enhanced luminescence in camoo4: eu3+ red phosphor nanoparticles prepared by mechanochemically...

Enhanced luminescence in CaMoO4:Eu3+ red phosphornanoparticles prepared by mechanochemically assisted solid statemeta-thesis reaction method

Anthuvan John Peter • I. B. Shameem Banu •

Jagannathan Thirumalai • Samuel Paul David

Received: 15 June 2013 / Accepted: 1 August 2013 / Published online: 15 August 2013

� Springer Science+Business Media New York 2013

Abstract For the first time, CaMoO4:xEu3? (x = 0.02,

0.04, 0.06, 0.08, 0.1) red phosphor nanoparticles were

synthesized using the simple mechanochemically assisted

solid state meta-thesis (SSM) reaction method and the

luminescence properties as a function of Eu3? ion con-

centration was investigated. The characteristics of the

phosphor materials were analyzed using X-ray diffraction,

fourier transform infrared spectroscopy, photolumines-

cence (PL) and diffuse reflectance spectroscopy. For

8 mol% of Eu3? concentration, the phosphor shows an

intensified excitation peak at 392 nm indicating a strong

absorption. The PL emission spectra of CaMoO4:Eu3?

phosphors showed an intense peak at 615 nm (red) which

corresponds to 5D0 ? 7F2 transition of Eu3?. The optimal

Eu3? concentration in CaMoO4 phosphors for enhanced

red emission occurs for 8 mol% and above this concen-

tration, the emission intensity decreases due to quenching

effect. The CIE colour coordinates of the Ca-

MoO4:0.08Eu3? red phosphor coincide very well with the

standard values of NTSC. The red emission intensity of the

SSM prepared CaMoO4:0.08Eu3? red phosphor is 4.7

times greater than that of the commercial Y2O2S:Eu3? red

phosphor and 1.6 times more than the same phosphor

prepared by the solid state reaction method.

1 Introduction

White light emitting diodes (LEDs), the next generation of

solid state lighting, have got much deliberate attention

recently due to their leverage over conventional light

sources such as, high efficiency, long life time, energy

saving, stability, environmental friendly, no pollutant and

have potential applications in many fields such as devices

like indicators, back lights, automobile head lights and

general illumination, etc. [1–5]. In general, conventional

white LEDs are assembled by combining a blue LED with

yellow emitting phosphor material, such as Y3Al5O12:Ce3?

[6] in which white light is generated when blue light from

the LED chip and yellow light from phosphor get blended.

However, such white light emitting diodes do not generate

warm white light due to deficiency of red emission [7].

This drawback is overcome by combining near UV-LED

chip (370–410 nm) with tricolor phosphors such as red,

green, blue phosphors to generate white light that can yield

a high colour rendering index. The UV light emitted by the

near UV-LED excites the tricolor phosphors giving white

light. The commercially available tricolor phosphors for

white LED applications are Y2O2S:Eu3? for red [8],

BaMgAl10O17:Eu2? for blue [9] and ZnS (Cu?, Al3?) for

green [10]. While comparing with blue and green phos-

phors, the thermal and chemical stability of the sulphide

based red phosphors is inadequate. They show poor

absorbance near UV region and their efficiency is also

approximately eight times lesser than blue and green

phosphors for white LED applications [11]. Therefore,

A. John Peter (&)

Department of Physics, St. Anne’s College of Engineering and

Technology, Panruti, Tamil Nadu, India

e-mail: [email protected]

I. B. Shameem Banu (&) � J. Thirumalai

Department of Physics, B. S. Abdur Rahman University,

Vandalur, Chennai, Tamil Nadu, India

e-mail: [email protected]

S. P. David

The College of Optics and Photonics, University of Central

Florida, Orlando, FL, USA

123

J Mater Sci: Mater Electron (2013) 24:4503–4509

DOI 10.1007/s10854-013-1433-6

now-a-days, special attention is focused on discovering an

alternative novel red phosphor which is thermally and

chemically more stable and also shows better luminous

efficiency. To obtain a novel red emitting phosphor among

many rare earth ions, Eu3? is the best choice as an activator

ion because it can be effectively excited by near UV and

blue light and then emit stronger red fluorescence which is

ascribed to 5D0–7FJ (J = 0, 1, 2, 3) transitions [12–15].

