Electrospinning preparation and luminescence propertiesof one-dimensional SrWO4: Sm3+ nanofibers

Xuetao Xu • Suqing Zhao • Kanyi Liang •

Jiaying Zeng

Received: 21 April 2014 / Accepted: 16 May 2014

� Springer Science+Business Media New York 2014

Abstract One-dimensional Sm3? doped SrWO4 with or

without different charge compensation approaches (co-

doping Li?, Na? and K?) nanofibers were prepared by

electrospinning. The structure, morphology and lumines-

cence properties of the obtained nanofiber phosphors were

investigated. The X-ray diffraction, Fourier transformation

infrared and thermogravimetric results show that the

Sr(1-x)WO4: Smx3? samples crystallize at 700 �C. Scanning

electron microscope results indicate that as prepared

nanofibers before/after calcination present uniform fiber-

like morphology. The luminescence results show that

Sr(1-x)WO4: Smx3? phosphors can be excited efficiently by

ultraviolet (UV) and near-UV light. The emission spectrum

consists of three emission peaks at 561, 596 and 643 nm,

corresponding to 4G5/2 ? 6H5/2, 4G5/2 ? 6H7/2 and 4G5/2

? 6H9/2 transitions of Sm3?, respectively. The optimal

doping concentration of Sm3? in SrWO4 is experimentally

ascertained to be 4 mol%. The introduction of charge

compensator R? (R = Li, Na and K) can enhance the

emission intensity of phosphors significantly. The co-dop-

ing of Li? has the best compensation effect. The present

investigation indicates that Sm3? doped SrWO4 is a

promising orange phosphor for light-emitting diode based

on UV chip technology.

1 Introduction

One dimensional (1D) nanomaterials (nanofibers, nano-

wires, nanorods, nanotubes, etc.), due to their transverse

nanoscale and large length to diameter ratio, are endowed

with unique optical, electrical, mechanical and magnetic

properties [1]. Many methods have been used to prepare

1D nanostructured materials, including chemical or phys-

ical vapor deposition, laser ablation, solution, template-

based method and electrospinning method [2]. In these

methods, electrospinning method is an effective and simple

technique [3–6]. 1D materials prepared by electrospinning

have many excellent properties, such as exceptionally long

length, uniform diameter, diverse composition and large

surface, which can be applied in biomedical fields, rein-

forced composites, catalyst supports, sensors, electronic

and optical devices, as well as sacrificial templates [7–10].

As far, many 1D luminescent materials are synthesized by

electrospinning, such as SrAl2O4: (Eu2?, Dy3?), CaWO4:

Tb3?, SrMoO4: Sm3?, Y3Al5O12: Ce3?, YBO3: Eu3?, etc.,

[1, 2, 11–14]. All reported 1D nanomaterial phosphors

prepared by electrospinning have high uniformity nano-

particles within single nanofibers.

As a kind of scheelite structure, the alkaline-earth metal

tungstates MWO4 (M = Ca2?, Sr2?, Ba2?) have been

investigated extensively as a self-activating phosphor

emitting blue or green light under ultraviolet (UV) or X-ray

excitation [15–17]. At present, MWO4 were reported to be

efficient luminescent hosts for rare earth ions [12, 18–23].

SrWO4 is an important optical material used in Raman

converters which has an intrinsic strong blue emission

X. Xu (&) � S. Zhao

Faculty of Chemical Engineering and Light Industry,

Guangdong University of Technology, Guangzhou 511458,

People’s Republic of China

e-mail: xuetaoxu@126.com

K. Liang

Faculte des Sciences et Techniques, Universite du Maine

Avenue Olivier Messiaen, 972085 Le Mans Cedex, France

J. Zeng

School of Materials Science and Engineering, South China

University of Technology, Guangzhou 510000,

People’s Republic of China

123

J Mater Sci: Mater Electron

DOI 10.1007/s10854-014-2021-0

band. However, its luminescence covers a broad range of

wavelengths that are insensitive to external changes. It is

known that the emission spectral profile of lanthanide ions

includes a series of well-defined and narrow bands. In

recent decades, some rare earth ions activated tungstates

have been well researched due to the special properties of

WO42- group. These phosphors provide excellent thermal

and hydrolytic stability, as well as strong absorption within

the near-UV region. Hence, tungstates are good choice as

host materials for white LEDs.

