Synthesis and characterization of luminescent SiO2@Eu(phen–Si) core–shell nanospheres

Article abstract of DOI:10.1002/bio.3721

Four core–shell structured nanometre luminescent composites with different kernel sizes and different shell layer thicknesses (SiO₂₍₅₀₀₎@Eu (phen–Si)₍₅₀₎, SiO₂₍₅₀₀₎@Eu (phen–Si)₍₁₅₎, SiO₂₍₂₅₀₎@Eu (phen–Si)₍₅₎ and SiO₂₍₂₅₀₎@Eu (phen–Si)₍₁₀₎) were made by changing synthesis conditions. Here, initial subscript numbers in parentheses refer to the particle size of the SiO₂ core, whereas the final subscript numbers in parentheses refer to shell layer thickness. In these composites, silica spheres of 500?nm or 250?nm were identified as the core. The shell layer was composited of silicon, 1,10-phenanthroline and europium perchlorate, abbreviated as Eu(phen–Si); the chemical formula of phen–Si was phen-N-(CONH (CH₂)Si(OCH₂CH₃)₃)₂. The composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and infrared spectroscopy. The monodispersed spherical SiO₂ showed characteristics of a regular microstructure and a smooth surface, as well as the advantage of dispersity, shown by SEM. The Eu(phen–Si) complex was able to self-assemble into monodispersed SiO₂ spheres, as seen using TEM. Fluorescence spectra indicated that the four composites had excellent luminescence properties. Furthermore, composites composed of a SiO₂ core and a 250?nm kernel size exhibited stronger fluorescence than 500?nm kernel-sized composites. Fluorescence properties were affected by shell thickness: the thicker the shell, the greater the fluorescence intensity. For the four composites, quantum yield values and fluorescence lifetime corresponded to fluorescence emission intensity data as quantum yield values and fluorescence lifetime were higher, and luminescence properties increased.

Full text of DOI:10.1002/bio.3721

Received: 7 November 2016
DOI: 10.1002/bio.3721
Revised: 17 April 2018
Accepted: 22 September 2019
R E S E A R C H A R T I C L E
Synthesis and characterization of luminescent SiO @Eu(phen–
2
Si) core–shell nanospheres
1
2
2
1
1
|
|
|
|
|
Wen‐Xian Li
Yu‐Shan Zheng
Hong‐Bo Zhang
Jin‐Rong Bao
Yi‐Lian Li
1
1
1
|
|
Yang‐Yang Ma
Li‐Na Feng
Shu‐Yan Feng
1
College of Chemistry and Chemical
Engineering, Inner Mongolia University,
Hohhot, People's Republic of China
Abstract
Four core–shell structured nanometre luminescent composites with different kernel
sizes and different shell layer thicknesses (SiO2(500)@Eu (phen–Si)(50), SiO2(500)@Eu
(phen–Si)(15), SiO2(250)@Eu (phen–Si)(5) and SiO2(250)@Eu (phen–Si)(10)) were made
by changing synthesis conditions. Here, initial subscript numbers in parentheses refer
2
Inner Mongolia Autonomous Region Food
Inspection Testing Center, Hohhot, People's
Republic of China
Correspondence
Wen‐Xian Li, College of Chemistry and
Chemical Engineering, Inner Mongolia
University, Hohhot 010021, People's Republic
of China.
2
to the particle size of the SiO core, whereas the final subscript numbers in parenthe-
ses refer to shell layer thickness. In these composites, silica spheres of 500 nm or
250 nm were identified as the core. The shell layer was composited of silicon, 1,10‐
phenanthroline and europium perchlorate, abbreviated as Eu(phen–Si); the chemical
Email: nmglwx@163.com
Funding information
formula of phen–Si was phen‐N‐(CONH (CH
characterized by scanning electron microscopy (SEM), transmission electron micros-
copy (TEM), and infrared spectroscopy. The monodispersed spherical SiO showed
2 2 3 3 2
)Si(OCH CH ) ) . The composites were
Major projects of Natural Science Foundations
of Inner Mongolia Science Foundation, Grant/
Award Number: 2015ZD01; Natural Science
Foundations of Inner Mongolia Science Foun-
dation, Grant/Award Number: 2015MS0502
2
characteristics of a regular microstructure and a smooth surface, as well as the advan-
tage of dispersity, shown by SEM. The Eu(phen–Si) complex was able to self‐
2
assemble into monodispersed SiO spheres, as seen using TEM.
