Matrix-inducing synthesis and luminescence of microcrystalline red phosphors YVO4:Pb2+,Eu3+ derived from the in situ coprecipitation of hybrid precursors

Article abstract of DOI:10.1134/S0020168506010122

Using rare-earth coordination polymers with o-hydroxylbenzoate as a precursor, composing with poly vinyl alcohol as a dispersing medium, a novel red-emitting material of YVO₄:xPb²⁺, yEu³⁺ (x = 0, 1.0, 1.2, 1.5, 1.8, 2.0, and 5.0 mol %; y = 5 mol %) was synthesized by an in situ coprecipitation process. Its microstructure and micromorphology have been analyzed by x-ray powder diffraction and scanning electronic microscopy, which indicates that there exist some novel cobblestone-like microcrystalline particles. With Pb²⁺ as a sensitizer, these materials all exhibit strong red emission near 618 nm due to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. At x = 1.5, YVO₄:Pb²⁺,Eu³⁺ shows the strongest emission intensity, which indicates an efficient energy transfer from Pb²⁺ to Eu³⁺. Pleiades Publishing, Inc., 2006.

Full text of DOI:10.1134/S0020168506010122

ISSN 0020-1685, Inorganic Materials, 2006, Vol. 42, No. 1, pp. 59–63. © Pleiades Publishing, Inc., 2006.
Matrix-Inducing Synthesis and Luminescence
2+
3+
of Microcrystalline Red Phosphors YVO :Pb ,Eu
4
Derived from the In Situ Coprecipitation
of Hybrid Precursors1
Xue-Qing Su and Bing Yan
Department of Chemistry, Tongji University, Shanghai, 200092 People’s Republic of China
e-mail: byan@tongji.edu.cn
Received May 26, 2005; in final form, July 14, 2005
Abstract—Using rare-earth coordination polymers with o-hydroxylbenzoate as a precursor, composing with
2
+
3+
polyvinyl alcohol as a dispersing medium, a novel red-emitting material of YVO :xPb , yEu (x = 0, 1.0, 1.2,
4
1
.5, 1.8, 2.0, and 5.0 mol %; y = 5 mol %) was synthesized by an in situ coprecipitation process. Its microstruc-
ture and micromorphology have been analyzed by x-ray powder diffraction and scanning electronic micros-
2
+
copy, which indicates that there exist some novel cobblestone-like microcrystalline particles. With Pb as a
sensitizer, these materials all exhibit strong red emission near 618 nm due to the D
ions. At x = 1.5, YVO :Pb ,Eu shows the strongest emission intensity, which indicates an efficient energy
transfer from Pb2+ to Eu3+.
5
7
3+
F2 transition of Eu
0
2
+
3+
4
DOI: 10.1134/S0020168506010122
1
INTRODUCTION
host phosphor materials have been fabricated, such as
2
+
2+
2+
3+
Sr Gd Si O :Pb ,Mn
and NaY Si O :Pb ,Dy
3
2
6
18
9 6 26
Rare-earth vanadates have been studied extensively,
[
14, 15]. The traditional synthesis methods for rare-
and they are of interest as better hosts for luminescence
and laser materials [1–9]. In the past, much research has
been focused on Eu -activated yttrium vanadate
earth vanadate luminescent materials were solid-state
reactions at temperatures above 1300 K or simple wet-
chemical technologies, such as chemical coprecipita-
3
+
3
+
(YVO :Eu ) particles, which are interesting candidates tion and sol–gel and colloidal reactions [12, 16].
4
for red phosphors and have been used as cathodolumi- Recently, a new sol–gel technology based on hydroly-
nescent materials in color television screens for more sis and polycondensation processes has been found
than twenty years [10]. It is well known that the lumi- very useful in the synthesis of nonagglomerated nano-
nescence intensity strongly depends on the efficiency of particles [17, 18].
ligand absorption, the efficiency of ligand-to-metal
In this paper, we select rare-earth o-hydroxylben-
energy transfer, the efficiency of metal luminescence,
zoate coordination polymers as the precursors of lumi-
and some other factors [11]. In order to obtain brighter
nescent species, polyvinyl alcohol (PVA) as dispersing
3
+
red emission of YVO :Eu , higher concentrations of
4
medium template, which were assembled with other
3+
Eu ions have been used by cross relaxation in which functional components such as ammonium vanadate
the blue and green luminescence could be quenched
12]. Otherwise, if the doping level is too high, concen-
tration quenching will appear, and the intensity will
3–
(
NH VO ) as the source for VO and precipitation
4 3
4
[
components and urea as fuel. Through an in situ wet
chemical coprecipitation process, the doubly doped
2
+
decrease. Consequently, Nirwan et al. [13] added Pb
2
+
3+
phosphors of YVO :Pb ,Eu were obtained. It was
4
as a sensitizer to the host to increase the intensity, and
Pb has been found to be a good sensitizer of lumines-
cence, which transfers energy to the activator, resulting
in an increase of luminescence intensity. The Pb ion
belongs to ns -type impurities, and its luminescence
can be useful in obtaining a low-cost green- and red-
2
+
found that the luminescent intensity was affected by the
2
+
sensitizer concentration of Pb .
2
+
2
EXPERIMENTAL
2
+
2+
3+
emitting phosphor. Furthermore, various Pb -activated
YVO :Pb ,Eu phosphor particles were prepared
4
by an in situ coprecipitation method. The initiative
1
The text was submitted by the authors in English.
materials Y O and RE O were first dissolved in con-
2
3
2
3
5
9

