Rapid synthesis of size-controllable YVO4 nanoparticles by microwave irradiation

Article abstract of DOI:10.1016/j.ssc.2004.02.045

Sized-controlled YVO₄ nanoparticles have been synthesized by a simple microwave irradiation processing. The products were characterized by X-ray diffraction, transmission electron microscopy, and ultraviolet-visible spectroscopy. The results showed that the size of as-synthesized YVO₄ powders was in the range of 5-18 nm and was extremely dependent on the solution pH value. The optical measurements displayed the obvious quantum-size effect of the products.

Full text of DOI:10.1016/j.ssc.2004.02.045

Solid State Communications 130 (2004) 465–468
www.elsevier.com/locate/ssc
Rapid synthesis of size-controllable YVO4 nanoparticles by
microwave irradiation
a
HaiYan Xu , Hao Wang , YongQiang Meng , Hui Yan
a,
b
a
*
aThe Key Laboratory of Advanced Functional Materials, Education Ministry of China, Beijing University of Technology, Beijing 100022, China
bCollege of Materials Science and Engineering, HeBei University of Science and Technology, Shijiazhuang 050054, China
Received 18 January 2004; received in revised form 23 February 2004; accepted 24 February 2004 by M. Cardona
Abstract
Sized-controlled YVO4 nanoparticles have been synthesized by a simple microwave irradiation processing. The products
were characterized by X-ray diffraction, transmission electron microscopy, and ultraviolet–visible spectroscopy. The results
showed that the size of as-synthesized YVO4 powders was in the range of 5–18 nm and was extremely dependent on the
solution pH value. The optical measurements displayed the obvious quantum-size effect of the products.
q 2004 Elsevier Ltd. All rights reserved.
PACS: 81.05.Ys; 81.20.Zx; 81.40.Tv
Keywords: A. Nanostructures; B. Chemical synthesis; E. Microwave irradiation
1. Introduction
mediated method [9], hydrothermal processing [10], and
wet chemical method [11–13], etc. have been developed to
synthesize YVO4 nanoparticles in view of its important
application in optoelectronic field. However, these methods
need either long reaction time, high temperature treatment,
or complicated processing.
Yttrium orthovanadate (YVO4) has been extensively
used as a red phosphor with several rare-earth metal ions as
dopant in cathode ray tubes (CRTs) and color television in
powder form [1,2]. Bulk YVO4:Eu is a highly photolumi-
nescence material with 70% photoluminescence quantum
yield of the europium [3] and has a strong luminescence
efficiency upon electron-beam excitation. Moreover, YVO4
is also a promising polarizer [4] and laser host material in
single crystal form [5].
The microwave synthesis is a fast, simple and efficient
method to prepare nanosized inorganic materials [14–19].
Compared with the conventional methods, the microwave
synthesis has the advantages of rapid growth, small particle
size and narrow particle size distribution due to fast
homogenous nucleation [20]. In this study, a simple and
rapid microwave irradiation method was adopted to
synthesize YVO4 nanoparticles with controlled particle
size, and their optical property dependent on particle size
was investigated.
In recent years, much attention has been paid to the
synthesis and characterization of nanomaterials due to their
interesting properties, which mainly come from the
quantum-size effect in nano-systems, as well as the high
surface/volume ratio [6]. Some new synthetic methods
including solution combustion process [7], hydrolyzed
colloid reaction (HCR) technique [8], microemulsion-
2. Experimental
*
Corresponding author. Address: Department of Materials
Science and Engineering, Beijing University of Technology,
ChaoYang district, Beijing 100022, China. Tel.: þ86-106-739-
2733; fax: þ86-106-739-2412.
All reagents were of analytical grade and used without
further purification. The NaVO3 stock solution was prepared
by mixing V2O5 and sodium hydroxide (NaOH) and
E-mail address: haowang@bjut.edu.cn (H. Wang).
0038-1098/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ssc.2004.02.045

