Synthesis of blue-emitting CaMgSi2O6:Eu2+ phosphor using an electrostatic self-assembly deposition method

Article abstract of DOI:10.1111/j.1551-2916.2006.00919.x

Eu²⁺-doped CaMgSi₂O₆ phosphor was prepared by depositing mixed hydroxides of Ca, Mg, and Eu over spherical SiO₂ particles (300 nm) pre-coated with polycations (polyethyleneimine), followed by calcination at 1200°C in a reducing atmosphere. The prepared phosphor showed intense blue emission, ascribable to the 4F⁷-4f⁶5d transition of Eu²⁺. In contrast, the luminescence intensity of the phosphor was considerably decreased when prepared without polycations. It was suggested that negatively charged hydroxides are deposited on positively charged SiO₂ surfaces pre-coated with polycations through electrostatic self-assembly interaction. On calcination, the hydroxide shells react with the SiO₂ cores to produce Eu²⁺:CaMgSi₂O ₆.

Full text of DOI:10.1111/j.1551-2916.2006.00919.x

J. Am. Ceram. Soc., 89 [5] 1492–1498 (2006)
DOI: 10.1111/j.1551-2916.2006.00919.x
r 2006 The American Ceramic Society
ournal
J
21
Synthesis of Blue-Emitting CaMgSi O :Eu Phosphor Using an
2
6
Electrostatic Self-Assembly Deposition Method
w
Tetsuya Kida, Mohammed Mastabur Rahman, and Masamitsu Nagano
Department of Chemistry and Applied Chemistry, Saga University, Saga, Japan
21
Eu -doped CaMgSi O phosphor was prepared by depositing
2
2
present method is that spherical SiO particles with a narrow
6
mixed hydroxides of Ca, Mg, and Eu over spherical SiO par-
2
size distribution are used both as the morphology-determining
template and as the precursor. Furthermore, it is expected that if
the deposition of precursor hydroxides on SiO particles is con-
ticles (300 nm) pre-coated with polycations (polyethyleneimine),
followed by calcination at 12001C in a reducing atmosphere.
The prepared phosphor showed intense blue emission, ascribable
2
2
trolled and thus the spherical morphology of SiO particles is
7
6
21
to the 4f -4f 5d transition of Eu . In contrast, the luminescence
intensity of the phosphor was considerably decreased when pre-
pared without polycations. It was suggested that negatively
charged hydroxides are deposited on positively charged SiO2
surfaces pre-coated with polycations through electrostatic self-
assembly interaction. On calcination, the hydroxide shells react
retained, fine spherical powders with a narrow size distribution
could be obtained. Such particles are preferable for the manu-
facture of phosphor screens with good brightness and high res-
olution owing to their improved packing density and low
scattering of evolved light. In this study, we also attempted to
prepare spherical CMS phosphor particles by the method we
developed, and studied the effects of the calcination temperature
on the morphology of the resulting particles.
21
with the SiO cores to produce Eu :CaMgSi O .
2
2
6
I. Introduction
II. Experimental Procedure
ILICATE-BASED phosphors have been widely used owing to
their high luminescence efficiency and high chemical stabil-
(
1) Materials
An aqueous solution of 30 wt% polyethyleneimine (PEI)
(CH CH NH) : PEI, MW5 50 000–100000} was purchased
S
fluorescent lamps, cathode ray tubes (CRTs), and plasma dis-
21
2 4
ity. For example, Mn -doped Zn SiO has been utilized for
{
2
2
x
1
–3
from MP Biomedicals LLC (Irvine, CA). Tetraethyl orthosili-
cate (TEOS), ethanol, Ca(NO ) , Mg(NO ) Eu(NO ) , and
28% NH solutions were purchased from WAKO Pure Chem-
play panels (PDPs).
Rare-earth-doped silicates such as
are also important phosphors for the above
31
3
2
3 2,
3 3
Y
2
5
SiO :Ce
1
–3
applications. Recently, Eu -doped CaMgSi
21
3
2 6
O (CMS) has
ical Industries (Osaka, Japan).
attracted considerable attention as a new blue phosphor for
PDPs. This phosphor has been developed to overcome the
4
drawbacks of the conventional blue phosphor, BaMgAl10
O
17
:
Eu (BAM), which undergoes degradation by ion bombard-
(2) Preparation of Spherical SiO
2
21
SiO cores were prepared by hydrolysis and polycondensation of
2
TEOS following a procedure of a modified Stober method.
