Variation in Eu3+ luminescence properties of GdF 3:Eu3+ nanophosphors depending on matrix GdF3 polytype

Article abstract of DOI:10.1016/j.jallcom.2010.10.143

Hexagonal and orthorhombic GdF₃:Eu³⁺ nanophosphors separately synthesized at room temperature were well characterized by X-ray diffraction (XRD) analysis and photoluminescence excitation and emission spectral measurements. Hexagonal GdF₃:Eu³⁺ nanophosphors intrinsically exhibited stronger Eu³⁺ luminescence intensity under ultraviolet excitation. The Rietveld fitting of well-defined XRD data elucidated that the interatomic distances between Gd³⁺ ions in the hexagonal structure were shorter than those in the orthorhombic structure and that most Eu ions in GdF₃:Eu³⁺ occupy Gd sites. The stronger luminescence in the hexagonal structure was conclusively explained by the much more efficient energy transfer from Gd to Eu in the hexagonal structure than in the orthorhombic structure, as determined on the basis of the interatomic distance between Gd and Eu.

Full text of DOI:10.1016/j.jallcom.2010.10.143

Journal of Alloys and Compounds 509 (2011) 2076–2080
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
3+
3+
Variation in Eu luminescence properties of GdF :Eu nanophosphors
3
depending on matrix GdF polytype
3
a,∗
a
a
a,b
Xiaoting Zhang , Tomokatsu Hayakawa , Masayuki Nogami , Yukari Ishikawa
a
Ceramics Division, Department of Materials Science and Engineering, Nagoya Institute of Technology, Showa, Nagoya 466-8555, Japan
Japan Fine Ceramics Center, 2-4-1 Mutsuno, Atsuta, Nagoya 456-8587, Japan
b
a r t i c l e i n f o
a b s t r a c t
3
+
Article history:
Received 30 August 2010
Received in revised form 13 October 2010
Accepted 28 October 2010
Available online 4 November 2010
Hexagonal and orthorhombic GdF :Eu nanophosphors separately synthesized at room temperature
3
were well characterized by X-ray diffraction (XRD) analysis and photoluminescence excitation and emis-
sion spectral measurements. Hexagonal GdF3:Eu nanophosphors intrinsically exhibited stronger Eu
luminescence intensity under ultraviolet excitation. The Rietveld fitting of well-defined XRD data elu-
3+
3+
3
+
cidated that the interatomic distances between Gd ions in the hexagonal structure were shorter than
3
+
those in the orthorhombic structure and that most Eu ions in GdF3:Eu occupy Gd sites. The stronger
luminescence in the hexagonal structure was conclusively explained by the much more efficient energy
transfer from Gd to Eu in the hexagonal structure than in the orthorhombic structure, as determined on
the basis of the interatomic distance between Gd and Eu.
Keywords:
Gadolinium trifluoride
Hexagonal
Orthorhombic
Rietveld method
Polytype
© 2010 Elsevier B.V. All rights reserved.
Luminescence
1
. Introduction
60–100 nm in width) nanocrystals form with NH F as the fluoride
4
3+
precursor. It has also been pointed out that hexagonal GdF :Eu
3
The lanthanide fluoride compounds LnF3 and ALnF4 (A = alkali
nanophosphors emit stronger luminescence than orthorhombic
nanophosphors and the growth mechanism of GdF3 nanocrystals
has been discussed [17].
metal, Ln = rare-earth element) have been widely used in many
fields, such as optical telecommunication, lasers, new optoelec-
tronic devices, diagnostics, and biological labels [1–5]. The polytype
engineering of these materials has recently attracted attention.
In the present work, our objective is to obtain reliable struc-
tural parameters via the Rietveld refinement procedure [18] using
3+
In fact, polytype NaYF4 (or NaGdF ) with hexagonal and cubic
polytype GdF :Eu X-ray diffraction (XRD) patterns and to inves-
4
3
structures have been well documented [6–10]. However, studies
tigate the correlation between polytype and photoluminescence
(PL) properties. PL properties were estimated by PL and photolu-
minescence excitation (PLE) spectral measurements as well as by a
dynamic process of PL.
of polytype LnF , including GdF , with hexagonal and orthorhom-
3
3
bic structures are very few, most of which were focused on
the phase transition mechanism at high temperatures [11–15].
Recently, stronger luminescence from Eu3 in hexagonal EuF than
+
3
2
.
Experimental
in orthorhombic EuF has been reported [16]. This suggests that the
3
polytype control of matrix LnF3 makes it possible to increase the
All reagents were obtained from Aldrich Chem. Co. and used as received without
light-emitting probability of rare-earth-doped LnF by the chang-
further purification. Typical procedures for the synthesis of GdF :Eu3+ nanocrys-
3
3
ing of atomic coordination around the doped rare earth.
tals are described as follows. First, 0.005 mol of Gd(NO3)3·6H2O and 0.00025 mol of
EuCl3·6H2O were dissolved in 100 ml of deionized water in a beaker at room temper-
ature. After mechanical stirring for about 20 min, an aqueous solution of 0.015 mol
of NaBF4 (sample A) or 0.015 mol of NH4F (sample B) was added dropwise. After con-
stant stirring for 12 h at room temperature, a white precipitate was formed. Each
precipitate was collected by three cycles of centrifugation and successive washing
3+
Very recently, it has been demonstrated that GdF :Eu
3
nanophosphors with hexagonal and orthorhombic structures can
be individually prepared using different fluoride precursors at room
3+
temperature [17]. Hexagonal GdF :Eu “plate”-like nanocrystals
3
◦
(
∼100 nm) form with NaBF as the fluoride precursor, while
with water and ethanol. Subsequently, the final product was dried in an oven at 80 C.
4
3
+
3+
3
+
The nominal Eu concentration was fixed at 5 mol%. However the Eu concentra-
tions of sintered samples A and B were estimated to be 4% by energy-dispersive X-ray
spectroscopy [17]. To study the change in the lattice parameter upon adding Eu3+ to
GdF3, Eu-free GdF3 polytype samples were also prepared by the same method. The
Eu-free samples A and B are denoted as A0 and B , respectively.
orthorhombic GdF :Eu “spindle”-like (300–400 nm in length and
3
0
∗ Corresponding author.
E-mail address: chn13305@stn.nitech.ac.jp (X. Zhang).
XRD analysis was performed on a Philips X’pert system using Cu K␣ radiation
at a 45 kV voltage and a 40 mA current. The excitation and PL spectra were obtained
0
925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2010.10.143

