exhibit the tunable color from green to red. The Y-BTC host doped
by the sounding ion Tb3+ and silent ion Sm3+ (denoted as Tb
Sm
x
y
x
z
-
Figure 1. (a) Rietveld refinement result and crystal structure along c axis of Y-
BTC) has the naked-eye-sensitive green emission at ~ 541 nm
with tunable lifetime (from about 300 to 600 μs). In addition, these
developed samples exhibit the internal quantum efficiencies
3
BTC host compound. (b) Fourier transform infrared (FT-IR) spectra of H BTC
reactant and Y-BTC host compound. (c) Scanning electron microscopy (SEM)
images of Y-BTC host and mapping results of Y, C, and O elements. (d) Fourier
ranging from
~
20% to
~
46% and their luminescence
transform of L
3
-edge EXAFS of Eu-BTC sample in r-space and its fitting result,
3+
the inset shows the coordination environment of Eu ion.
2
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RESEARCH ARTICLE
3
between phenyl groups of H BTC along c axis and the hydrogen-
bonding between carboxyl oxygen and water hydrogen lead to the
Y-BTC framework structure [32], as illustrated in the inset of Figure
1
a and Figure S2.The XRD patterns and Rietveld refinement
3+
3+
3+
results of Tb , Eu , Sm doped samples (abbreviated as
Tb/Eu/Sm-BTC) are also presented in Figure S3 and Table S2-
S6, indicating that the doping of lanthanide ions would not
significantly change the Y-BTC host structure.
The bonding properties of synthesized samples were
investigated by using Fourier transform infrared (FT-IR) spectrum
at RT. Figure 1b shows that the H
3
BTC reactant exhibits the C=O
-1
stretching vibration band (νC=O, ~ 1702 cm ) and O-H wagging
-
1
vibration band (ωO-H, ~ 895 cm ) of nonionized carboxyl groups.
[33]
While in Y-BTC case these vibration bands disappear, and
-1
some new bands appear in the range of 1611-1557 cm and
-1
1
435-1371 cm , which can be assigned to the characteristic
asymmetric (νas) and symmetric (ν ) stretching vibration bands of
carboxylate, respectively. [34] This phenomenon indicates that the
yttrium ions are bonded to the oxygen of H BTC ligands in Y-BTC
s
3
host [34], which supports the structural information of Y-BTC host
from XRD data. The FT-IR results of doped samples in Figure S4
are like to that of Y-BTC host, implying that the incorporated
lanthanide ions are also linked to the oxygen ions in a similar way.
The morphology of synthesized samples was checked by
scanning electron microscopy (SEM). Figure 1c presents a rod-
like shape of Y-BTC host with about 4-5 μm in length and 400-
500 nm in width, and the related elemental mapping demonstrates
a homogeneous distribution of Y, C and O elements. The SEM
results of doped samples are also given in Figure S5, showing
that they possess the similar morphology to Y-BTC host while with
some aggregations.
Figure 2. (a) Highest-height-normalized excitation (λem = 541, 613, 590 nm) and
emission (λex = 300 nm) spectra of Ln0.01-BTC (Ln = Tb3+, Eu3+, Sm3+) samples
at RT. (b) Concentration-dependent internal quantum efficiencies of Tb
0.10-1.00), Eu -BTC (y = 0.10-1.00) and Sm -BTC (z = 0.01-0.10) samples at
RT. (c) Area-normalized emission spectra (λex = 300 nm) of Tb Eu -BTC
samples at RT. (d) CIE color coordinates and representative luminescence
images of Tb Eu -BTC emissions. (e) Emission spectra (λex = 300 nm) of
Tb Sm -BTC samples at RT and the enlarged curves in the range of 550-750
nm. (f) Luminescence decay curves (λex = 300 nm, λem = 541 nm) of Tb3+ ions
x
-BTC (x
=
y
z
x
y
The oxidation state and local bonding of doping ions were
studied by applying X-ray absorption spectroscopy (XAS).
x
y
x
z
3
Specifically, by performing the L -edge X-ray absorption near-
edge structure (XANES) measurement at RT, the incorporated
lanthanide ions (Tb and Eu) are found to be as 3+ oxidation state
x z
in Tb Sm -BTC samples at RT and the corresponding fitting results via Yokota-
Tanimoto (Y-T) ET model, the inset demonstrates the Tb3+-Sm3+ ET dynamics.
