Properties of a novel Ba5Si8O21:Eu2+, Nd3+ phosphor: Bulk and 1D nanostructure with PVP synthesized by sol-gel and electrospinning

Article abstract of DOI:10.1016/j.jallcom.2017.04.102

In this study, a sunlight-activated Ba₅Si₈O₂₁:Eu²⁺, Nd³⁺ (BSEN) persistent luminescent particles were firstly synthesized by sol-gel method, and then combined with polyvinyl pyrrolidone (PVP) to fabricate one-dimensional functional fiber by electrospinning. XRD, photoluminescence, fluorescence microscope, SEM and TEM were used to investigate the crystal structure, the morphology, the luminescent properties and water resistance of BSEN particles and functional fibers. The results show that BSEN owns a monoclinic crystalline and can be effectively and repeatedly excited by both ultraviolet and sunlight. The BSEN particles were water-resistant and uniformly dispersed in the PVP fibers. Both BSEN particles and functional fibers possessed broad excitation spectra from 250?nm to 450?nm with maximum at 341?nm and exhibited a fluorescent and phosphorescent emission band from 365?nm to 650?nm with maximum at around 489?nm with long afterglow up to 240?min. The new functional fiber has potential to be used in flexible coating, textile and optical display.

Full text of DOI:10.1016/j.jallcom.2017.04.102

Journal of Alloys and Compounds 712 (2017) 213e218
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
2þ
3þ
Properties of a novel Ba Si O :Eu , Nd phosphor: Bulk and 1D
5
8 21
nanostructure with PVP synthesized by sol-gel and electrospinning
*
Yuanlin Yao, Zhufa Zhou , Feng Ye
College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, PR China
a r t i c l e i n f o
a b s t r a c t
In this study, a sunlight-activated Ba Si O :Eu2 , Nd (BSEN) persistent luminescent particles were
þ
3þ
Article history:
Received 19 December 2016
Received in revised form
5
8 21
firstly synthesized by sol-gel method, and then combined with polyvinyl pyrrolidone (PVP) to fabricate
one-dimensional functional fiber by electrospinning. XRD, photoluminescence, fluorescence microscope,
SEM and TEM were used to investigate the crystal structure, the morphology, the luminescent properties
and water resistance of BSEN particles and functional fibers. The results show that BSEN owns a
monoclinic crystalline and can be effectively and repeatedly excited by both ultraviolet and sunlight. The
BSEN particles were water-resistant and uniformly dispersed in the PVP fibers. Both BSEN particles and
functional fibers possessed broad excitation spectra from 250 nm to 450 nm with maximum at 341 nm
and exhibited a fluorescent and phosphorescent emission band from 365 nm to 650 nm with maximum
at around 489 nm with long afterglow up to 240 min. The new functional fiber has potential to be used in
flexible coating, textile and optical display.
6
April 2017
Accepted 11 April 2017
Available online 12 April 2017
Keywords:
Sol-gel
Barium silicate
Persistent luminescence
Fiber
Electrospinning
© 2017 Elsevier B.V. All rights reserved.
1. Introduction
[13]. Usually, the latter demands high synthesis temperature, and
particles prepared by this method are not small enough. Electro-
Persistent luminescent material, which can emit visible or near-
infrared light for a long time after the excitation source been cut off,
is a potential solution to the energy issue [1,2]. Persistent lumi-
nescent material has various applications in in-vivo imaging [3],
nano probe [4], night vision [5] owing to its long afterglow. Many
persistent luminescent materials are in application. For example,
ZnS:Co, Cu [6] is used for watch dials but sensitive to moisture.
spinning is a facile method to fabricate one-dimensional fibers
which draw considerable efforts in research and have various ap-
plications in optics, sensors and lasers due to their superior physical
and chemical property [14,15].