In the recent years, an increasing attention is focused on

CaMoO4 as host matrix for luminescent ions due to their

good chemical and thermal stability and good lumines-

cence properties [16, 17]. CaMoO4 has scheelite structure

with a tetragonal unit cell (space group I41/a) and the

crystal structure has an inversion centre. Several works

have been reported on the luminescence properties of Ca-

MoO4:Eu3? red phosphors prepared by different methods.

Campos et al. and Longo et al. investigated the origin and

mechanisms behind photo luminescence properties of Ca-

MoO4 [18, 19]. Hu et al. [20] reported that CaMoO4:Eu3?,

red emitting phosphor can be excited by near UV light

(394 nm) to show strong red luminescence (616 nm) from

the Eu3? transition of 5D0–7F2 and thus considered to be a

good candidate for white LED application. Parchur and

Ningthoujam [21] described the luminescence properties of

Eu3? activated CaMoO4 phosphor and observed lattice

fringes by using FFT method. Chunlei et al. [22] studied

the luminescence properties of molybdate based phosphor

and they reported that scheelite host showed much stronger

UV absorption than wolframite host. There are several

routes to prepare calcium molybdate based LED phosphors

such as co-precipitation method [23], hydrothermal method

[24] and conventional solid state reaction (SSR) method.

SSR approach usually requires high temperature and con-

sumes a lot of power and time. The detailed literature

survey shows that so far no work has been reported on the

preparation of rare earth ion doped CaMoO4 phosphors by

mechanochemically assisted solid state meta-thesis (SSM)

route which can be performed at room temperature. The

solid state metathesis reaction method is an existing

method of synthesizing inorganic materials and has merits

compared to other traditional methods in terms of reaction

rate with little or no need for external energy. Using this

method, fine, chemically homogenous, pure and highly

crystalline phase phosphor material can be prepared in a

short time [25] at room temperature.

Based on these investigations, in this paper, the prepa-

ration of Eu3? doped CaMoO4 phosphors by mechano-

chemically assisted solid state meta-thesis (SSM) reaction

route is reported along with the observation of its red

emission enhancement for an optimal Eu3? doping con-

centration. The red emission intensity of the SSM prepared

sample has been compared with that of the same phosphor

prepared by SSR method and the commercially used

Y2O2S:Eu3? red phosphors to elucidate the advantage of

SSM method.

2 Experimental method

2.1 Preparation of phosphors

The red phosphors of CaMoO4:xEu3? (x = 0.02, 0.04,

0.06, 0.08, 0.10) were prepared by mechanochemically

assisted solid state meta-thesis route at room temperature

by using AR grade Na2MoO4�2H2O, CaCl2 and EuCl3(99.9 %) as the starting materials without any further

purification. The appropriate stoichiometric mixtures of

CaCl2, Na2MoO4�2H2O and EuCl3 were mixed and were

milled for a period of one hour in a planetary ball mill

Pulverisette 7 (FRITSCH). Milling was carried out in two

grinding vials of 15 ccm volume containing balls with

diameter of 12 mm. Both the container and balls were

made of tungsten carbide material. The number of milling

balls and the rotation speed of the planetary system of

milling device were kept constant. The resultant powder

was washed with distilled water to remove sodium chloride

and then dried at 80 �C for 3 h in a muffle furnace in air

and sieved.

CaCl2 þ Na2MoO4 � 2H2O! CaMoO4 þ NaCl

2.2 Characterization

X-ray powder diffraction (XRD) analysis was carried out

using Pan Analytical X’pert pro X-ray diffractometer with

Cu K-alpha radiation (k = 1.5406 A) at scanning rate of

0.02� per second. The XRD patterns were obtained in the

range of 0� B 2h B 70� and compared with the joint

commission on powder diffraction standards (JCPDS).

