Transparent red -emitting silicone resin for color conversion and encapsulation of NUV light-emitting diodes

Article abstract of DOI:10.1111/jace.16140

Herein, a novel transparent phenyl vinyl silicone resin nanocomposite containing exfoliated fluorescent Eu-containing hydrotalcite-like compound (EFHSN) is developed to serve as a dual role of color conversion and encapsulation material. Excited by near-NUV light, the EFHSN emits a strong characteristic red light (614?nm). Meanwhile, the EFHSN shows not only excellent transparency (T?>?95%) in the UV-Vis region and high refractive index (1.46) but also superior thermal stability, which could meet the need of commercial encapsulation materials and optical application. Therefore, the EFHSN is expected to be used in InGaN-based NUV light-emitting diodes and flexible optoelectronic device.

Full text of DOI:10.1111/jace.16140

DR HONG CHEN (Orcid ID : 0000-0002-5799-3520)
Article type
: Article
Transparent Red-emitting Silicone Resin for Color Conversion and
Encapsulation of NUV Light-emitting Diodes
Hong Chen*, Yao Wang, Jianhui Lin, Minmin Shuai, Haidi Zhu, Wengong Zhang, Qidan
Ling*
Fujian Key Laboratory of Polymer Materials, College of Chemistry and Materials
Science, Fujian Normal University, Fuzhou 350007, PR China.
*
Corresponding author: chengh5678@126.com, lingqd@fjnu.edu.cn
Abstract
Herein, a novel transparent phenyl vinyl silicone resin nanocomposite containing exfoliated
fluorescent Eu-containing hydrotalcite-like compound (EFHSN), is developed to serve as a dual
role of color conversion and encapsulation material. Excited by near-NUV light, the EFHSN
emits a strong characteristic red light (614 nm). Meanwhile, the EFHSN shows not only
This article has been accepted for publication and undergone full peer review but has not
been through the copyediting, typesetting, pagination and proofreading process, which may
lead to differences between this version and the Version of Record. Please cite this article as
doi: 10.1111/jace.16140
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excellent transparency (T >95%) in the UV-Vis region and high refractive index (1.46), but also
superior thermal stability, which could meet the need of commercial encapsulation materials and
optical application. Therefore, the EFHSN is expected to be used in InGaN based NUV LEDs
and flexible optoelectronic device.
Keywords: Layered double hydroxides; Light-emitting diodes; Exfoliation; Silicone
Introduction
Light emitting diode (LED) is a new type of luminescent source that has many advantages over
conventional incandescent and halogen lamps in low-power consumption, small volume long lifetime
and reliability [1, 2]. The luminescence of a traditional LED is mostly realized by a InGaN chip coated
with phosphor. Phosphor absorbed and down-convert the blue light from LED chip and emit longer
wavelength light. It is the simplest and most common way. However, this method is facing stability
and luminous strength reduction problems that often limits the application of LEDs. On one hand,
phosphors are directly coated on the chips, causing the device age easily due to the accumulated heat
emitted from the chips. On the other hand, poor compatibility between phosphors and packaging resin
(epoxy or silicone resin) may lead to the aggregation of the phosphors, and high concentration of
phosphors may cause scattering as a result [3, 4]. Thus, to meet the fast-developing LED requirements,
it is inperative to develop a new practical alternative to the phosphor-converted LEDs.
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Lanthanide β-diketonate complexes are desirable materials owing to their narrow band emission
spectra, high quantum efficiency and long luminescence lifetimes. However, they have so far been
excluded from practical applications as LED devices due to their poor photo and thermal stability, and
mechanical properties. In our previous work [5], we incorporated
Eu(III)-thenoyltrifluoroacetone-1,10-phenanthroline complex [Eu(TTA) phen] into Hydrotalcite-like
3
compounds (HTlc) and synthesized red light-emitting Eu-containing hydrotalcite-like compound
(Eu-HTlc), in which aluminum (III) was partially substituted by Europium (III) in the hydrotalcite-like
layers, and thenoyltrifluoroacetone, 1,10-phenanthroline were dispersed into the anions in the
interlayer region. Research shows that the Eu-HTlc possess excellent photoluminescent property and
thermal stability.