Sm3? is one of the most frequently used activator ions in

luminescent materials. The reddish orange emission of

Sm3? due to its 4G5/2 ? 6HJ (J = 5/2, 7/2, 9/2, 11/2)

transitions is the most suitable source for lighting and

display from a practical viewpoint [15, 23–27]. Moreover,

Sm3? can act as a spectroscopic probe of local structure

around rare-earth ions in condensed matter.

To the best of our knowledge, SrWO4: Sm3? 1D phos-

phors via electrospinning have not been reported. In this

paper, SrWO4: Sm3? fibers were prepared via electros-

pinning process. The structure, morphology and lumines-

cence properties were investigated in detail. The charge

compensation effect of alkaline metal ions on the structure

and luminescence intensity of prepared phosphors was also

discussed.

2 Experimental

Sr(NO3)2, (NH4)6W7O24�6H2O and Sm2O3 were used as

the starting materials for the synthesis of Sr(1-x)WO4:

Smx3? (x = 2–6 %) nanofibers. Polyvinylpyrrolidone

(PVP) (MW = 1,300,000) was used to control the viscos-

ity of the solution. Firstly, Sm2O3 was dissolved in nitric

acid and the excess acid was removed by slow evaporation.

The stoichiometric amounts of Sr(NO3)2 and (NH4)6-

W7O24�6H2O were added, then were dissolved in water–

ethanol solution (final mass ratio of water to ethanol is 1:1).

A certain amount of PVP (the weight percentage of PVP is

8 % in the water–ethanol solution) was added and the

solution was stirred for 4 h to obtain a homogeneous hybrid

sol for further electrospinning. The mixture was then loa-

ded in 20 ml plastic syringe of 25 gauges with stainless

steel needle. The distance between the spinneret and col-

lector was fixed at 10 cm and the high voltage supply was

maintained at 15 kV. The spinning rate was controlled at

1 mL h-1. The composite nanofibers were annealed at

700 �C for 3 h in air with a heating rate of 2�C/min. The

Sr0.92WO4: Sm0.043? , R0.04

? (R = Li, Na and K) nanofibers

were synthesized by similar method.

X-ray diffraction (XRD) patterns were recorded using

Rigaku Geiger flux instrument equipped with Cu-Ka(k = 0.15406 nm) radiation. The size and morphology of

SrWO4: Sm3? fibers were characterized by JEOL JSM-

6390 scanning electron microscope (SEM). Energy dis-

persive X-ray (EDX) spectrograph was recorded for the

elemental analysis to investigate the phase purity of

SrWO4: Sm3? nanofibers using INCA 200 EDS, attached

with SEM. Thermogravimetric analysis and Fourier trans-

formation infrared (FT-IR) spectroscopy were performed

on a TA-Q50 and Thermo Nicolet 6,700 spectrometer,

respectively. The photoluminescence measurement was

carried out by Hitachi F-4500 spectrophotometer equipped

with a 150 W xenon lamp as the excitation source at room

temperature.

3 Results and discussions

In order to determine the crystal structure of the phosphors,

all phosphors were characterized by XRD. Figure 1 shows

the XRD pattern of phosphor with maximum doping

(Sr0.92WO4: Sm0.043? , K0.04

? ) and the standard pattern JCPDS

Card No. 08-0490. The results show that all phosphors are

purity phases. Sm3? and R? ions can dissolve effectively

into the SrWO4 host lattice after annealed at 700 �C for

3 h. Due to the slight radius difference between doped ions

and replaced ions (Sm83? (0.1079 nm), Li8

? (0.092 nm),

Na8? (0.118 nm), K8

? (0.151 nm) and Sr82? (0.126 nm).

The subscript here indicates the coordination number of

Sr2? in SrWO4 host lattice, and the main diffraction peaks

may shift slightly [28]. However, due to the low doping

concentration of incorporation ions (Sm3?, Li?, Na? and

K?), the shift of diffraction peaks has not been detected in

our experiments.

Fig. 1 The XRD pattern of Sr0.92WO4: Sm0.043? , K0.04

? and JCPDS card

No. 08-0490 of scheelite phase SrWO4

J Mater Sci: Mater Electron

123

Figure 2a, b shows the SEM images of the sample

Sr0.96WO4: Sm0.043? before and after calcination. Before

calcination, randomly oriented hybrid fibers with smooth

surface and average diameter of 300–500 nm can be

observed (Fig. 2a). After annealed at 700�C (Fig. 2b), the

fibrous structure is retained on the whole except that a

small amount of fibers are broken during the calcinations

process. And the average diameter is reduced to

100–200 nm. The fibers surface becomes rough because of

the decomposition of PVP and the formation of crystallites.

