Facile large-scale synthesis of monodisperse REF3 (RE = Y, Ce, Nd, Sm-Lu) nano/microcrystals and luminescence properties

Article abstract of DOI:10.1039/c4tc00808a

Highly monodisperse YF₃:Ln³⁺ (Ln = Eu, Ce, Tb, Yb/Er, Yb/Ho, and Yb/Tm) nano/microcrystals with controllable size and morphology have been synthesized by an innovative low-temperature (≤0 °C) precipitation route free of any surfactant. Interestingly, the monodispersity and morphology are independent of the pH value and reactant concentration at a low temperature even when the reactant concentrations are close to saturation. This allows for a high yield production at 150 g L^-1 of reaction system. A detailed investigation of the growth process reveals that a low temperature can ensure a more definite separation of nucleation and growth. Simultaneously, the low temperature-induced diffusion-controlled growth model gives rise to a size focusing effect, which further insures the monodispersity of the final products. Furthermore, our synthetic strategy can be extended to other lanthanide fluorides (REF₃, RE (rare earth) = Ce, Nd, Sm-Lu), and the obtained YF₃:Ln³⁺ samples exhibit strong down/upconversion emissions. Such a facile synthetic strategy fits well with the green concept in current synthetic innovations for nanocrystals and may provide some guidance in the kinetically controlled synthesis of inorganic nanocrystals. the Partner Organisations 2014.

Full text of DOI:10.1039/c4tc00808a

Journal of
Materials Chemistry C
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PAPER
Facile large-scale synthesis of monodisperse REF3
RE ¼ Y, Ce, Nd, Sm-Lu) nano/microcrystals and
luminescence properties†
(
Cite this: J. Mater. Chem. C, 2014, 2,
666
7
ab
ab
ab
ab
ab
ab
Baiqi Shao, Qi Zhao, Yongchao Jia, Wenzhen Lv, Mengmeng Jiao, Wei Lu
¨
and Hongpeng You*a
3+
Highly monodisperse YF
3
:Ln (Ln ¼ Eu, Ce, Tb, Yb/Er, Yb/Ho, and Yb/Tm) nano/microcrystals with
ꢀ
controllable size and morphology have been synthesized by an innovative low-temperature (#0 C)
precipitation route free of any surfactant. Interestingly, the monodispersity and morphology are
independent of the pH value and reactant concentration at a low temperature even when the reactant
ꢁ1
concentrations are close to saturation. This allows for a high yield production at 150 g L of reaction
system. A detailed investigation of the growth process reveals that a low temperature can ensure a more
definite separation of nucleation and growth. Simultaneously, the low temperature-induced diffusion-
controlled growth model gives rise to a size focusing effect, which further insures the monodispersity of
the final products. Furthermore, our synthetic strategy can be extended to other lanthanide fluorides
3+
Received 22nd April 2014
Accepted 18th July 2014
(
REF
3
, RE (rare earth) ¼ Ce, Nd, Sm-Lu), and the obtained YF
3
:Ln samples exhibit strong down/
upconversion emissions. Such a facile synthetic strategy fits well with the green concept in current
synthetic innovations for nanocrystals and may provide some guidance in the kinetically controlled
synthesis of inorganic nanocrystals.
DOI: 10.1039/c4tc00808a
www.rsc.org/MaterialsC
temperatures, and low yields were oen involved in these
synthetic routes and are both cost-consuming and becoming
1
. Introduction
Nano/micromaterials have attracted intensive research interest matters of environmental concern. The stringent control over
due to their prolic, fascinating size-/shape-dependent proper- experimental variables and the unavoidable surface contami-
ties and potential applications in many areas of modern science nation further restricts the technological applications of these
1–3
and technology. Precise control over physical parameters, materials. Therefore, it is a current trend to seek a green
including size, shape, and phase enables us to purposively synthetic route for nano/micromaterials.