(Figure S6). The extended X-ray absorption fine structure
(EXAFS) was further applied to study the local structure of
incorporated ions in the representative Eu-BTC sample. The
the weak peaks at ~ 557, ~ 590, ~ 638, and ~ 701 nm related to
4G5/2 → H
6
(J = 5/2, 7/2, 9/2, 11/2) transitions of Sm3+ ions [35]
,
extracted EXAFS signal χ(k) in Figure S7 shows a nice oscillation
J
2
structure in k regime. Its Fourier transform and fitting results in r-
but also the broad-band fluorescence of Y-BTC host at ~ 400 nm
(Figure S1). The distinctive properties confirm that the Y-BTC
host can exhibit the differential sensitization effect for lanthanide
luminescence. In essence, this effect is mainly determined by the
variable energy difference (ΔE) from the lowest triplet energy level
space in Figure 1d (R-factor of 0.49%) reveals that the
incorporated Eu3+ ions are bonded to nine oxygen ions in the first
coordination shell with a bond length of ~ 2.45(4) Å as shown in
3+
2-
Table S7, which expands somewhat than Y -O bond (~ 2.14 Å)
due to the larger effective ionic radius of Eu3+ ion (~ 1.12 Å, C. N.
(T
1
) of host to the excited states of different lanthanide ions. [22]
=
9) relative to Y3+ ion (~ 1.075 Å, C. N. = 9).
Empirically, a ΔE value in 2000-4000 cm-1 energy range would
ensure the enough energetic resonance condition for sensitizing
process, and simultaneously alleviate the possible energy back-
transfer, which eventually leads to the good host sensitization for
lanthanide luminescence. [37] In our case, as shown in Scheme
Tunable Photoluminescence Mechanisms for Multiplexing.
Firstly, the fundamental luminescence properties of singly-doped
3+
3+
3+
Ln0.01-BTC (Ln = Tb , Eu , Sm ) samples were studied in detail.
Their excitation spectra show the similar bands in the wavelength
range of 250-300 nm at RT (Figure 2a), which can be ascribed to
the π–π* transitions of benzene rings of Y-BTC host as analyzed
in Figure S1.[31, 34] Under the excitation of 300 nm at RT, the
Tb0.01-BTC sample exhibits intense green emission comprising
3
-1
1c, the lowest triplet energy level (T
host is ~ 2603 cm-1 away from the Tb3+ 5D
~ 1649, ~ 4122 and ~ 5862 cm-1 higher than the Eu3+ 5
1
= ~ 23.1×10 cm ) of Y-BTC
level, simultaneously
(J = 2,
4
D
J
1, 0) levels, respectively. Hence, the Y-BTC host should exhibit
stronger sensitization for Tb3+ luminescence than Eu3+ case, and
both of them can be served as ‘sounding ion’. While for the Sm3+
four sharp peaks at ~ 486, ~ 541, ~ 581, and ~ 617 nm, which are
5
→ 7F
(J = 6, 5, 4, 3) 4f-4f transitions of Tb3+ ions,
originated to D
4
J
respectively. [35] While Eu0.01-BTC sample emits strong red light
1
ion, its excited levels almost overlap to the host T level, the
with peaks at ~ 590, ~ 613, ~ 647, and ~ 687 nm, which are
severe energy back-transfer results in the poor sensitization for
Sm3+ ion, which is denoted as ‘silent ion’. Furthermore, Figure 2b
and Table S8 exhibit the concentration-dependent internal
5
→ 7F
individually attributed to D
0
J
(J = 1, 2, 3, 4) transitions of
Eu3+ ions. [36] Differently, the Sm0.01-BTC sample shows not only
3
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RESEARCH ARTICLE
quantum efficiencies (IQE) of these singly-doped samples under
the obtained physical parameters are meaningful (Table S10). It
3+
3
00 nm excitation at RT. Tb
x
-BTC (x = 0.10-1.00) and Eu
y
-BTC (y
indicates that the slow EM process between donor Tb plays a
3+
3+
=
0.10-1.00) samples manifest efficient luminescence among the
leading role in Tb -Sm ET dynamics and similar phenomenon
3
+
3+
nanocrystals.[40]
Ln-BTC samples, with a top value of ~ 46.3 % when x = 0.70 and
is also observed in Tb , Eu doped LaPO
4
3
+
3+
~
0
=
z
20.6 % at y = 0.60, respectively. While the Sm -BTC (y = 0.01-
Moreover, the main Tb -Sm ET mechanism is electric dipole-
3+
3+
.10) samples are inefficient with a peak efficiency of ~ 3.3% at z
0.01. In brief, this efficiency order among Ln-BTC samples is
dipole (EDD) interaction, the microparameter CDA for Tb -Sm
-
52
6
ET process is ~ 7.203×10 m /s and the microparameter CDD for
Tb -Tb EM process is ~ 3.134×10-54 m /s. See Figure S13 for
detailed fitting procedures. Benefiting from the above tunable
color and lifetime features, the high-degree optical multiplexing
application of information storage and security based on these
LCP samples in spatial and temporal domains are demonstrated
below.