Hydrotalcite-like compounds (HTlc), also called layered double hydroxides (LDH) [6] are a large
family of inorganic lamellar materials which are constructed by positively charged brucite-like layers
together with exchangeable charge-balancing anions and water in interlayer regions. HTlc have
received wide attention on account of plenty of advantages such as exchangeable layer metals and
interlayer anions, which can be beneficial for various applications such as catalysts, energy storage,
electrochemistry, magnetization, and biomedicalscience, etc [7-11]. Recently, exfoliation of HTlc into
single-layer nanosheets with ultimate two-dimensional anisotropy has drawn much interest due to this
novel materials has drastically improved surface activity, unusual physicochemical properties,
quantum effects and versatility in compositions [12-15].
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In a typical LED package, epoxys or silicone resins are usually applied on top of the LED chip to
provide the mechanical and chemical protection [16-18]. Silicone resins could be a good choice due to
their excellent integrated properties, including high transparency, flexibility, moisture resistance,
tunable harness, and stable thermo-mechanical property [19].
Inspired by these information, in this work, we first designed and synthesized a novel luminescent
silicone resin serving as a color conversion and encapsulation material simultaneously for the
construction of InGaN based near-UV LEDs. Exfoliated fluorescent hydrotalcite-like compound was
chosen as a fluorescent 2D component to be incorporated into a phenyl vinyl silicone resin (PVS) to
prepare a transparent fluorescent silicone resin (EFHSN) nanocomposite (Scheme 1). The uniform and
homogeneous distribution of HTlc nanosheets in polymer matrix could overcome the main drawback
of incompatibility between luminescent materials and packaging materials, while simultaneously
preventing aggregation of the luminescent materials. In addition, the versatile nature of this system
enables to improve the transparency and the thermal stability of the final nanocomposite.
Experimental
Materials and reagents
Phenyltrimethoxysilane (PhSi(OMe) ) and 1,3-divinyltetramethyldisiloxane
3
(
Me Vi Si O) were provided by Qufu Chenguang Chemical Co., Ltd, China.
4 2 2
3
-aminopropyltriethoxysilane (KH-550) was purchased from Aladdin. Eu O (mass
2 3
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ratio 99.99%) was commercially obtained from Shanghai Yuelong Coloured metal Co.,
Ltd; Thenoyltrifluoroacetone (HTTA) was of A. R. grade from Fluka chemical reagent
company; 1,10-phenanthroline (o-phen) purchased from Sinopharm Chemical Reagent
Co., Ltd was of A. R. grade. All other reagents were of analytical grade. All chemicals
were used without further purification.
Synthesis of phenyl vinyl silicone resin (PVS)
The vinyl end-capped phenyl silicone resin (PVS) was prepared by
hydrolysis-polycondensation method from Phenyltrimethoxysilane (PhSi(OMe) ) and
3
1
,3-divinyltetramethyldisiloxane (Me Vi Si O) in ethanol/methylbenzene mixture
4 2 2
catalyzed by trifluoromethanesulfonic acid (Scheme 1).
3.6mL deionized water, 0.43mL ethanol and 4.8mL methylbenzene were added to a
o
three-necked, round-bottomed flask and the temperature was held constant at 40 C. A
certain quantity of PhSi(OMe) was slowly drop-wised into the flask with vigorous
3
agitation within 30 minutes and then trifluoromethanesulfonic acid in an amount of 0.5
mol% to the total precursors used as a catalyst was dropped into the system followed by
o
refluxing and stirring for 3 h, and subsequent refulxing for 5 hours at 75 C, then
quantified Me Vi Si O was added as an end-blocking agent. After the 1 h reaction,
4
2
2
NaHCO was added to neutralize the acid catalyst and resulting salt was removed by
3
filtration. The byproduct was removed by vacuum heating.
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Synthesis of exfoliated KH-550-Eu(TTA) Phen-HTlc/PVS silicone nanocomposite
3
Exfoliated KH-550-Eu(TTA) Phen-HTlc/PVS silicone nanocomposite (EFHSN)
3
was synthesized by hydrolysis and condensation processes under stirring by a magnetic
bar. The reaction process is divided into five steps as follow.