The secret of sunlight-activated persistent luminescence is to
broaden the width of excitation spectra so that the material can be
2
þ
3þ
directly activated by solar irradiation. Take Ba
5 8
Si O21:Eu , Dy as
2
þ 3þ
SrAl
but bad hydrolysis resistance [7]. M
2 4
O :Eu , Dy has super long afterglow and high brightness
an example, even if the persistent luminescence can last 8 h after
2
þ
3þ
2þ
3þ
2
MgSi
2
7
O :Eu ,Dy (M: Sr, Ca,
solar irradiation, the width of excitation spectra of Eu , Dy co-
2
þ
Ba) possesses excellent afterglow and stable chemical property but
lack of color diversity [8,9]. However, very few studies are reported
in the sunlight-activated persistent luminescent material. It is
economic and environmental friendly to use sunlight to activate
persistent luminescent material. So far, the outstanding sunlight-
doped Ba
Ba Si 21 [16]. One effective method to tune the photo-
luminescence spectra is change the co-doping ions. Therefore, a
5 8
Si O21 do not get any broader than Eu single doped
5
8
O
2
þ
3þ
5 8
persistent luminescent material of Ba Si O21:Eu , Nd (BSEN) has
been synthesized by sol-gel method, which have broader excitation
spectra and low cost due to the rare earth price and act as precursor
for electrospinning. The precursors were used to synthesize one-
dimensional functional fibers by electrospinning [17,18]. The
problem is that, the pure inorganic non-metallic fibers are instable
and brittle, thus not suitable for application. To solve this issue,
persistent luminescent material were mixed with polymer, and
made into fibers by electrospinning [19e21]. Here, polyvinyl pyr-
3þ
activated material is Zn
3
Ga
2
Ge
2
O
10:Cr
, which emits near-
infrared light beyond 360 h with excitation spectrum from
3
00 nm to 650 nm [10].
Sol-gel preparation [11,12] is an effective method to synthesize
persistent luminescent material compared to solid-state method
2
þ 3þ
rolidone (PVP) and Ba
synthesize functional fiber through electrospinning. The fiber owns
5 8
Si O21:Eu , Nd (BSEN) were mixed to
*
Corresponding author.
E-mail address: zhouzhufa@suda.edu.cn (Z. Zhou).
http://dx.doi.org/10.1016/j.jallcom.2017.04.102
925-8388/© 2017 Elsevier B.V. All rights reserved.
0

214
Y. Yao et al. / Journal of Alloys and Compounds 712 (2017) 213e218
the properties of luminescence from BSEN and flexibility from PVP.
2
. Experimental
2
21:Eu2 , Nd fiber
þ 3þ
5 8
.1. Synthesis and preparation of PVP/Ba Si O
21:0.02Eu2
þ
,
A series of persistent luminescent materials Ba
5
Si
8
O
xNd3 (x ¼ 0, 0.02, 0.04, 0.06, 0.08) were synthesized by sol-gel
method. The selection of molar ratio of lanthanides in this study
is based on the past experience and random [16]. The raw materials
þ
were analytical grade Ba(NO
Ltd, abbreviated as SCR), Si(OC
and Nd (4N, Aladdin). Firstly, Eu
in nitric acid and then stirred with the distilled water. Secondly,
Ba(NO , TEOS and ethanol were added into the solution, and the
3
)
2
(Sinopharm Chemical Reagent Co.,
(TEOS, SCR), Eu (4N, SCR)
and Nd were dissolved
2
5
H )
4
2 3
O
2
O
3
2
O
3
2 3
O
3 2
)
pH was adjusted to 2 by adding nitric acid dropwise. The solution
ꢀ
was stirred at 60 C until formation of transparent gel. Thirdly, the
ꢀ
gel was dried at 110 C for 12 h. The resulting white gel was then
ꢀ
sintered at 1250 C for 3 h in a graphite reducing atmosphere.