Specifically, 42 mL absolute ethanol, 6.7 mL of NH (28%), and
5
–7
21
12
ment or ultraviolet radiation. In addition, Eu -doped CMS
can also be used as a long phosphorescent phosphor when co-
3
31 8
doped with Dy
.
3.1 mL of TEOS were mixed and treated in an ultrasonic bath in
a well-sealed glass flask for 30 min. The resulting dispersions
contained spherical SiO of 300 nm diameter, as confirmed by
Normally, phosphors are prepared by solid-state reactions
SSR) between raw materials at high temperatures. This route
(
2
produces agglomerated particles of irregular shapes. However,
such particles are not suitable for making phosphor screens ow-
ing to their low packing density, which leads to a decrease in
luminescence efficiency. In this study, CMS phosphors were
prepared using an electrostatic self-assembly deposition (ESAD)
method to control the morphology of the phosphor particles.
The newly developed method we used here utilizes ESAD of
precursor hydroxides onto colloidal particles as schematically
tranmission electron microscopy (TEM) analysis (Fig. 2).
(
3) Coating of Spherical SiO with Polycations
2
2
The spherical SiO particles of 300 nm prepared were treated
with a polyelectrolyte solution (PEI in water) under constant
stirring to charge the SiO surfaces positively. The particles were
2
then washed several times with water by centrifugation to re-
move excess polycations. This washing step is critical to prevent
2
shown in Fig. 1. Spherical SiO particles with a narrow size dis-
tribution are first coated with polycations to make their surfaces
positively charged. Then, negatively charged Ca, Mg, and Eu
the aggregation of SiO
by Chen and Somasundaram. After washing and centrifuga-
tion, the resultant PEI-coated SiO particles were used for the
preparation of CMS phosphors by the ESAD method.
2
particles by polymer bridging, as noted
10
2
2
hydroxide particles are deposited over the SiO particles pre-
coated with polycations via electrostatic interaction. The
prepared core-shell structured particles are finally calcined to
produce CMS phosphors by a reaction between the shells
(
4) Preparation of CMS Phosphors
21
(
polycations or polyanions for preparing core-shell particles have
2
mixed hydroxides) and the cores (SiO ). Such processes using
Eu (5 mol%)-doped CaMgSi
pared from PEI-coated spherical SiO
and Eu(NO at a stoichiometric molar ratio (Ca:Mg:-
Si:Eu 5 1:1:2:0.05), as shown in Fig. 3. PEI-coated SiO (0.006
2
O
6
(CMS) phosphors were pre-
2
, Ca(NO , Mg(NO
3
)
2
3 2
) ,
9
–11
recently been well exploited.
The distinct feature of the
3 3
)
2
mol) particles were re-dispersed in an aqueous solution (50 mL)
containing nitrates of Ca (0.003 mol), Mg (0.003 mol), and Eu
J. Ballato—contributing editor
(
coated SiO surfaces with mixed hydroxides of Ca, Mg, and Eu,
0.00015 mol) (precursor nitrate solution). To cover the PEI-
2
Manuscript No. 20904. Received August 22, 2005; approved December 7, 2005.
This work was financially supported in part by the Sasagawa Scientific Research Grant,
Japan (Project number 17-118).
an aqueous NH3 (28%) solution (10 mL) was added to the
above solution drop-by-drop under vigorous stirring until the
pH of the solution reached 12. The products were then dried in
wAuthor to whom correspondence should be addressed. e-mail: kida@cc.saga-u.ac.jp
1
492

21
May 2006
Synthesis of Blue-Emitting CaMgSi O :Eu Phosphor
2
1493
6
Fig. 1. Schematic diagram of the procedure used for preparing CaMgSi
2
O
6
(CMS) phosphors by the electrostatic self-assembly deposition (ESAD) method.
ison, CMS phosphors were also prepared by the above method
an oven (801C), ground in a ceramic crucible, and calcined first
at 5001C in O atmosphere to burn the adsorbed PEI and then at
2001C in a reducing atmosphere (5%H in Ar). For compar-
2
without PEI and by a conventional SSR, where CaCO
3
, MgO,
1
2
SiO , and Eu powders were mixed and ground well at a sto-
2
2 3
O
ichiometric molar ratio and calcined at 12001C in the reducing
atmosphere. In addition, to investigate the effects of the calci-
nation temperature on the morphology of the resulting particles,
CMS phosphors were prepared at different calcination tem-
peratures, e.g., 9001, 10001, 11001, and 12001C, in a reducing
atmosphere.