3+
3+
6
well consistent with the degree of host sensitization for lanthanide
ions discussed above. Moreover, their luminescence decay
curves in Figure S8 indicate the single-exponential properties.
Then the emission color and lifetime tunability of as-designed
co-doped Tb
lying ET dynamics were studied in depth. Figure 2c exhibits the
area-normalized emission spectra of Tb Eu -BTC (x = 0.40, y = 0-
x y x z
Eu -BTC and Tb Sm -BTC samples and the under-
x
y
Information Storage and Security in Spatial and Temporal
0
.20) and Eu0.30-BTC samples under host excitation (λex = 300 nm) Domains. Some representative samples including the color-
3
+
at RT. With the increase of ‘sounding’ Eu ion, the relative
emission intensity of ‘sounding’ Tb3+ gradually decreases, while
that of Eu3+ rises, which jointly form the color tunability from green
to red as demonstrated by the corresponding Commission
Internationale de L'Eclairage (CIE) color coordinates and
representative luminescence images (Figure 2d and Table S9).
Thereinto, a yellow-emitting Tb0.40Eu0.10-BTC sample with color
coordinate (0.50, 0.45) is found to have an IQE of ~ 23.1%.
tuned system of Tb0.70-BTC (green), Eu0.60-BTC (red), Tb0.40Eu0.10
-
BTC (yellow) and the lifetime-tuned system of Tb0.70Sm -BTC (z
z
= 0-0.10) are fabricated with some polar solvents to make the
homogeneous and colorless security inks [45, 46]. They can show
intense emissions under UV lamp irradiation (Figure S14). Then
by using the highly-accurate inkjet printing and sophisticated
computer pattern design (Figure 3a), the color-tuned security inks
loaded into cartridges are firstly printed on the filter paper to
emerge the designed patterns. Figure 3b manifests that these
patterns are invisible with daylight while vivid and colorful under
254 nm lamp irradiation, which implies that these inks possess
the decent information storage and security performance in
spatial dimension. As for the blue background in patterns, it
results from the fluorescence of paper that contains the organic
brightener, and surely can be alleviated by using non-fluorescent
papers such as matte Canson paper and parchment paper in
actual applications. [11, 45]
x y
Basically, the color tunability of Tb Eu -BTC samples is
determined by both the efficient sensitization of Tb3+ and Eu3+
emissions by host and cross-relaxation energy transfer (CRET)
from Tb3+ to Eu3+ ions. As shown in Figure S9, the luminescence
decay curves of donor Tb3+ ions gradually drop faster and the
corresponding lifetime values decrease from ~ 588 to ~ 301 μs
with the increase of Eu3+ ions, which confirm the depopulation of
Tb3+ excited states by CRET process from Tb3+ to Eu3+ ions.