4
–7
manipulate their properties as desired. Among the parame-
ters of the nano/micromaterials, monodispersity has a pre- in the functional material areas of modern science and tech-
Lanthanide-doped crystals have played an irreplaceable role
19–21
determined role because the full performance of the size-/ nology.
Rare earth uorides have been intensively studied
shape-dependent properties are based on their uniformity and due to their wide band gap (>10 eV) and low vibrational energy,
8,9
dispersity. Thus, the controlled synthesis of monodisperse which can effectively minimize the quenching of the excited
22
nano/micromaterials with uniform morphologies is a central state of rare earth ions during the luminescence process.
issue in nanoscience and nanotechnology. The last decades Among them, YF is emphasized as a potential candidate for a
have witnessed rapid developments in the synthesis of mono- uorescent host due to its efficient light emissions, and higher
3
1
0–12
disperse inorganic nano/micromaterials.
The notable yttric content in the earth's crust. So far, the general synthetic
13
14
examples include noble metals, metal oxides, and semi- methodologies towards YF nano/micromaterials suffer from
conductors, which are mainly synthesized by hydro-/sol- drawbacks including harsh reaction conditions, unavoidable
vothermal, micro-emulsion, sol–gel methods, etc. However, surface contamination, and low yields which act as barriers to
toxic organic reagents or organometallic precursors, high further commercial interest. Therefore, it is highly desirable to
seek a process for a cost-effective, large-scale yield and green
3
15
16
17
18
3
synthetic route for YF nano/micromaterials.
Herein, we describe a precipitation route, free of surfactants,
with a post-calcination process to synthesize YF :Ln nano-
structures at large-scale with high uniformity and mono-
dispersity. Of particular interest to our research is the ability to
conduct the precipitation process at a low temperature (#0 C),
a
State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China.
E-mail: hpyou@ciac.ac.cn
3+
3
b
Graduate School of the Chinese Academy of Sciences, Beijing 100049, P. R. China
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c4tc00808a
ꢀ
1
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ꢀ
differing from the conventional precipitation techniques. We instrument (SDT2960, TA Instruments, New Castle, DE) at 5 C
3
+
ꢁ1
ꢁ1
have found that highly monodisperse YF :Ln nano/micro- min in an air ow of 100 mL min . Down-conversion (DC)
3
spheres and octahedrons with controllable size can be photoluminescence (PL) excitation and emission spectra were
obtained, and the morphology and monodispersity are unaf- recorded with a Hitachi F-4500 spectrophotometer equipped with
fected by the reactant concentration and pH value, even when a 150 W xenon lamp as the excitation source. Up-conversion (UP)
the reactant concentration is close to saturation. Such inter- PL spectra were measured by the same instrument equipped with
esting results have never been reported before, and we also got a an external 980 nm diode laser and a R928P photomultiplier tube.
high production yield of 150 g per L for the rst time.
3
+
Furthermore, the obtained YF
3
:Ln (Ln ¼ Eu, Yb/Er, and Yb/
3
. Results and discussion
Tm) samples exhibit strong down/upconversion emissions. This
low-temperature synthetic strategy may be of academic interest
and practical signicance.
3.1 Phase and composition
Fig. 1 shows the XRD pattern of the as-prepared sample. All the
diffraction peaks can be indexed to the orthorhombic YF3
[
JCPDS no. 74-0911; space group: Pnma (62)] without any other
2. Experimental section
impurity peaks, suggesting high phase purity. It is notable that
Y(NO
3
)
3
, Eu(NO
3
)
3
, Yb(NO
3
)
3
, Tm(NO
3
)
3
, and Er(NO
3
)
3
stock the relative reection intensity of (020) is enhanced compared
solutions were obtained by dissolving the corresponding Ln O
with the standard diffraction pattern, which may reveal the
99.99%) in dilute HNO under heating with agitation. All the possible tropism of the particles and the anisotropy growth
2
3
(
3
other chemicals are of analytical grade and used without any behavior. The as-formed precursor is a YF $xNH F$yH O
3
4
2
3
+
purication.