Fluorescence spectra indicated that the four composites had excellent luminescence
properties. Furthermore, composites composed of a SiO core and a 250 nm kernel
2
size exhibited stronger fluorescence than 500 nm kernel‐sized composites. Fluores-
cence properties were affected by shell thickness: the thicker the shell, the greater
the fluorescence intensity. For the four composites, quantum yield values and fluo-
rescence lifetime corresponded to fluorescence emission intensity data as quantum
yield values and fluorescence lifetime were higher, and luminescence properties
increased.
KEYWORDS
2
europium perchlorate complex shell, fluorescence, fluorescence life time, quantum yieldSiO core
1
|
INTRODUCTION
affinity contribute to the form in which a nanometre material is cov-
ered with another nanometre material. Nanometre composites pro-
duce a higher standard of structural material. Difference between
core–shell nanometre composites and single compounds are due to
Core–shell nanometre composites are a new style of structural mate-
rial that can be assembled stably. Chemical bonds or other types of
Abbreviations used: IR, Infrared; SEM, Scanning electron microscopy; TEM, Transmission electron microscopy; TEOS, Tetraethyl orthosilicate; TEPIC, 3‐(Triethoxysilyl)‐propyl isocyanate
Luminescence. 2019;1–10. wileyonlinelibrary.com/journal/bio © 2019 John Wiley & Sons, Ltd.
1

2
LI ET AL.
[
1–6]
the novel attributes of the composite, as described previously.
was selected as the core, and a rare earth organic complex was chosen
to be the shell, which were combined with a silane coupling agent.
Core–shell nanometre materials can be widely applied as functional
fluorescent materials, magnetic materials, and in electronics, medicine,
Core–shell materials incorporate chemical bonds between the SiO
2
[7–12]
[34–37]
and biological applications.
Chemical and optical characteristics in
core and the coating material.
By using the silane coupling
nanometre particles can be enhanced by covering these with a layer of
another material, by altering features of the coating layer such as
structure, thickness, size, or by composition. Some studies have
described lower toxicity, larger efficient Stokes’ conversion, intense
release bands, and photochemical decrease for nanometre particles.
method, the performance the material remained unaltered and chem-
ical bonds were stable, in addition the material was difficult to manip-
ulate. The rare earth organic complex was applied as a coating layer at
nanometre scale thickness, therefore the amount of rare earth organic
complex was able to be decreased, consequently decreasing the cost
of materials. The rare earth complex was able to be compatibly
2
The structure of a SiO core and a shell, to some extent, contributes
to improvements in luminescent materials. Some studies have
reported changes in the advantageous attributes of luminescence
intensity, efficient fluorescence quantum yield, and fluorescence life-
time found with the nanometre core–shell structure. In addition,
changes in these features were due to the coordinating influence of
the multi‐element complex, not just because of simplified coordinated
behaviour. It is important to establish new approaches to improve the
2
repaired by the SiO core and the improvement in luminous efficiency
was significant when comparing hybrid materials. Conversely, the
structure of the core–shell, which is almost equivalent in size to the
SiO
performance.
In the current study, a chemical with formula phen‐N‐(CONH(CH
Si(OCH CH , abbreviated to phen–Si, was used as the silane cou-
2
core, including the cladding layer thickness, affected fluorescence
2
)
2
3 3 2
) )
design of the core–shell structure. SiO
2
is considered one of the most
pling agent. The double nitrogen atoms of phen–Si groups are able
to assemble easily with rare earth europium ions. Si–O–Si bonds
undergo hydrolysis involving a chemical reaction between three eth-
important and extensive core materials and is used world‐wide due to
its unique features such as formation of spherical monodispersed par-
ticles, simple manipulation of particle size, low cost, and security, as
well as lower toxicity compared with other core materials. Some stud-
oxy groups in phen–Si and hydroxyl groups found in SiO
2
core
spheres. Consequently, rare earth Eu ions and the SiO core can be
2
ies have shown that when SiO
2
is used as a core material, extremely
combined by a ‘molecular bridge’ determined by phen–Si, and primar-
ily used to boost the attributes of the compound material. Very few
studies have focused on rare earth organic materials combined with
strong affinity is always found between Si–OH groups and exterior
hydrogen bonds on the surface. In addition, a few studies have
described that the materials that are joined by chemical bonds and
electrostatic interactions are formed easily. Crucial advanced features
2 2
a SiO core and shell (to give SiO @RE(phen–Si)). The molecular
bridge improved luminescence properties such as brightness and
intensity. In addition, due to the reduced thickness of the shell, con-
sumption, and cost of the rare earth was much less, making it
favourable for use.