From Fig. 2b, it also can be seen that the 1D Sr0.96WO4:

Sm0.043? nanofibers are further composed of fine and closely

linked nanoparticles. The nanoparticles are arranged

orderly along the axial direction of single fiber.

Figure 2c shows the energy dispersive spectrum (EDX)

of Sr0.96WO4: Sm0.043? nanofibers. In the EDX pattern, all

peaks correspond to Sr, W, Sm and O, except Au peak,

indicate the formation of SrWO4: Sm3?. Au peak appears

because Au is sprayed onto the nanofibers before scanning

in order to get high quality morphology images. The results

show that the Sr0.96WO4: Sm0.043? nanofibers hold good

purity after removal of PVP.

Figure 3a–c shows the FT-IR spectra of PVP, Sr0.96-

WO4: Sm0.043? /PVP composite fibers and Sr0.96WO4: Sm0.04

3?

nanofibers, respectively. For PVP sample (Fig. 3a), the

broad band around 3,600–3,200 cm-1 corresponds to

hydrogen bonded O–H stretching vibration. The triplet

peaks present at 2,954 cm-1 corresponds to the asymmetric

and symmetric C–H stretching vibrations of methyl groups

Fig. 2 The SEM images of

samples a before annealed,

b annealed at 700 �C and

c EDX of Sr0.96WO4: Sm0.043?

nanofibers

Fig. 3 The FT-IR spectra of Sr0.96WO4: Sm0.043? nanofibers. a PVP

fibers, b Sr0.96WO4: Sm0.043? /PVP composite fibers, c Sr0.96WO4:

Sm0.043? nanofibers

J Mater Sci: Mater Electron

123

(from acetate) [29, 30]. While the other three dominant

peaks at about 1,654, 1,442 and 1,292 cm-1 are due to the

stretching vibration of C=O, C–H and C–N bond, respec-

tively [31]. For composite fibers shown in Fig. 3b, the C=O

stretching vibration characteristic peak red-shifts to

1,657 cm-1 in the composite fibers. The C–H stretching

vibration peaks red-shift to 2,955 and 1,443 cm-1 respec-

tively. The C–N stretching vibration peaks red-shift to

1,293 cm-1. A new peak appears at 1,384 cm-1, which

corresponds to N–O (from the NO3- group) stretching

vibration. After Sr0.96WO4: Sm0.043? /PVP fibers are annealed

at 700 �C, all the PVP peaks vanish (Fig. 3c), indicating

the full decomposition of PVP from the sample. And a

strong absorption peak at 819 cm-1 and a weak peak at

414 cm-1 appeared, which can be attributed to the

adsorption of W–O (from the WO42- group) [32–34].

Figure 4 shows the TG curve of Sr0.96WO4: Sm0.043? /PVP

composite nanofibers with a heating rate of 5 �C/min in

nitrogen atmosphere. The TG curve shows three stages of

weight loss. The first weight loss (8.1 %) below 150 �C is

due to the removal of water and organic solvents. The

second weight loss (15.3 %) from 150 to 350 �C is caused

by the decomposition of PVP. The third weight loss step

(52.5 %) between 350 and 600 �C may be due to the fur-

ther combustion of the organic groups in PVP, nitrates and

tungstates. The weight loss is completed below 600 �C and

total weight loss is about 75.9 %. No weight loss has been

observed beyond the temperature value of 600 �C as the

TG curve becomes horizontal. The TG curve confirms the

formation temperature of the sample to be around 600 �C.

The typical excitation spectra of SrWO4: Sm3? is shown

in Fig. 5. The excitation spectra of SrWO4: Sm3? moni-

tored at 595 nm consists of a series of peaks at 318, 345,

362, 375,403, 419 and 443 nm, which can be ascribed to

the transitions from the ground state to the excited states of

Sm3?. The relatively strongest peak at 403 nm is assigned

to the 6H5/2–4L13/2 transition of Sm3? [35]. It also can be

seen from Fig. 5, the peaks of Sr(1-x)WO4: Smx3?