Fourier transform infrared spectroscopy (FTIR) measure-

ments were carried out in the wavenumber range of

400–4,000 cm-1 with a Nicolet 6700 FTIR equipped with

a deuterated triglycine sulfate detector. Photo luminescent

excitation and emission spectra were measured using a

Jobin Yuvon Flurolog 3-11 Spectrofluorometer at room

temperature with 450 W xenon lamp which was used as the

excitation source (200–700 nm). The phosphor powders

were slackly positioned on a solid stand and were excited

straight. The excitation and emission slit width were set to

2 nm. Optical absorption spectra were recorded using

Systronics-2101 UV–visible double beam spectrophotom-

eter. All spectroscopic measurements of the phosphors

were carried out at room temperature.

4504 J Mater Sci: Mater Electron (2013) 24:4503–4509

123

3 Results and discussion

3.1 XRD analysis

The XRD profiles of CaMoO4:xEu3? (x = 0.02, 0.04, 0.06,

0.08, 0.10) are displayed in Fig. 1 with the corresponding

peaks indexed. Diffraction peaks of all the samples were

found to be similar without noticeable shift in the positions.

The XRD patterns of the doped samples match with the

diffraction pattern of the tetragonal scheelite structure of

CaMoO4 (JCPDS card no. 851267). The XRD pattern

signifies that the Eu3? ions have no obvious influence on

the structure of the host. No impurity peaks related to the

starting materials Na2MoO4�2H2O, CaCl2 and EuCl3 were

observed and this also suggests that doped Eu3? ions uni-

formly entered into the crystal lattice of CaMoO4. Since

the ionic radius of Eu3? (0.107 nm) is closer to Ca2?

(0.112 nm) [26], it is clear that Eu3? ion replaces the Ca2?

ion. The strong and sharp diffraction peaks indicate the

high crystallinity of the prepared samples [27] and hence it

clear that limited doping of Eu3? ions do not produce any

significant change in the crystal structure of the synthesized

phosphors [28]. The average crystallite size was deter-

mined according to the Scherrer’s equation. As described

in the literature [29]. Scherrer’s equation is D = 0.9 k/bcos h, where k is the X-ray wave length (0.15406 nm), b is

the full-width at half maximum (FWHM) of the diffraction

line and h is the diffraction angle. The average crystallite

size of the Eu doped CaMoO4 varies from 20 to 40 nm

which indicates that the particles are suitable for the

preparation of solid state lighting devices.

3.2 FTIR analysis

The FTIR spectra of CaMoO4:xEu3? (x = 0.02, 0.04, 0.06,

0.08, 0.1) phosphors are shown in Fig. 2. A very weak

absorption band lies around 430 cm-1 and it is associated

with the bending modes of vibration of Mo–O. A very

broad strong absorption band around 810 cm-1 is due to

anti-symmetric stretching vibrations of O–Mo–O in

MoO42- tetrahedron [21, 39]. The weak absorption band

around 3,400 cm-1 is due to O–H stretching vibration and

the bands around 1,630 cm-1 can be assigned to H–O–H

bending vibration of water absorbed from air [40].

3.3 Photoluminescence properties of CaMoO4:Eu3?

3.3.1 Excitation spectra analysis

Figure 3 shows the excitation spectra of CaMoO4:xEu3?

(x = 0.02, 0.04, 0.06, 0.08, 0.1) phosphors for monitoring

the 5D0–7F2 (kem = 615 nm) transitions of Eu3?. The

excitation spectrum consists of two parts: (1) a most

intense and broad excitation band in the range from 225 to

350 nm. (2) very sharp peaks with less intensity in the

range from 350 to 500 nm. The first region (200–350 nm)

is due to the overlapping of two charge transfer bands: (1)

Charge transfer transition from oxygen (O2- ligand) to

molybdenum (Mo6? ion) [ligand to metal charge transfer].