such as the size and morphology of SiO
2
composites are manipulated
easily, a vital study area for nanometre materials. Research into SiO
2
and its use as a core material has increased widely and significantly
in recent years, incorporating rare earth inorganic materials as the
coating layer, but very few rare earth organic complexes have been
In the present study, four nanometre luminescent complexes with
core–shell structures of different kernel sizes and shell layer thick-
nesses (SiO2(500)@Eu(phen–Si)(50), SiO2(500)@Eu(phen–Si)(15), SiO2(250)
@Eu(phen–Si)(5) and SiO2(250)@Eu(phen–Si)(20))) were made by chang-
ing the synthesis conditions (that is using 500 nm or 250 nm silica
spheres as the core, and the phen–Si–Eu(III) complex as the shell layer
(abbreviated to Eu(phen–Si)). Preparation of the nanometre lumines-
cence composites is described.
[13–27]
used and applied as coating layers.
Two crucial technologies have been applied to prepare the core–
shell material. One technology is direct deposition, however perfor-
mance of the core–shell material was limited when using this technol-
ogy, as the material was not stable to ultrasound. The other
technology is silane coupling. Silane coupling agents are organic mate-
rials with two functions. Their formula is defined as Y(CH
2
)
n 3
SiX when
[24–28]
used in the preparation of hybrid materials
, where Y is organic
2
|
MATERIALS AND METHODS
Materials
functional groups such as amino, carboxyl, or double nitrogen, and X
is an alkoxy group. This chemical formula ensures that the Y group
can be assembled easily with rare earth ions. Some research has indi-
cated that the chemical bonds for Si–O–Si could be hydrolyzed, refer-
ring to the chemical reaction between the X group and hydroxyl
2.1
|
Purity of chemicals used in the present study, such as Eu
exceeded 99.99%. To make europium perchlorate (abbreviated to Eu
(III) perchlorate) the relevant oxide from perchloric acid (HClO
2 3
O ,
2
groups in SiO . Therefore rare earth ions could be combined with
SiO using a silane coupling agent, a process defined as a ‘molecular
2
4
)
bridge’, to produce an inorganic–organic hybrid material. Vibrations
in the bonds have been found with this type of hybrid material. How-
ever, energy loss was markedly decreased and luminous efficiency of
the rare earth ions was enhanced, as shown in the study by Yan Bing
(1 mol/L) was used. 1,10‐Phenanthroline was used as the starting
material without further purification. Tetraethoxysilane (TEOS,
Aldrich), 5% Pd/C (Aldrich) and 3‐(triethoxysilyl)‐propyl isocyanate
(96%, TEPIC, Aldrich) were applied as received. Hydrazine
[
28–33]
and Zhang Hong Jie.
The present study focused on the compo-
sphere
monohydrate, H
2 2 2 4 3
O (30%), hexane, concentrated H SO and HNO
sition and synthesis of core–shell structural materials. The SiO
2
and other chemicals were of analytical analysis grade.

LI ET AL.
3
2
.2
|
Physical measurements
500 nm values were found using the average diameter for SiO
2
and
confirmed by SEM.