A. Synthesis of silicone intermediate (SI)
SI was synthesized by the hydrolysis of PhSi(OMe) . 3.6mL deionized water, 0.43mL
3
ethanol and 4.8mL methylbenzene were added to a three-necked, round-bottomed flask
o
and the temperature was held constant at 40 C. A certain quantity of PhSi(OMe) was
3
slowly drop-wised into the flask with vigorous agitation within 30 minutes and then
trifluoromethanesulfonic acid in an amount of 0.5 mol % to the total precursors used as
a catalyst was dropped into the system followed by refluxing and stirring for 3 h, and
transparent silicon intermediate with silanol group (PhSi(OH) , SI) was obtained.
3
B. Synthesis of Eu-HTlc
The process of synthesis of Eu-HTlc was similar to that described in our previous
work[4]. Typically, 0.34g (0.0015mol) HTTA and 0.1g (0.0005mol) o-phen, were
dissolved independently in the least quantity of absolute ethanol. The ethanolic
solutions of HTTA and phen were added into 15.4g aqueous solution of sodium stearate
(
5% mass ratio), it was solution A. 0.09g (0.0005mol) of Eu O was dissolved in
2 3
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hydrochloric acid solution of 2.5% (mass fraction) and mixed with 2.9g aqueous
solution of MgCl (20% mass ratio), it was solution B. 0.8g aqueous solution of
2
NaAlO /NaOH, (NaAlO : 20%, NaOH: 10% mass ratio) was solution C. Slowly
2
2
drop-wised the solution B and the solution C into the solution A at the same time. The
o
pH was adjusted to 10 using NaOH. The resulting white precipitate was aged at 80 C for
12h. After the aging step, the obtained precipitate was separated by centrifugation,
o
washed extensively with distilled water until pH=7, dried at 100 C for 5h and
abbreviated here as Eu-HTlc.
C. Surface Modification of Eu-HTlc (KH-550-Eu-HTlc)
The as-synthesized Eu-HTlc was surface-treated with KH-550 by 1 wt.%
concentration. The mixture was refluxed at 80 °C for 6 h. After that, the products were
centrifuged and rinsed with ethanol, followed by drying at 80°C.
D. Synthesis of exfoliated KH-550-Eu-HTlc
0.5 g of KH-550-Eu-HTlc was shaken in a certain quantity of as-synthesized SI by
high-power ultrasonic treatment for 15 minutes to produce a colloidal suspension of
exfoliated KH-550-Eu-HTlc nanosheets. To remove the unexfoliated particles, the
resulting translucent colloidal suspension was further treated by centrifugation at 6000
rpm for 4 min. After that, the rest of colloidal suspension was transparent and stable.
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E. Preparation of exfoliated KH-550-Eu-HTlc/silicone nanocomposite
At last, the obtained exfoliated KH-550-Eu-HTlc/SI was transferred into another
three-necked, round-bottomed flask. After stirring reaction solution and refulxing for 5
o
hours at 75 C, then quantified Me Vi Si O was added as an end-blocking agent. After
4
2
2
the 1 h reaction, NaHCO was added to neutralize the acid catalyst and resulting salt was
3
removed by filtration. The byproduct was removed by vacuum heating.
For comparison purpose, MgAl-LDH was also prepared by using the same way as
Eu-HTlc. Solution A was 15ml distilled water, solution B was 2.9 g aqueous solution of
MgCl (20% mass ratio), and solution C was 0.8g aqueous solution of NaAlO /NaOH,
2
2
(
NaAlO : 20%, NaOH: 10% mass ratio).
2
Characterization methods
The infrared spectra (FT-IR) of the samples were obtained with Thermo`s Nicolet 5700 using KBr
disc method. X-ray powder diffraction patterns (XRD) were collected within the range of 3°-80°(2θ)
on a PANalytical B.V. X`’Pert Powder diffractometer equipped with a Cu Kα radiation source (λ =
0.15406 nm). Scanning electron microscopy (SEM) was performed with a JSM-7500F at 30 kV,
10.0μA. The thermogravimetry study (TG) performed on a NETZSCH DIL 402C thermal analyzer at
o
a heating rate of 10 C/min under Ar atmosphere. Emission, excitation spectra and decay curves of
samples were recorded at room temperature on an Edinburgh CompanyFLS920 spectrofluoremeter at
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room temperature. External QY is defined as the ratio of the emitted photons to the absorbed photons,
and was measured by a standard Edinburgh Instruments FLS920 spectrometer equipped with an
Edinburgh instruments integrating sphere. The HASS-2000 instrument (Everfine, China) was utilized
to characterize optical properties of the LED device under a forward current of 20 mA. The refractive
index of the samples was measured by an Abbe's Refractometer WYA/2WAJ (Shengguang, China).