(2) Charge transfer transition from an oxygen 2p orbital to

an empty 4f orbital of europium [30–32]. Many weak sharp

lines in the second region between 350 and 500 nm cor-

respond to the typical Eu3? intra—4f transitions in the host

lattice. The strong absorptions at 392 and 462 nm were

attributed to the 7F0 ? 5L6 and 7F0 ? 5D2 transitions of

Eu3? which are in good agreement with the near-UV or

blue output wavelengths of GaN based LED chips [31].

Fig. 1 Powder XRD patterns of CaMoO4:xEu3? (x = 0.02, 0.04,

0.06, 0.08, 0.1)

Fig. 2 FTIR spectrum of CaMoO4:xEu3? (x = 0.02, 0.04, 0.06,

0.08, 0.1)

J Mater Sci: Mater Electron (2013) 24:4503–4509 4505

123

3.3.2 Emission spectra analysis

Figure 4 shows the PL spectra of the CaMoO4:xEu3?

(x = 0.02, 0.04, 0.06, 0.08, 0.1) under 392 nm near-UV

excitation. The PL spectra of the synthesized samples are

similar with respect to the shape and peak positions and

differ in their peak intensities. The photoluminescence

emission spectra consists of sharp lines with wavelength

ranging from 530 to 710 nm, which are associated with the

5D0 ? 7FJ (J = 1, 2, 3, 4) transitions from the excited

Eu3? to the ground state. The main emission peak at

615 nm is strong which is due to the 5D0 ? 7F2 transitions

of Eu3? and the other transitions such as 5D0 ? 7F1,5D0 ? 7F3, and 5D0 ? 7F4 located in the range of

530–710 nm are weak [12]. The 5D0 ? 7F2 electric dipole

transition of Eu3? is highly sensitive to its surroundings

and occurs dominantly only when the Eu3? ion is in a non-

centrosymmetric site. Due to the lack of symmetry, the

4f orbitals mix with the opposite parity orbitals and thus the

electric dipole transition has occurred [34]. For this reason,

the intensity of 5D0 ? 7F2, was found to be much stronger

than those of 5D0 ? 7F1, which suggests that the Eu3? is

located in a distorted (or asymmetric) cation environment

and indicates that Eu 3? ions occupy the sites of Ca. Other

transitions from 5DJ (J = 1, 3, 4) are relatively weak,

which is advantageous when seeking to obtain high-quality

red light [35, 36].

3.3.3 Eu3? concentration effect

The doping concentration of Eu3? ions is one of the

important factors which influence the properties of lumi-

nescent materials. Hence, the optimum Eu3? doping con-

centration in CaMoO4:xEu3? (x = 0.02, 0.04, 0.06, 0.08,

0.1) phosphors for enhanced red emission was studied by

comparing the PL intensities obtained for various concen-

trations at the excitation wavelength of 392 and 462 nm.

Figure 5 shows the comparison of PL intensity ofFig. 3 PLE spectrum of CaMoO4:xEu3? (x = 0.02, 0.04, 0.06, 0.08,

0.1) phosphors monitored at 615 nm

Fig. 4 Photoluminescence

emission spectrum of

CaMoO4:xEu3? (x = 0.02,

0.04, 0.06, 0.08, 0.1) phosphors

under 392 nm excitation and the

inset shows PL spectra of

CaMoO4:0.08Eu3? phosphor


123

Ca1-xMoO4:xEu3? (x = 0.02, 0.04, 0.06, 0.08, 0.1) (SSM)

phosphors excited by 392 and 462 nm as a function of

Eu3? concentration. For both the excitation wavelengths,

the PL intensity is observed to enhance with Eu3? con-

centration reaching a maximum at 0.8 % content which is

followed by a decrease with further increase in the con-

centration. This comparison reveals that the emission

intensity of phosphors excited at 392 nm (near UV) is

stronger as compared to that excited at 462 nm at almost

all the concentrations of Eu3?. Even though the maximum

red emission is obtained at 0.8 % for these two wave-

lengths, it is to be noted that the emission intensity for

392 nm (UV near) is much greater than that for 462 nm. It

signifies that they may be used as a potential red-emitting

phosphor in near-UV based White LEDs than blue GaN

based White LEDs. The optimum Eu3? content in CaMoO4

for the enhanced red emission is found to be 8 mol%.