X. Zhang et al. / Journal of Alloys and Compounds 509 (2011) 2076–2080
2077
c = 0.439 nm). Only the lattice parameters of hexagonal SmF3 and
EuF3 are listed in Table 1, owing to the lack of data for hexagonal
GdF3 and TbF3 in the JCPDS (Joint Committee for Powder Diffrac-
tion Standards) database. In hexagonal LnF3, a linear decrease in
the lattice parameters with the rare-earth ion radius was also con-
firmed. The fitting results of samples A and B are shown in Fig. 2.
The solid line and dots are the Rietveld fitting and observed XRD
patterns, respectively. Comparing the Rietveld refinement results
(
002) (111)
110)
Hexagoanl
(
3
+
(
113)
A : Eu doped
(
004)
(
300)
(
302)
(
112)
(221)
0
3+
3+
3+
A : Eu free
of Eu -free and Eu -doped samples, the lattice parameters of
both Eu3+-doped hexagonal and orthorhombic samples are slightly
3+
larger than those of the Eu -free samples. As the valence and radius
of the Gd ion were similar to those of the Eu ion, the replacement of
3
+
Orthorhombic
B : Eu doped
(020)
Gd ion by the Eu ion doped into GdF is reasonable. Taking account
3
(
111)
of the linear relation between the lattice parameters and the lan-
thanide ion radius, an expected increase in the lattice parameters
can be calculated using
(
101)
(210)
(
301)
(230)
(
121)
(212)
(321)
(
221)
0
3+
B : Eu free
d
= dGdF3 + (dGdF3 − dEuF )x
(1)
GdF :Eu
3
3
2
0
30
40
50
60
where
2θ (degree)
Fig. 1. XRD patterns of hexagonal (upper panel) and orthorhombic (lower panel)
GdF3 nanophosphors. Upper and lower patterns in a panel are Eu doped and Eu free,
respectively.
d
: lattice constant of GdF :Eu;
3
GdF3:Eu
dGdF : lattice constant of GdF3;
3
dEuF : lattice constant of EuF ;
3
3
x: Eu concentration in GdF :Eu.
using a F-7000 fluorescence spectrophotometer (Hitachi Co.). The PL decay curves
3
5
7
of D0 → F1,2 transitions were recorded using a time-resolved fluorescence system
TM
(
Oriel Instruments: InstaSpec V) under excitation with a 337.1 nm N2 laser (Usho,
KEC-200).
In the case of 4% Eu doping, the increases in lattice parameters
were ꢀahc = 0.17 pm and ꢀchc = 0.10 pm in hexagonal GdF , and
3
3
. Results and discussion
ꢀaoc = 0.23 pm, ꢀboc = 0.18 pm and ꢀcoc = 0.03 pm in orthorhom-
bic GdF3.
Fig. 1 shows the X-ray powder diffraction patterns of samples
The measured values indicated that the increases in the lattice
parameters upon 4% Eu doping in hexagonal GdF3 were approxi-
mately ꢀa = 0.16 pm and ꢀc = 0.18 pm; and those in orthorhom-
0
0
A, A , B, and B . By comparison with those of hexagonal SmF (PDF
3
0
No. 05-0563), most of the diffraction peaks of samples A and A
h
h
were assigned to the hexagonal structure, although there are some
minor residual orthorhombic structural peaks (marked with aster-
isks). For samples B and B , all peaks were identified by comparison
bic GdF3 were approximately ꢀa = 0.23 pm, ꢀb = 0.26 pm and
0 0
ꢀc = 0.56 pm. The good consistency of the calculated increases
0
0
in the lattice parameters with the measured values indicates that
most Eu ions in GdF3 can substitutionally be positioned at the Gd
site.
with the orthorhombic GdF (PDF No. 12-0788) structure.
3
On the basis of the XRD patterns, the crystal structures of the
prepared samples were refined by the Rietveld refinement using
the software program RIETAN-FP (Izumi and Ikeda, 2000) [18]. For
On the basis of the Reitveld refinement results, crystal structures
were drawn using VEST software and are shown in Fig. 3. In both the
3+
fitting, space groups of LnF Pnma (D162h, No. 62) and P3-C1 (D43d,
hexagonal and orthorhombic structures, the numbers of Gd ions
3
0
0
3+
No. 165) [19] were used for samples A (A ) and B (B ), respectively.
In Table 1, the reported and fitted lattice parameters of
LnF3 materials are listed. The lattice parameters of LnF3 linearly
around the center Gd ion are the same but the distances between
3+
Gd ions are different as listed in Table 2. In the hexagonal struc-
ture, there are four equivalent nearest-neighbour Gd ion sites from
the center Gd ion and the distance was calculated to be 0.38553 nm.
On the other hand, there are two equivalent nearest-neighbour Gd
ion sites from the center Gd site in the orthorhombic structure and
the distance was 0.39307 nm. According to the Förster resonance
energy transfer theory, the energy transfer probability is expressed
decreased in the sequence of SmF , EuF , GdF , and TbF , depend-
3
3
3
3
ing on the rare-earth ion radius in the orthorhombic structure. The
lattice parameters a, b, and c of orthorhombic GdF3 in this work
(
a = 0.6563 nm, b = 0.6971 nm, and c = 0.4387 nm) were slightly
smaller than the reported data (a = 0.6571 nm, b = 0.6984 nm, and
Table 1
Lattice parameters of LnF3.
Lattice parameter (nm)
SmF3 (P63/mcm) (12-0792a)
EuF3(p3-c1) (32-0373a)
GdF (P3-c1) (this work A0)
GdF3:Eu3+ (P3-c1) (this work A)
Hexagonal
a = b
c
0.6952
0.7122
0.6920
0.7086
0.687823 ± 0.000014
0.706216 ± 0.000025
0.687979 ± 0.000022
0.706396 ± 0.000023
Lattice parameter (nm)
SmF3 (Pnma)
EuF3(Pnma)
(33-0524 )
GdF (Pnma)
(49-1804 )
GdF (Pnma)
(this work B )
GdF3:Eu3+ (Pnma)
(this work B)
TbF3(Pnma)
(37-1487 )
a
a
a
0
a
(
32-0981 )
Orthorhombic
a
b
c
0.6672
0.7058
0.4404
0.6620
0.7015
0.4396
0.6571
0.684
0.439
0.656308 ± 0.000016
0.697124 ± 0.000018
0.438739 ± 0.000011
0.656534 ± 0.000017
0.697388 ± 0.000028
0.439295 ± 0.000014
0.6508
0.6948
0.4391
a
JCPDS number.