−
1
Infrared spectra (IR, v = 400–4000 cm ) were prepared according to
the KBr pressed disc method using a spectrophotometer, assembled
1
as a Nicolet NEXUS‐670 FT‐IR spectrometer. HNMR spectra were
|
2
.4.2
SiO cores were grafted by phen–Si
2
6
prepared using DMSO‐d and a Bruker AC‐500 nuclear magnetic res-
onance spectrophotometer. Emission spectra and fluorescence excita-
tion were confirmed using a FLS920 fluorescence photometer with a
For the grafting process, as described previously, chemical bonds in
Si–O–Si can be hydrolyzed through three ethoxy groups in phen–Si
1
‐nm slit width. Fluorescence decay curves were determined using a
2 2
and hydroxyl groups on the SiO core surface. The SiO core was
FLS920 Combined Steady State and Lifetime spectrometer. Micro-
structure was confirmed using SEM and TEM on Hitachi S‐4800 and
FEI Tecnai F20 instruments, respectively.
coated by phen–Si through this interaction. Double nitrogen atoms
in phen–Si can interact with rare earth ions. Different modification
conditions were used for grafted composites such that different shell
thickness were obtained. The details are as follows.
For phen–Si:SiO
Si was dissolved in 5 ml anhydrous alcohol; 0.1 g SiO
500 nm or 250 nm) were dissolved in a mixture composed of anhy-
2
:ethanol volume = 0.1 g:0.1 g:10 ml, 0.1 g phen–
microspheres
2
.3
|
Synthesis of the ligand phen–Si
2
(
The synthesis of phen–Si is shown in Scheme 1. The phen–Si ligand
drous alcohol and distilled water, respectively. Both solutions (5 ml)
were dispersed for about 10 min using ultrasound. The pH was
adjusted using ammonia. Then, the phen–Si anhydrous alcohol solu-
[
38]
was synthesized using published techniques
The solid was purified through recrystallization from alcohol. Element
values were: yield: 40%. mp: 46–48°C. Anal. calcd. for C32 Si
M = 689 g/mol): C, 56.23%; H, 7.31%; N, 10.21%, found: C, 55.73%;
and was a white solid.
H N
51 5
O
8
2
2
tion was added dropwise to the activated SiO microspheres solution.
(
The mixture was stirred for 2 h at room temperature, and then sepa-
rated by centrifugation at 5000 rpm. The resulting white precipitate
was washed several times with water and anhydrous ethanol until
the washing liquid was clear. Drying at 40°C was commenced. Two
1
H, 7.43%; N, 10.16%. HNMR: δ0.45 ppm (2H, –CH
2H, –CH –), δ3.06 ppm (2H, –CH –), δ3.70 ppm (12H,–CH
δ1.12 ppm (18H, –CH ), δ7.8 ppm (2H, –NH–).
2
–), δ1.43 ppm
(
2
2
2
–),
3
grafted SiO
phen–Si)(50) and SiO2(250)@Eu (phen–Si)(10)) were then obtained.
For phen–Si:SiO :ethanol volume = 1 g:1 g:10 ml, using the previ-
ous method. Two grafted SiO microspheres of different shell layer
2
cores of different shell layer thickness (SiO2(500)@Eu
(
2
.4
|
Synthesis of the SiO @Eu(phen–Si) core–shell
2
2
structure nanometre luminescent composites
2
thickness (SiO2(500)@Eu (phen–Si)(15) and SiO2(250)@Eu (phen–Si)(5)
)
2
.4.1
|
Synthesis of monodispersed spherical SiO2
were obtained.
Cores were identified to be monodispersed spherical SiO
2
formed
Information inTable 1 is focused on the moderate
dosage of anhydrous ethanol, water, ammonia solution, and TEOS.
SiO microspheres of different sizes were formed; 250 nm and
[
39]
based on Stöber.