6
0
XUE-QING SU, BING YAN
2
00
1
12
3
12
0
1
0
20
30
40
50
60
2
θ, deg
Fig. 1. The XRD pattern of YVO :Pb2+,Eu3+
.
4
centrated nitric acid. The preparation of the precursors ing Pb2+ ions to the system does not affect the micro-
is described in detail in the following: salicylic acid structure of the material. The XRD pattern of the crys-
(
6.0 mmol) was dissolved in 95% ethanol, and its pH talline powder is completely consistent with the
value was then adjusted to 7.0–8.0 with an ammonia tetragonal zircon structure known from bulk YVO4.
solution. Then, rare-earth nitrate (Y(NO3)3 and
Using the SEM, we obtain cobblestone-like mor-
Eu(NO ) ) and Pb(NO ) solutions were added and
3
3
3 2
2+
3+
phologies of the YVO :Pb ,Eu samples (Fig. 2). It
4
mixed homogeneously, whose molar ratio is Y(NO ) :
3
3
can be seen the products mainly consist of solid micron
crystalline structures, which exist with some agglomer-
ation among crystalline grains for the high temperature
Eu(NO ) : Pb(NO ) = (0.95 – x) : 0.05 : x (x = 0, 0.01,
3
3
3 2
0
.02, 0.03, 0.04, 0.05, respectively). After being stirred
for half hours, the urea and PVA were added to the
above solutions with appropriate ratio. After an hour,
the solutions were heated to 70°C, and the pH value
was adjusted to about 7.5. At the same time, the
NH VO powder was added into the solutions. After
(
1100°C) of thermal decomposition. The typical crys-
talline grain is estimated to be about 1.0 µm in dimen-
sion. Besides this, the three-dimensional sizes of
4
3
this, the solutions were stirred until they became homo-
geneous systems. After being deposited for several
days, they were filtered, and the precursors were
achieved. Finally, the samples were heat-treated at
1
100°C for about 5 h.
The particle size was characterized by x-ray diffrac-
tion (XRD) (Bruke, D8-Advance, 40 kV and 20 mA,
CuK ). The morphology and microstructure were char-
α
acterized with scanning electronic microscope (SEM)
(
Philips XL-30). Excitation and emission spectra at
room temperature were determined with Perkin-Elmer
LS-55 model fluorophotometer (excitation slit width
1
0 nm, emission width 5 nm).
1
µm
RESULTS AND DISCUSSION
The crystalline phase of these particles is deter-
mined by XRD (Fig. 1). It has been observed that add-
Fig. 2. SEM micromorphology of YVO :Pb2+,Eu3+
.
4
INORGANIC MATERIALS Vol. 42 No. 1 2006