3+
Furthermore, it’s well studied that the main mechanism of Tb -
Eu3+ CRET process is electric dipole-dipole (EDD) interaction and
To clarify the information security application of lifetime-tuned
5
(Tb ), 7F0, 1 (Eu ) → 7F
(Eu )] (Figure S10) [38-40]. As for Tb
Sm -BTC (x =
.70, z = 0-0.10) samples, under the host excitation the green
3+
3+
the dominant CRET channel is [ D
4
4
Tb0.70Sm
z
-BTC samples, a 5×7 dots array is printed by using two
security inks denoted as GK1 and GK2, which are made from the
z
Tb0.70Sm -BTC samples (z = 0, 0.3), respectively. As shown in
3+
5
3+
(
Tb ), D
0
x
z
0
emission of ‘sounding’ Tb3+ is dominant while that of ‘silent’ Sm3+
Figure 4a[i], the printed dots display identical green emission
under 254 nm lamp irradiation, making the encrypted information
impossible to extract under steady excitation. But when we
is negligible (Figure 2e), which results from the differential
3+
3+
sensitization effect of host. With the increase of Sm , the Tb
emission intensity regularly decreases and turns to be ~32% of
the Tb0.70-BTC emission when z = 0.10 due to the CRET from Tb3+
to Sm3+ ions, while that of negligible Sm3+ emission slightly
increases, which in total cause that the green color of sample
emission almost remains unchanged as illustrated by the CIE
color coordinates in Figure S11. More importantly, manipulated
via the CRET from Tb3+ to Sm3+ ions, this unchanged green color
emission of samples is nicely endowed with a lifetime tunability in
a range of 300-600 μs (Figure 2f), i.e. ~ 588 (z = 0), ~ 485 (0.03),
~
409 (0.05), and ~ 338 (0.10) μs, which fall in the suitable time
scope for optical multiplexing applications in temporal dimension
[5].
Fundamentally, the Tb -Sm CRET channels include [ D
4
3+
3+
5
3+
6
3+
7
3+
4
3+
[35,
(Tb ), H5/2 (Sm ) → F
6
(Tb ), I9/2, 11/2 (Sm )] (Figure S12)
Considering the high content (~ 0.70) of Tb3+ ions, the statistic
38].
ET models involving the energy migration (EM) between donor
3+
Tb , such as Yokota-Tanimoto (Y-T) model with slow EM (diffuse)
process [41, 42] and Burshteĭn model with fast EM (hopping)
Figure 3. (a) Schematic illustration of pattern encryption in spatial dimension
via pattern design and inkjet printing process with green, red, and yellow
security inks. (b) Photographs of [i-ii] printed ‘L’ as a contrast (black ink) and ‘N’
process [43, 44], are applied to analyze the luminescence decay
curves of donor Tb3+ in concentrated Tb
x
z
Sm -BTC (x = 0.70, z =
(green ink) dot patterns, [iii] Dr. Isaac Newton and his saying ‘If I have seen
3+
3+
0-0.10) samples, to deliver a deeper insight into the Tb -Sm
further than others, it is by standing upon the shoulders of giants.’ (green ink),
[iv] logo of Sun Yat-sen University (red ink), [v] Mr. Sun Yat-sen (yellow ink),
and [vi] rose with butterflies (multiple colors) under daylight or 254 nm lamp
irradiation. The length of bars in part b represents 2 cm.
CRET dynamics. The results show that only the Y-T model can
well fit the decay curves of Tb3+ (Figure 2f) and simultaneously
4
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RESEARCH ARTICLE
Figure 4. (a) Information encryption in lifetime imaging: [i] 5 × 7 dots array printed by using GK1 and GK2 inks under steady 254 nm lamp irradiation. [ii] Lifetime
distributions of printed dot emissions. [iii] Dots array in the view of luminescence lifetime imaging method. (b) Information protection involving misinformation. (c) [i]
z
Schematic illustration of the home-made time-gated microscope. [ii] Time-gated images of Tb0.70Sm -BTC (z = 0-0.10) samples with different delay times. (d) [i]
Printed pattern by using four security inks of GK1-GK4 and its photograph under 254 nm lamp irradiation. [ii] Lifetime distributions of printed bar emissions. [iii]
Demonstration of information protection with high load and four different decryption time stages. The lengths of bars in parts a, b, d, c represent 1, 1, 2 cm and 400
μm, respectively.
measure the luminescence decay curves of these dots (Figure
S15), their extracted lifetime values (Figure 4a[ii]) show two
narrow and discrete distributions located at ~ 588.8 and ~ 486.3
μs with small relative standard deviation (RSD) of ~ 0.21% and ~
above, implying that the blended organic solvents show little effect
on the samples in security inks.