(x = 2–6 %) are similar expect the fluorescence intensity.

The fluorescent intensity increases (from 300 to 450 nm)

with the content increase of Sm3?, and reaches the highest

intensity with content of Sm3? of 0.04. After that, the

fluorescent intensity begins to decrease.

Figure 6 shows the typical emission spectra of SrWO4:

Sm3? excited by 403 nm at room temperature. Lumines-

cence (PL) spectra of phosphors exhibited three sharp

emission peaks corresponding to 4G5/2 ? 6H5/2 (561 nm),4G5/2 ? 6H7/2 (596 nm) and 4G5/2 ? 6H9/2 (643 nm)

transitions of Sm3? [36]. The peak at 596 nm is the

strongest one. And two secondary peaks exist at 561 and

643 nm, respectively. From the emission spectra of

Sr(1-x)WO4: Smx3? (x = 2–6 %) excited by 403 nm, we

can find that the fluorescent intensity of phosphors depends

on the concentrations of Sm3?. As shown in the inset of

Fig. 6, the fluorescent intensity (from 500 to 700 nm)

increases with the increasing concentration of Sm3? ion up

to x = 4 %, then decreases above the concentration due to

concentration quenching. This quenching process is usually

attributed to energy migration among Sm3? ions, which

bring the excitation energy to killer sites such as surface

defects in powders (as shown in Fig. 7) [37]. This is

dependent on the critical distance Rc as the shortest aver-

age distance between the nearest activator Sm3? ions at a

critical concentration xc. As calculated by Blasse and

Grabmaier [38], Rc can be obtained using the following

equation [39, 40]:

Fig. 4 The TG curve of Sr0.96WO4: Sm0.043? /PVP composite

nanofibers

Fig. 5 The typical excitation spectra of Sr(1-x)WO4: Smx3? phosphors

(x = 2–6%) (kem = 595 nm)

J Mater Sci: Mater Electron

123

Rc ¼ 23V

4pxcN

� �13

ð1Þ

where V is the unit cell volume, xc is the critical concen-

tration of the activator ions, and N is the number of host

cations per unit cell. According to JCPDS card No.

08-0490 and the crystal structure, V, N and xc are

0.351 nm3, 1 and 0.04, respectively. The critical transfer

distance is calculated to be about 2.375 nm.

Comparing the spectral properties of SrWO4: Sm3?

nanofibers with the reported SrWO4: Sm3? spherical

nanoparticles [24], it is shown that the excitation and

emission spectra for the phosphor samples have the similar

profiles, but the maximum spectral positions are different

to some extent. For SrWO4: Sm3? nanofibers and nano-

particles, the strongest excitation peaks are at 403 and

405 nm, respectively. They are assigned to the 6H5/2–4L13/2

transition of Sm3?. The three emission peaks of SrWO4:

Sm3? nanofibers are at 561, 596 and 643 nm, while the

three emission peaks of SrWO4: Sm3? spherical nanopar-

ticles are at 562, 596 and 642 nm. The three emission

peaks also correspond to 4G5/2 ? 6H5/2, 4G5/2 ? 6H7/2 and4G5/2 ? 6H9/2 transitions of Sm3?. It is believed that the

morphology of Sm3? activated phosphors has a slight

influence on the luminescence properties of Sm3? because

the 4f–4f transitions of Sm3? are shielded by the outside 5s

and 5p orbitals. But due to the one-dimensional orientation

and confinement effect of SrWO4 single crystalline

nanofibers, it can be inferred that the emission of individual

SrWO4 single crystal nanofibers containing an emission

activator of Sm3? is polarized linearly, which can be

potentially used as linearly polarized light resource, pho-

todetectors, sensors etc. [41].

According to Huang’s rule [42, 43], the relationship

between the integral luminescent intensity I and doping

concentration x can be expressed as follows:

I1a 1�sdð ÞC 1þ s

d

� �ð2Þ

a ¼ xC 1� d

s

� �X0

ð1þ AÞc

� �ds

ð3Þ

where c is the intrinsic transition probability of the sensi-

tizer, s is index of electric multipole, which is 6, 8 and 10

for electric dipole–dipole, electric dipole-quadrupole, and

electric quadrupole–quadrupole interactions, respectively.

If s = 3, the interaction type is an exchange interaction.

Fig. 6 The typical emission spectra of SrWO4: Sm3? (kex = 403 nm).