The quenching of PL intensity for concentrations above

0.8 % may be due to the exchange interaction of energy

occurred between a number of excited Eu3? ions. For

europium activated phosphors, the quenching process is

attributed to the energy migration among the activators

(Eu3? ions) which brings excitation energy to the nearby

quenching centers (traps). These centers are typically

impurities or defects on the particle [37, 38].

3.3.4 Diffuse reflectance spectra and CIE analysis

It is known that the PLE spectrum is comparable to

absorption spectrum and so, the excitation band and peak

in the PLE spectra can be reasonably referred to one

absorption process (Fig. 3). To investigate the energy

absorption, the diffuse reflectance spectra (DRS) of Ca-

MoO4:xEu3? (x = 0.02, 0.08, 0.10) phosphors were mea-

sured and are shown in Fig. 6. The absorption band from

220 to 350 nm corresponds to overlapping of the (O–Mo)

ligand to metal CT in the MoO42- group and electron

transfer from oxygen (O2-) to europium (Eu3?). The

absorptions at 392 and 462 nm are ascribed to the 4f–

4f electron transitions of Eu3? ions, which is consistent

with the conclusion of the excitation spectrum analysis.

Figure 7 shows the CIE chromaticity diagram for the

emission spectra of CaMoO4:0.08Eu3? phosphor. The CIE

Fig. 5 Comparison of red emission intensities of CaMoO4:xEu3?

(x = 0.02, 0.04, 0.06, 0.08, 0.1) phosphors under 392 and 462 nm

excitation as a function of Eu3? concentration

Fig. 6 Diffuse reflectance spectra of CaMoO4:xEu3? (x = 0.02,

0.08, 0.1) phosphors

Fig. 7 CIE chromaticity diagram for CaMoO4:0.08Eu3? phosphor

(kex = 392 nm)


123

chromaticity coordinates (x, y) of the CaMoO4:0.08 Eu3?

phosphor upon 392 nm excitation wavelength lie at

x = 0.678 and y = 0.322 which are very close to the

standard chromaticity coordinate values of NTSC

(x = 0.670, y = 0.330). Hence, the CIE diagram illustrates

that the obtained phosphor nanoparticles show red emis-

sions when excited by a single wavelength (kex = 392 nm)

and thus the obtained results confirm that the SSM pre-

pared CaMoO4:0.08Eu3? phosphor is a promising red

emitting components for near-UV InGaN-based white

LED.

3.3.5 Comparison of the photoluminescence

of CaMoO4:0.08Eu3? (SSM) with Y2O2S:Eu3?

and CaMoO4:Eu3? (SSR)

As the present work is focused for the purpose of red

phosphor application in WLED with near UV/blue GaN

based chips as excitation sources, the results of the PL

spectra of the present work (SSM) are compared with that

of (1) the PL spectra of CaMoO4:0.08Eu3? phosphor pre-

pared by SSR method and (2) the PL spectra of the con-

ventional red phosphor Y2O2S:Eu3? prepared by SSR

method. For this purpose, Y2O2S:Eu3? and CaMoO4:Eu3?

phosphors were prepared by SSR method and the lumi-

nescence properties were also studied. The red emission

spectra of these three red phosphors are presented in Fig. 8

which reveals that red emission intensity of Ca-

MoO4:0.08Eu3? (SSM) is about 4.7 times more than that of

commercially used Y2O2S:Eu3? red phosphor and 1.6

times more than that of CaMoO4:Eu3? (SSR) phosphor,

indicating that CaMoO4:0.08Eu3? phosphor prepared by

mechanochemically assisted solid state meta-thesis (SSM)

route at room temperature is a promising red phosphor for

WLEDs.

