Synthesis, morphology and spectroscopy of Nd:GSAG nano-powders

Article abstract of DOI:10.1016/j.jallcom.2012.02.048

Nd³⁺-doped gadolinium scandium aluminum garnet (Nd:GSAG) precursors were obtained from a mixed nitrate solution with precipitant of ammonium hydrogen carbonate. The precursors were sintered at different temperatures and the phase developments in heat treatments were investigated through methods of XRD and IR, showing the precursors transformed to pure-GSAG phase with no intermediate phases appeared at 900 °C. The TEM observation revealed that the powders sintered at 900-1000 °C were well-dispersed with average crystalline sizes of 30-80 nm. Photoluminescence analysis of the Nd:GSAG nano-powders showed that the PL intensities changing significantly with the Nd³⁺ doping concentration, and the concentration quenching was observed as the Nd³⁺ concentration reached to 1.5 at.%.

Full text of DOI:10.1016/j.jallcom.2012.02.048

Journal of Alloys and Compounds 525 (2012) 25–27
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Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Synthesis, morphology and spectroscopy of Nd:GSAG nano-powders
∗
Jing Su , Yijun Yao, Bin Liu, Linhua Xu
School of Physics and Optoelectronic Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China
a r t i c l e i n f o
a b s t r a c t
Nd3+-doped gadolinium scandium aluminum garnet (Nd:GSAG) precursors were obtained from a mixed
nitrate solution with precipitant of ammonium hydrogen carbonate. The precursors were sintered at
different temperatures and the phase developments in heat treatments were investigated through meth-
ods of XRD and IR, showing the precursors transformed to pure-GSAG phase with no intermediate
Article history:
Received 18 December 2011
Received in revised form 27 January 2012
Accepted 5 February 2012
Available online 16 February 2012
◦
◦
phases appeared at 900 C. The TEM observation revealed that the powders sintered at 900–1000 C were
well-dispersed with average crystalline sizes of 30–80 nm. Photoluminescence analysis of the Nd:GSAG
Keywords:
3
+
nano-powders showed that the PL intensities changing significantly with the Nd doping concentration,
Chemical synthesis
Phase transitions
Optical spectroscopy
Luminescence
3
+
and the concentration quenching was observed as the Nd concentration reached to 1.5 at.%.
©
2012 Elsevier B.V. All rights reserved.
1
. Introduction
high-performance, well-sinterable Nd:GSAG powders are neces-
sary. In this work, Nd:GSAG nano-powders were prepared via
co-precipitation. Phase transition of the precursors, morphology
and luminescence of Nd:GSAG powders were investigated.
The special wavelength regions around 940 nm have been spec-
ified to be a space-borne differential absorption LIDAR (DIAL) for
atmospheric water vapor detection [1,2]. Although the laser out-
puts at these wavelengths can be easily obtained by conventional
ways of optical parametric oscillator (OPO), Ti:Sapphire laser gen-
eration and Raman-shifter, they exhibit many disadvantages, such
as low efficiency and complex set-up. To solve these problems,
development for suitable laser crystals pumped by laser diode (LD)
has become a good choice and attracted wide interests. Being a
type of crystals that can generate LD pumped 940 nm laser out-
put, the garnet crystals, such as Nd3 -doped gadolinium scandium
aluminum garnet (Nd:GSAG) single crystal, have achieved a great
development [3,4]. However, as a traditional laser material, sin-
gle crystal has shown some disadvantages, such as the difficulties
in grow large-size, uniform and high rare earth ion-doped crys-
tal for the limitation of crystal growth technique. Recently, the
2. Methods
Gd(NO3)3, Sc(NO3)3 and Nd(NO3)3 solution were prepared by dissolving Gd2O3,
Sc2O3, Nd2O3 with purity of 99.995% into diluted HNO3. Al(NO3)3 solution was
obtained by dissolving Al(NO ) ·9H O (>99%) in de-ionized water. Nitrate solutions
3
3
2
were mixed according to the molar ratio of (Gd1−xNdx)3Sc2Al3O12 (x = 0.01, 0.015,
0.02), then were dropped synchronously together with NH4HCO3 solution, to a lit-
tle amount of NH4HCO3 solution with initial pH = 9 under vigorous stirring, then
the pH value was kept in the range of 8–9. The precipitate slurry was stirred suf-
ficiently after the reaction. Then it was separated and was washed with deionized
+
+
−
−
water for several times to remove NH4 , NO3 and OH , etc. The slurry cake was
◦
dried at 120 C followed by repeated grinding. Finally, the dried precursor powders
were sintered in the temperature range 800–1000 C for 1 h.
◦
The infrared (IR) spectra were recorded on a Fourier transform infrared spec-
trometer (Nicolet MAGNA-IR 750, USA). The phase development was characterized
by Philips X’pert PRO x-ray diffractometer with Cu Ka1 radiation. The morphology
and microstructure of the sintered powders were observed by transmitted electron
microscopy (Hitachi H-800, Japan). The photoluminescence spectra were measured
using a Jobin-Yvon spectrophotometer (FLUOROLOG 3 TAU, France). All the experi-
ments were completed at room temperature.
transparent laser ceramics seem to be an alternative replacement
for laser crystals. Since the first Nd3+-doped yttrium aluminum
garnet (Nd:YAG) ceramic laser was developed in 1995 [5], the
advantages of transparent ceramics, such as fabrication of large
size and high doping concentration, low price, ease of manufac-
ture and mass production, have attracted great interests to develop
this potential laser material [6–8]. Although, to our knowledge,
few results reported on the Nd:GSAG transparent ceramics had
been found. For fabrication of Nd:GSAG transparent ceramics with
3. Results and discussion
Fig. 1 shows the XRD patterns of the precursor and the pow-
ders sintered for 1 h at various temperatures. No obvious diffraction
peaks was observed for the precursor and the powder sintered
◦
at 800 C, indicating that the samples are mainly amorphous. At
9
◦
00 C, strong characteristic diffraction peaks corresponding to
∗ Corresponding author. Tel.: +86 25 58731031; fax: +86 25 58731174.
E-mail address: zlj007@126.com (J. Su).
cubic GSAG (JCPDS 43-0659) appeared. No other crystalline phase
was observed, indicating the precursors transform into pure cubic
0
925-8388/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2012.02.048

