Bright white upconversion luminescence in β-NaGd 0.794Yb0.20Ho0.001Tm0.005F 4 nanoparticles

Article abstract of DOI:10.1246/cl.2010.1158

β-NaGd_0.794Yb_0.20Ho_0.001Tm _0.005F₄ nanoparticles were synthesized through a simple hydrothermal method. The nanoparticles crystallized well and exhibited nearly hexagonal morphology and ellipsoidal spheres, as characterized by X-ray powder diffraction and transmission electron microscopy. The β-NaGd _0.794Yb_0.20Ho_0.001Tm_0.005F ₄ nanoparticles have an average size of about 23 nm. Room-temperature bright white upconversion luminescence in β-NaGd_0.794Yb _0.20Ho_0.001Tm_0.005F₄ nanoparticles was obtained under single-wavelength diode laser excitation of 980 nm.

Full text of DOI:10.1246/cl.2010.1158

doi:10.1246/cl.2010.1158
1158
Published on the web October 5, 2010
Bright White Upconversion Luminescence in ¢-NaGd0.794Yb0.20Ho0.001Tm0.005F4 Nanoparticles
Gejihu De,*1,2 Menggenqilavuqi Yu,1 and Siqin Bao1
1College of Chemistry and Environment Science, Inner Mongolia Normal University,
81 Zhawuda Road, Hohhot 010022, P. R. China
2Physics and Chemistry of Functional Materials, Inner Mongolia Key Laboratory,
81 Zhawuda Road, Hohhot 010022, P. R. China
(Received July 8, 2010; CL-100617)
¢-NaGd0.794Yb0.20Ho0.001Tm0.005F4 nanoparticles were syn-
thesized through a simple hydrothermal method. The nano-
particles crystallized well and exhibited nearly hexagonal
morphology and ellipsoidal spheres, as characterized by X-ray
powder diffraction and transmission electron microscopy. The
¢-NaGd0.794Yb0.20Ho0.001Tm0.005F4 nanoparticles have an aver-
age size of about 23 nm. Room-temperature bright white
of 0.01 M aqueous Gd0.794Yb0.20Ho0.001Tm0.005(NO3)3 solution
was added into the above colloid solutions, after stirring
vigorously at 30 °C. Then the resulting colloid solution was
then transferred into a 100.0-mL stainless Teflon-lined autoclave
and heated at 180 °C for 24 h. The resulting suspension was
cooled to room temperature right after the heating and was then
stored at a constant temperature of 25 °C. After aging for 12 h,
the resultant material was collected and washed several times
with absolute ethanol and distilled water. The powder was
obtained after centrifuging and drying in vacuum at 80 °C.
Finally, the sample was immediately placed in a furnace at a
heat-treatment temperature beforehand and was heated at 600 °C
in a nitrogen gas stream for another 30 min.
upconversion luminescence in ¢-NaGd0.794Yb0.20Ho0.001Tm0.005
-
F4 nanoparticles was obtained under single-wavelength diode
laser excitation of 980 nm.
Metal fluorides doped with rare-earth ions have been
demonstrated many applications such as lasers, optical commu-
nications, three-dimensional display devices, and biological
fluorescent labels.1 Upconversion (UC) is a generation process
that higher-energy light is converted from lower-energy radia-
tion, usually near-infrared (NIR) or infrared (IR), in transition-
metal and rare-earth (RE) ions doped into a solid-state host
material.2 White emission by frequency UC in Yb3+, Ho3+, and
Tm3+ triply doped nanoparticles deserves increasing attention.3
The realization of strong white emission requires the generation
and an adequate combination of the three fundamental red, green,
and blue light colors, which is a great challenge to material
design including host composition and the suitable combination
of sensitizers and activator ions. In 2004, Cheah et al. obtained
white light in Er3+ and Yb3+ codoped porous silicon.4 In 2005,
van Veggel et al. reported that white light could be easily
generated from thin film made with La0.45Yb0.5Er0.05F3,
La0.75Yb0.2Tm0.05F3, and Yb0.75La0.2Eu0.05F3 nanoparticles.5 Re-
cently, important progress on white UC emission was obtained in
glass ceramics containing YF3 or Pb1¹xCdxF2 nanoparticles.6-9
But the combination of sensitizer and activator ions is mainly
limited to Yb3+, Er3+, and Tm3+ triply doped systems. Few
investigations have focused on other activator ions, such as
Yb3+, Ho3+, Tm3+ and Yb3+, Nd3+, Tm3+ systems. In this letter,
we report the preparation and white UC emission of ¢-
NaGd0.794Yb0.20Ho0.001Tm0.005F4 nanoparticles.
Phase identification was performed via X-ray diffractometry
(XRD) (Philip Co., PW 1830), using nickel-filtered Cu K¡
radiation (- = 1.5406 ¡). The size and morphology of the
nanocrystals were characterized by JEM-2010 transmission
electron microscopy (TEM), and high-resolution transmission
electron microscopy (HRTEM). The specimen for TEM obser-
vations was placed on perforated copper grids. The UC emission
spectra were recorded with a Hitachi F-4600 fluorescence
spectrophotometer with a 980 nm diode laser as the excitation
source.
Figure 1 shows the powder XRD patterns of the ¢-
NaGd0.794Yb0.20Ho0.001Tm0.005F4. It is evident from the intensity
of the peaks in the obtained patterns that the materials in
question are highly crystalline in nature. All the diffraction
peaks can be readily indexed to those of the hexagonal ¢-
NaGdF4 phase with lattice constants a = 0.6020 nm, and c =
0.3061 nm, which are in good agreement with the standard
values for the bulk hexagonal ¢-NaGdF4 (JCPDS No. 27-0699).
In addition, two peaks from other YbF3 phase were observed.
An average crystallite size of 23 nm of the ¢-NaGd0.794Yb0.20
-
Ho0.001Tm0.005F4 sample was calculated using the (110), (101),
2500
2000
1500
1000
500
The 0.01 M Gd0.794Yb0.20Ho0.001Tm0.005(NO3)3 solution was
prepared by dissolving the corresponding metal oxide in nitric
acid at elevated temperature. The method of fabricating ¢-
NaGd0.794Yb0.20Ho0.001Tm0.005F4 is as follows: First, solution A
was prepared by adding 5.0 mL of 12.0 M aqueous NaOH solu-
tion and 5.0 mL of 4.0 M aqueous NH4HF2 solution added in to
0
the 50.0 mL of alcohol solution of oleic acid (Voleic acid:Valcohol
=
20
30
40
50
60
2:1). Second solution B was prepared by dissolving sodium
dodecyl sulfate (SDS, Aldrich) (1.25 g) in 10 mL of deionized
water. Solutions A and B were mixed and stirred for 30 min and
the resultant colloid solution was obtained. Subsequently 5.0 mL
2θ/degree
Figure 1. XRD patten of ¢-NaGd0.794Yb0.20Ho0.001Tm0.005F4 nano-
particles.
Chem. Lett. 2010, 39, 1158-1159
© 2010 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

