Crystal structure transformation and luminescent behavior of the red phosphor for plasma display panels

Article abstract of DOI:10.1016/j.jallcom.2004.07.065

To improve the chroma of red phosphor for plasma display panels, Eu ³⁺ activated phosphors were prepared by combustion method, and were investigated in detail by XRD and PL spectra. With the decreasing of the amount of H₃BO₃

Full text of DOI:10.1016/j.jallcom.2004.07.065

Journal of Alloys and Compounds 390 (2005) 220–222
Crystal structure transformation and luminescent behavior of the red
phosphor for plasma display panels
∗
Zhijian Yu, Xiaowei Huang, Weidong Zhuang , Xiangzhong Cui, Hongwei Li
National Engineering Research Center for Rare Earth Materials, General Research Institute for Non-ferrous Metals,
and Grirem Advanced Materials Co. Ltd., Beijing 100088, China
Received 26 April 2004; accepted 8 July 2004
Abstract
To improve the chroma of red phosphor for plasma display panels, Eu3+ activated phosphors were prepared by combustion method, and
were investigated in detail by XRD and PL spectra. With the decreasing of the amount of H BO , the phosphor crystal structures transform
from hexagonal ortho-borate to monoclinic RE BO , and then to cubic oxide. The dominating emissions of the phosphors also change from
transition. Accordingly, CIE coordinates of the phosphors show that x values are increasing while y values are
decreasing. Thus, phosphor with higher color purity could be achieved by adjusting the mole ratio of H BO
2004 Elsevier B.V. All rights reserved.
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D – F transition to D – F
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Keywords: Phosphors; Chemical synthesis; Crystal structure and symmetry; Luminescence
1
. Introduction
Y,Gd,Eu)BO3 is widely employed as red phosphor for
method. Results reveal that phosphor with certain amount of
a new phase exhibits higher color purity than that of common
ortho-borate phosphor while the relative brightness is almost
equal.
(
plasma display panels (PDP) [1–3] for the high emission in-
tensity under excitation of vacuum ultra violet (VUV) of 147
and 172 nm. However, the main emission line of the phosphor
situates at 593 nm (in orange–red region), which leads to a
low color purity [4]. Many works were carried out for years
to improve the chroma properties. One of the ways is to in-
troduce (Y,Eu)2O3 in coating process as red pigment. But the
2. Experimentals
According to our recent researches, nano-phosphor has
higher quenching concentration than that of bulk ones [7]. In
this work, we select mole ratio of Y, Gd, Eu as 0.45:0.4:0.15.
The differences between compositions of the samples are that
the content of H3BO3 is gradually decreased from 1.5 to 0
times of total RE quantities. The phosphors were prepared
by combustion method using amino acetic acid as the com-
(Y,Eu)2O3 phosphor is known to have low light output under
VUV excitation, which lead to a big loss of efficiency. Also
vanadates and phosphates activated by Eu3+ had been tried
to apply in PDP [5], which proved to be less efficient than the
(Y,Gd)BO3:Eu phosphor. Zhenggui Wei et al. reported that
the emission intensity and color purity could be improved
in nano-sized YBO3:Eu [6]. Considering lack of data on the
forming process of this phosphor, phase transformation with
the quantities of boric acid should be studied. In this work,
phosphors activated by Eu3+ were prepared by combustion
◦
bustion agent and then heated at 1000 C for 30 min.
Luminescent spectra of the phosphors were measured
by PDP-II Vacuum Ultraviolet spectro-radiometer (made in
China). X-ray powder diffraction data were collected using
a MXP21VAHF-M21X X-ray diffractometer having a CuKa
radiation with the application of an electric current of 250 mA
at an accelerating voltage of 40 kV.
∗
Corresponding author.
E-mail address: wzhuang@chinarem.com (W. Zhuang).
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925-8388/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2004.07.065

