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Photoluminescence Characterization of Zn- and Cs-Vanadate
Phosphors
Tingting Li, Zentaro Honda, Takeshi Fukuda, Jiaolian Luo and Norihiko Kamata
Graduate School of Science and Engineering, Saitama University, 255 Shimo-Ohkubo,
Sakura-ku, Saitama 338-8570, Japan
Keywords: Zn
3
V
2
O
8
,
Csvo
3
,
Cs
3
VO
4
, Sol-gel Process, Quantum Yield.
Abstract: We synthesized Zn
3
V
2
O
8
, CsVO
3
and Cs
3
VO
4
by sol-gel process and studied their crystalline and
luminescent properties. By optimizing the sintering conditions, pure phases of aim samples including
Cs
3
VO
4
were obtained. The annealing temperatures of 450℃ for CsVO
3
, 600℃ for Cs
3
VO
4
, respectively,
are lower than that of 750℃ for Zn
3
V
2
O
8
at the same duration of 12h. The Cs
3
VO
4
showed quantum yield of
90% with the half-width of 120nm. It became clear that the Cs-V-O system, especially Cs
3
VO
4
, is
promising for white LED applications.
1 INTRODUCTION
White light-emitting diodes (W-LEDs) are replacing
traditional incandescent and fluorescent lamps due
to their superior efficiency, lifetime, and
controllability of lighting environment (Li et al.,
2013). However, recent widespread W-LEDs,
realized by blue LED and yellow phosphor of Ce-
doped yttrium aluminum garnet, lack red emission
component and show a low color rendering index
(CRI) (Kim et al., 2009). It is necessary, therefore,
to find phosphor materials with higher CRI together
with keeping efficiency and reliability. As a kind of
efficient phosphor materials, a family of vanadates
has been widely investigated for various types of W-
LEDs and flat-panel displays due to their better
chromaticity (Huang et al., 2012); (Nakajima et al.,
2009).
The VO4 unit of a central vanadium ion and
coordinating four oxygen ions in a tetrahedral (Td)
symmetry is known as the luminescent center of the
vanadate group. Unlike sharp emission lines due to
4f transitions of rare earth ions as Eu3+, Tb3+ etc., a
family of zinc and cesium vanadates, Zn3V2O8,
CsVO3 and Cs3VO4, shows efficient and broad
emission spectra in a visible wavelength region.
Each VO4 tetrahedron in Zn3V2O8 is isolated in an
orthorhombic structure, while that in CsVO3 is two-
dimensionally arrayed as the VO4 sheet in an
orthorhombic pyroxene structure (Nakajima et al.,
2010).
In the present work, we synthesized Zn3V2O8,
CsVO3 and Cs3VO4 by a sol-gel method and
studied their X-ray diffraction (XRD) patterns,
surface images, photoluminescence (PL), PL
excitation (PLE) spectra and the value of PL-
quantum yield (QY). The synthesized Cs3VO4 was
most efficient with the PL-QY of 90%. Different
luminescence properties and synthesis conditions
among three phosphors were discussed.
2 EXPERIMENTAL
2.1 Preparation
We chose Zn(CH3COO)2•2H2O, Cs2CO3 and
NH4VO3 as starting materials of Zn3V2O8, CsVO3
and Cs3VO4 by a sol-gel process. First, we weighed
these starting materials, and dissolved them in
aqueous ammonia, respectively. The first stirring
step was performed for two hours with 250 rpm at
room temperature (RT) in order to prevent the
evaporation of aqueous ammonia and make sure that
materials fully react with each other in ionic states.
Then the temperature was increased to 80ºC with
keeping 250 rpm stirring until the solution became a
semitransparent gel. Second, the semitransparent gel
was dried at 120ºC about 4h, then ground thoroughly
by a mortar, and transferred into a crucible which
63
Li T., Honda Z., Fukuda T., Luo J. and Kamata N..
Photoluminescence Characterization of Zn- and Cs-Vanadate Phosphors.
DOI: 10.5220/0004704800630065
In Proceedings of 2nd International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS-2014), pages 63-65
ISBN: 978-989-758-008-6
Copyright
c
2014 SCITEPRESS (Science and Technology Publications, Lda.)