.1 Preparation
4
double salt, which is easy formed when Y ions react with NH F
23
in the aqueous phase at relative low temperatures. The
precursor was characterized by a combination of the XPS
spectrum and TGA results. The XPS spectrum (ESI, Fig. S1†)
clearly displays the existences of Y, F, O, and N elements, and
the molar ratio for F/O/N is calculated to be 80.37/15.65/3.98.
The TG curve (ESI, Fig. S2†) suggests that the total weight loss is
2
In a typical procedure, 5 mL aqueous solution containing a
stoichiometric amount of NH F was rapidly added into 20 mL of
aqueous solution containing a certain amount of Y(NO ) in an
3 3
4
ice-water bath under magnetic stirring. Both reaction solutions
were pre-adjusted to the given temperature. Aer magnetic stir-
ring for 3 h, the white precipitate was collected by centrifugation,
washed 3 times with water and absolute ethanol and nally dried
1
7
2.16% and includes two distinct stages. The rst weight loss of
.76% before 140 C is caused by the loss of crystalline water
ꢀ
from the particles. The following weight loss of 4.4% around
ꢀ
ꢀ
320 C arises from the thermal decomposition of YF
3
$xNH F via
4
at 60 C in air for 12 h. The nal products were obtained through
ꢀ
3+
the reaction: YF
3
$xNH
4
F / YF
3
+ xNH
3
[ + xHF[. The values of
a heat treatment at 400 C for 1 h in air. The YF :Ln samples
3
x and y can be calculated to be 0.2 and 0.72 based on the TG
analysis, and the approximate composition formula can be
were prepared by the same process except that an extra given
3
+
amount of Ln was added to the reaction solution.
expressed as YF
3 4 2
$0.2NH F$0.72H O, which is consistent with
To alleviate the post-separation process, we have developed
an ammonia-assisted sedimentation method, which can be
described as follows: when the precipitation reaction was
the elemental ratio calculated by XPS analysis.
3.2 Effect of reactant concentrations

nished, several drops of 25% ammonia were added to the
suspension liquid (to increase the pH value of the mixture,
NaOH can be also used), and the white product was precipitated
immediately. The upper clear solution was drained away, and
The SEM images directly illustrate the morphologies and
dimensions of the samples prepared with different reactant
concentrations, as shown in Fig. 2. It can be found that all the
ꢀ
the product was dried at 60 C in air for 12 h. The white
precipitate does not need a further washing process because the
byproduct (NH
NH F and NH
treatment.
4
NO
3
) and the trace residual contaminants
(
4
4
OH) can be decomposed in the post heat
2.2 Characterization
The phase structure and purity of the as prepared products were
characterized by powder X-ray diffraction with a D8 Focus
diffractometer (Bruker). The morphologies of the as-prepared
samples were inspected with a eld-emission scanning electron
microscope equipped with an energy-dispersive spectrometer
(EDS) (FE-SEM, S-4800, Hitachi, Japan). Transmission electron
microscopy images were obtained using a JEOL-2010 trans-
mission electron microscope operating at 200 kV. Thermogravi-
metric analyses (TGA) were performed on a thermal analysis Fig. 1 XRD pattern of the as-prepared YF samples.
3
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ꢀ
Fig. 2 SEM images of the samples prepared under 0 C at increasing reactant [Y(NO
3
)
3
] concentrations of (A) 0.5 mmoL, (B) 1 mmoL, (C) 3 mmoL,
(
D) 9 mmoL, (E) 20 mmoL, and (F) 45 mmoL. The reactant concentration unit is per 25 mL and the scale bar in the images is 10 mm.
samples consist of uniform and monodisperse nanospheres
c
It is well established that the critical radius (r ) of a nucleus
25
with almost 100% morphological yield. A close-up observation is dependent on the saturation ratio (S), which can be
shows the indistinct octahedral contour of the products (ESI, expressed by eqn (1).