In the following, PVP was dissolved in distilled water with a
concentration of 0.2 g/mL and the solution was stirred at room
2þ 2þ 3þ
5 8 5 8
Si O21:0.02Eu and Ba Si O21:0.02Eu , 0.04Nd particles.
Fig. 1. XRD patterns of Ba
JCPDS Card No. 83e1443.
2
þ
3þ
5 8
temperature for 2 h. The Ba Si O21:0.02Eu , 0.04Nd particles
(
10 wt% of the functional fiber) were added in the solution and
BSEN functional fibers. Fig. 2a shows the fine size distribution of
BSEN particles after being sintered at 1250 C with an average size
of 0.45 mm. Fig. 2b shows that the functional fibers are randomly
dispersed in ultrasonic vibrator for 1.5 h. The suspension was
loaded in an injector and the injector was fixed on electrospinning
equipment. The flow rate was set at 1.5 mL/h and the voltage 15 KV,
the distance between collector and syringe needle was 15 cm. The
fibers ejected on the collector were the target product. Then the
ꢀ
oriented and possess relatively uniform diameter. Because the
process of electrospinning is complicated, every factor can affects
the result more or less, including the orifice size, collector distance,
flow rate and voltage. Therefore, it is hard to control the diameter of
fibers precisely. The functional fibers would have evaporated liquid
solvent since synthesized and shrinked a little which can be seen in
Fig. 2c that some tiny wrinkles appeared on its appearance. Fig. 2d
shows various shapes and sizes of BSEN particles are randomly
distributed in the PVP fibers successfully and the functional fibers'
ꢀ
fibers were dried in vacuum oven at 30 C for 12 h.
2
.2. Characterizations
XRD patterns were taken on a Rigaku S/Mx diffractometer (PAN
analytical, The Netherlands) using Cu K
a
radiation (
l
¼ 1.5406 Å).
Excitation and emission spectra and afterglow decay curves were
collected by a fluorescence spectrophotometer (Hitachi F-2500,
Japan). Absorption spectra were collected by a UVeViseNIR spec-
trophotometer equipped with an integrating sphere (Shimadzu
UV-3600, Japan). Morphology images were taken on SEM (Hitachi
S-4700, Japan) and TEM (FEI, America). Fluorescence microscopic
images were taken on an inverted fluorescence microscope (EVOS,
USA) at room temperature.
diameter is approximately 2
mm.
þ
3þ
3.3. Photoluminescence of Ba
5
Si
8
O
21:Eu2 , Nd particles and PVP/
2
þ 3þ
5
Ba Si
8
O21:Eu , Nd fiber
In this work, a series of persistent luminescent material
2
þ
3þ
Ba
5 8
Si O21:Eu , Nd were synthesized by sol-gel method. All the
samples show single monoclinic crystalline. For the purpose of
3
. Results and discussion
21:Eu2 , Nd particles
þ 3þ
8
.1. XRD analysis of Ba Si O
confirming the best doping ratio of Eu/Nd, the univariate analysis of
doping concentration of Nd was conducted. As shown in Fig. 3a,
the excitation spectra of BSEN particles cover a broad band from
3
þ
3
5
250 nm to 450 nm with a maximum at 341 nm which correspond to
We synthesize
a
new persistent luminescent material
the absorption spectra in Fig. 3c. Under the excitation of 341 nm,
the BSEN particles exhibit an asymmetric broad band from 365 nm
to 650 nm with a maximum at 489 nm which can be ascribed to the
2
þ
3þ
Ba
5 8
Si O21:Eu , Nd (BSEN) using sol-gel method. Fig. 1 shows the
2
þ
2þ
XRD patterns of Ba
5
Si
8
O
21:0.02Eu
and Ba
5
Si
8
O21:0.02Eu
,
.04Nd3 . The main diffraction peaks are consistent with the
þ
typical transition of the excited state ( F
4 5
D
) to the ground state
0
6
1
4
2þ
2þ
monoclinic Ba
5
Si
8
O
21 (JCPDS Card No.83e1443, a ¼ 32.675,
( F
7
) configurations of Eu ions [23]. The PL spectra reveal that the
ꢀ
3þ
b ¼ 4.695, c ¼ 13.894,
b
¼ 98.10 ). There are two conceivable sites
Eu ions are reduced to Eu because the typical emission peaks of
2
þ
3þ
3þ
that Eu ions (1.25 Å) and Nd ions (1.109 Å) to be incorporated,
Eu around 580 nm, 590 nm, 612 nm, 650 nm and 698 nm due to
one is Ba2 (1.42 Å) sites and the other is Si
þ
4þ
(0.42 Å) sites.