The inset shows the relation between the relative fluorescent intensity

and the concentration of Sm3? for the Sr(1-x)WO4: Smx3? (x = 2–6 %)

phosphors

Fig. 7 Energy level diagrams,

visible emission transitions for

Sm3?, and the resonance energy

transfer among Sm3? ions

J Mater Sci: Mater Electron

123

The dimension of the sample is d, which was accounted as

3 in this case. A and X0 are the constants and C(1 ? s/d) is

a C function. From Eqs. (2) and (3), it can be derived that

logI

x

� �¼ s

dlog xþ log f ð4Þ

where f is independent of the doping concentration.

Figure 8 shows the Log (I/x)-Logx plot for the 4G5/2

? 6H7/2 transitions of Sm3? ions in Sr(1-x)WO4: Smx3?

phosphors. According to Eq. (4), using linear fitting to deal

with the experimental data in the region of high concen-

trations, the value of the slope parameter -s/d is obtained

to be -1.783 for the 4F9/2 ? 6H15/2 transition. The slope

was determined to be -2. Therefore, the index of the

electric multipole energy transfer is 6. The results indicate

that the electric dipole–dipole interaction mechanisms are

dominant by the energy transfer of the Sm3? ions in the

network of the investigated phosphors.

In this paper, three charge compensators were employed

to offset the net positive charge involved by the substitu-

tion of Sm3? for Sr2?, namely, Li?, Na?, K? at strontium

sites. The doping concentration of Sm3? was selected to be

0.04 according to the above analysis about the concentra-

tion quenching of Sm3? luminescence.

Figure 9 shows the emission spectra of three samples

with charge compensation under the excitation at 403 nm.

It is observed that all three samples with charge compen-

sation present a better luminescence performance than the

one without charge compensation. This indicates that

charge compensation is a powerful method to enhance the

luminescent intensity of phosphors when necessary. From

Fig. 9, the sequence according to the effect on luminescent

intensity is Li?, Na?, and K?. The integrated emission

intensity (from 500 to 700 nm) of phosphors with Li?,

Na?, and K? as charge compensators are enhanced by 1.9,

1.6, and 1.3 times, respectively.

When Sm3? is incorporated into SrWO4 host, it sub-

stitutes for a Sr2? ion, which may induce structural defect.

According to the principle of charge balance, the intro-

duction of Sm3? in SrWO4 should lead to the appearance

of calcium ion vacancy. Generally, this negative vacancy is

deleterious to the luminescence intensity of the Sm3? ions

because the energy transfer from the luminescence centers

to the vacancy defects becomes more effective. As a charge

compensator, alkali metals such as Li?, Na?, and K? can

sometimes be added to the host lattice. Thus, the intro-

duction of R? ions leads to the decrease of non-radiative

transitions probability and increases significantly the

emission efficiency of Sm3?-doped SrWO4 phosphors.

For R?, it is found that Li? anion can exhibit the

strongest charge compensation abilities, Na? anion being

the second, and K? anion is the weakest. The evident

change of the emission intensity is due to differences of the

ionic radii of alkali metal ions. The alkali metal ions of

Li?, Na?, and K? have the valence electronic configura-

tions. The ionic radii increase in the order of Li?

(0.092 nm) \ Na? (0.118 nm) \ K? (0.151 nm) [28]. The

difference of ionic radii would give rise to the diversity of

sub-lattice structure around the luminescent center ions,

which influences the spin–orbit couplings and crystal field

of Sm3? ions. Among them, the emission intensity of as-

prepared phosphor with Li? as the charge compensator is

higher than that of phosphors co-doped by Na?, and K?.

The reason may be that Li? ions are easy to enter into

SrWO4 crystal lattice than the others due to its smaller

ionic radius.

The commission International de I’Eclairage (CIE)

chromaticity coordinates of Sm3? and R? (R = Li, Na and

K)) doped phosphors excited at 403 nm were calculated

Fig. 8 The relation of the concentration of Sm3? ions Log(x) and the

Log (I/x) for the 4G5/2 ? 6H7/2 (596 nm) transition by 403 nm light

Fig. 9 Influence of charge compensation ions on the emission

intensity of Sr0.92WO4: Sm0.043? , R0.04

? phosphors (R = Li, Na, K)

J Mater Sci: Mater Electron

123

using the CIE system. All phosphors own the approximate

coordinates for their similar spectral shape. As shown in

Fig. 10, the CIE chromaticity coordinates of typical chro-

maticity coordinates of Sr0.92WO4: Sm0.043? , Li0.04

? is located

in the orange region (x = 0.537 and y = 0.444).