Fig. S3†), which explains the enhancement of the relative
r
c
¼ 2gV
m
/RT ln S
(1)
reection intensity of the (020) peak due to the special tropism
24
3
of the YF crystal with octahedral morphology. The crystalline
Where g is the surface free energy per unit area (g> 0), and V
m
is
sizes decrease nearly hyperbolically from 410 to 150 nm as a
function of reactant concentration, which increases from 0.5 to
the molar volume of the bulk crystal. An increase of S leads to a
decrease of r , and a smaller r would give rise to a smaller size
c
c
4
5 mmoL per 25 mL as depicted in Fig. 3. The histogram of the
particle size distribution was deduced from the overview of the
SEM image of the sample prepared with a Y(NO concentra-
of the nal products aer the same growth process. Therefore,
the nal crystal size would decrease when the reactant
concentration is increased because a high reactant concentra-
tion means a high value of S.
3 3
)
tion of 1 mmoL per 25 mL (Fig. 2B), which shows a very narrow
size distribution.
3.3 Effect of reaction temperature
It is well-established that the saturation ratio is dependent on
temperature at a given pressure. In our case, a lower tempera-
ture can lead to a higher saturation of Y(NO ) or NH F. As such,
3 3 4
the reaction temperature should also have similar effect to that
of reactant concentration on the crystalline size. Fig. 4 exhibits
3 3
the SEM images of the samples obtained with a Y(NO )
concentration of 40 mmoL per 25 mL with increasing temper-
ature. One can see that all the samples are monodisperse
spheres with increasing crystalline size from 90 to 160 nm as the
ꢀ
ꢀ
reaction temperature is increased from ꢁ10 C to 5 C. These
results lead to a clear indication that precise control over the
size of monodisperse YF
3
nanocrystals can be monotonously
realized by proper tuning of just one synthetic parameter.
3.4 Mechanism of the electric double layer on the
inhibitation of particle aggregation
Fig. 3 Plot of the crystalline size as a function of Y(NO
tration. Inset is the histogram of the particle size distribution of the
3 3
sample prepared with a Y(NO ) concentration of 1 mmoL per 25 mL. particle contact may lead to aggregation driven by the relief of
3 3
) concen-
Generally, during the growth of the nanocrystals, the inter-
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the premise that Y(NO
3
)
3
does not transform into hydroxides.
Fig. 5 demonstrates the SEM images of the products prepared at
different pH values of the Y(NO ) solution. It can be seen that
3
3
the products are all still monodisperse and uniform sub-
microspheres in a wide pH range (pH # 7). The fact reveals that
the uniformity and monodispersity are independent of the
reactant concentration and pH value at a low temperature. Such
an interesting result is rare in nano/micromaterials synthesis,
and it is signicant for industrial mass production. However,
when Y(NO3)3 transforms into hydroxides and precipitates
before it reacts with NH F, the as-obtained products are
4
monodisperse Y(OH)xF
six-arris shuttles (XRD pattern,
3ꢁx
magnied SEM image, and corresponding EDX spectrum can be
seen in the ESI, Fig. S5†) with 2 mm length and 300 nm diameter
x
at the middle part (Fig. 5D). Such Y(OH) F3ꢁx nanocrystals with
novel morphologies may have potential applications in some
functional material areas.
3 3
Fig. 4 SEM images of the samples prepared with reactant a [Y(NO ) ]
concentration of 40 mmoL per 25 mL under increasing temperature:
ꢀ
ꢀ
ꢀ
ꢀ
(
A) ꢁ10 C, (B) ꢁ5 C, (C) 0 C, and (D) 5 C. The scale bar in the images
is 5 mm.