the transition D
cated that the emitter center is Eu ions, and there are three
nonequivalent Ba sites in the matrix which can be substituted by
the Eu ions [16], therefore the asymmetric emission spectra are
well-fitted by three Gaussian profiles (dark yellow dashed lined) in
Fig. 3b.
5
/ FJ (J¼0, 1, 2, 3, 4) are not found [24]. It is indi-
7
0
2
þ
Considering the effective ionic radii of cations with different coor-
2
þ
3þ
2þ
dination numbers [22], Eu ions and Nd ions prefer to occupy
one of the [BaO ] site rather than [Si ] sites. Moreover, no im-
purities are found in the range of the scanning scope, which reveals
2
þ
8
3
O
8
that Eu2 ions and Nd
þ
3þ
ions had been incorporated in the
5
Si
8
O
21:Eu2 , the
þ
monoclinic lattice without distorting the matrix remarkably [16].
Moreover, compared with the PL intensity of Ba
2
þ
3þ
3þ
PL intensity of Ba
5
Si
8
O
21:Eu , Nd is enhanced along with the
3
.2. Morphologies of PVP/Ba
21:Eu2 , Nd functional fiber
þ 3þ
5 8
Si O
increase of the concentration of Nd at the beginning and reaches
3
þ
the highest intensity when the concentration of Nd at 0.04 and
then starts to decrease. The reason can be ascribed to the
Fig. 2 shows the SEM and TEM images of BSEN particles and PVP/

Y. Yao et al. / Journal of Alloys and Compounds 712 (2017) 213e218
215
Fig. 2. SEM images of BSEN particles (a) and PVP/BSEN fibers (b, c) and TEM image of PVP/BSEN functional fiber (d).
Fig. 3. Excitation and emission spectra of BSEN particles and PVP/BSEN fibers (a). Excitation and emission spectra of BSE and BSEN particles (b). Absorption spectra of BSEN particles
c). Fluorescence and persistent luminescence emission spectra (1 min after removing excitation) of PVP/BSEN fiber (d).
(

216
Y. Yao et al. / Journal of Alloys and Compounds 712 (2017) 213e218
Fig. 6. Emission and persistent luminescence spectrum of BSEN water solution under
65 nm and after stopping activation for 1 h (a). Freshly prepared BSEN water solution
3
activated by UV lamp at 365 nm (b) and aged solution for 1 h with UV lamp turn off (c)
and turn on (d) at 365 nm.
lower the intensity [27]. Besides, Fig. 3d shows the fluorescence and
persistent luminescence emission of PVP/BSEN fibers. The two
curves both cover from 365 nm to 650 nm under 341 nm excitation.
Moreover, the trend of fluorescence and persistent luminescence
emission spectra is similar except different magnitude.
In addition, the BSEN particles own a good property of sunlight-
activation and persistent luminescence. Fig. 4a shows a broad band
excitation spectrum of BSEN and solar irradiation spectrum from
Fig. 4. Normalized excitation spectrum of BSEN particles. The red dashed line repre-
sents the solar irradiation at Earth's surface at AM 1.5G (a). Persistent luminescence
spectra of BSEN particles after activation by solar irradiation for 30 min, the inset is the
emission spectra of BSEN particles irradiated by sunlight and with 280 nm, 310 nm and
400 nm cutoff filters for 30 min (b). (For interpretation of the references to colour in
this figure legend, the reader is referred to the web version of this article.)