2
.4.3
|
Self‐assembly of the europium perchlorate
organic core–shell structure nanometre luminescent
2
composite (SiO @Eu(phen–Si))
2
Europium ions were self‐assembled with the SiO
molecular bridge determined by phen–Si. Double nitrogen atoms of
phen–Si groups on the grafted SiO microspheres shell interact with
Eu ions. Therefore, the SiO core was coated with the Eu(III) perchlo-
rate phen–Si complex through chemical bonds. Four kinds of modified
2
cores through a
2
2
SiO
2
microspheres were dissolved in 20 ml anhydrous ethanol, and
3
dispersed using ultrasound for about 10 min. The molar ratio of Eu
+
:phen–Si was 1:2, a moderate dose of Eu perchlorate was dissolved
SCHEME 1 Synthesis of phen–Si
in 5 ml anhydrous ethanol. The resulting solution was then added
dropwise to the anhydrous ethanol solution of modified SiO micro-
2
spheres. The mixture was stirred for 30 min at room temperature,
and then separated by centrifugation at 5000 rpm. The resulting white
precipitate was washed several times with anhydrous ethanol and
then dried. Four types of the white nanometre luminescent complex
TABLE 1 Preparation conditions of monodisperse spherical SiO
2
Average
diameter
CH
3
CH
2
OH
H
2
O
TEOS
(ml)
NH
3
H
2
O
Time
(h)
(ml)
(ml)
(ml)
that formed the core–shell structure (SiO2(500)@Eu(phen–Si)(50), SiO
500)@Eu(phen–Si)(15) SiO2(250)@Eu(phen–Si)(5) and SiO2(250)@Eu
phen–Si)(10)) were obtained.
2
2
5
50 nm
00 nm
5
5
2
2
0.5
0.5
0.39
0.65
2
2
(
,
(

4
LI ET AL.
3
|
RESULTS AND DISCUSSION
shell composition was clearly shown in the TEM photographs. EDX
spectra (Figure 6) of composites of SiO
phen–Si)(50) indicated the emission peaks of europium in the coating
layer of the core–shell composite, demonstrating that the europium
complex contained a coating layer. The SiO cores were clad with
the Eu(phen–Si)complex resulting in the synthesis of the SiO @Eu
phen–Si) core–shell structure.
2
core and shell SiO2(500)@Eu
(
3
.1
|
SEM of monodisperse spherical SiO2
SEM photographs showing features of the monodispersed spherical
SiO are shown in Figure 1 demonstrating the regular microstructure,
smooth surface, and moderate dispersity. Here, a 250 nm and 500 nm
average particle size of SiO spheres.
2
2
2
(
2
3
.3
|
Formation of the core–shell structure
3
.2
|
TEM of the SiO @Eu (phen–Si) core–shell
2
nanometre luminescent composite
structure nanometre luminescent composites
2
Synthesis of the composites from the SiO core and shell is shown in
Scheme 2. Chemical bonds in Si−O−Si were established via hydrolysis,
by a chemical reaction between ethoxy groups in phen–Si and
TEM photographs show the SiO2(250)@Eu (phen–Si)(5) and SiO2(250)
@
Eu (phen–Si)(10) nanometre luminescent structures (Figures 2 and
hydroxyl groups in SiO
ble nitrogen atoms in phen–Si groups on the grafted SiO
spheres shell were able to interact with Eu(III) perchlorate. SiO
2
core spheres. This process indicated that dou-
3
). The size of the SiO kernel was c. 250 nm. The SiO core surface
2
2
micro-
was clad with a thin layer of c. 5 nm or 10 nm, europium complexes
and double nitrogen atoms in the phen–Si groups on the surface of
2
2
3+
cores and Eu ions were combined by a ‘molecular bridge’, deter-
2 4 3
the SiO core were made using Eu(ClO ) . This was further confirmed
2
mined from phen–Si. The rim of SiO core was clad by the Eu(phen–
by infrared spectra. TEM photographs of the SiO2(500)@Eu(phen–Si)(15)
Si) complex.
nanometre luminescent structures are shown in Figure 4. The size of
2 2
the SiO kernel was c. 500 nm. The surface of the SiO core also
was clad with a thin layer of c. 15 nm. The thin shell also was made
|
3
.4
Infrared spectra
up of europium complexes in which the double nitrogen atoms of
phen–Si groups on the surface of the SiO
2
core coordinated with Eu
2
The IR spectra of phen–Si, SiO , SiO2(500)@Si‐phen and SiO2(500)@Eu
(
ClO . This was further confirmed by infrared spectra. TEM photo-
4
)
3
(phen–Si)(50) can be seen in Figure S1(a–d). The IR spectra of the four
nanometre luminescent composites formed by the core–shell struc-
ture are very similar. IR spectra indicated that the composition of the
shell layer was the most significant factor that contributed to the com-
position of the Eu–phen–Si complex.
