DSpace at VNU: Structural and luminescent properties of (Eu,Tb)PO4·H2O nanorods nanowires prepared by microwave technique

JOURNAL OF RARE EARTHS, Vol. 29, No. 12, Dec. 2011, P. 1170

Structural and luminescent properties of (Eu,Tb)PO4·H2O nanorods/
nanowires prepared by microwave technique
Nguyen Thanh Huong1, Nguyen Duc Van1, Dinh Manh Tien1, Do Khanh Tung1, Nguyen Thanh Binh1, Tran Kim Anh1,
Le Quoc Minh1, 2
(1. Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Cau Giay Distr., Hanoi, Vietnam; 2. University of Engineering
and Technology, National University Hanoi, Vietnam, 144 Xuan Thuy Road, Cau Giay Distr., Hanoi, Vietnam)
Received 15 August 2011; revised 5 September 2011

Abstract: Nanowires/nanorods of europium/terbium orthophosphate monohydrate with Eu3+ concentration of 6, 11, and 20 at.% were prepared by microwave synthesis method. The effects of Eu3+ doping concentration on structure, morphology and optical properties of nanomaterials were also investigated. The results showed that, for all studied Eu3+ doping concentrations, a single-crystalline phase of rhabdophane-type (Eu,Tb)PO4·H2O nanowires/nanorods was obtained by using microwave heating of an aqueous solution of terbium(III) nitrate,
europium(III) nitrate and NH4H2PO4 with pH=2. The length and width of these nanowires/nanorods ranged from 150 to 300 nm and from 10
to 50 nm, respectively. The evidence of energy transfer from Tb3+ to Eu3+ due to the energy overlap between the donor Tb3+ and the acceptor
Eu3+ was observed obviously via a significant enhancement in the luminescent intensity of Eu3+.
Keywords: microwave technique nanowires/nanorods energy transfer fluorescence spectroscopy; rare earths

Recently, nanosized inorganic luminescent materials have
been studied intensively due to their high potential applications such as nanobiophotonics, biological fluorescence labeling[1– 4]. Among them, rare-earth orthophosphates (LnPO4
with Ln: Y, Sc, and La-Lu) nanomaterials exhibit a number
of fascinating properties such as very high thermal stability,
low water solubility[5] and, especially, their luminescent
properties[6,7]. Numerous researches on preparation and luminescent property of these compounds with or without
dopants have been carried out[8–17]. Many preparative methods have been used to synthesize rare-earth orthophosphates
such as conventional solid-state reaction[18], sonochemical
synthesis[11,19], or wet chemistry routes[20,21]. For the case of
terbium orthophosphate, the doping Eu3+ of ions into the host
lattice with the concentration ranging from 0.1 at.% up to
5 at. was reported to enhance the energy transfer efficiency of both anhydrous TbPO4 and TbPO4·H2O[11,12].
However, effects of higher concentrations of doped Eu3+
ions on structure, morphology and optical properties of
TbPO4·H2O nanowires/nanorods have not been not studied

to date.
In our work, (Eu,Tb)PO4·H2O nanorods/nanowires were
prepared by microwave heating and characterized by
field-emission scanning electron microscopy (FESEM) and
X-ray diffraction. The microwave-assisted synthesis technique was employed for the reasons of its high possibility of
providing low dimensional nanomaterials in a simple, fast,
clean, efficient, economical, non-toxic, and eco-friendly way.

PL spectra of (Eu,Tb)PO4·H2O nanorods/nanowires were
measured in the UV region under 370 nm excitation. The
effects of the Eu3+ doping concentration on structure and
photoluminescent properties of prepared samples were also
discussed.

1 Experimental
1.1 Synthesis
Terbium(III) nitrate pentahydrate, europium(III) nitrate
pentahydrate and NH4H2PO4 with purity of 99% were purchased from Aldrich Co. and used as received without further purification. (Eu,Tb)PO4·H2O nanomaterials were prepared by microwave heating of an aqueous solution of terbium(III) nitrate, europium(III) nitrate and NH4H2PO4 at
ambient pressure in an open system. In a typical synthesis
procedure, 20 ml of 0.25 mol/L NH4H2PO4 solution were
added to a 50 ml round-bottomed flask containing 20 ml of a
0.25 mol/L aqueous solution of Tb(NO3)3 and Eu(NO3)3 during stirring. A colloidal precipitate was obtained upon the
addition of NH4H2PO4 to Tb(NO3)3 and Eu(NO3)3 solution at
the pH value of 2. The Eu3+ doping concentration was intentionally selected in the range of 6 at.%–20 at.%. The reacting
solution was then microwave irradiated using a MAS-II microwave synthesis extraction workstation, Sino Co., China,
for 30 min with an irradiated power of 500 W. The resulted
products were collected, centrifugated, and washed several