3.6 Growth mechanism at low temperature
the high surface energy. Thus, it is necessary to inhibit this To shed light on the effect of the low temperature on the
aggregation in the preparation of the monodisperse particles. monodispersity and uniformity of the products, we designed a
Among the commonly used strategies, protective agents, series of contrast experiments. Fig. 6 shows the SEM images of
ꢀ
including surfactants, complexing agents, and lyophilic poly- the products prepared by two combined steps: 0 C for 1 h
ꢀ
ꢀ
ꢀ
mers are oen employed to protect the individual particles from followed by 50 C for 2 h (denoted as 0 C-1 h–50 C-2 h process)
26
ꢀ
the inter-particle contact. However, our synthesis is free of and products prepared at 50 C for 3 h directly (denoted as
protective agents, and therefore, the electric double layer takes 50 C-3 h process). One can see that the reaction temperature
ꢀ
their role. The zeta potentials of the suspension liquid with and has a remarkable inuence on the nal products. The product
without ammonia (or NaOH) addition before centrifugation of the low temperature process exhibits a spherical morphology
were measured to be 18 and 49.7 mV (ESI, Fig. S4†), respectively. with good monodispersity and uniformity while the product
ꢀ
This is a clear indication that the charge of the adsorbed ions on prepared at 50 C directly consists of ill-shaped bundles and
the surface of the particles is positive and the isoelectric point of rough particles. These distinct results strongly indicate that a
the system is located in the range of alkalinity. This also low temperature can ensure the monodispersity and uniformity
explains the fast precipitation of the suspension liquid upon the of the products and that it mainly plays a role in the early
addition of ammonia. On the basis of the components of the reaction stage. The mechanism can be qualitatively elucidated
suspension liquid containing YF $0.2NH F nanoparticles, as follows.
3
4
ꢁ
+
3+
NO3 , and NH4 ions (and trace ions of Y ), we proposed that
the electric double layer could be expressed by the follow
formula:
+
/(n ꢁ x)NO3ꢁ
x+
3ꢁ
/xNO
{
[YF
3
$0.2NH
4
F]nNH
4
}
These positively charged nanoparticles are repulsed by each
other in the liquid due to the strong electrostatic repulsion
force. Therefore, direct inter-particle contact was effectively
avoided and high monodispersity could be maintained.
3 3
3.5 Effect of the initial pH value of the Y(NO ) solution
It is worth noting that the morphological uniformity and
monodispersity were very consistent even when the reactant
concentration reached as high as 45 mmoL per 25 mL (Fig. 2F),
which is close to its saturation for Y(NO ) , the saturation is
3
3
Fig. 5 SEM images of the samples prepared at different pH values of
the Y(NO solution (A: 1, B: 5, C: 7, and D: 8.3) with a reaction
concentration of 1 mmoL per 25 mL. The scale bar in the images
ꢀ
60 mmoL per 25 mL at 0 C). We also found that the pH value of
3 3
)
the reaction solution [Y(NO ] has little inuence on the
3 3
)
monodispersity and uniformity of the nal products based on is 10 mm.
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Fig. 6 SEM images of the samples prepared with a Y(NO
3
)
3
concen-
ꢀ
tration of 1 mmoL per 25 mL by different processes: (A) two steps: 0 C
ꢀ
ꢀ
for 1 h followed by 50 C for 2 h and (B) one step: 50 C for 3 h. The
scale bar in the images is 10 mm.
Fig. 7 SEM images of the samples prepared with a Y(NO
3 3
) concen-
tration of 1 mmoL per 25 mL by different combined two-step
ꢀ
ꢀ
ꢀ
ꢀ
processes: (A): 0 C-0.5 h–50 C-2.5 h, (B) 0 C-5 min–50 C-3 h, (C)
0
ꢀ
ꢀ ꢀ ꢀ
C-5 min–80 C-3 h, and (D) 0 C-0.5 h–50 C-12 h. The two-step
It is well known that the formation of monodisperse nano-
25
process expression style is “low temperature-time–high temperature-
time”. The scale bar in the images is 10 mm.
crystal needs separate nucleation and growth. According to the
27,28
modied diffusion-controlled growth model,
if the diffusion
rate of monomer ux is relative small, the whole growth rate
would be dominated by the diffusion rate. It is established that
a linear decrease of T leads to an exponential decrease of the
29
diffusion coefficient. Thus, the growth rate of the newly
formed nuclei would be greatly decreased and be controlled by
the diffusion rate at a low temperature in the nucleation stage.