In this study, the effects of the starting composition on the
morphology of the resulting particles were also investigated, in an
attempt to produce phosphor particles with a narrow-size distri-
bution. The starting molar composition was changed by diluting
the concentration of the precursor nitrate solution to Ca:Mg:Si:
Eu 50.2:0.2:2.0:0.01 (1/5 concentration) and Ca:Mg:Si:Eu 5
0.1:0.1:2.0:0.005 (1/10 concentration). Hereafter, these two sam-
ples are referred to as CMS1/5 and CMS1/10, respectively.
(5) Characterization
Crystallographic phases of the products were identified by X-ray
diffraction (XRD; Rigaku, RINT-1000, Tokyo, Japan) using
CuKa radiation. The surface morphology of the products was
analyzed by a field-emission scanning electron microscope (FE-
SEM; JEOL, JSM-6700 FSS, Tokyo, Japan). The emission and
excitation photoluminescence (PL) spectra were obtained by a
spectrophotometer (JASCO, FP-750, Tokyo, Japan). For PL
measurements, the powdered samples prepared were tightly
pressed onto plates and set in the sample holder attached to
the spectrometer. The emission intensity for all the prepared
21
phosphors was normalized to a commercial BaMgAl O :Eu
0 17
1
phosphor.
III. Results and Discussion
1) Preparation of CMS Phosphors by the ESAD Method
(
21
Fig. 2. Tranmission electron microscopy image of precursor SiO
templates prepared from tetraethyl orthosilicate.
2
Figure 4 shows the XRD patterns of CaMgSi O :Eu phos-
2 6
phors prepared by the ESAD method using polycations (a),

1
494
Journal of the American Ceramic Society—Kida et al.
Vol. 89, No. 5
CaMgSi O
2
SiO (crystobalite)
2
6
(d) 1200°C
(c) 1100°C
(b) 1000°C
(a) 900°C
1
0
20
30
40
50
60
2
theta/Degree
2 6
Fig. 5. X-ray diffraction patterns of CaMgSi O (CMS) phosphors
prepared by the electrostatic self-assembly deposition (ESAD) method
at different temperatures, i.e., 9001C (a), 10001C (b), 11001C (c), and
1
2001C (d).
the above alkaline solution, as reported for PEI-coated quartz
1
3
14
2
substrates and ZrO particles. In contrast, the surfaces of the
hydroxide particles produced should be negatively charged be-
cause of the deprotonation of surface hydroxyl groups in the
alkaline solution. Therefore, it is possible that the negatively
charged hydroxide particles are deposited on the positively
charged SiO surfaces soon after being produced through elec-
2
trostatic interaction. The results obtained suggest that the ad-
sorption of polycations onto the SiO particles allows the
2
uniform deposition of Ca and Mg hydroxides onto the SiO2
particles to give a CMS phase by a complete reaction between
shells (hydroxides) and cores (SiO
without polycations, mixed (Ca and Mg) hydroxides and SiO
particles are inhomogeneously mixed to give CMS together with
the unreacted SiO cores.
Figure 5 shows the XRD patterns of CaMgSi
phors prepared by the ESAD method using polycations at dif-
ferent calcination temperatures. A clear CMS phase appeared
even at the low calcination temperature of 9001C, although a
2
) on calcination. However,
2
Fig. 3. Experimental procedures for the preparation of CaMgSi
CMS) phosphors by the electrostatic self-assembly deposition (ESAD)
method.
2 6
O
2
21
6
O :Eu phos-
(
2
without polycations (b), and by the SSR method (c) at 12001C.
The SSR method gave CMS together with unreacted SiO , sug-
gesting that the preparation of CMS is rather difficult. In con-
2
SiO
2
phase remained and other unknown phases were present.