Z. Yu et al. / Journal of Alloys and Compounds 390 (2005) 220–222
221
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. Results and discussions
Crystal structure transformations of the phosphors could
be interpreted by XRD patterns, which were illustrated in
Fig. 1. According to the XRD patterns, when H3BO3 is 1.5,
pure rare earth ortho-borate is produced. In this work, main
structure type of the RE ortho-borate must be vaterite, as
3+
3+
3+
cations are heavier RE ions [8]: Y , Gd and Eu . Dif-
ference between radii of the cations must lead to distortion
in the vaterite structure. As the concentration of H3BO3 is
decreased to 1.0–0.4, a new phase with monoclinic structure
can be detected clearly. Compared with JCPDS No. 34–0291,
the new phase may be RE3BO . The monoclinic phase is
6
very high in the sample with 1.0 mol H3BO3, which indicates
that H3BO3 had not been fully used to build (Y,Gd,Eu)BO3
crystal. That is, a small amount of H3BO3 was vaporized in
Fig. 2. Emission spectra of the samples (excitation: 147 nm VUV).
the combustion process. The diffraction of RE3BO becomes
6
weaker and weaker, when H3BO3 is gradually decreased. The
phosphor with less than 0.4 mol H3BO3 exhibits pure cubic
phase as common (Y0.95,Eu0.05)2O3 phosphor, in which Eu3+
2
B2O3 + 2RE3BO → 6REBO3
(4)
6
Luminescent spectra of the phosphors are illustrated in
occupies C2 and S symmetry sites [9,10].
Fig. 2. As known to all, intensities of transitions between
different J levels are dependent on symmetry of the lo-
cal environment of Eu3+ [9]. When H3BO3 is 1.5, pure
(Y,Gd,Eu)BO3 crystal of vaterite structure has strong absorp-
tion in VUV region, and vaterite phase offers D3d inversion
6
Reactions in the synthesis process might include
the following processes. If there is no boric acid,
Oxidation–reduction between combustion agent and RE ni-
trates will occur [11]:
3
+
symmetry site and T symmetry site for activator Eu [12].
6
RE(NO3)3 + 10H2NCH2COOH + 18O2 → 3RE2O3
20CO2 + 5N2 + 25H2O + 18NO2 (1)
5
7
D0– F1 magnetic-dipole transition that obeys parity selec-
tion rule is allowed, which causes the phosphor to mainly
exhibit strong line emission at 593 nm. Just as discussed
above, distorted vaterite crystal of (Y,Gd,Eu)BO3 also leads
+
The reaction will finish in less than 1 min. When boric acid
is added in the reaction, it decomposes to B2O3 and H2O
firstly. Then the RE oxide achieved in reaction 1 will react
with boric oxide:
5
7
to the emission due to D0– F2 electric-dipole transition that
5
7
is rather high. Also the crystal field splits D0– F2 transition
into two main lines at 611 and 626 nm. When the H3BO3 is
decreased to about 1 mol, the crystal structure changes into
3
RE2O3 + B2O3 → 2RE3BO6
(2)
certain amount of RE3BO monoclinic crystal mixed with
6
After added more amount of H3BO3, reaction (3) and (4) will
take place:
hexagonal borate. Monocline crystal has low structure sym-
3+
5
7
metry, that offers an uneven ambient to Eu , so the D0– F2
transition caused line emissions at 615 and 619 nm that can
be seen, especially the emission at 615 nm. It is the existence
of this monoclinic phase that improves the color purity of
the phosphor. When H3BO3 is less than 0.4, the main crys-
tal structure is body centered cubic, the typical emission of
RE2O3 + B2O3 → 2REBO3
(3)
5
7
3+
6
11 nm due to D0– F2 becomes the strongest line. The Eu
ions in C2 sites lead to intense emission in 611 nm due to the
5
7
D0– F2 transition [10]. Wei et al. [6] reported that the im-
provement of color purity in nano-sized YBO3:Eu is because
surface defects in nanophosphor has increased the degree of
3+
disorder and lowered the local symmetry of Eu , thus in-
5
7
creased transition probability of D0– F2. After checked in
detail, the spectrum of sample ‘a’ in Ref. [6] is found to be
very similar to that of the sample with 1.3 mol H3BO3 in
this work. This similarity means that maybe there exists very
small amount of RE3BO in their sample ‘a’ that leads to the
6
color purity improvement.
CIE coordinates of samples are shown in Fig. 3, from
which we can find that x values of the samples are increasing
Fig. 1. XRD patterns of the samples (peaks of monoclinic phase, hexagonal
phase, cubic phase are marked by “+”, “#”, “o”, respectively).

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Z. Yu et al. / Journal of Alloys and Compounds 390 (2005) 220–222
4. Conclusions
Eu3+ activated borate phosphors with different crystal
structures could be achieved by combustion method. Through
adjustment of the amount of boric acid, crystal structure will
transform among cubic, monoclinic, and hexagonal. And the
strongest emission peak of the phosphors will change be-
tween line emission at 611 nm and line emission at 593 nm
according to the above saying transformation of crystal struc-
ture. Chroma improved phosphor can be prepared by con-
trolling amount of H3BO3 due to the appropriate existence
of RE3BO , while the luminescent brightness is almost equal
6
to that of ortho-borate.
Fig. 3. CIE coordinates of samples (excitation: 147 nm VUV).
Acknowledgements
Financial support from the National Hi-Tech R&D Pro-
gram of China (863 Program, No. 2002AA302604) and the
National Natural Science Foundation of China (50372086) is
gratefully acknowledged.
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ratio of H3BO3. This result is coincident with that of emission
intensities.
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[
[
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