Moreover, in this diffusion-controlled growth model, the
growth rate is inversely proportional to the radius of the parti-
cles, and thus, the difference among the particle radii would
shrink. Such a process is generally referred to as the focusing
30
effect, and it is nished quickly in the early stage of the
reaction. Briey, the inuence of the low temperature can be
summarized as the following two main points: (1) the newly
formed nuclei have a very low growth rate at a low temperature
in the early nucleation stage, which ensures a denite separa-
tion of nucleation and growth; (2) the low temperature-induced
diffusion-controlled growth of the particles gives rise to a
focusing effect, which further insures the monodispersity of the
Fig. 8 Schematic illustration of the growth process of the products.

nal products.
On the basis of the above conclusion, we have designed a
series of two-step synthesized experiments to study the whole
growth process of the particles. Fig. 7 demonstrates the evolu-
tion of the sizes and morphologies of the products prepared by
different two-step synthesis routes. We can see that the prod-
ꢀ
ꢀ
ucts prepared by a 0 C-5 min–50 C-3 h process (Fig. 7B) or a by
0
ꢀ
ꢀ
C-5 min–80 C-3 h process (Fig. 7C) are still monodisperse
and uniform sub-microspheres. The results indubitably reveal
that the main growth, including the nucleation and focusing
processes nish within the initial 5 min. When the post time at
high temperature was prolonged to 12 h, the as-obtained
products are ripened into monodisperse and well-dened
octahedral sub-microcrystals with smooth surfaces and 380 nm
in hemline length. On the basis of the above elucidation, the
whole growth process can be described as the three follow steps:
burst nucleation, fast growth with size focusing, and Ostwald
ripening, as illustrated in Fig. 8.
3
+
3
Fig. 9 TEM images of the as-prepared YF :0.05Eu samples with (A)
spherical and (B) octahedral morphologies, and corresponding (C) EDX
spectrum and (D) HRTEM image of sample with octahedral
morphology. The inset panel is the corresponding FFT pattern.
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The TEM images and EDX spectrum showed in Fig. 9 give 3.7 Extending to other lanthanide uorides REF3
more detailed structure and composition information about
the as-prepared products. The overview and individual
particle images (Fig. 9A and B) illustrate the corresponding
morphological characters well, and the distinct bright/dark
contrast between the edge and center conrms the spherical
and octahedral prototypes, respectively. The HRTEM image
To establish the generality of our synthetic method, we
extended our efforts to synthesize other lanthanide uorides
with the formula REF
Ho, Er, Tm, Yb, and Lu). Fig. 10 shows the corresponding
morphologies of 25 mL of the as-obtained REF
3
(RE ¼ La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy,
ꢀ
3
samples at 0 C.
It is clear that all the LnF products (except LaF
3
3
and PrF
3
, ESI,
(
Fig. 9D) exhibits well-resolved 2D lattice fringes with adja-
Fig. S6†) are nano/microcrystals with high monodispersity and
uniformity. Corresponding size and morphology data are listed
in Table 1 and the corresponding XRD patterns are listed in
Fig. S7, ESI.†
cent lattice spacings of 0.288 and 0.248 nm, corresponding to
ꢀ
the (210) and (121) planes respectively. The bright dots in the
fast Fourier transform (FFT) pattern can be assigned to the
(
210) planes, suggesting that the octahedral structure pref-
erentially grows perpendicular to the (210) planes. The EDX
spectrum of the YF :0.05Eu sample conrms the existence
3
3.8 Down/up-conversion luminescence properties
3
+
As mentioned above, YF is emphasized as a widely used uo-
3
of F, Y, and Eu and the atomic ratios agree well with the
stoichiometric formula.