4 Conclusion

Well crystalline CaMoO4:Eu3? phosphor nano powders of

Scheelite-type have been successfully prepared by me-

chanochemically assisted solid state metathesis (SSM)

route at room temperature. The FT-IR spectra shown a very

intense and broad absorption band of the vibration in the

MoO42- tetrahedron. Upon 392 nm near UV excitation, the

CaMoO4:0.08Eu3? phosphor showed strong red emission

lines at 615 nm corresponding to forced electric dipole

transitions. The optimum doping concentration of Eu3?

content in CaMoO4 for the enhanced red emission is found

to be 8 mol%. The intensity of emission spectra of Ca-

MoO4:0.08Eu3? excited at 392 nm is remarkably stronger

than that of the same phosphor excited at 462 nm and this

suggests that CaMoO4:0.08Eu3? nanoparticles are suitable

red-emitting phosphor in near-UV based White LEDs than

blue GaN based White LEDs. The red emission intensity of

CaMoO4:0.08Eu3? reported in the present work is stronger

by a factor of about 4.7 times than that of the commercial

red emitting sulphide based phosphor, Y2O2S:Eu3? and

also it is about 1.6 times more as compared to that of

CaMoO4:Eu3? prepared by solid state reaction (SSR)

method. All these favourable properties indicate that SSM

prepared CaMoO4:0.08 Eu3? red phosphor is a promising

candidate for the phosphor converted white LEDs.

References

1. C.-H. Chiu, C.-H. Liu, S.-B. Huang, T.-M. Chen, J. Electron.

Chem. Soc. 155(3), J71 (2008)

2. H. He, R.L. Fu, F.J. Qian, X.F. Song, J. Mater. Sci. Mater.

Electron. 23(2), 599 (2012)

3. F.-B. Cao, Y.-W. Tian, L.-S. Li, Y.-J. Chen, L.-J. Xiao, J. Mater.

Sci. Mater. Electron. 22, 510 (2011)

4. G. Du, W. Guo, J.M. Khalaf Al-zyadi, Y. Han, P. Liu, Z. Liu, J.

Nanopart. Res. 15, 1619 (2013)

5. S. Ye, F. Xiao, Y.X. Pan, Y.Y. Ma, Q.Y. Zhang, Mater. Sci. Eng.,

R 71, 1 (2010)

6. L.T. Su, A.I.Y. Tok, F.Y.C. Boey, X.H. Zhang, J.L. Woodhead,

C.J. Summers, J. Appl. Phys. 102, 083541 (2007)

7. M. Thomas, P. Prabhakar Rao, M. Deepa, M.R. Chandran, P.

Koshy, J. Solid State Chem. 182, 203 (2009)

8. J. Dhanaraj, R. Jagannathan, D.C. Trivedi, J. Mater. Chem. 13(7),

1778 (2003)

9. H.-K. Jung, D.-W. Lee, K.Y. Jung, J.-H. Boo, J. Alloys Compd.

390, 189 (2005)

10. Y.Y. Chen, J.G. Duh, B.S. Chiou, C.G. Peng, Thin Solid Films

392(1), 50 (2001)

Fig. 8 PL spectrum of CaMoO4:0.08Eu3?(SSM prepared) phosphor,

commercial Y2O2S:Eu3? phosphor and CaMoO4:0.08Eu3? (SSR

prepared) phosphors for comparison


123

11. K.-S. Hwang, B.-A. Kang, S. Hwangbo, Y.-S. Kim, J.-T. Kim,

Electron. Mater. Lett. 6(1), 27 (2010)

12. I.L.V. Rosa, A.P.A. Marques, M.T.S. Tanaka, D.M.A. Melo, E.R.

Leite, E. Longo, J.A. Varela, J. Fluoresc. 18(2), 239 (2008)

13. J. Thirumalai, R. Krishnan, I.B. Shameem Banu, R. Chandra-

mohan, J. Mater. Sci. Mater. Electron. 24(1), 253 (2013)

14. R. Krishnan, J. Thirumalai, I.B. Shameem Banu, A. John Peter, J.

Nanostruct. Chem. 3, 1 (2013)

15. R. Krishnan, J. Thirumalai, R. Chandramohan, J. Nanostruct.

Chem. 4, 1 (2013)