graphs of the SiO2(500)@Eu (phen–Si)(50) nanometre luminescent struc-
ture are shown in Figure 5. The interface of the coating layer of the Eu
(
phen–Si) complex and the SiO
graphs. TEM photographs showed that the size of the SiO
was c. 500 nm, and the surface of the SiO core was clad in a shell
layer. The thickness of the grey shell layer was c. 50 nm, and core–
2
core was clearly seen in the photo-
2
kernel
2
The phen–Si IR spectra presented here (Figure S1a), demonstrated
−
1
νC=O group stretching at 1708 cm . The νC=O stretching frequency
FIGURE 1 SEM photograph of (a) SiO
50 nm; (b) SiO 500 nm
2
2
2
FIGURE 2 TEM photograph of SiO2(250)@Eu
phen–Si)(5)
(

LI ET AL.
5
FIGURE 3 TEM photograph of SiO2(250)@Eu(phen–Si)(10)
FIGURE 4 TEM photograph of SiO2(500)@Eu(phen–Si)(15)
FIGURE 5 TEM photograph of SiO2(500)@Eu(phen–Si)(50)
FIGURE 6 EDX spectrum of core–shell structure SiO2(500)@Eu(phen–Si)(50)

6
LI ET AL.
2 3 4
SCHEME 2 Self‐assembly of SiO @Eu(phen–Si) (ClO )
−
1
belonged to excitation transitions of the Eu ions in the excitation spec-
tra. The maximum peak appeared at 325 nm. The corresponding
shifted to 1699 cm in nanometre luminescent composites that
formed the core–shell structure (Figure S1d). ν‐CONH– group
−
1
−
1
−1
energy had a a wave number of c. 30,078 cm that indicated that
stretching appeared at 1649 cm and 1597 cm . In nanometre lumi-
7
5
the strongest excitation peak was due to the
F
0
→ L
3
transition of
nescent composites with the core–shell structure, the ν‐CONH–
3
+ [40,41]
−1
Eu .
No energy transfer band for phen appeared in the excita-
group expressed
a
lower wave number at 1598 cm
504 cm . The current results indicated that the Eu–phen–Si com-
plex was composed of a shell layer of nanometre luminescent compos-
ite formed from a SiO core and shell.
and
−
1
tion spectra. The observed excitation spectra could be due to the
1
half‐order of the 612 nm band or due to diffusion from the host
SiO
Five emission peaks in the fluorescence emission spectra (Fig-
ures 7(right) and 10(right)) were exhibited that contributed to the
2
matrix.
2
5
7
characteristic
0 J
D → F (J = 0, 1, 2, 3, 4) convection of Eu(III), corre-
3
.5
|
Fluorescence spectra of the SiO @Eu(phen–Si)
2
sponding emission peaks were at 579, 592, 612, 650 and 700 nm.
core–shell structure nanometre luminescent
composites
5
7
0 2
The D → F transition of Eu(III) at 612 nm was the strongest signal.
The fluorescence emission intensity of these four nanometre lumi-
nescent composites formed by core–shell structure was very differ-
ent under the same test conditions. SiO2(250)@Eu(phen–Si)(10) has
the largest fluorescence emission intensity, the strongest fluores-
cence emission peak intensity was 29,609 a.u. (Figure 7(left)). The
second fluorescence emission intensity was SiO2(500)@Eu(phen–Si)
In this study, excitation and emission spectra of the solid state material
were tested at room temperature. Some excellent luminescence attri-
butes were demonstrated by the nanometre luminescent composites
that formed the core–shell structure (see spectra data in Figures 7–
1
0 and Table 2).
(
50) with
a strongest fluorescence emission peak intensity of
The excitation spectra of the four types of composites structured
19,762 a.u. (Figure 8 (right)). The third fluorescence emission inten-
by a SiO
2
core and shell (SiO2(250)@Eu(phen–Si)(10), SiO2(500)@Eu
sity was SiO2(250)@Eu(phen–Si)(5) with the strongest peak intensity
at 10,225 a.u. (Figure 9(right)). The final fluorescence emission inten-
sity was SiO2(500)@Eu(phen–Si)(15) with the strongest peak intensity
(
phen–Si)(50), SiO2(250)@Eu(phen–Si)(5) and SiO2(500)@Eu(phen–Si)(15)
)
demonstrated a peak related to the Eu ion at 612 nm. These excitation
spectra were very similar, with many sharp peaks at 320–420 nm that
FIGURE 7 Fluorescence excitation spectrum (left) and fluorescence emission spectrum (right) of SiO2(250)@Eu(phen–Si)(10)

LI ET AL.