This means that the reaction between PIE-coated SiO
2
and
trast, the peak intensity of SiO was significantly decreased when
2
mixed (Ca and Mg) hydroxides occurred even at the low calci-
nation temperature, which could have been owing to the inti-
mate contact between them. With an increase of the calcination
CMS was prepared by the ESAD method using polycations as
the bridging aids between mixed (Ca, Mg, and Eu) hydroxides
and SiO particles, whereas unreacted SiO cores remained when
temperature up to 12001C, the SiO phase almost disappeared.
2
2
2
there were no polycations. With the present method, precursor
hydroxide particles are produced in situ by adding NH as the
precipitating agent to the precursor solution containing PEI-
XRD results suggested that the use of polycations as the bridg-
ing aids between SiO and hydroxides was very effective in
2
producing the CMS phase at relatively low calcination
temperatures.
3
21
21
31
coated SiO , Ca , Mg , and Eu ions. The surfaces of PEI-
2
coated SiO
2
particles should remain positively charged even in
Figure 6(a) shows the SEM images of the CMS phosphor
prepared at 12001C by the SSR method. The particle size was
larger than 10 mm and largely aggregated particles were formed.
Figure 6(b) shows the morphology of the as-prepared precursor
3
mixed hydroxides, which were prepared by adding NH as the
precipitating agent to the precursor nitrate solution. This indi-
cates that the precipitated hydroxides were significantly aggre-
gated. Figures 6(c) and (d) show SEM images of the CMS
phosphors prepared by the ESAD method without PEI before
and after calcination at 12001C, respectively. In this case, it ap-
pears that aggregated particles, in which SiO particles are em-
2
bedded in mixed hydroxides, were formed and the original
morphology almost remained even after the calcination, pro-
ducing aggregated CMS particles. By contrast, with PEI, smaller
particles of less than 500 nm were formed before calcination as
shown in Fig. 6(e), suggesting that mixed hydroxides were uni-
formly coated over the SiO surfaces. Calcination of the com-
2
posite particles produced less aggregated fine CMS phosphor
particles of ca. 1 mm, as shown in Fig. 6(f). The above SEM
observation also confirmed that PEI adsorbed on SiO
a bridging aid between SiO and the hydroxides.
2
Figure 7 shows SEM images of CMS phosphors prepared by
the ESAD method using PEI at different calcination tempera-
2
acted as
2 6
Fig. 4. X-ray diffraction patterns of CaMgSi O (CMS) phosphors
prepared by the electrostatic self-assembly deposition (ESAD) method
with polyethyleneimine (PEI) (a), without PEI (b), and by the solid-state
reactions (SSR) method (c).

21
May 2006
Synthesis of Blue-Emitting CaMgSi O :Eu Phosphor
2
1495
6
2 6
Fig. 6. Scanning electron microscope images of CaMgSi O (CMS) prepared by the solid-state reactions method (a), mixed hydroxides (Ca, Mg, and
Eu) (b), CMS without polyethyleneimine (PEI) before (c) and after the calcination at 12001C (d), and CMS with PEI before (e), and after the calcination
at 12001C (f).
tures. With increasing calcination temperature, the particle size
increased owing to aggregations among the particles, which
could be suppressed by lowering the calcination temperature.
On the other hand, calcination at higher temperatures, e.g.,
Eu hydroxides onto SiO particles. On the other hand, the peak
2
intensity of the phosphor prepared without polycations was sig-
nificantly lower than that of the phosphor prepared with poly-
cations. This obviously resulted from the inhomogeneous
12501C resulted in the melting of CMS.
2
mixing of hydroxides and SiO , as described above. The high-
Figures 8 and 9 show PL excitation and emission spectra, re-
er emission intensity of the CMS phosphor prepared by the
ESAD method is probably owing to an improvement in crys-
tallinity. Consideration should also be given to the fact that for
powdered phosphors, luminescence characteristics are depend-
ent on morphology such as particle size and agglomeration. Less
aggregated fine particles are believed to show a better emission
spectively, of the phosphors prepared by the ESAD method us-
ing polycations (a), without polycations (b), and by the SSR
method (c). Two broad excitation peaks at 265 and 359 nm were
observed for the prepared phosphors; all showed blue emission
centered at 450 nm when excited at 359 nm. This emission is
6
7
owing to the transition from the 4f 5d-excited state to the 4f
intensity than aggregated particles owing to their higher packing
The fine morphology
21
15,16
ground state of Eu ions. Among the phosphors prepared, the
one prepared by the ESAD method using polycations showed
the strongest emission intensity, clearly indicating the successful
deposition of not only the Ca and Mg hydroxides but also the
density, as discussed in the literature.