16. A.P.A. Marques, F.V. Motta, E.R. Leite, P.S. Pizani, J.A. Varela,

E. Longo, D.M.A. De Melo, J. Appl. Phys. 104, 043505 (2008)

17. A.P.A. De Marques, V.M. Longo, D.M.A. De Melo, P.S. Pizani,

E.R. Leite, J.A. Varela, E. Longo, J. Solid State Chem. 181, 1249

(2008)

18. V.M. Longo, A.T. De Figueiredo, A.B. Campos, J.W. Espinosa,

A.C. Hernandes, C.A. Taft, J.R. Sambrano, J.A. Varela, E.

Longo, J. Phys. Chem. A 112, 8920 (2008)

19. A.B. Campos, A.Z. Simoes, E. Longo, J.A. Varela, V.M. Longo,

A.T. De Figueiredo, F.S. De Vicente, A.C. Hernandes, Appl.

Phys. Lett. 91, 051923 (2007)

20. H. Wu, Y. Hu, W. Zhang, F. Kang, N. Li, G. Ju, J. Sol Gel Sci.

Technol. 62, 227 (2012)

21. A.K. Parchur, R.S. Ningthoujam, Dalton Trans. 40, 7590 (2011)

22. Z. Chunlei, H. Yunsheng, Z. Weidong, H. Xiaowei, H. Tao, J.

Rare Earth. 27, 758 (2009)

23. Y. Yang, X. Li, W. Feng, W. Yang, W. Li, C. Tao, J. Alloys

Compd. 509, 845 (2011)

24. Y. Jin, J. Zhang, S. Lu, H. Zhao, X. Zhang, X.-J. Wang, J. Phys.

Chem. C 112, 5860 (2008)

25. P. Parhi, S.S. Singh, A.R. Ray, A. Ramanan, Bull. Mater. Sci.

29(2), 115 (2006)

26. D. Lide, The CRC Hand Book of Chemistry and Physics on CD-

ROM (CRC Press, Version, 2002), pp. 12–13

27. Q. Xiao, Q. Zhou, M. Li, J. Lumin. 130, 1092 (2010)

28. Q. Li, J. Huang, D. Chen, J. Alloys Compd. 509, 1007 (2011)

29. P. Klug, L.E. Alexander, X-ray Diffraction Procedure (Wiley,

New York, 1954)

30. V. Sivakumar, U.V. Varadaraju, J. Electrochem. Soc. 152, H168

(2005)

31. X.X. Wang, J. Wang, J.X. Shi, Q. Su, M.L. Gong, Mater. Res.

Bull. 42, 1669 (2007)

32. F.N. Shi, J. Meng, Y. Ren, J. Solid State Chem. 121(1), 236

(1996)

33. X.-H. He, M.-Y. Guan, J.-H. Sun, N. Lian, T.-M. Shang, J. Mater.

Sci. 45(1), 118 (2010)

34. A. Xie, X. Yuan, F. Wang, Y. Shi, Z. Mu, J. Phys. D Appl. Phys.

43, 055101 (2010)

35. J. Wang, X. Jing, C. Yan, J. Lin, J. Electrochem. Soc. 152(3),

G186 (2005)

36. S.K. Mahesh, P. Prabhakar Rao, M. Thomas, A.N. Radhakrish-

nan, P. Koshy, J. Mater. Sci. Mater. Electron. 23(9), 1605 (2012)

37. Z. Ci, Y. Wang, J. Zhang, Y. Sun, Phys. B Condens. Matter. 403,

670 (2008)

38. Y. Tian, X. Qi, X. Wu, R. Hua, B. Chen, J. Phys. Chem. C

113(24), 10767 (2009)

39. A.P.A. Marques, M.T.S. Tanaka, E. Long, E.R. Leite, I.L.V.

Rosa, J. Fluoresc. 21(3), 893 (2011)

40. G. Li, Z. Wang, Z. Quan, C. Li, J. Lin, J. Cryst. Growth Des. 7(9),

1797 (2007)


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