2
6
J. Su et al. / Journal of Alloys and Compounds 525 (2012) 25–27
o
1
000 C,1h
o
o
1
000 C, 2at.%
8
00 C,1h
o
1
000 C, 1.5at.%
precursor
o
1
000 C, 1at.%
o
9
00 C, 1at.%
o
8
00 C, 1at.%
Precursor, 1at.%
1
0
20
30
40
50
60
70
80
2
theta (degree)
5
00
1000
1500
2000
2500
3000
3500
4000
-
1
wave number (cm )
Fig. 1. X-ray diffraction patterns of the Nd:GSAG precursor and the samples sintered
at different temperatures for 1 h.
◦
Fig. 2. FT-IR spectra of the Nd:GSAG precursor and the samples sintered at 800 C
and 1000 C for 1 h.
◦
GSAG polycrystalline. As the sintering temperature increases, the
diffraction peaks became stronger and sharper, indicating the
growth of Nd:GSAG crystallites. Additionally, the XRD pattern of
Nd:GSAG polycrystalline with different Nd3 concentration has no
to the stretching mode of the tetrahedral units present in garnet
structure [10].
+
Fig. 3(a) and (b) shows TEM morphologies of the 2 at.% Nd:GSAG
3+
◦
◦
significant differences, indicating that at 2 at.% Nd doping-level,
powders sintered at 900 C and 1000 C, respectively. Both the sam-
ples are well-dispersed with nearly spherical shape, and grand
the effect of doping Nd3+ on the crystal structure is unremarkable.
3+
◦
◦
Fig. 2 shows the FT-IR spectra of the 1 at.% Nd doped-precursor
dimension of nanosizes (900 C, 30–60 nm; 1000 C, 50–80 nm).
The average sizes of nanocrystallites could be determined from the
broadening of diffraction lines of X-ray according to Scherer’s for-
mula (d = 0.9ꢀ/ˇcos ꢁ), and were estimated to be 37 and 50 nm for
the samples sintered at 900 C and 1000 C, respectively. A slightly
larger particle size observed in TEM micrographs than that in XRD
patterns might be due to the resolution of instrumentation.
Fig. 4(a) shows the emission spectra of the Nd:GSAG samples
◦
◦
and the samples sintered at 800 C and 1000 C for 1 h, respectively.
The wide bands at 3424 cm
−1
can be assigned to O–H stretch-
ing modes of the crystal and absorbed water. The sharp band
−
1
−1
◦
◦
at 1386
and the weak band around 1513 cm
are associated
−
with NO3 , which became weaker with increasing of tempera-
ture due to the decomposition of NO3 . As raised to 800 C, the
spectrum changed greatly because the structure of the precursor
was destroyed. The new bands at 479 cm and 744 cm should
be due to certain molecular modes of AlO4 units [9], indicating
the structure of the sample sintered at 800 C is not completely
−
◦
−1
−1
◦
sintered at 1000 C for 1 h. The spectra obtained by excitation in
transition of Nd ion at 808 nm consist three
main characteristic bands at 850–950, 1000–1150 and 1300–1380,
4
4
3+
the I9/2 → F
5/2
◦
◦
4
4
4
4
4
4
amorphous. For the sample sintered at 1000 C, new bands at
which attribute to F3/2 → I9/2, F3/2 → I11/2, F3/2 → I
tran-
13/2
−
1
−1
−1
−1
−1
3+
4
13 cm , 475 cm , 651 cm , 679 cm , 745 cm
appeared in
sition of Nd , respectively. It shows that the emission peak at
1062 nm is most strong and the peak at 942 nm is relatively
weak. Comparing the spectra of different Nd3+ concentration, no
the low frequency range of 800–400 cm 1, which correspond to
−
characteristic metal–oxygen (M-O) vibrations and can be attributed
◦
◦
Fig. 3. TEM morphologies of Nd:GSAG samples sintered at 900 C (a) and 1000 C (b) for 1 h.