of the prepared phosphor might account for the improved emis-
sion intensity. However, it is still difficult to estimate such an
effect appropriately, because no theory has been postulated that

1
496
Journal of the American Ceramic Society—Kida et al.
Vol. 89, No. 5
2 6
Fig. 7. Scanning electron microscope images of CaMgSi O (CMS) phosphors prepared by the electrostatic self-assembly deposition (ESAD) method
with polyethyleneimine (PEI) at different calcination temperatures, i.e., 9001C (a), 10001C (b), 11001C (c), and 12001C (d).
discusses the relation between emission intensity and mor-
phology or particle size. Figure 10 shows the emission spectra
of CMS phosphors prepared at different calcination tempera-
tures. It was found that they all showed blue emission centered
at 450 nm when excited at 359 nm, indicating that Eu -doped
CMS phosphors can be formed even at 9001C. Among the
phosphors prepared at different temperatures, CMS prepared
at 12001C showed the highest emission intensity owing to the
improved crystallinity, but calcination at higher temperatures,
e.g., 12501C resulted in a decrease in the emission intensity
owing to melting.
21
(2) Preparation of Spherical CMS Phosphors by the ESAD
Method: Effects of the Starting Composition
It is expected that phosphor particles with a narrow-size distri-
bution could be obtained if the amount of hydroxides deposited
onto spherical SiO is small. To obtain such particles, CMS
2
0
0
0
0
0
.25
.20
.15
.10
.05
0
0
0
0
0
0
.25
.20
.15
.10
.05
0
(
a) CMS
(
(
(
a) CMS
(
c) CMS by
SSR
c) CMS by SSR
(
b) CMS without PEI
b) CMS without PEI
350
4
00
450
500
550
2
50
300
Wavelength/nm
400
Wavelength/nm
Fig. 9. Photoluminescence emission spectra of CaMgSi
2
O
6
(CMS)
Fig. 8. Photoluminescence excitation spectra of CaMgSi
phosphors prepared by the electrostatic self-assembly deposition
ESAD) method with polyethyleneimine (PEI) (a), without PEI (b),
and by the SSR method (c). The emission wavelength is set to 450 nm.
2
O
6
(CMS)
phosphors prepared by the electrostatic self-assembly deposition
(ESAD) method with polyethyleneimine (PEI) (a), without PEI (b),
and by the solid-state reactions (SSR) method (c). The excitation wave-
length is set to 359 nm.
(

21
May 2006
Synthesis of Blue-Emitting CaMgSi O :Eu Phosphor
2
1497
6
0
0
0
0
0
.25
.20
.15
.10
.05
0
4
00
450
500
Wavelength/nm
550
Fig. 10. Photoluminescence emission spectra of CaMgSi
2
O
6
phosphors
prepared by the electrostatic self-assembly deposition method with po-
lyethyleneimine at different temperatures, i.e. 9001C (a), 10001C (b),
11001C (c), and 12001C (d). The excitation wavelength is set to 359 nm.
phosphors were prepared from diluted precursor nitrate solu-
tions and the effects of the starting compositions on the XRD
pattern, morphology, and PL property of the resulting phosphor
particles were investigated.
Figure 11 compares XRD patterns of CMS (a), with those of
CMS1/5 (b), and CMS1/10 (c) prepared by the ESAD method
at 12001C. By decreasing the concentrations of Ca, Mg, and Eu
nitrates in the precursor solutions, unreacted SiO
2
cores re-
mained and furthermore crystallized into not only crystobalite
but also quartz. The crystallization of amorphous SiO with the
2
1
7–19
aid of a small amount of impurities has been reported.
This
suggests that the amount of hydroxides deposited on the SiO
particles is quite low, as expected, and that deposited metal el-
ements may aid in the crystallization of SiO templates. Never-
theless, it was confirmed that the CMS phase was also formed
on the SiO templates in these cases.
