Hydrothermal synthesis of ultraviolet-emitting cerium phosphate single-crystal nanowires

Article abstract of DOI:10.1246/cl.2004.612

Cerium phosphate single-crystalline nanowires with a narrow distribution of diameters have been successfully synthesized by a mild and simple hydrothermal approach. Photoluminescence of cerium phosphate single-crystalline nanowires show that these nanowires can emit ultraviolet laser light.

Full text of DOI:10.1246/cl.2004.612

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Chemistry Letters Vol.33, No.5 (2004)
Hydrothermal Synthesis of Ultraviolet-emitting Cerium Phosphate Single-crystal Nanowires
ꢀ
Wen-Bo Bu, Zi-Le Hua, Hang-Rong Chen, Ling-Xia Zhang, and Jian-Lin Shi
State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics,
Chinese Academy of Sciences, Shanghai, 200050, P. R. China
(Received January 27, 2004; CL-040103)
Cerium phosphate single-crystalline nanowires with a nar-
row distribution of diameters have been successfully synthesized
by a mild and simple hydrothermal approach. Photolumines-
cence of cerium phosphate single-crystalline nanowires show
that these nanowires can emit ultraviolet laser light.
I
Nanostructured materials have attracted much attention in
recent years and been expected to play a crucial role in the future
nanotechnological advance in electronics, optoelectronics, and
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0
20
30
40
50
60
2θ / °
1
memory devices. In particular, 1D nanostructures have become
Figure 1. X-ray diffraction pattern of CePO nanowires.
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a class of attractive materials for both fundamental research and
technological applications because of their unique chemical and
physical properties, which can be attributed to their dimensional
anisotropy. During the past decade, considerable research ef-
forts have been directed toward the preparation of carbon nano-
tered, and washed with absolute alcohol, and distilled water sev-
eral times. The final products were dried at room temperature.
The crystal structure and phase purity of the CePO4 samples
was examined by X-ray diffraction (XRD) technique (Figure 1).
All diffraction peaks can be perfectly indexed as the hexagonal
cell of CePO4 [space group: P6222 (180)] with lattice constants
comparable to the values in JCPDS card 31-1380, and no impur-
ities can be detected, which indicates that the nanowires ob-
tained by our current synthetic methods consist of a pure hexag-
onal CePO4 phase.
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tubes and semiconductor, metallic binary oxide nanowires,
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and ternary metal oxide nanorods. However, few reports can
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be found concerning phosphate single-crystalline nanowires.
Since phosphate represents a big branch of many important
and interesting materials, development of straightforward and
controllable methods to construct phosphate single-crystalline
nanowires is of importance to nanotechnology and still remains
a key research challenge.
(
a)
(b)
Among various phosphates, rare earth phosphates are partic-
ularly suitable for applications as light emitters owing to their
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well-defined transitions within the 4f shell. Very recently, the
8
cerium phosphate 1D nanostructures have been reported. How-
ever, some limitations such as broad distribution of diameters
(
5–100 nm) and special conditions should be circumvented for
[001]
8
practical utilities. Furthermore, to the best of our knowledge,
the reports on photoluminescence of cerium phosphate nano-
wires have not been found up to now. In this letter, we report
a facile, surfactant-directed hydrothermal approach to fabricate
cerium phosphate single-crystalline nanowires at low tempera-
ture with a narrow size distribution (10–12 nm) and its photolu-
minescence properties. The availability of cerium phosphate
nanowires with narrow size distribution should enhance the
photoluminescence.
In a typical procedure for the synthesis of single-crystalline
CePO4 nanowires, 7.45 g CeCl3ꢁ7H2O and 7.6 g Na3PO4ꢁ12H2O
were dissolved in 80-g distilled water, respectively, and then
were mixed, stirring for about 20 min. The resulting precipitate
was recovered by centrifugation and washed with distilled water.
The precipitate was added into a mixture of nonionic pluronic
Figure 2. (a) TEM image of CePO4 nanowires; (b) TEM image
of an 11-nm diameter CePO4 nanowire. Left inset: selected area
electron-diffraction (SAED) pattern obtained from the same
nanowire. Right inset: A high-resolution TEM image of the
nanowire that shows lattice fringes perpendicular to the [001]
direction.
The morphology and microstructure of the products were
further investigated with transmission electron microscopy
(TEM), selected area electron diffraction (SAED), and high res-
olution transmission electron microscopy (HRTEM), accompa-
nied by energy dispersive X-ray spectroscopy (EDS). Represen-
tative TEM images (Figure 2a) show that the products obtained
ꢂ
at 100 C for 12 h are composed of nanowires in high yield, and
amphiphilic triblock copolymers (P123, 2 g), H3PO4 (30 mL,
these nanowires are straight with an average diameter of 10–
12 nm and the length up to several micrometers, which is much
more uniform, especially in diameter, than the previously report-
ed ones. Figure 2b shows a typical CePO4 nanowire. Its corre-
sponding SAED pattern at the top left corner of Figure 2b reveals
that the nanowire exhibits sharp diffraction spots characteristic
ꢂ
2
M), and deionized water (30 g) under stirring at 35–40 C.
The resulting solution was stirred for 2 h and then sealed in a
stainless steel autoclave with a Teflon liner. This autoclave
8
ꢂ
was maintained at 100 C for 12 h. Subsequently, the autoclave
was allowed to cool to room temperature. The precipitate was fil-
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.5 (2004)
613
of a single-crystalline CePO4, in agreement with X-ray diffrac-
tion results. Moreover, the SAED patterns taken from the differ-
ent nanowires were found to be identical within experimental ac-
curacy, indicating that all CePO4 nanowires synthesized by
current synthetic methods are single crystalline. Representative
HRTEM image of corresponding nanowire (inset in Figure 2b)
showed that the nanowire is highly crystalline without defects
or dislocations, which provides another evidences that these
nanowires are single crystalline. The calculated interplannar dis-
tance of 0.61 nm corresponds to the d spacing of (100) crystal
planes, consistent with the SAED pattern. The (100) crystal
planes are parallel to the long axis of the nanowire, that is, the
preferred growth direction is [001]. Both the SAED pattern
and the HRTEM image in Figure 2b showed that the c axes of
the CePO4 unit cells are aligned along the nanowire axis. The
chemical stoichiometry of CePO4 nanowires was investigated
with energy dispersive spectrometry (EDS), which gave the mo-
lar ratio of Ce, P, and O close to the stoichiometric proportions of
the formula CePO4. It is also interesting to note that CePO4 sin-
gle-crystalline nanowires, synthesized by the current approach,
have much narrower distribution of diameters (10–12 nm) than
further investigations in this area are in progress.
In summary, we have demonstrated that cerium phosphate
single-crystalline nanowires with a narrow distribution of diam-
eters, synthesized by a mild and simple hydrothermal approach,
can emit ultraviolet laser light. We consider this work as a pre-
liminary and important step towards the development of lantha-
nide phosphate based 1D nanostructures with potential lumines-
cent and catalytic application.
This work was supported by the Chinese National Founda-
tion of Nature Science Research (No. 50232050, 50172057)
and China Postdoctoral Science Foundation (No. 2002032162).
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λ
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Figure 3. Excitation (200–300 nm, ꢀobs ¼ 345 nm) and emis-
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3þ
state F5=2 of Ce to the different components of the excited
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3þ
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2
2
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1
3þ
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2
2
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3þ
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phology and its optical properties should exist. Systematic and
Published on the web (Advance View) April 24, 2004; DOI 10.1246/cl.2004.612