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H.Y. Xu et al. / Solid State Communications 130 (2004) 465–468
vigorously stirring in deionized water for 12 h. A solution of
Y(NO3)3 (5.0 mmol) was blended with the NaVO3 stock
solution (5.0 mmol). To investigate the influence of pH
value, a series experiments were designed. The pH of the
final mixture was adjusted to 4, 6, 7, 8 and 11 by adding
acetic acid (CH3COOH) or ammonia (NH3·H2O). The
ready-adjusted mixture was stirred constantly in a beaker
at room temperature for 20 min. The beaker was then placed
in a household type microwave oven of 700 W power with a
refluxing system and the reaction was performed under
ambient air for 10 min. The microwave oven followed a
working cycle of 6 s on and 10 s off (37% power). After
cooling to room temperature, the precipitate was centri-
fuged, washed with deionized water, and dried in air.
The final products were characterized by X-ray diffrac-
tometry (XRD, Bruker Advance D-8) using Cu Ka radiation
roughly determined from the full width at half maximum
(FWHM) of (200) peaks by using the Scherrer formula. The
mean size of the particles obtained at different pH (4, 6, 7, 8
and 11) is 18, 12, 5, 8 and 15 nm, respectively. In Fig. 2 the
particle size is plotted as a function of pH value. It shows
that the smallest size appears at the neutral medium
(pH ¼ 7). Apart from this point, both the increasing and
decreasing of pH value lead to the increase of the particle
size.
The morphology and particle size of the YVO4 powders
were characterized by TEM. Fig. 3 shows the typical TEM
image of YVO4 particles obtained at pH ¼ 7. The average
size of the particles is about 5 nm, which is consistent with
the result of XRD pattern. The particles have mono-shape
and are well dispersed. The YVO4 powders obtained at the
other pH values display similar shape to the particles
obtained at pH ¼ 7, the micrographs of which are not shown
here. Moreover, the particle size of the samples obtained at
the other pH conditions observed by TEM is essentially in
agreement with the XRD data.
ꢀ
ðl ¼ 1:5405 AÞ; and transmission electron microscopy
(TEM, JEM-2000FX microscopy, 160.0 KV). Optical
absorption studies were carried out using a UV–Vis-NIR
spectrophotometer (Shimadzu UV-3101PC).
From the above results we can see that the particle size of
as-synthesized YVO4 samples is sensitive to the pH of
solution. The dependence of particle size on pH value has
also been investigated in hydrothermal synthesis of YVO4
[9,10]. In the basic media, the following reactions would
occur:
3. Results and discussion
Fig. 1 shows the XRD patterns of the products obtained
via microwave irradiation at different pH value, which was
varied from 4 to 11. Despite the broadening caused by the
small mean size of the particles, all the five patterns are
found to be consistent with the tetragonal zircon-type
structure of YVO4 (JCPDS card No. 17-0341). It indicates
that phase-pure tetragonal structure YVO4 has been
successfully synthesized at different pH value via micro-
wave irradiation for 10 min. The mean particle size can be
Y
3þ þ OH2 ! YðOHÞ3
ð1Þ
ð2Þ
ð3Þ
VO32 þ OH2 ! VO342 þ Hþ
YðOHÞ3 þ VO342 ! YVO4 þ 3OH2
Here nanosized Y(OH)3 precipitates served as nucleation
sites. VO342 were mobile species which incorporated into
Y(OH)3 grains, resulting in the nucleation and growth of
YVO4. According to Eq. (2), high pH favors the formation
of VO342 species, which consequently favors the formation
Fig. 1. XRD patterns of YVO4 powders synthesized by microwave
irradiation for 10 min. at different pH values: pH ¼ (a) 4, (b) 6, (c)
7, (d) 8, (e) 11.
Fig. 2. Variation of particle size of as-synthesized YVO4 powders
with different pH values.

H.Y. Xu et al. / Solid State Communications 130 (2004) 465–468
467
ize the optical property of the YVO4 particles. Fig. 4 gives
the UV–Vis absorption spectra of the YVO4 particles
obtained at different pH (4, 6, 7, 8 and 11). As seen from Fig.
4, the absorption peaks of the particles vary from each other.
The dependence of absorption peaks on the particle size of
the samples is illustrated in Fig. 5. Obviously, with
increasing particles size, the position of absorption peak of
the as-synthesized YVO4 samples shifts considerably to
lower wavelength. This is the typical behavior of the
quantum-size effect of nano-system. As the host matrix for
rare-earth metal ions, YVO4 can be excited by UV radiation
owing to VO342 absorption. The energy then transfers to the
localized states of the doping ion, which results in the
emission at the luminescence center. The blue shift of
the absorption peak will affect the emission properties of the
rare-earth metal doped YVO4. Further work is under way to
apply the microwave method to synthesize nano-sized rare-
earth metal doped YVO4 phosphors and investigate their
luminescent properties.
Fig. 3. TEM image of an YVO4 sample synthesized at pH ¼ 7.
of YVO4 products in Eq. (3). Therefore, the higher the pH
value, the faster the YVO4 particles form, a fact which leads
to the formation of larger particles.
4. Conclusion
We have fabricated YVO4 nanoparticles with controlled
particle size through a microwave irradiation method in a
solution with a wide pH range. The particle size of the
YVO4 powders ranges from 5 to 18 nm and is very sensitive
to the pH value. The smallest size appears at pH ¼ 7 while
both increasing and decreasing the pH results in forming
larger particles. UV–Vis spectra demonstrate an obvious
blue shift of absorption peak with decreasing particle size,
which is due to the quantum-size effect. This microwave
irradiation method, without using surfactants or templates
and requiring no expensive equipments, ensures higher
purity in the products and greatly reduces the production
In acidic media, the vanadium species exists as anionic
oligomers [10], while Y(OH)3 would dissolve to form
yttrium reactive species Y3þ based on the reaction:
YðOHÞ3 þ 3Hþ ! Y3þ þ 3H2O
ð4Þ
Then a normal base–acid reaction between yttrium cations
and vanadium anions yielded YVO4 products. From Eq. (4)
we can see that, low pH favors the formation of the Y3þ
species, which benefits the formation of large YVO4
particles.
Sun et al. [9] used a microemulsion-mediated hydro-
thermal process to synthesize YVO4 nanoparticles with the
size of 8.9–47.2 nm in the pH range of 7–10. The
microemulsion droplets afforded a confinement environ-
ment for the growth of nanoparticles. However, the
surfactant used in the microemulsion process might
introduce organic impurities in the final products, which is
detrimental to the optical performance of YVO4-based
phosphors. Wu et al. [10] found that micrometer size YVO4
crystals were obtained in the acidic media, while YVO4
nanoparticles with size of about 50 nm were obtained in the
basic media. In this study, YVO4 nanoparticles with the size
less than 20 nm have been obtained in the pH range of 4–11
by the surfactant-free microwave irradiation method for
only 10 min. Microwave synthesis is considered as a fast,
simple and energy efficient synthesis method, it can also
avoid competing reactions in the known processes [21]. The
energy transfer from microwaves to reactive species is so
efficient that the nucleation and growth of YVO4 crystallites
can be achieved in a very short time. In other words, the
reaction time is too short to form large particles.
Fig. 4. UV–Vis spectra of as-synthesized YVO4 powders at
UV–Vis spectroscopy has been employed to character-
different pH values: pH ¼ (a) 4, (b) 6, (c) 7, (d) 8, (e) 11.

468
H.Y. Xu et al. / Solid State Communications 130 (2004) 465–468
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