High-quality sodium rare-earth fluoride nanocrystals: Controlled synthesis and optical properties

Article abstract of DOI:10.1021/ja060212h

We report a general synthesis of high-quality cubic (α-phase) and hexagonal (β-phase) NaREF₄ (RE: Pr to Lu, Y) nanocrystals (nanopolyhedra, nanorods, nanoplates, and nanospheres) and NaYF ₄:Yb,-Er/Tm nanocrystals (nanopolyhedra and nanoplates) via the co-thermolysis of Na(CF₃COO) and RE(CF₃-COO)₃ in oleic acid/oleylamine/1-octadecene. By tuning the ratio of Na/RE, solvent composition, reaction temperature and time, we can manipulate phase, shape, and size of the nanocrystals. On the basis of its α → β phase transition behavior, along the rare-earth series, NaREF₄ can be divided into three groups (I: Pr and Nd; II: Sm to Tb; III: Dy to Lu, Y). The whole controlled-synthesis mechanism can be explained from the point of view of free energy. Photoluminescent measurements indicate that the value of / ₆₁₀//₅₉₀ and the overall emission intensity of the NaEuF₄ nanocrystals are highly correlative with the symmetries of the Eu³⁺ ions in both the lattice and the surface.

Full text of DOI:10.1021/ja060212h

Supporting Information for ja060212h
High-Quality Sodium Rare-Earth Fluoride Nanocrystals: Controlled Synthesis and Optical Properties
Hao-Xin Mai,† Ya-Wen Zhang,*,† Rui Si,† Zheng-Guang Yan,† Ling-dong Sun,† Li-Ping You,‡ and Chun-Hua
Yan*,†
Beijing National Laboratory for Molecular Sciences, State Key Lab of Rare Earth Materials Chemistry and
Applications & PKU-HKU Joint Lab in Rare Earth Materials and Bioinorganic Chemistry, Peking University,
Beijing 100871, China, Electron Microscopy Laboratory, Peking University, Beijing 100871, China.; E-mail:
yan@pku.edu.cn
Table S1. Crystal Structure and Morphology of α-NaREF4 (RE = Pr to Lu, Y) Nanocrystals Obtained
from the Co-thermolysis of Na(CF3COO) (A) and RE(CF3COO)3 (B) in Oleic Acid (OA)/Oleylamine
(OM)/1-Octadecene (ODE).
A:B
1
OA:OM:ODE
1:1:2
t [min] Phase
Morphology
polyhedron
polyhedron
polyhedron
polyhedron
polyhedron
polyhedron
polyhedron
polyhedron
polyhedron
polyhedron
polyhedron
polyhedron
polyhedron
Size [nm]
6.5(7%)[a]
5.9(7%)
T [°C]
290
290
290
260
260
250
250
250
250
250
250
250
250
NaPrF4
NaNdF4
NaSmF4
NaEuF4
NaGdF4
NaTbF4
NaDyF4
NaHoF4
NaYF4
30
30
30
30
30
45
45
45
45
45
45
45
45
cubic
cubic
cubic
cubic
cubic
cubic
cubic
cubic
cubic
cubic
cubic
cubic
cubic
1
1:1:2
1
1:1:2
5.7(6%)
1
1:1:2
6.3 (7%)
5.7 (6%)
9.9(6%)
1
1:1:2
1
1:1:2
1
1:1:2
15.1(4%)
12.4 (5%)
12.2 (6%)
12.6(5%)
12.5(5%)
15.9(5%)
15.7 (4%)
1
1:1:2
1
1:1:2
NaErF4
NaTmF4
NaYbF4
NaLuF4
1
1:1:2
1
1:1:2
1
1:1:2
1
1:1:2
[a] Numbers in brackets represent the standard deviation statistic from at least 60 particles.
S1