MATRIX-INDUCING SYNTHESIS AND LUMINESCENCE
61
with organic polymers to obtain interpenetrating poly-
mer network structures, because They have similar infi-
nite polymeric structures [21]. Therefore, the particle
sizes of rare-earth oxysalts can be controlled and deter-
mined by the structures of hybrid precursors. Then, this
preparation technology connects the assembly of
hybrid material with synthesis of micrometer material,
which can be expected to be a candidate for the synthe-
sis of other luminescent materials based on rare-earth
oxides. All the excitation spectra have similar features,
and, here, we show some representative excitation
2
+
3+
YVO :Pb ,Eu (5, 5 mol %)
λem = 613 nm
4
HAB
CTS
2
+
3+
spectrum ofYVO :Pb ,Eu (5.5 mol %) recorded with
4
an emission wavelength of 613 nm at room temperature
(
Fig. 3). It can be seen clearly that the excitation spec-
trum consists of five peaks between 220 and 280 nm,
located at 223.8, 243.5, 258.0, 270.9, and 276.8 nm.
Obviously, this is mainly the character of a localized
charge-transfer state where electron density shifts from
the oxygen ligands to the central vanadium atom. How-
ever, the absorption in the shorter wavelength UV
2
00
220
240
260
280
Wavelength, nm
Fig.
3.
Representative
excitation
spectra
of
YVO :Pb2+,Eu3+ under 613 nm emission.
4
(
200–220 nm) is relatively low, and this absorption is
ascribed to the host absorption band. At longer wave-
micrometer crystalline grains are thick enough to
obtain high strength, which would be very useful for
the application as efficient phosphors with high intensi-
ties [19]. Rare-earth complex of o-hydroxylbenzoic
acid has polymeric structure [20] and is used as a pre- YVO :Pb ,Eu with different doping concentrations
cursor to prepare luminescent species. The organic of Pb (0, 1.0, 1.2, 1.5, 1.8, 2.0, and 5.0 mol %) and
polymer PVA was combined as dispersing medium to 5.0 mol % Eu are shown in Fig. 4 monitored with an
form the polymeric hybrid precursor template and excitation wavelength of 223 nm. The spectra of Eu
shows a higher temperature of thermolysis process. remain unchanged with addition of Pb . In the range
These rare-earth coordination polymers can compose 570–750 nm, the emission curve shows peaks at 593.1,
lengths (350–500 nm), the f–f transitions within the
3+
6
Eu 4f electron configuration cannot be detected.
The corresponding emission spectra
of
2
+
3+
4
2
+
3
+
3
+
2
+
λex = 223 nm
5D0
7F2
x = 1.5%
x = 1%
x = 2%
x = 1.2%
x = 0
5D1
7F1
5D
7F
x = 5%
x = 1.8
0
1
5D0
7F3
5D1 7F2
5D
7F
0
4
5
00
550
600
650
700
750
Wavelength, nm
Fig. 4. Emission spectra of YVO :Pb2+,Eu3+ phosphor particles under 223 nm excitation.
4
INORGANIC MATERIALS Vol. 42 No. 1 2006