Foundation item: Project supported by Vietnamese National Foundation for Science and Technology Development (NAFOSTED) (103.06-2010.16)
Corresponding author: Nguyen Thanh Huong (E-mail: ; Tel.: +84 4 66599000)

DOI: 10.1016/S1002-0721(10)60619-9


Nguyen Thanh Huong et al., Structural and luminescent properties of (Eu,Tb)PO4·H2O nanorods/nanowires prepared by…

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times with ethanol and distilled water. The final products
were dried at 60 ºC for 24 h in air.
1.2 Characterization
The crystalline phase identification of the as-synthesized
samples are carried out by X-ray diffraction (XRD) analysis
with a Siemens D5000 diffractometer (using Cu KĮ radiation with Ȝ=0.15406 nm). The morphology of the products
was characterized by using a field emission scanning electron microscope, Hitachi, S-4800. The excitation spectroscopy measurements were carried out with a Varian Carry
eclipse fluorescence spectrometer. The emission spectra of
studied samples were recorded on luminescence spectrophotometer system, Horiba Jobin Yvon IHR 550.

2 Results and discussion
SEM images of (Eu,Tb)PO4·H2O samples synthesized by
using microwave heating with different Eu3+ doping concentrations are shown in Fig. 1. For EuPO4·H2O sample, nanorods are found with lengths from 150–200 nm and widths of
about 50 nm. The decrease in Eu3+ concentration led to the
increase in length of nanorods/nanowires from 150 to 300
nm and, at the same time, the decrease in their width from 50
to 10 nm.
XRD patterns of the as-synthesized (Eu,Tb)PO4·H2O
nanorods/nanowires indicate that only single crystalline phase
of (Eu,Tb)PO4·H2O existed in obtained samples (Fig. 2). All
reflections can be distinctly indexed to a rhabdophane-type
pure hexagonal phase. This implies that the crystal structures
of all Eu3+-doped terbium orthophosphate monohydrates are

isostructural to that of pure TbPO4·H2O (space group: P3121,
PDF card No. 20–1244). These results are the same as those
reported previously[3]. As shown in Fig. 2, no impurity
phases were observed for all measured samples with different Eu3+ concentrations. Thus, by using microwave synthesis
method and an aqueous solution containing nitrates of

Fig. 1 FESEM images of EuPO4·H2O (a) TbPO4·H2O:20 at.% Eu3+
(b), TbPO4·H2O:11 at.% Eu3+ (c) and TbPO4·H2O:6 at.%
Eu3+ (d) nanorods/nanowires synthesized by microwave-assisted
method

Fig. 2 XRD patterns of EuPO4·H2O (1) TbPO4·H2O:20 at.% Eu3+
(2), TbPO4·H2O:11 at.% Eu3+ (3) and TbPO4·H2O:6 at.%
Eu3+ (4) nanorods/nanowires synthesized by microwaveassisted method

trivalent rare-earth ions and NH4H2PO4 at a suitable pH
value of 2 the hexagonal phase of europium/terbium orthophosphate monohydrate, (Eu,Tb)PO4·H2O, was obtained as a
unique product with Eu3+ concentration ranging from 6 up to
20 at.%.
The photoluminescence excitation (PLE) spectrum of the
as-synthesized TbPO4·H2O sample is shown as an example
in Fig. 3.
For this sample, excitation bands of 310, 350, 370 and 480 nm
were observed in PLE spectra monitored at 542 nm. This
result coincided to that of the previous work reported by
Yang M. and co-workers[2]. In order to investigate the luminescent emission of prepared samples in the visible and infrared regions that were required for biomedical fluorescence
labeling as well as to study the energy transfer from Tb3+ to
Eu3+ ions, the excitation wavelength of 370 nm was selected
for emission (PL) spectroscopy measurements.
The PL spectra of (Eu,Tb)PO4·H2O nanorods/nanowires

of all investigated Eu3+ doping concentrations were recorded
under 370 nm excitation (Fig. 4). The intensity of four emission peaks found at 589, 615, 650, and 695 nm varied as a
function of the Eu3+ doping concentration and reached a
maximum value with the Eu3+ concentration of 11 at.%. This
originated from the energy transfer from Tb3+ to Eu3+ ions