Table S2. Crystal Structure and Morphology of β-NaREF4 (RE = Pr to Lu, Y) Nanocrystals Obtained
from the Co-thermolysis of Na(CF3COO) (A) and RE(CF3COO)3 (B) in Oleic Acid (OA)/Oleylamine
(OM)/1-Octadecene (ODE).
A:B
OA:OM:ODE T [°C] t [min] Phase
Morphology
Size [nm]
NaPrF4 1.7
1.8:0.2:2
2:0:2
330
330
330
330
330
330
330
330
330
330
330
330
330
330
330
330
330
330
20
30
20
20
20
20
20
45
45
15
15
30
25
25
15
15
20
25
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
rod
42.5×108(11%)
26.1×43.8 (6%)
non-uniform
non-uniform
19.3×42.7 (9%)
non-uniform
non-uniform
non-uniform
non-uniform
425 (5%)
NaNdF4 1.6
NaSmF4 1.4
NaEuF4 1.7
1.7
rod
2:0:2
rod
2:0:2
ill shape
1.55:0.45:2
2:0:2
rod
NaGdF4 1.7
1.7
ill shape
1.55:0.45:2
2:0:2
rod
NaTbF4 1.5
1.5
ill shape
1.55:0.45:2
2:0:2
rod
NaDyF4 1.5
NaHoF4 1.5
NaYF4 1.8
2.1
hexagonal plate
hexagonal plate
rod
2:0:2
52.7×43.2 (5%)
26.6×47.6 (6%)
155×76 (5%)
20.1 (5%)
2:0:2
2:0:2
hexagonal plate
polyhedron
hexagonal plate
hexagonal plate
hexagonal plate
hexagonal plate
NaErF4 1.6
2
2:0:2
2:0:2
130×55(5%)
460 (5%)
NaTmF4 2
2:0:2
NaYbF4
NaLuF4
2
2
2:0:2
152×93 (5%)
427 (5%)
2:0:2
Table S3. Crystal Structure and Morphology of β-NaREF4 Nanocrystals Obtained from the Thermolysis
of Na(CF3COO) (A) in the Presence of α-NaREF4 (B) Seeds (RE = Nd, Sm, Eu, Gd, Tb, Y) in Oleic Acid
(OA)/Oleylamine (OM)/1-Octadecene (ODE).
A:B
OA:OM:ODE T [°C] t [min] Phase
Morphology
Size [nm]
NaNdF4
1
2:0:2
2:0:2
2:0:2
2:0:2
2:0:2
2:0:2
330
330
330
330
330
330
30
20
20
20
15
15
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
hexagonal
rod
rod
rod
rod
26.1×64.1 (6%)
23.7×36.0 (7%)
24.6×35.7 (7%)
26.9×31.2 (7%)
NaSmF4 1
NaEuF4
NaGdF4 1
1
NaTbF4
NaYF4
1
1
hexagonal plate 42.8×37.3 (7%)
hexagonal plate 216×113 (6%)
S2

Table S4. Synthesis Conditions and Several Products of NaREF4 (RE = Nd, Eu, Y).
Sample
N1
Precursor A
1 mmol
Precursor B
OA:OM:ODE T [°C] t [min] Product
[a]
1 mmol
2:0:2
280
30
NdF3
Na(CF3COO)
1 mmol
Nd(CF3COO)3
1 mmol
N2
2:0:2
330
30
NdF3 + β-NaNdF4
Na(CF3COO)
-
Nd(CF3COO)3
1 mmol α-NaNdF4
1 mmol
N3
N4
2:0:2
1:1:2
330
330
30
30
NdF3 + β-NaNdF4
α-NaNdF4 +
1.6 mmol
Na(CF3COO)
1.2 mmol
Nd(CF3COO)3
1 mmol
β-NaNdF4 + NaF
β-NaEuF4
E1
E2
E3
E4
E5
Y1
Y2
Y3
Y4
Y5
Y6
2:0:2
280
280
260
300
300
320
330
330
250
250
250
45
45
30
45
45
45
25
25
45
45
45
Na(CF3COO)
1 mmol
Eu(CF3COO)3
1 mmol
2:0:2
α-NaEuF4 +
β-NaEuF4
α-NaEuF4 +
β-NaEuF4
β-NaEuF4
Na(CF3COO)
1 mmol
Eu(CF3COO)3
1 mmol
2:0:2
Na(CF3COO)
1 mmol
Eu(CF3COO)3
1 mmol
2:0:2
Na(CF3COO)
1 mmol
Eu(CF3COO)3
1 mmol
1:1:2
α-NaEuF4 +
β-NaEuF4
α-NaYF4
Na(CF3COO)
1 mmol
Eu(CF3COO)3
1 mmol
2:0:2
Na(CF3COO)
1.5 mmol
Y(CF3COO)3
1 mmol
2:0:2
α-NaYF4 + β-NaYF4
α-NaYF4 + β-NaYF4
α-NaYF4
Na(CF3COO)
2.1 mmol
Y(CF3COO)3
1 mmol
1.5:0.5:2
1.5:0.5:2
0.5:1.5:2
0:2:2
Na(CF3COO)
1 mmol
Y(CF3COO)3
1 mmol
Na(CF3COO)
1 mmol
Y(CF3COO)3
1 mmol
α-NaYF4 + NaF
α-NaYF4 + NaF
Na(CF3COO)
1 mmol
Y(CF3COO)3
1 mmol
Na(CF3COO)
Y(CF3COO)3
[a] NaF was washed off by the post-treatment during the synthesis in OA/ODE.
S3

Figure S1. XRD patterns of α-NaREF4 (a) and β-NaREF4 (b) (RE = Pr to Lu) nanocrystals.
Figure S2. Energy-dispersive X-ray analysis (EDAX) spectrum of α-NaYF4 nanopolyhedra, from which the
atomic ratio of Na:Y was determined as 1.01:1.
S4

Figure S3. TEM images of α-NaPrF4 (a), α-NaSmF4 (b), α-NaGdF4 (c), α-NaTbF4 (d), α-NaDyF4 (e),
α-NaHoF4 (f), α-NaErF4 (g), α-NaTmF4 (h), and α-NaLuF4 (i) nanocrystals.
S5