J. Su et al. / Journal of Alloys and Compounds 525 (2012) 25–27
27
◦
Fig. 4. Photoluminescence spectra of 1 at.%, 1.5 at.% and 2 at.% Nd:GSAG samples sintered at 1000 C for 1 h: (a) emission spectra, ꢀex = 808 nm and (b) excitation spectra,
ꢀ
em = 942 nm.
significant difference in peak positions was found. The intensity
at 1.5 at.% Nd-doped is strongest, while that of 2 at.% Nd-doped is
decreased greatly, suggesting that concentration quenching of Nd3
emission in GSAG observed is 1.5 at.%. As a suitable laser medium for
quasi-three-level Nd3 laser operation around 942 nm, Nd:GSAG
crystal could be applied for atmospheric water vapor detection due
Acknowledgments
+
This work is supported by the National Natural Science Founda-
tion of China (nos. 51002079 and 90922003).
+
References
to the fluorescence ratio of Nd3 F3/2 → I
+
4
4
is relatively large
9/2
[
[
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[
9
11,12]. Thus we measured the excitation spectra monitored at
2
4
4
42 nm ( F → I ) of the Nd:GSAG nano-powders. According to
3
/2
9/2
3+
the energy level of Nd ion in GSAG [11–13], the excitation bands
were assigned as Fig. 4(b) shows. It shows the intensities of the
excitation bands changed significantly with the Nd3 concentra-
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in the emission spectra. The intensities of the excitation band at
+
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1
8
08 nm are very strong, indicating the quasi-three-level Nd:GSAG
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. Conclusions
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1
34–150.
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[
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solutions with NH HCO3 as precipitant. Pure GSAG phase was
4
◦
obtained from sintering the precursors at 900 C for 1 h. TEM
and XRD results show that the precursor powders sintered at
[
12] J. Su, B. Liu, L.H. Xu, Q.L. Zhang, S.T. Yin, J. Alloys Compd. 512 (2012)
30–234.
◦
9
00–1000 C were well-dispersed with average crystalline sizes
2
of 30–80 nm. The photoluminescence intensities of the nano-
[13] A.A. Kaminskii, Crystalline Lasers: Physical Processes and Operating Schemes,
1st ed., CRC Press, Boca Raton, 1996.
3+
powders change significantly with the Nd doping concentration
and quenching concentration of Nd3 in GSAG is about 1.5 at.%.
+