1159
(a)
1.0
0.8
0.6
0.4
0.2
0.0
400
450
500
550
600
650
700
Wavelength/nm
Figure 2. (a) The TEM image of the ¢-NaGd0.794Yb0.20Ho0.001
-
Tm0.005F4 nanoparticles, (b) and (c) HRTEM image of an individual
¢-NaGd0.794Yb0.20Ho0.001Tm0.005F4 ellipsoidal shape and hexagonal
nanoparticle.
Figure 3. (a) Room-temperature UC emission spectra of the ¢-
NaGd0.794Yb0.20Ho0.001Tm0.005F4 nanoparticles under the 980-nm LD
excitation with powers 350 mW, (b) (color online) CIE (X, Y)
coordinate diagram showing the chromaticity points of the UC
luminescence in the ¢-NaGd0.794Yb0.20Ho0.001Tm0.005F4 nanoparticles.
and (201) diffraction peaks through the Debye-Sherrer formula.
This value matches closely the particle size determined from the
TEM results, which are shown in Figure 2.
The morphology of the final product was characterized
by the TEM observation. As shown in a typical TEM image
Figure 2a, most of the particles dispersed on the copper grids
show hexagonal and ellipsoidal sphere morphology. The
average edge length of the hexagon is about 23 nm. Figures 2b
and 2c present typical HRTEM images of an ellipsoidal
shape nanoparticle and a hexagonal nanoparticle indicated in
Figure 2a, respectively. This image revealed that the crystals are
structurally nonuniform with a clearly resolved interplanar
spacing of about 0.294 and 0.516 nm which corresponds to (101)
and (100) planes, respectively.
NaGd0.794Yb0.20Ho0.001Tm0.005F4 nanoparticles have an average
size of about 23 nm. Room-temperature bright white UC
luminescence in ¢-NaGd0.794Yb0.20Ho0.001Tm0.005F4 nanoparti-
cles was obtained under single-wavelength diode laser excitation
of 980 nm. The white light consists of the blue, green, and red
UC radiations which correspond to the transitions 1G4 ¼ 3H6 of
5
5
Tm3+, F4 ¼ 5I8, and F5 ¼ 5I8 of Ho3+ ions, respectively. The
spectral positions of the three colors produced CIE-X = 0.2717
and CIE-Y = 0.2673 coordinates.
The authors thank the support of the National Science
Foundation of China (Grant No. 20863005).
The room-temperature UC emission spectrum of the ¢-
NaGd0.794Yb0.20Ho0.001Tm0.005F4 nanoparticles with the pump
power is presented in Figure 3a. The excitation wavelength is
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980 nm, which agrees well with the Yb3+ ions F5/2 ¼ 2F7/2
transition. This fluorescence corresponds to the following Tm3+
transitions: 1G4 ¼ 3F4 (ca. 450 nm), 1G4 ¼ 3H6 (ca. 476 nm)
and Ho3+ transitions: 5F5 ¼ 5I8 (ca. 480 nm), 5S2, 5F4 ¼ 5I8 (ca.
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542 nm), F5 ¼ 5I8 (ca. 650 nm), respectively.
Figure 3b shows that the calculated color coordinates are
0.2717, 0.2673. They fall within the white region of the 1931
CIE diagram. This white light is bright and can been seen by
naked eye even at a laser pump power of only 350 mW.
In conclusion, the ¢-NaGd0.794Yb0.20Ho0.001Tm0.005F4 nano-
particles were synthesized through a simple hydrothermal
method. The nanoparticles crystallized well and exhibited nearly
hexagonal and ellipsoidal sphere morphology, as characterized
by powder XRD, TEM, and HRTEM. TEM showed that the ¢-
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Chem. Lett. 2010, 39, 1158-1159
© 2010 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/