Fig. 3 Photoluminescence excitation spectrum monitored at 542 nm
of TbPO4 ·H2O


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Fig. 4 Photoluminescence spectra of EuPO4·H2O (1) TbPO4·H2O: 20
at.% Eu3+ (2), TbPO4·H2O:11 at.% Eu3+ (3) and TbPO4·H2O:
6 at.% Eu3+ (4) nanorods/nanowires synthesized by microwave-assisted method

due to the energy overlap between the donor Tb3+ and the
acceptor Eu3+.
The emission spectra with characteristic red emission of
Eu3+ ions corresponding to the transitions from 5D0 to the
ground states 7Fj (j=1, 2, 3, 4) are observed, respectively. It is
quite interesting that the strongest energy transfer from Tb3+
to Eu3+ ions was found with the Eu3+ concentration of 11
at.%. This value is significantly higher than that reported in
previous works (about 5 at.%)[22,23]. The characteristic fluorescence emission peak of 543 nm (5D4ĺ7F5) for all samples
containing Tb3+ ions was observed (Fig. 5) while it disappears for EuPO4·H2O sample. The intensity of this peak,
however, was unchanged with the concentration of Eu3+
ranging from 6 to 11 at.% and was almost suppressed when
the Eu3+ concentration reached to 20 at.% (Figs. 4 and 5) due
to the inhibition of spontaneous emission[23].

Fig. 6 presents the emission spectra of EuPO4·H2O,
TbPO4·H2O:11 at.% Eu3+, and TbPO4·H2O samples. The
enhancement in intensity of four emission peaks of
TbPO4·H2O:11 at.% Eu3+ sample at 589, 615, 650 and 695 nm
with respect to that of the pure EuPO4·H2O sample confirms
once again the energy transfer in (Eu,Tb)PO4·H2O nanorods/nanowires.

Fig. 5 Photoluminescence spectra of EuPO4·H2O (1) TbPO4·H2O:6
at.% Eu3+ (2) and TbPO4·H2O:11 at.% Eu3+ (3) samples

JOURNAL OF RARE EARTHS, Vol. 29, No. 12, Dec. 2011

Fig. 6 Photoluminescence spectra of EuPO4·H2O, TbPO4·H2O:11
at.% Eu3+ and TbPO4·H2O samples synthesized by microwave-assisted method

3 Conclusions
Nanorods/nanowires of (Eu,Tb)PO4·H2O were successfully fabricated using microwave techniques. The length and
width of these nanowires/nanorods were 150–300 nm and
10–50 nm, respectively. Structure of these (Eu,Tb)PO4·H2O
materials was corresponding to rhabdophane-type hexagonal
phase. (Eu,Tb)PO4·H2O nanowires/nanorods exhibited the
characteristic narrow emission peaks of trivalent europium
ions. The evidence of energy transfer from Tb3+ to Eu3+ due
to the energy overlap between the donor Tb3+ and the acceptor Eu3+ was observed clearly via a significant enhancement
in the luminescent intensity of Eu3+ together with the suppression in intensity of the characteristic fluorescence emission peak of Tb3+ ion at 543 nm. The emission intensity of
Eu3+ ions reached a maximum value with the Eu3+ concentration of 11 at.%.
Acknowledgements: The authors are also thankful to the Key
Laboratory of Electronic Materials and Devices, Institute of Materials Science, Vietnam Academy of Science and Technology.

References:

[1] Patra C R, Bhattacharya R, Patra S, Basu S, Mukherjee P,
Mukhopadhyay D. Inorganic phosphate nanorods are a novel
fluorescent label in cell biology. J. Nanobiotechnology, 2006,
4: 11.
[2] Yang M, You H, Song Y, Huang Y, Jia G, Liu K, Zheng Y,
Zhang L, Zhang H. Synthesis and luminescence properties of
Sheaflike TbPO4 hierarchical architectures with different phase
structures. J. Phys. Chem. C, 2009, 113: 20173.
[3] Wang F, Banerjee D, Liu Y, Chen X, Liu X. Upconversion
nanoparticles in biological labeling, imaging, and therapy.
Analyst, 2010, 135: 1839.
[4] Binnemans K. Lanthanide-based luminescent hybrid materials.
Chem. Rev., 2009, 109: 4283.
[5] Patra C R, Alexandra G, Patra S, Jacob D S, Gedanken A,
Landau A, Gofer Y. Microwave approach for the synthesis of
rhabdophane-type lanthanide orthophosphate (Ln La, Ce, Nd,


Nguyen Thanh Huong et al., Structural and luminescent properties of (Eu,Tb)PO4·H2O nanorods/nanowires prepared by…