4 Conclusions

In summary, one-dimensional Sm3? doped SrWO4 without

or with different charge compensation approaches (co-

doping Li?, Na? and K?) nanofibers are prepared by

electrospinning. As-prepared precursor composite fibers

present uniform fiberlike morphology and smooth surface

with diameters ranging from 300 to 500 nm. After calci-

nation at 700 �C for 3 h, well-crystallized Sr(1-x)WO4:

Smx3? (x = 2–6 %) nanofibers consist of linked nanopar-

ticles with the diameters ranging from 100 to 200 nm. Its

excitation spectra show broad absorption from 300 to

450 nm suggesting that the phosphors can be excited

effectively by UV and near-UV light. The PL spectra of

SrWO4: Sm3? phosphors exhibits a strong orange light

emission with emission peaks at 561, 596 and 643 nm and

the optimal doping concentration of Sm3? in SrWO4 is

ascertained experimentally to be 4 mol%. The introduction

of R? (R = Li, Na and K) as charge compensators for

SrWO4 host can enhance the luminescence intensity. The

Li?, Na? and K? increase the luminescence intensity by

1.9, 1.6, and 1.3 times, respectively. It because that the

ionic radius of Li? is smaller than that of Na? or K?, which

makes Li? ions enter into SrWO4 crystal lattice easily. The

results indicate that Sr0.92WO4: Sm0.043? , Li0.04 with maxi-

mum excitation around 403 nm is expected to be a

potential candidate for the orange component used for

light-emitting diode based on UV chip technology.

References

1. G.P. Dong, X.D. Xiao, L.L. Zhang, Z.J. Ma, X. Bao, M.Y. Peng,

Q.Y. Zhang, J.R. Qiu, J. Mater. Chem. 21, 2194 (2011)

2. C. Peng, G. Li, X. Kang, C. Li, J. Lin, J. Colloid Interface Sci.

355, 89 (2011)

3. Y. Ner, J.G. Grote, J.A. Stuart, G.A. Sotzing, Angew. Chem. Int.

Ed. 121, 5234 (2009)

4. H. Wu, Y. Sun, D.D. Lin, R. Zhang, C. Zhang, W. Pan, Adv.

Mater. 21, 227 (2009)

5. Z.Y. Zhang, C.L. Shao, F. Gao, X.H. Li, Y.C. Liu, J. Colloid

Interface Sci. 347, 215 (2010)

6. Y.L. Cheng, Y. Zhao, Y.F. Zhang, X.Q. Cao, J. Colloid Interface

Sci. 344, 321 (2009)

7. C. Peng, M.M. Shang, G.G. Li, Z.Y. Hou, D.L. Geng, J. Lin,

Dalton Trans. 41, 4780 (2012)

8. W.Y. Liu, Y.C. Yeh, J. Lipner, J.W. Xie, H.W. Sung, S. Thom-

opoulos, Y.N. Xia, Langmuir 27, 9088 (2011)

9. A.B. Suryamas, M.M. Munir, T.O. Khairurrijal, K. Kuyama, J

Mater Chem 21, 12629 (2011)

10. G.P. Dong, Y.Z. Chi, X.D. Xiao, X.F. Liu, B. Qian, Z.J. Ma, E.

Wu, H.P. Zneg, D.P. Chen, J.R. Qiu, Opt. Express 17, 22514

(2009)

11. Y.L. Cheng, Y. Zhao, Y.F. Zhang, X.Q. Cao, J. Colloid Interface

Sci. 344, 321 (2010)

12. Z.Y. Hou, C.X. Li, J. Yang, H.Z. Lian, P.P. Yang, R.T. Chai,

Z.Y. Cheng, J. Lin, J. Mater. Chem. 19, 2737 (2009)

13. Z.Y. Hou, G.G. Li, H.Z. Lian, J. Lin, J. Mater. Chem. 22, 5254

(2012)

14. P.F. Du, L.X. Song, J. Xiong, H.B. Cao, Z.Q. Xi, S.Y. Guo, N.Y.

Wang, J.J. Chen, J. Alloys Compd. 540, 179 (2012)