Results and discussion
The EFHSN nanocomposite was synthesized according to the procedures presented in Scheme 1
and Scheme 2. Firstly, the reaction was carried out to form a silicon intermediate with silanol group
(
SI) from the methoxy group of monomer PhSi(OMe) . Secondly, the Eu-HTlc was prepared
3
according to our previous work [5]. In addition, surface modification was carried out using silane
coupling agent (3-aminopropyltriethoxysilane, KH-550) to improve the dispersion of Eu-HTlc in SI.
Thirdly, exfoliated KH550-Eu-HTlc was prepared using just SI as the processing solvent through
ultrasound. Finally, the resulting transparent SI colloidal suspension containing Eu-HTlc nanosheets
was further carried out the polycondensation and end-blocking reactions.
Fig. 1 shows the photoluminescent emission (PL) and the photoluminescent excitation (PLE)
spectra of the EFHSNs containing different amounts of KH550-Eu-HTlc. When excited at 392 nm, all
samples exhibit fluorescence emission peaks located at 595 nm, 613 nm, and 653 nm, revealing the
5
7
5
7
5
7
well-known bands of europium red luminescence based on D → F , D → F , and D → F ,
0
1
0
2
0
3
respectively, similar to the case of the KH-550-Eu(TTA) Phen-HTlc powder [5]. The PLE spectra of
3
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the EFHSNs were monitored at around 390 nm and closely matched the emission of an InGaN
near-UV-LED chip. It can be seen that the sample exhibits bright red color when under 365 nm UV
illumination. Obviously, the intensity of the emission and excitation bands depended on the
KH550-Eu-HTlc amount. The stronger peaks were found with the larger amounts of KH550-Eu-HTlc,
simply because more KH550-Eu-HTlc participate in the emission and excitation process.
The lifetimes of EFHSNs with various doping concentrations were measured. Fig. 2(a) and Table 1
show the excited fluorescent decay and their fitting results. It can be noted that the average lifetimes
gradually increase from 498.34 μs to 603.59 μs with increasing the KH550-Eu-HTlc amount from
0.3% to 0.5%. Photoluminescence quantum yield (QY) is the number of photons emitted per absorbed
photon [20]. In an attempt to investigate the absorption of the EFHSN at 392 nm, we have carried out
external quantum yield (QY) measurements as a function of doping concentrations, also listed in Table
1. It is clearly seen that the QY increased considerably with increasing KH550-Eu-HTlc
concentration. The QY value of the EFHSN (0.5%) was measured to be about 76%, which is much
higher than the reported values in commercial YVO : Eu (QY=38%) [21] and Gd MoO : Eu
4
2
6
(QY=38%) [22]. It indicates that the red-emitting EFHSN could be considered to act as red component
in the fabrication of near-NUV WLEDs.
The thermal decomposition behavior of the neat PVS and the EFHSN (0.5%) was monitored by a
TG analysis as shown in Fig. 2(b). Note that the 5wt% decomposition temperature of the EFHSN
nanocomposite at 540°C is much higher than that of the neat PVS at 254°C, this is believed to be
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attributed to the existence of thermallystable HTlc nanosheets. The HTlc nanosheets have a significant
barrier effect that can slow down product volatilization and thermal transport during PVS
decomposition, and this effect enhances the thermal stability of the EFHSN nanocomposite [23], thus
the EFHSN meets the usage demand of LED.
The temperature-dependence PL intensity is an essential property for high power LED application.
A set of PL spectra at different temperatures heating from 25 to 175 °C with a step of 25 °C are shown
in Fig.3. When the temperature increasing from 25 °C to 150 °C, its PL intensity keeps approximately
52%, which demonstrating that the EFHSN (0.5%) has good thermal stability.