250 nm to 650 nm at Earth's surface under an air mass of 1.5 global
(AM 1.5G). Generally speaking, the broader the excitation spectra is,
the more energy the material can store and transfer into lumines-
cence from solar irradiation. Obviously, the excitation spectra of
BSEN(FWHM
¼
104.47 nm) is broader than the BSE's
(
FWHM ¼ 93.64 nm) in Fig. 3b, and the excitation spectrum of BSEN
Fig. 5. Afterglow images of BSEN particles taken from 0 s to 4 h after exposure to
sunlight for 30 min.
overlaps with the solar irradiation spectrum from UV to visible
light, which suggests that BSEN can be effectively activated by
sunlight (Fig. 5). Fig. 4b shows the persistent luminescence spectra
2þ 3þ
of Ba
irradiation for 30 min. The inset shows the emission spectra of
5 8
Si O21:0.02Eu , 0.04Nd particles after activation by solar
concentration quenching effect [25,26] that Eu2þ and Nd3þ are
induced in the matrix as activator to create defects to enable the
matrix the property of photoluminescence, the defects and PL in-
tensity are in a competitive relation and there always exist a suit-
able status that balance the structure and PL intensity. Therefore,
2þ 3þ
5 8
Ba Si O21:0.02Eu , 0.04Nd particles irradiated by sunlight and
with 280 nm, 310 nm and 400 nm cutoff filters for 30 min. It is safe
to say that the BSEN particles still exhibit persistent luminescence
even if the UV is filtered from sunlight.
2þ 3þ
we take Ba Si O21:0.02Eu , 0.04Nd as an example to show its
5 8
In addition, BSEN owns an excellent property of water resis-
tance, which ensures the material suitable for outdoor decoration
and illumination. In order to prove this property, we performed
water resistance experiments by preparing a BSEN water solution.
Fig. 6a shows the PL intensity of BSEN water solution under 365 nm
and after stopping activation for 1 h. Fig. 6b is the picture of the
freshly prepared solution activated by UV lamp at 365 nm, Fig. 6c
and d are pictures of aged solution for 1 h with UV lamp turn off and
on at 365 nm respectively. Clearly, we can see that the solution still
emit green visible light after 1 h with a lower brightness. Also the
other excellent properties in the following.
The PL spectra of PVP/BSEN fiber is shown in the Fig. 3a. The
fiber can emit 489 nm light under 341 nm excitation. However, the
PVP may decrease the PL intensity of fiber. The reasons are: (i) PVP
polymer has reflection, scattering, absorption and other effects on
light, when PVP/BSEN fibers excited by UV or sunlight, the energy
can not be efficiently transmitted to the BSEN luminescent mate-
rials embedded in the fibers, and thus, the emission energy is
weakened by PVP polymer. (ii) the physical properties of PVP
polymer such as transparency and UV-resistant property may also

Y. Yao et al. / Journal of Alloys and Compounds 712 (2017) 213e218
217
Fig. 7. Fluorescence microscope image (a,
l
¼ 400 nm) and phosphorescence microscope images (b) of PVP/BSEN functional fibers after removing excitation for 5min.