Furthermore, we also focus on the green emission intensity
z
evolution of lifetime-tuned Tb0.70Sm -BTC samples. In general, a
0
.67%, respectively. Further by applying the concept of
shorter luminescence lifetime of the sample leads to a faster
emission fadeout after ceasing excitation. With the help of a
home-made time-gated microscope (Figure 4c[i], see SI for
detailed information) [48, 49], the true-color emission images of
luminescence lifetime imaging method [47], the printed dots with
different lifetimes are then re-rendered in the blue-yellow color
range, which corresponds to 450-600 μs lifetime range (Figure
4a[iii]). Therefore, an encrypted symbol ‘S’ can be clearly read
z
Tb0.70Sm -BTC (z = 0-0.10) samples with different delay times
out. In addition, some misinformation can also be purposely
introduced into the printed patterns to improve the confidentiality.
For example, Figure 4b[i] shows a misleading information of ‘Y’
symbol by adjusting the emission intensity of security inks and the
printing patterns. However, the real encrypted ‘U’ symbol can be
deciphered (Figure 4b[iii]) by investigating the lifetime
distributions of printed dots (Figure 4b[ii], Figure S16) and re-
rendered with the luminescence lifetime imaging method. It
should also be noted that these collected lifetime values of printed
dots in Figure 4a[ii] and 4b[ii] are closed to those of powder
samples from which the printed inks are made as discussed
after excitation are shown in Figure 4c[ii]. The Tb0.70-BTC sample
still exhibits a perceptible green emission with a delay of ~ 200 μs.
With the increase of Sm3+ content, the relative upper delay limits
for emission fadeout of Tb0.70Sm
z
-BTC samples successively get
-BTC
around 50, 100, and 150 μs shorter than that of Tb0.70Sm
0
sample, respectively, as marked by the yellow rectangles.
Consequently, we can utilize this time-driven emission intensity
evolution feature of lifetime-tuned samples to accomplish a
superior information encryption with larger information load and
more available decryption channels. For example, a bars pattern
z
printed by four security inks (GK1-GK4 made from Tb0.70Sm -BTC
5
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
(
z = 0-0.10) samples, respectively.) shows a ‘8888’ blended
systems, but also put forward a new choice of LCPs for optical
multiplexing.
information under 254 nm lamp irradiation (Figure 4d[i]).
Furthermore, the lifetime measurements of bar emissions
demonstrate four narrow and discrete distributions, which
correspond to the lifetime values of four lifetime-tuned samples
Acknowledgements
(Figure 4d[ii]). Inspired by the successive fadeout of sample
emissions in Figure 4c[ii], it is conceivable that this pattern will
exhibit evolutive content due to the different combination of bar
emissions at different delay time. As a demonstration, we
schematize the time-driven evolution of bars pattern with four
main stages (Figure 4d[iii]): stage 1st gives a ‘8888’ information
when the delayed time is quite short; stage 2nd exhibits a ‘A96H’
information when the emission of GK4 ink with shortest lifetime
turns invisible; similarly, stage 3rd and 4th show ‘P3E4’ and ‘F7C1’
information, respectively. It is sure that only when the true
decryption time stage is known one can read out the secret.
Luminescence Stability Analysis. Finally, the luminescence
stability of security inks was investigated. As shown in Figure S17,
the color-tuned inks remain the emission intensities of ~ 89%
The work is financially supported by the National Natural Science
Foundation of China (Grants 21671201, U1632101 and
61905289). We appreciate Dr. Yan Huang in Beijing Synchrotron
Radiation Facility for the assistance in measurement of vacuum
ultraviolet-ultraviolet (VUV-UV) spectra of samples.
Keywords: lanthanide coordination polymer • host differential
sensitization • energy transfer • optical multiplexing
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Entry for the Table of Contents
Based on host differential sensitization concept, the efficient and stable color/lifetime-tuned lanthanide coordination polymers have
been developed as a novel option for stable and high-degree optical multiplexing applications, such as information storage and security
in spatial and temporal domains. These results will further inspire tunable luminescent materials exploration for optical multiplexing.
8
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