6
2
XUE-QING SU, BING YAN
5
2
. Gerner, P., Kramer, K., and Udel, H.U.G., Broad-Band
6
17.5, 649.0, and 696.0 nm, which are due to D
0
5
+
3+
7
5
7F
Cr -Sensitized Er Luminescence in YVO , J. Lumin.,
F (J = 1–4) transitions. Moreover, the D
4
J
0
2
transition is assigned to the Eu3+ electric dipole transi-
2003, vol. 102/103, pp. 112–118.
tions, while the weaker emission centered at 593.1 nm
is ascribed to the magnetic dipole transitions. Among
3. Erdei, S., Ainger, F.W., Ravichandran, D., et al., Prepa-
3
+
3+
3+
ration of Eu :YVO Red and Ce ,Tb :LaPO Green
4
4
5
these transitions, the hypersensitive transition D
Phosphors by Hydrolyzed Colloid Reaction (HCR)
Technique, Mater. Lett., 1997, vol. 30, pp. 389–393.
0
7
3+
F is dominant, since Eu is located at low-symmetry
local sites (without inversion center) [22]. Besides this,
two additional transitions with lower intensity com-
F are observed, which can be
assigned to transitions originating from the D level.
Due to weaker interaction, Eu and O ions in
YVO :Pb ,Eu , no little level split can be caused by
2
4. Huignard, A., Buissette, V., Franville, A.C., et al., Emis-
sion Processes in YVO :Eu Nanoparticles, J. Phys.
4
5
7
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0
2
5
5. Jagannathan, R., Eu3+ Luminescence in BiSr V O —A
1
2
3
11
3
+
2–
Potential Red Phosphor, J. Lumin., 1996, vol. 168,
pp. 211–216.
2
+
3+
4
3
+
the crystal field, and no obvious split of Eu emission
bands has been observed. From the spectra, we can also
6. Zhang, H.J., Wang, J.Y., Wang, C.Q., et al., A Compara-
tive Study of Crystal Growth and Laser Properties of
Nd:YVO4, Nd:GdVO4, and Nd:GdxLa1 – xVO4 (x = 0.80,
0.60, 0.45) Crystals, Opt. Mater., 2003, vol. 23,
pp. 449−454.
2
+
observe that the sensitization effect of the Pb ion on
3
+
2+
the Eu activator ion depends on the Pb ion concen-
tration. When the Pb ion concentration reaches
.5 mol %, the intensity becomes the strongest, and it is
appreciably higher than that in YVO :Eu powders.
This increase in intensity may be due to a strong energy
transfer process from Pb to Eu . When x continues
increasing, the intensity decreases. It can be explained
that, for higher concentration, Pb aggregates may be
formed [12]. The aggregates act as trapping centers and
dissipate the absorbed energy nonradiatively, instead of
2
+
7
. Jiang, H.D., Zhang, H.J., Wang, J.Y., et al., Optical and
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1
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001, vol. 198, pp. 447–452.
2
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3+
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vol. 198/199, pp. 444–448.
2
+
9
. Yan, B. and Su, X.Q., In-Situ Chemical Coprecipitation
Composition of Hybrid Precursors to Synthesize
3
+
transferring to the Eu activator ion.
3
+
YP V O :Eu Micron Crystalline Phosphors, Mater.
x
1 − x
4
In summary, we obtained doubly doped particles of
Sci. Eng., B., 2005, vol. 116, p. 196.
2
+
3+
YVO :Pb ,Eu by a modified coprecipitation technol-
4
10. Neeraj, S., Kijima, N., and Cheetham, A.K., Novel Red
Phosphors for Solid State Lighting; the System
ogy with hybrid precursors. SEM micrographs indicate
that these phosphor particles exhibit novel crystal mor-
phology, and the size of the particles is about 1.0 µm.
3
+
3+
Bi(x)Ln(1 – x)VO(4); Eu /Sm (Ln = Y, Gd), Solid
State Commun., 2004, vol. 131, pp. 65–69.
2
+
The XRD pattern indicates that adding Pb ions does
not affect the structure of the material, which is com-
pletely consistent with the tetragonal zircon structure
1
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4
3
+
characteristic red fluorescence of Eu at 618 nm, and
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1
1
2. Yu, Y.Q., Zhou, S.H., and Zhang, S.Y., Luminescence of
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+
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2+
3+
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4
ACKNOWLEDGMENTS
The work was supported by the Science Foundation
of Shanghai University for Excellent Youth Scientists 14. Chuai, X.H., Zhang, H.J., Sh, F., et al., Synthesis and
and by the National Natural Science Foundation of
China (grant no. 20 301 013).
Luminescence Properties of Oxyapatite NaY Si O
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