ꢀ
ꢁ
ꢀ
ꢁ
t
t
t
2
I ¼ I01exp ꢁ
þ I02exp ꢁ
(1)
t
1
where I represents the photoluminescence intensity. I01 and I02 are
constants. and are decay constants, deciding rates for the rapid
and slow exponentially decay components respectively. The fitting
results of constants. and are shown in Table 1. BSEN can be
t
1
t
2
t
1
t
2
excited by both UV lamp at 365 nm as well as sunlight. The two
green lines display the same decay trend and both have an after-
glow more than 45 min, but the intensity of sunlight-activated
BSEN particles is lower. Meanwhile, the PVP/BSEN functional fiber
show the similar trend to that of BSEN particles. The afterglow was
more than 45min and the intensity was also lower. However,
compared with the other three samples, the slow decay process of
2
þ
Ba
5 8
Si O21:0.02Eu is rather weak, which can be seen more evident
in the fitting results in Table 1. These results indicate that the dope
3
þ
of Nd
greatly improve the afterglow time. Actually, it is not
enough for persistent luminescent materials to meet the com-
mercial utilization demand without doping [28]. Many researches
have conducted studies on the persistent luminescence, however,
the defects caused by doping is very hard to confirm experimen-
tally [29]. The probable mechanism may be that the luminescence
21:0.02Eu2
þ
5 8
Fig. 8. Decay curves of BSEN particles excited by UV and sunlight, Ba Si O
and PVP/BSEN functional fiber. Dynamic data were collected under 341 nm excitation
at fixed time interval.
4
5
Table 1
originates from the transition of the excited state ( F
6
D
1
) to the
) of Eu ions [30], the afterglow comes from the
slow release of electrons captured in trap energy level which pro-
4
2þ
The fitting results of samples decay curves.
ground state ( F
7
Sample
t
1
(min)
2
t (min)
3
þ
duced in the matrix by doping with co-activator Nd ions. The
BSEN(UV activated)
BSEN(Sunlight activated)
BSE
2.66
0.54
12.62
0.69
42.74
6.44
2.35
8.67
2
þ
energy level lies between excitation state and ground state of Eu
ions [31]. When the material is excited, a part of the electrons re-
turn to the lower energy level and produce luminescence. The other
electrons are captured in the trap energy level. When the electrons
in the trap energy level absorb energy, they return to the excitation
state again, and then transfer to the ground state and produce
luminescence. The release of captured electrons is a continuous
process; thus the material exhibits afterglow and the decay time is
determined by the depth and concentration of trap energy level.
PVP/BSEN
aged solution is as bright as the freshly prepared solution once been
activated again.
The fluorescent properties of PVP/BSEN functional fibers were
investigated by fluorescence microscope. Fig. 7a shows the fluo-
rescence image of PVP/BSEN fiber excited by blue light
3
þ
Although the doping of Nd is unlikely to deepen the trap energy
level, the concentration of trap energy level is increased than the
original state [32], which still prolong the decay time.
(
l
¼ 400 nm). The fibers emit green visible light. Fig. 7b are
phosphorescence images of PVP/BSEN functional fiber after stop-
page of excitation for 5min. The fibers also emit green visible light
although the brightness is getting weak with time lapse.
4. Conclusions
Here, the decay curves of different samples were shown in
Fig. 8. The decay curves can be divided into two parts, one is the
rapid attenuation whose slope is very steep, and the other is the
slow decay whose slope is very gentle. The decay curves can be
well-fitted with a double exponential equation which reflects
the trend of the decay. The form of the equation is as follows
2þ 3þ
5 8
Persistent luminescent material Ba Si O21:Eu , Nd was syn-
thesized by sol-gel method successfully and a new functional fiber
PVP/BSEN was prepared by electrospinning. The photo-
luminescence spectra and persistent luminescence spectra of the
BSEN and PVP/BSEN fiber exhibit a broad band emission spectra
from 365 nm to 650 nm with a maximum at 489 nm, which can be
[
9]:

218
Y. Yao et al. / Journal of Alloys and Compounds 712 (2017) 213e218
ascribed to the transition of 4
F D / F of Eu . The afterglow is
5
4
2þ
Chem. Phys. 85 (2004) 68e72.
[12] L.L. Hench, J.K. West, The sol-gel process, Chem. Rev. 90 (1990) 33e72.