3
+
rescent host. Herein, we selected Ln (Ln ¼ Eu, Ce, Tb, Yb/Er,
Yb/Ho, and Yb/Tm) as dopants to exhibit the luminescence
ꢀ
Fig. 10 SEM images of the samples prepared with a Re(NO
E) GdF , (F) TbF , (G) DyF , (H) HoF , (I) ErF , (J) TmF , (K) YbF
3
)
3
concentration of 1 mmoL per 25 mL at 0 C. (A) CeF
3
, (B) NdF
3
, (C) SmF
3
, (D) EuF
3
,
(
3
3
3
3
3
3
3
, and (L) LuF
3
. The scale bars in (A) and (B) are 1 mm, in (C)–(L) are 5 mm. LaF
3
and PrF
3
are irregular particles, which are shown in the ESI (Fig. S6†).
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Table 1 The size and morphology information of the as-prepared
a
Acknowledgements
3
REF products
This work is nancially supported by the National Basic
Research Program of China (973 Program, grant no
2014CB6438003), the National Natural Foundation of China
REF
3
Size
Morphology
LaF
CeF
3
D ¼ 30–60 nm
Irregular particle
Quasi sphere
Irregular particle
Quasi disk
Quasi disk
Disk
3
D ¼ 50 nm
(Grant no. 21271167) and the Fund for Creative Research
PrF
3
D ¼ 20–60 nm
Groups (Grant no. 21221061).
NdF
SmF
3
D ¼ 80 nm & T ¼ 20 nm
D ¼ 350 nm & T ¼ 130 nm
D ¼ 400 nm & T ¼ 50 nm
D ¼ 800 nm & T ¼ 120 nm
L ¼ 600 nm & D ¼ 300 nm
L ¼ 700 nm & D ¼ 150 nm
L ¼ 700 nm & D ¼ 150 nm
D ¼ 350 nm
3
EuF
GdF
3
Notes and references
3
Disk
Cacti
TbF
DyF
HoF
3
1
T. S. Ahmadi, Z. L. Wang, T. C. Green, A. Henglein and
M. A. ElSayed, Science, 1996, 272, 1924–1925.
3
Shuttle-like bundle
Shuttle-like bundle
Sphere
Quasi octahedron
Sphere
3
2
3
A. R. Tao, S. Habas and P. Yang, Small, 2008, 4, 310–325.
Y. Sun and Y. Xia, Science, 2002, 298, 2176–2179.
ErF
TmF
YbF
3
3
D ¼ 70 nm
3
D ¼ 100 nm
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LuF
3
D ¼ 270 nm
Octahedron
a
D ¼ diameter, L ¼ length, T ¼ thickness.
6
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performance of the as-prepared YF
3
:Ln nano/microcrystals
3
1
due to their high luminescence efficiency.
The YF :Ln nano/microcrystals exhibit strong down/up-
conversion emissions. (ESI, Fig. S8 and S9† show the excitation
and emission spectra of YF :Ln ) The as-prepared YF :0.05Eu
3 3
exhibits strong orange-red emission of Eu dominated by a
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3
+
3
7
8
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3+
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5
7
3+
D
0
- F
1
magnetic dipole transition, YF
3
:0.05Ce exhibits a
9
3
+
3+
3
characteristic emission of Ce 5d-4f transition, YF :0.05Tb
2
3
+ 5
7
exhibits green emissions of Tb
D
0
- F
J
(J ¼ 6-3) transitions,
1
1
1
0 Y. Xia, Y. Xiong, B. Lim and S. E. Skrabalak, Angew. Chem.,
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+
3+
and YF :0.05Ce ,0.05Tb exhibits intense green emissions of
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Tb
D - F (J ¼ 6-3) transitions through energy transfer from
0
J
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. Conclusion
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ꢀ
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3
an advantage, we have obtained a high yield production at 150 g
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L
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3+
¼
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