7
FIGURE 8 Fluorescence excitation spectrum (left) and fluorescence emission spectrum (right) of SiO2(500)@Eu(phen–Si)(50)
FIGURE 9 Fluorescence excitation spectrum (left) and fluorescence emission spectrum (right) of SiO2(250)@Eu(phen–Si)(5)
FIGURE 10 Fluorescence excitation spectrum (left) and fluorescence emission spectrum (right) of SiO2(500)@Eu(phen–Si)(15)
at 6543 a.u. (Figure 10(right)). These results showed that lumines-
cence of the nanometre composites was affected by the structure
of the core–shell. Kernel size and shell thickness will affect lumines-
cence properties. By comparing Figure 7(left) and Figure 8(right), it
can be seen that the fluorescence emission intensity of SiO2(250)
composites was smaller. Comparing Figure 7(right) and Figure 9(right)
or Figure 8(right) and Figure 10(right), it can be seen that the fluores-
cence emission intensity of the SiO2(250)@Eu(phen–Si)(10) was 2.63‐
fold as great than that of SiO2(250)@Eu(phen–Si)(5) or the fluores-
cence emission intensity of the SiO2(500)@Eu(phen–Si)(50) was 3.02‐
fold greater than that of SiO2(500)@Eu(phen–Si)(15). These findings
indicated that increasing the cladding layer thickness improved the
luminescence properties.
@
Eu(phen–Si)(10) was 1.50‐fold higher than that of SiO2(500)@Eu
phen–Si)(50), indicating that luminescence properties improved when
the kernel size of the core–shell structure nanometre luminescent
(

8
LI ET AL.
TABLE 2 Fluorescence emission spectra data of the core–shell
structure luminescent composites
where I(t) was the fluorescence intensity varying with time t, and τ
and τ were lifetime. Lifetimes of the four nanometre luminescent
complexes (SiO2(250)@Eu(phen–Si)(10), SiO2(500)@Eu(phen–Si)(50), SiO
1
2
2
Core–shell
composites
Slit width
(nm)
λ
(nm)
ex
λ
(nm)
em
Energy
I (a.u.) transition
(250)@Eu(phen–Si)(5) and SiO2(500)@Eu(phen–Si)(15)) were 778.68 μs,
734.97 μs, 734.90 μs and 643.78 μs, respectively.
5
5
5
5
5
7
SiO2(250)@Eu
1.0
1.0
1.0
1.0
325
579
592
2061
6289
29609
2278
5620
D
D
D
D
D
0
0
0
0
0
→ F
0
1
2
3
4
7
(
phen–Si)(10)
→ F
7
6
6
7
12
50
00
→ F
|
3
.7
Fluorescence quantum yield studies
7
→ F
7
→ F
Depending on the determination of fluorescence emission intensity
5
5
5
5
5
7
SiO2(500)@Eu
phen–Si)(50)
325
325
325
579
592
1516
5363
19762
1347
5796
D
D
D
D
D
0
0
0
0
0
→ F
0
1
2
3
4
5
and lifetime, the intrinsic luminescence quantum yields of the
D
0
7
(
→ F
7
emission in the four core–shell nanometre luminescent composites
were able to be determined. Quantum yield η, indicated distinctly
the competition between the radiative processes and the
nonradiative processes. Eqn (2) confirmed the η values of the
6
6
7
12
50
00
→ F
7
→ F
7
→ F
5
5
5
5
5
7
SiO2(250)@Eu
phen–Si)(5)
579
592
744
D
D
D
D
D
0
0
0
0
0
→ F
0
1
2
3
4
7
(
1643
10225
1023
2673
→ F
[42]
result here:
7
6
6
7
12
50
00
→ F
7
→ F
Ar
η ¼
(2)
7
→ F
Ar þ Anr
5
5
5
5
5
7
SiO2(500)@Eu
579
592
744
D
D
D
D
D
0
0
0
0
0
→ F
0
1
2
3
4
7
where A
respectively. The denominator in eqn (1) was determined from the
lifetime of the emitting level (1/τ = A + Anr, where τ is fluorescence
r
and Anr are radiative and nonradiative transition rates,
(
phen–Si)(15)
1715
6543
602
→ F
7
6
6
7
12
50
00
→ F
7
→ F
r
7
1315
→ F
lifetime). For europium luminescence the value of A
from eqn (3):
r
was calculated
3
.6
|
The fluorescence decay curve
Ar ¼ ∑A0J ¼ A00 þ A01 þ A02 þ A03 þ A04
(3)
Figures S2 and S3 show the fluorescence decrease, as well as the dou-
7
where, J is the final
eqn (4):
F0–4. A0J values could be calculated using
ble exponential fit curve of SiO2(500)@Eu(phen–Si)(50) and SiO2(250)
@
Eu(phen–Si)(10)
.