13] I.P. Sahu, D.P. Bisen, N. Brahme, R.K. Tamrakar, Structural characterization and
optical properties of dysprosium doped strontium calcium magnesium di-
silicate phosphor by solid state reaction method Ishwar, Displays 8 (2015)
6 1 7
3
þ
prolonged due to the co-doping of Nd . The BSEN particles own a
good water resistance and can be excited by sunlight directly which
endows the BSEN particles wider application. The PVP/BSEN fiber
owns the properties of luminescence from BSEN and flexibility
from PVP, and can emit visible green light by excitation of sunlight.
For these properties above, the new functional fiber may be
potentially commercial useful in display, textile and flexible
coating.
[
104e109.
[
14] K.M. Mayer, J.H. Hafner, Localized surface plasmon resonance sensors, Chem.
Rev. 111 (2011) 3828e3857.
[15] S. Babin, A.E. El-Taher, P. Harper, et al., Tunable random fiber laser, Phys. Rev.
A 84 (2011) 021805.
[
16] P. Wang, X. Xu, D. Zhou, et al., Sunlight activated long-lasting luminescence
2þ 3þ
5 8
Si O21:Eu ,Dy phosphor, Inorg. Chem. 54 (2015) 1690e1697.
from Ba
17] Y. Cheng, Y. Zhao, Y. Zhang, X. Cao, Preparation of SrAl
electrospinning combined with sol-gel process, J. Colloid Interface Sci. 344
2010) 321e326.
:Eu2 fibers
þ
2 2 7
18] C. Xu, J. Guo, Y. Li, H.J. Seo, Enhanced luminescence of Ca MgSi O
2
þ 3þ
[
2 4
O :Eu , Dy fibers by
Acknowledgments
(
[
[
[
This work was supported by the Priority Academic Program
Development (PAPD) of Jiangsu Higher Education and State and
Local Joint Engineering Laboratory for Novel Functional Polymeric
Materials.
by solegel assisted electrospinning, Opt. Mater. 35 (2013) 893e897.
19] S. Agarwal, A. Greiner, J.H. Wendorff, Functional materials by electrospinning
of polymers, Prog. Polym. Sci. 38 (2013) 963e991.
2þ 3þ
2 2 7
MgSi O :Eu , Dy
20] F. Ye, S. Dong, Z. Tian, et al., Fabrication of the PLA/Sr
long-persistent luminescence composite fibers by electrospinning, Opt. Mater.
6 (2013) 463e466.
3
[21] J. Li, H. Li, H. Hu, et al., Preparation and application of polymer nano-fiber
doped with nano-particles, Opt. Mater. 40 (2015) 49e56.
References
[
22] R.D. Shannon, Revised Effective Ionic Radii and Systematic Studies of Inter-
atomie Distances in Halides and Chaleogenides bond strength-bond length
relationships, and plots of (1) radii vs volume, (2) radii vs coordination partial
occupancy of cation sites, coval, Acta Crystallogr. A32 (1976) 751e767.
[
1] J. Hols €a , Persistent luminescence beats the afterglow: 400 Years of persistent
luminescence, Electrochem Soc. Interface 4 (2009) 42e45.
[
2] T. Aitasalo, P. Dere nꢀ , J. H o€ ls €a , et al., Persistent luminescence phenomena in
materials doped with rare earth ions, J. Solid State Chem. 171 (2003)
[
[
[
[
2 4
23] B. Cheng, H. Liu, M. Fang, et al., Long-persistent phosphorescent SrAl O :
114e122.
2þ
3þ
Eu ,Dy nanotubes, Chem. Commun. (2009) 944e946.
[
3] T. Maldiney, B. Viana, A. Bessi eꢁ re, et al., In vivo imaging with persistent
luminescence silicate-based nanoparticles, Opt. Mater. 35 (2013) 1852e1858.