The transmission spectrum and photograph in Fig. 4 (a) and (b) clearly reveals that the EFHSN
(
0.5%) have high optical transmittance (T > 95%) in the UV-Vis region (300-800 nm), which can be
attributed to the surface modification that improves the dispersion of exfoliated HTlc nanosheets in the
silicone matrix. Because of the difference of refractive indexes between the LED chip (n ≈ 2.4 for GaN
LED) and air (n ≈ 1.0), high refractive index is critical characteristic for the LED encapsulation
materials [24]. It can effectively reduce the reflection, so that light can be successfully refracted
through the encapsulation material, herebyenhancingthe light extraction efficiency [25]. In this work,
refractive index value of the EFHSN (0.5%) was measured to be 1.46, which also could satisfy the
commercial need of LEDs. The colloidal suspension of exfoliated HTlc nanosheets in the
EFHSN was confirmed by the Tyndall phenomenon, where a discernible track is observed
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when a laser beam passes through a colloidal solution as a result of light scattering (as shown in
Fig. 3(c), the wavelength of laser beam is 650 nm).
The FT-IR spectra of the neat PVS and the EFHSN (0.5%) are shown in Fig. 5. Both samples
-1
-1
displayed the strong peaks at around 1134 cm and 1060 cm , which are the typical peaks of
-1
asymmetric stretching ofSi-O-Si groups [26]. The EFHSN exhibitedthe new peaks at about 3423 cm
belongs to the characteristic stretching vibrations of hydroxyl groups in the brucite-like layer and
-1
physisorbed water. The peak vibration of C-H at 803 cm , indicating that o-phen has coordinated with
3+
-1
the Eu [27]. The absorption peak at about 1593 cm which is due to the carbonyl group in TTA,
-1
meanwhile the absorption peaks due to the stretching vibration of Eu-O appeared at about 590 cm ,
3+
which demonstrates the coordination of HTTA with Eu [28]. All these new peaks detected in FT-IR
spectrum of EFHSN demonstrated that exfoliated Eu-HTlc had been successfully introduced into the
PVS matrix.
The XRD patterns of MgAl-LDH, KH550-Eu-HTlc, and EFHSN (0.5%) are shown in Fig. 6. It
can be seen that the diffraction peaks of MgAl-LDH are typical of the layered compounds [6] with
sharp and symmetric reflections, indexed to a hexagonal unit cell with R-3m rhombohedral symmetry.
The peaks corresponding to the 003, 006, and 009 reflections are attributed to the characteristic
reflection of the LDH structure with a series of (00l) peaks [29]. In KH550-Eu-HTlc, the intercalation
of the mixed ligands (HTTA and o-phen) into the LDH was clearly evidenced by the net increase of
the interlayer distance (the 003 basal peak shifted to lower angle), from 0.78 nm (2θ=11°) for
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MgAl-LDH to 1.57 nm (2θ=5.5°) for KH550-Eu-HTlc, according to the Bragg equation. The 00l
series peaks of LDH disappeared in the XRD pattern of the EFHSN, and the low intensity and broad
peaks shows amorphous nature, suggesting the possible exfoliation of the KH550-Eu-HTlc. The
exfoliation was further confirmed bythe Tyndall effect observed upon irradiation of the EFHSN with a
laser beam (Fig. 3c). A clear Tyndall light scattering effect was observed, which confirmed the
colloidal nature of the solution [29].
In order to investigate the possibility of the as-synthesized EFHSN nanocomposite in application
for near-NUV LED, a red-LED device was fabricated by using a 384 nm emitting InGaN chip. The
basic packaging elements of a conventional phosphor-based LED include the chip, phosphor,
encapsulation material, substrate, and lens [30]. In this work, EFHSN (0.5%) nanocomposite was act a
dual role of luminescence and encapsulation material in the red-LEDs without any addition of
phosphor and encapsulation resin, as depicted in Scheme 3.
The electroluminescence emission spectrum of the fabricated EFHSN nanocomposite based LED
(red-LED) was measured at an operating current of 350 mA. Several emission peaks are observed in
Fig. 7. The first one comes from the InGaN chip and the others are from the prepared red-LED,
indicating that the near-UV light around 390 nm emitting from the chip was absorbed by the EFHSN,
and simultaneously down-converted into a red light. The CIE 1931 chromaticity coordinate of the
red-LED (inset) is at (0.6154, 0.3228). The yielded luminescence from the red-LED device is very
bright, as demonstrated in the inset of Fig. 7.