Fluorescence lifetimes for the four composites were determined
A0J ¼ A01ðI0J=I01Þðν01=ν0JÞ
(4)
using the double exponential mode. Lifetime of the Eu(III) ion was cal-
culated using eqns (1) and (2):
where, ν0J = 1/λ
J
, and λ is wavelength. A01 is the Einstein coeffi-
5
7
ꢀ
ꢁ
ꢀ
ꢁ
cient of spontaneous emission between the
D
0
and the
1
F Stark
−
−
IðtÞ ¼ I0 þ A1 exp t1=τ1 þ A2 exp t2=τ2
(1)
(2)
5
7
levels. The D → F transition was not based on the local ligand
0
1
field as shown by the Eu(III) ion and, therefore, may be used as a ref-
−1
À
Á
2
1
2
2
erence for the whole spectrum in vacuo, A01 = 14.65 s . From the
<
τ > ¼ A1τ þ A2τ =ðA1τ1 þ A2τ2Þ
above equations, fluorescent quantum yields of the four core–shell
TABLE 3 Fluorescence quantum yield of core–shell structure luminescent composites
SiO2(250)@Eu
phen–Si)(5)
SiO2(250)@Eu
SiO2(500)@Eu
SiO2(500)@Eu
(
(phen–Si)(10)
(phen–Si)(15)
(phen–Si)(65)
−
−
−
−
−
1
1
1
1
1
ν
ν
ν
ν
ν
00 (m
01 (m
02 (m
03 (m
04 (m
)
)
)
)
)
17 271
16 863
16 340
15 385
14 286
1643
17 271
16 863
16 340
15 385
14 286
6289
17 271
16 863
16 340
15 385
14 286
1715
17 271
16 863
16 340
15 385
14 286
5363
I
I
I
01 (a.u.)
02(a.u.)
02/I01
10 225
29 609
4.71
6543
19762
3.68
6.22
0.416
2403
3.82
τ (ms)
/τ
0.680
0.609
1643
0.735
1
1471
1361
Ar
501.91
20.89
365.87
24.87
312.22
19.00
317.81
23.35
η%

LI ET AL.
9
composites (SiO2(250)@Eu(phen–Si)(10), SiO2(500)@Eu(phen–Si)(50), SiO
2
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)
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[
2
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CONCLUSION
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(
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monodisperse spherical SiO
phen–Si complex self‐assembled on the monodispersed SiO
referred to as SiO @Eu(phen–Si) to synthesize the SiO core and shell.
2
. Based on TEM photographs, the Eu–
[
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2
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2
2
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Fluorescent spectra illustrated that the four nanometre luminescent
composites with the core–shell structure had excellent luminescence
attributes. The nanometre luminescent composites with a 250 nm ker-
nel size exhibited stronger fluorescent than composites with a 500 nm
kernel size. Fluorescence properties were affected by the thickness of
the shell, such that when the shell thickness was thicker, the fluores-
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earth organic complex applied as the coating layer, was at the
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excellent luminescence features for use as luminescent materials. This
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luminescent materials including information on europium luminescent
materials and assistance on development and improvement in the
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ACKNOWLEDGEMENTS
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This work was supported financially from Major Projects of the Natu-
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ORCID
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