4] T. Maldiney, C. Richard, J. Seguin, et al., Effect of core diameter, surface coating,
and PEG chain length on the biodistribution of persistent luminescence
nanoparticles in mice, ACS Nano 5 (2011) 854e862.
24] X. Zhang, H.J. Seo, Photoluminescence and concentration quenching of
3þ
NaCa
4
(BO
3
)
3
:Eu phosphor, J. Alloys Compd. 503 (2010) L14eL17.
[
25] D.L. Dexter, J.H. Schulman, Theory of concentration quenching in inorganic
phosphors, J. Chem. Phys. 22 (1954) 1063.
26] T.T.H. Tam, N.V. Du, N.D.T. Kien, et al., Co-precipitation synthesis and optical
[
5] C. Zhao, D. Chen, Synthesis of CaAl
combustion processes and its optical properties, Mater Lett. 61 (2007)
673e3675.
2
O
4
:Eu,Nd long persistent phosphor by
2þ
properties of green-emitting Ba
58e362.
2
MgSi
2
O
7
:Eu phosphor, J. Lumin 147 (2014)
3
3
[
[
[
27] J. Zhang, M. Ge, Effecting factors of the emission spectral characteristics of
[
[
6] W. Hoogenstraaten, H.A. Klasens, Some properties of zinc sulfide activated
with copper and cobalt, J. Electrochem Soc. 100 (1953) 366e375.
7] T. Matsuzawa, Y. Aoki, N. Takeuchi, Y. Murayama, A new long phosphorescent
rare-earth strontium aluminate for anti-counterfeiting application, J. Lumin
131 (2011) 1765e1769.
28] F. Clabau, X. Rocquefelte, T. Le Mercier, et al., Formulation of phosphorescence
mechanisms in inorganic solids based on a new model of defect conglomer-
ation, Chem. Mater. 18 (2006) 3212e3220.
2
þ 3þ
phosphor with high brightness, SrAl
1996) 2670e2673.
8] T. Aitasalo, D. Hreniak, J. H o€ ls a€ , et al., Persistent luminescence of Ba
MgSi O :
2 2 7
2 4
O :Eu , Dy , J. Electrochem Soc. 143
(
[
29] J. H o€ ls a€ , T. Laamanen, M. Lastusaari, P. Nov ꢀa k, Defect aggregates in the
2þ
Eu , J. Lumin 122e123 (2007) 110e112.
9] H. Wu, Y. Hu, Y. Wang, C. Fu, The luminescent properties of the substitution of
Sr
130e1136.
2 4
30] H. Yamamoto, T. Matsuzawa, Mechanism of long phosphorescence of SrAl O :
2 2 7
MgSi O persistent luminescence material, J. Rare Earths 29 (2011)
[
1
3þ
3þ
2þ 3þ
2 2 7
MgSi O :Eu , Dy (M: Sr,Ca)long afterglow phos-
Ho for Dy in the M
phors, Mater. Sci. Eng. B 172 (2010) 276e282.
10] Z. Pan, Y.-Y. Lu, F. Liu, Sunlight-activated long-persistent luminescence in the
[
[
[
2þ
3þ
2þ 3þ
Eu , Dy and CaAl O :Eu , Nd , J. Lumin 72e74 (1997) 287e289.
2 4
[
[
3þ
3þ
31] X. Teng, W. Zhuang, H. He, et al., Influence of La and Dy on the properties
of the long afterglow phosphor, Rare Met. 27 (2008) 2e6.
32] Y. Wang, L. Wang, Defect states in Nd -doped CaAl
01 (2007) 053108.
3þ
near-infrared from Cr -doped zinc gallogermanates, Nat. Mater. 11 (2011)
8e63.
11] T. Peng, L. Huajun, H. Yang, C. Yan, Synthesis of SrAl
nanometer powders by solegel processes and its optical properties, Mater
5
3þ
2þ
2 4
O :Eu , J. Appl. Phys.
2 4
O :Eu, Dy phosphor
1