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Furthermore, a WLED device was also fabricated by using InGaN chip (390nm) coated with
2+
3+
BaMgAl O :Eu blue-emitting phosphor, CeMgAl O :Tb green-emitting phosphor. The
10
17
11 19
EFHSN (0.5%) was used as red-emitting encapsulation material. Fig. 8 shows the electroluminescence
emission spectrum the fabricated WLED device (350 mA). Bright white light was observed, and the
CIE chromaticity coordinates CCT, CRI, and luminous efficiencywere measured to be (0.301, 0.308),
7493 K, 81.8, and 30.35 lm/W, respectively.
In our previous work [31], we have produced white light-emitting single-matrix material by
incorporation of Eu, Tb, and Zn complexes into layered double hydroxides, which is similar to
Eu-HTlc and can be used in the preparation of white light-emitting hydrotalcite/silicone
nanocomposite. The further studies are currently underway.
Conclusions
In summary, we have demonstrated the preparation of the EFHSN nanocomposite via hydrolysis,
exfoliation and polycondensation methods that could make fluorescent Eu-containing hydrotalcite-like
compound exfoliate and homogeneously disperse in silicon resin matrix. The obtained EFHSN is
suitable to be excited by NUV-chips and exhibits red light. In addition, the EFHSN possess high
transmission (>95% at 300-800 nm), high refractive index (1.46), and good thermal stability, which
were crucial factors for optical application. A red and a white LED devices were successfully
fabricated by using the EFHSN as color conversion and encapsulation material. The results indicate
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that the EFHSN can be applied in the white light-emitting diodes and flexible optoelectronic devices in
the future.
Acknowledgments
The authors would like to acknowledge the financial support from the National Natural
Science Foundation of China (21574021), Natural Science Foundation of Fujian Province
(2016J01212) and State Key Laboratoryof Comprehensive Utilization of Low-Grade RefractoryGold
Ores (Zijin Mining Group Co., Ltd.).
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Table Captions
Table 1. Biexponential fit values and absolute QY of EFHSNs
Figure Captions
Scheme 1. Schematic illustration of the processes involved in the synthesis of the EFHSN
Scheme 2. The synthesis of PVS
Scheme 3. Simplified model for a conventional phosphor-based LED package (a) and a red-LED
encapsulated by EFHSN nanocomposite (b)
Fig. 1. The emission spectra (a), excitation spectra (b) of EFHSNs containing 0.5, 0.45,
0.4, 0.35 and 0.3 wt. % of KH550-Eu-HTlc, and optical image of the EFHSN (0.5%) under 365 nm
UV illumination (insert).
Fig. 2. (a) Fluorescence decay curves for EFHSNs with various dopant concentrations; (b) TG curves
of neat PVS and the EFHSN (0.5%)
Fig. 3. 3D plots of the temperature-dependent PLspectra taken in the temperature range from 25to 175
°C with a step of 25°C for EFHSN (0.5%)
Fig. 4 (a) Transmission spectrum of EFHSN (0.5%) in the UV-Vis region; (b) Optical image of
EFHSN under visible light; (c) the Tyndall phenomenon of EFHSN
Fig. 5. FT-IR spectra of the neat PVS (a) and EFHSN (0.5%) (b)
Fig. 6. XRD patterns of MgAl-LDH, KH550-Eu-HTlc, and EFHSN (0.5%)
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Fig. 7. The emission spectrum of red-LED at IF=350 mA (Optical image and CIE chromaticity
coordinates of the red-LED device were shown in the inset)
Fig. 8. EL spectrum of the fabricated WLED lamp with 390 nm near-UV LED chip and blue-emitting
phosphors, green-emitting phosphors, and EFHSN nanocomposite driven by 350 mA current
Table 1. Biexponential fit values and absolute QY of EFHSNs
EFHSN λex/nm λ /nm
α1/%
τ1/μs
α2/%
τ2/μs
τ /μs
av
QY/%
em
0
0
0
0
0
.5%
392
392
392
392
392
614
614
614
614
614
100.00 603.59
100.00 591.09
603.59
76.2
64.0
12.6
7.98
5.57
.45%
.4%
591.09
547.49
522.71
498.34
9.33
5.75
9.15
269.92 90.67 576.05
171.06 94.25 544.16
197.13 90.85 528.68
.35%
.3%
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This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.

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