2
2
2
Figures 12(a) and (b) show SEM images of CMS1/5 and
CMS1/10, respectively, prepared by the ESAD method at
12001C. The CMS particles prepared from the solution with
the stoichiometric nitrate concentrations were aggregated as dis-
cussed above (Fig. 6(f)). On the other hand, when the concen-
tration of nitrates in the precursor solution was diluted,
aggregation was suppressed to some extent and so finer parti-
cles were formed. In addition, for CMS1/10, aggregation was
further suppressed by lowering the calcination temperature and
nearly spherical particles were then formed, as shown in Figs. 12
(c) and (d). This observation may be explained by the fact
that when the starting nitrate concentrations are stoichiometric,
CaMgSi O
SiO (crystobalite)
2
SiO (quartz)
2
2
6
(
(
(
c) CMS 1/10
b) CMS 1/5
a) CMS
10
20
30
40
50
60
2 6
Fig. 12. Scanning electron microscope images of CaMgSi O (CMS)1/
2
theta/Degree
5
(a), and CMS1/10 prepared by the electrostatic self-assembly depo-
sition method with polyethyleneimine at 12001C (b) and 11001C (c)
and (d).
Fig. 11. X-ray diffraction patterns of CaMgSi
b), and CMS1/10 (c) prepared by the electrostatic self-assembly
deposition method with polyethyleneimine (PEI) at 12001C.
2 6
O (CMS) (a), CMS1/5
(

1
498
Journal of the American Ceramic Society—Kida et al.
Vol. 89, No. 5
0
.25
.20
.15
.10
.05
intense blue emission than that prepared by a conventional SSR.
This would be owing to the uniform deposition of precursor
hydroxides onto SiO template particles pre-coated with poly-
2
(
a) CMS
cations. Furthermore, by controlling the deposition of precursor
hydroxides onto SiO templates and by lowering the calcination
0
0
0
0
2
temperature, it is possible to obtain fine particles, although the
emission intensity was low. The particle size of the resulting
phosphor could be tuned by using SiO templates with different
2
particle sizes. This study demonstrates the feasibility of the
present ESAD method as a new route to achieve silicate-based
phosphor particles.
(
b) CMS 1/5
(
c) CMS1/10
200°C
1
Acknowledgment
(
d) CMS 1/10
The authors would like to thank Dr. H. Ichinose and Mr. A. Shiraishi of Saga
Ceramic Research Laboratory, and Mr. Y. Kawakami and Mr. T. Enjoji of In-
dustrial Technology Center of Saga for SEM measurements. The authors also
thank Dr. M. Noto of Daiden Co. Ltd. for donating commercial BAM samples.
1
100°C
0
4
00
450
500
550
Wavelength/nm
Fig. 13. Photoluminescence emission spectra of CaMgSi
O
2 6
(CMS) (a),
References
CMS1/5 (b), and CMS1/10 prepared by the electrostatic self-assembly
deposition method with polyethyleneimine at 12001C (c) and 11001C (d).
The excitation wavelength is set to 359 nm.
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2
hydroxides completely cover the SiO surfaces and then react
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2
CMS particles without unreacted SiO cores, as schematically
2
4
21
2 6
sibility Study of Silicate Phosphor CaMgSi O :Eu as Blue PDP Phosphor,’’
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2 2
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6
21
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2
Figure 13 compares the emission intensity of CMS (a), with
those of CMS1/5 (b), and CMS1/10 (c). The CMS1/5 and
CMS1/10 phosphors prepared from the diluted precursor ni-
trate solution also showed blue emission centered at 450 nm,
7 21
K. Yokota, S.-X. Zhang, K. Kimura, and A. Sakamoto, ‘‘Eu -Activated
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L. Jiang, C. Chang, and D. Mao, ‘‘Luminescent Properties of CaMgSi
2
O
6
and
Phosphors Activated by Eu , Dy , and Nd ,’’ J. Alloy. Compd.,
21
31
31
21
Ca MgSi
2
O
2 7
confirming the formation of Eu -doped CMS on the surfaces
of the SiO templates. On the other hand, without polycations
3
60, 193–7 (2003).