[6]

[7]

[8]
[9]

[10]

[11]

[12]

[13]

[14]

Sm, Eu, Gd and Tb) nanorods under solvothermal conditions.
New J. Chem., 2005, 29: 733.
Yu L X, Liu H. The progress of photoluminescent properties
of rare-earth-ions-doped phosphate one-dimensional nanocrystals. J. Nanomaterials, 2010, January 2010, article ID 461309,
doi: 10.1155/2010/461309.
Filho P C de Sousa, Serra O A. Red, green, and blue lanthanum phosphate phosphors obtained via surfactant controlled
hydrothermal synthesis. J. Lumin., 2009, 129: 1664.
Wang D, Wang Y. Optical properties of (Y,Tb)PO4 under
VUV excitation. Mater. Chem. Phys., 2009, 115: 699.
Bao J, Yu R, Zhang J, Yang X, Wang D, Deng J, Chen J, Xing
X. Controlled synthesis of terbium orthophosphate spindle-like
hierarchical nanostructures with improved photoluminescence.
Eur. J. Inorg. Chem., 2009, 2009: 2388.
Yan B, Gu J F, Xiao X Z. LnPO4:RE3+ (Ln La, Gd RE Eu,
Tb) nanocrystals: solvo-thermal synthesis, microstructure and
photoluminescence. J. Nanopart. Res., 2010, 12(6): 2145.
Ruan Y, Xiao Q, Luo W, Li R, Chen X. Optical properties and
luminescence dynamics of Eu3+-doped terbium orthophosphate
nanophosphors. Nanotechnology, 2011, 22: 275701.
Buissette V, Moreau M, Gacoin T, Boilot J-P, Chane-Ching
J-Y, Le Mercier T. Colloidal synthesis of luminescent
Rhabdophane LaPO4:Ln3+·xH2O (Ln Ce, Tb, Eu|0.7)
nanocrystals. Chem. Mater., 2004, 16: 3767.

Wang W, Zou M, Chen K. Novel Fe3O4@YPO4:Re (Re=Tb,
Eu) multifunctional magnetic-fluorescent hybrid spheres for
biomedical applications. Chem. Commun., 2010, 46: 5100.
Stryganyuk G, Trots D, Voloshinovskii A, Shalapska T, Zakordonskiy V, Vistovskyy V, Pidzyrailo M, Zimmerer G. Lu-

[15]

[16]
[17]

[18]

[19]

[20]

[21]

[22]

[23]

1173

minescence of Ce3+ doped LaPO4 nanophosphors upon Ce3+
4f-5d and band-to-band excitation. J. Lumin., 2008, 128: 355.
Yu C, Yu M, Li C, Liu X, Yang J, Yang P, Lin J. Facile sonochemical synthesis and photoluminescent properties of lanthanide orthophosphate nanoparticles. J. Solid State Chem., 2009,
182: 339.
Lu C, Hu J, Xu Z, Ni Y. Preparation and IR spectra study of
rare earth orthophosphates. J. Rare Earths, 2007, 25: 273.

Sasum U, Kloss M, Rohmann A, Schwarz L, Haberland D.
Optical properties of some rare earth and alkaline rare earth
orthophosphates. J. Lumin., 1997, 72-74: 255.
Cho I-S, Choi G K, An J-S, Kim J-R, Hong K S. Sintering,
microstructure and microwave dielectric properties of rare
earth orthophosphates, RePO4 (Re La, Ce, Nd, Sm, Tb, Dy, Y,
Yb). Mater. Res. Bull., 2009, 44: 173.
Yu W, Li G, Zhou L. Sonochemical synthesis and photoluminescence properties of rare-earth phosphate core/shell nanorods. J. Rare Earths, 2010, 28: 171.
Wang X, Gao M. A facile route for preparing rhabdophane
rare earth phosphate nanorods. J. Mater. Chem., 2006, 16:
1360.
Gao R, Qian D, Li W. Sol-gel synthesis and photoluminescence of LaPO4:Eu3+ nanorods. Trans. Nonferrous Met. Soc.
China, 2010, 20: 432.
Di W, Wang X, Zhu P, Chen B. Energy transfer and heattreatment effect of photoluminescence in Eu3+-doped TbPO4
nanowires. J. Solid State Chem., 2007, 180: 467.
Yang Z, Huang X, Sun L, Zhou J, Yang G, Li B, Yu C. Energy transfer enhancement in Eu3+ doped TbPO4 inverse opal
photonic crystals. J. Appl. Phys., 2009, 105: 083523.