15. J.M. Liao, L.B. Liu, H.Y. You, H.P. Huang, W.X. You, Optik

123, 901 (2012)

16. T. Thongtem, A. Phuruangrat, S. Thongtem, Appl. Surf. Sci. 254,

7581 (2008)

17. L.S. Cavalcante, J.C. Sczancoski, J.W.M. Espinosa, J.A. Varala,

P.S. Pizani, E. Longo, J. Alloys Compd. 474, 195 (2009)

18. X.Y. Sun, X.D. Sun, X.G. Li, J. He, B.S. Wang, J. Mater. Sci.:

Mater. Electron. 25, 2320 (2014)

19. Y.G. Su, L.P. Li, G.S. Li, Chem. Mater. 20, 6060 (2008)

20. P.P. Yang, Z.W. Quan, C.X. Li, H.Z. Lian, S.S. Huang, J. Lin,

Mesoporous Mater. 116, 524 (2008)

21. J.S. Liao, B. Qiu, H. Wen, W. You, Opt. Mater. 31, 1513 (2009)

22. J.S. Liao, B. Qiu, H.R. Wen, J.L. Chen, W.X. You, L.B. Liu, J.

Alloys Compd. 487, 758 (2009)

23. Z.H. Ju, R.P. Wei, J.X. Ma, C.R. Pang, W.S. Liu, J. Alloys

Compd. 507, 133 (2010)

24. Y.H. Zheng, J.T. Lina, Q.M. Wang, Photochem. Photobiol. Sci.

11, 1567 (2012)

25. J. Mu, L. Liu, S. Kang, Nanoscale Res. Lett. 2, 100 (2007)

26. Y. Zhou, J. Lin, S. Wang, J. Solid State Chem. 171, 391 (2003)

27. E. De la Rosa, L. Diaz-Torres, P. Salas, R. Rodriguez, Opt.

Mater. 27, 1320 (2005)

Fig. 10 The CIE chromaticity coordinates of Sr0.92WO4: Sm0.043? ,

Li0.04? phosphor

J Mater Sci: Mater Electron

123

28. R.D. Shannon, Acta Cryst. A 32, 751 (1976)

29. H.Y. Tian, W.G. Luo, X.H. Pu, P.S. Qiu, X.Y. He, A.L. Ding,

Thermochim. Acta 360, 57 (2000)

30. J. Coates, (USA, 2000), pp. 10815–10837

31. Q.Z. Cui, X.T. Dong, J.X. Wang, M. Li, J. Rare Earths 26, 664

(2008)

32. S. Wannapop, T. Thongtem, S. Thongtem, Ceram. Int. 37, 3499

(2011)

33. G.M. Clark, W.P. Doyle, Spectrochim. Acta 22, 1441 (1966)

34. R.L. Frost, L. Duong, M. Weier, Spectrochim. Acta Part A 60,

1853 (2004)

35. X. Lin, X.S. Qiao, X.P. Fan, Solid State Sci. 13, 579 (2011)

36. P.L. Li, Z.J. Wang, Z.P. Yang, Q.L. Guo, X. Li, J. Lumin. 130,

222 (2010)

37. H.M. Yang, J.X. Shi, H.B. Liang, M.L. Gong, Mater. Sci. Eng. B

127, 276 (2006)

38. G. Blasse, B.C. Grabmaier, Luminescent Materials, 1st edn.

(Springer, Germany, 1994), pp. 91–107

39. J.C. Zhang, Y.H. Wang, Z.Y. Zhang, Z.L. Wang, B. Liu, Mater.

Lett. 62, 202 (2008)

40. P.L. Li, Z.J. Wang, Z.P. Yang, Q.L. Guo, X. Li, Mater. Lett. 63,

751 (2009)

41. G.P. Dong, X.D. Xiao, Y.Z. Chi, B. Qian, X.F. Liu, Z.J. Ma, H.P.

Zeng, D.P. Chen, J.R. Qiu, J. Mater. Chem. 20, 1587 (2010)

42. Y. Tian, X.H. Qi, X.W. Wu, R.N. Hua, B.J. Chen, J. Phys. Chem.

C 113, 10767 (2009)

43. X.Y. Sun, L.W. Lin, W.F. Wang, J.C. Zhang, Appl. Phys. A 104,

83 (2011)

J Mater Sci: Mater Electron

123