Figure S4. TEM images of β-NaPrF4 (a), β-NaSmF4 (b), β-NaGdF4 (c), β-NaTbF4 (d), β-NaDyF4 (e),
β-NaErF4 (f), β-NaTmF4 (g), β-NaYbF4 (h), β-NaLuF4 (i) nanocrystals.
1
Figure S5. H NMR (CDCl3) spectrum of α-NaYF4 nanopolyhedra, recorded on Varian Mercury 200 MHz
spectrometers with the number of transmit of 64, and referenced to TMS as internal-standard. δ 5.34(2H, br),
2.28(2H, br) 2.01(4H, br), 1.59(2H, br), 1.25(20H, sharp with a shoulder), 0.87(3H, t), indicating the presence
of capping ligands on the surface of the α-NaYF4 nanocrystals.
S6

Figure S6. TEM and HRTEM (inset: taken from the highlighted square) images of β-NaYF4 hexagonal
nanoplates standing via the side face.
Figure S7. Crystal structures of α-NaREF4 and β-NaREF4 built by CERIUS2 software (Ref.:
Http://www.accelrys.com/cerius2). In the structure of α-NaREF4, Na+ and RE3+ cations are randomly
distributed in the cationic sublattice; while, in the structure of β-NaREF4, the cation sites are of three types: a
onefold site occupied by RE3+, a onefold site occupied randomly by 1/2Na+ and 1/2RE3+, and a twofold site
occupied randomly by Na+ and vacancies (Ref. Thoma, R. E.; Insley, H.; Hebert. G. M.; Inorg. Chem. 1966, 5,
1222).
S7

Figure S8. XRD patterns of (a) NaNdF4 samples (N3: 1 mmol α-NaNdF4, OA/ODE = 1:1, 330 °C, 30 min;
N4: 1.6 mmol Na(CF3COO) and 1 mmol Nd(CF3COO)3, OA/OM/ODE = 1:1:2, 330 °C, 30 min), (b) NaEuF4
samples (E2: 1 mmol Na(CF3COO) and 1 mmol Eu(CF3COO)3, OA/ODE = 1:1, 280 °C, 45 min; E4: 1 mmol
Na(CF3COO) and 1 mmol Eu(CF3COO)3, OA/ODE = 1:1, 300 °C, 45 min; E5: 1 mmol Na(CF3COO) and 1
mmol Eu(CF3COO)3, OA/OM/ODE = 1:1:2, 300 °C, 45 min) and (c) NaYF4 samples (Y1: 1 mmol
Na(CF3COO) and 1 mmol Y(CF3COO)3, OA/ODE = 1:1, 320 °C, 45 min; Y3: 2.1 mmol Na(CF3COO) and 1
mmol Y(CF3COO)3, OA/OM/ODE = 1.5:0.5:2, 330 °C, 25 min).
S8

Figure S9. TEM images of the α-NaYF4 samples: (a) Y4 (OA:OM:ODE = 1.5:0.5:2, Na:Y = 1, 250 °C, 45
min) and (b) Y5 (OA:OM:ODE = 0.5:1.5:2, Na:Y = 1, 250 °C, 45 min). TEM images of 5 nm α-NaEuF4
nanopolyhedra (OA:OM:ODE = 2:2:0, Na:Eu = 1, 250 °C, 120 min) (c) and 8.1 nm α-NaEuF4 (OA:OM:ODE
= 1:1:2, Na:Eu = 1, 290 °C, 30 min) (d).
Figure S10. (a) TEM image of the product obtained under Na/Nd = 1.6:1 in OA/ODE (1:1) at 330 °C for 0
min. (b) TEM image of the β-NaNdF4 nanorods obtained in OA/ODE (1:1) at 330 °C for 60 min (precursor: 1
mmol α-NaNdF4 nanopolyhedra; injection: 1 mmol Na(CF3COO) dissolved in 1 mL OA/ODE after the 30
min reaction).
S9

Figure S11. TEM images of 12.1±0.7 nm (a) and 13.7±1.2 nm (b) NaEuF4 nanopolyhdera. Particle size
distribution histograms of Figure 8a (c), Figure S11a (d), Figure S11b (e) and Figure 8e (f). (g) HRTEM
image (inset: the FFT analysis) of Figure 8g, which showed the (10-10) and (0001) facets.
S10

Figure S12. TEM image at high-magnification of the snowflake-shaped β-NaYF4 particles.
Figure S13. (a) XRD patterns of NaYF4 samples synthesized under Na/Y = 2.1:1 in OA/ODE (1:1) at 330 °C
for 0−15 min. TEM images of the samples: (b) 0 min and (c) 15 min.
S11

Figure S14. (a) XRD patterns of β-NaYF4 and β-NaErF4 nanospheres. TEM images of β-NaErF4 nanospheres
obtained under Na/Er = 1.8:1 in OA/ODE (1:1) at 330 °C for 20 min (b), and of the β-NaErF4 nanospheres
and nanorods with prolonging the reaction time to 1 h (c).
S12

Figure S15. (a) XRD patterns of tetragonal LiYF4 (a = 5.147(3) Å and c = 10.67(1) Å; JCPDS: 17-874) and
cubic KYF4 (a = 5.708(1) Å) nanocrystals. TEM images of tetragonal LiYF4 (b) and cubic KYF4 (c)
nanocrystals.
S13