S. W. Keller, S. A. Johnson, E. S. Brigham, E. H. Yonemoto, and T. E. Mall-
2
9
the CMS1/5 and CMS1/10 phosphors showed almost no emis-
sion, suggesting that hydroxides were not uniformly deposited
onto the templates. This excludes the possibility of heterogene-
ouk, ‘‘Photoinduced Charge Separation in Multilayer Thin Films Grown by Se-
quential Adsorption of Polyelectrolyte,’’ J. Am. Chem. Soc., 117, 12879–80 (1995).
10
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Nanocomposite Particles by Controlled Polymer Bridging,’’ J. Am. Ceram. Soc.,
1, 140–4 (1998).
ous nucleation of hydroxide particles on the SiO templates.
2
8
11
However, the emission intensities of CMS1/5 and CMS1/10 are
much lower than that of CMS prepared from the precursor so-
lution with stoichiometric nitrate concentrations. This may be
F. Caruso, H. Lichtenfeld, H. Mohwald, and M. Giersig, ‘‘Electrostatic Self-
Assembly of Silica Nanoparticle-Polyelectrolyte Multilayers on Polystyrene Latex
Particles,’’ J. Am. Chem. Soc., 120 [33] 8523–4 (1998).
12
W. Stober, A. Fink, and E. Bohn, ‘‘Controlled Growth of Monodisperse Silica
Spheres in the Micron Size Rage,’’ J. Colloid Interf. Sci., 26, 62–9 (1968).
T. Sasaki, Y. Ebina, T. Tanaka, M. Harada, M. Watanabe, and G. Decher,
owing to the formation of thin CMS layers over the SiO tem-
2
13
plates. It thus appears that it is difficult to prepare spherical
CMS particles with high brightness by the present method. Fur-
ther, completely spherical particles were not obtained because of
the sintering between particles as shown in Fig. 12(d). Never-
theless, the results obtained suggest that the ESAD method we
developed may be a useful route for preparing fine CMS phos-
phor particles.
‘‘Layer-by-Layer Assembly of Titania Nanosheet/Polycation Composite Films,’’
Chem. Mater., 13, 4661–7 (2001).
14
T. Fengqiu, H. Xiaoxian, Z. Yufeng, and G. Jingkun, ‘‘Effect of Dispersants
on Surface Chemical Properties of Nano-Zirconia Suspensions,’’ Ceram. Int., 26,
93–7 (2000).
15
Y. C. Kang, S. B. Park, I. W. Lenggoro, and K. Okuyama, ‘‘Morphology
Control of Multicomponent Oxide Phosphor Particles Containing High Ductility
Component by High Temperature Spray Pyrolysis,’’ J. Electrocem. Soc., 146,
2
744–7 (1999).
16
B. S. Jeon, G. Y. Hong, Y. K. Yoo, and J. S. Yoo, ‘‘Spherical BaM-
21
O17:Eu
IV. Conclusion
gAl10
Phosphor Prepared by Aerosol Pyrolysis Technique for PDP
Applications,’’ J. Electrochem. Soc., 148, 128–31 (2001).
A. M. Venezia, V. La Parola, A. Longo, and A. Martorana, ‘‘Effect of Alkali
2
1
Eu -doped CaMgSi
deposition of Ca, Mg, and Eu mixed hydroxides over polycat-
ions-adsorbed spherical SiO template particles (300 nm), fol-
O
2 6
phosphor particles were prepared by
17
Ions on the Amorphous to Crystalline Phase Transition of Silica,’’ J. Solid State
Chem., 161, 373–8 (2001).
2
18
Y. Shinohara and N. Kohyama, ‘‘Quantitative Analysis of Tridymite and
Crystobalite Crystallized in Rice Husk Ash by Heating,’’ Ind. Health, 42, 277–85
2004).
lowed by calcination at 12001C in a reducing atmosphere. It was
found that the use of polycations (PEI) was effective in depos-
iting hydroxides on SiO particles by electrostatic self-assembly
attraction. The phosphor prepared in this way showed more
(
19
2
N. Perkas, V. G. Pol, S. V. Pol, and A. Gedanken, ‘‘Gold-Induced Crystal-
lization of SiO and TiO Powders,’’ Cryst. Growth Des., 6, 293–6 (2006).
2
2
&