2
078
X. Zhang et al. / Journal of Alloys and Compounds 509 (2011) 2076–2080
6
4
2
000
000
000
0
Hexagonal
A:Eu 3+doped
Rwp=3.592
S=1.5576
Re=2.306
d1=0.9535
Rp=2.765
d2=0.7999
RR=32.925
2
0
30
40
50
60
70
80
90
100
110
120
Orthorhombic
B:Eu3+doped
Rwp=3.549
S=1.6243
Re=2.185
d1=0.8106
Rp=2.728
d2=0.7378
RR=35.757
4
2
000
000
0
2
0
30
40
50
60
70
80
90
100
110
120
2
θ (degree)
Fig. 2. Rietveld fitting profiles for polytypes of GdF3 (sample A and B). Solid line and dots represent the calculated and measured profiles, respectively. The residual intensities
are shown at the bottom of figure (jagged line), stick marks below the profile indicated the positions of the Bragg reflections.
The probability of energy transfer depends inversely on the sixth
power of the distance between the donor and the acceptor. There-
fore, the shorter distance between Gd3+ and substituted Eu ions in
the hexagonal structure can induce a higher energy transfer prob-
ability from Gd3+ ions to Eu ions than that in the orthorhombic
structure.
3+
3+
The excitation spectra of 592 nm light emission from polytype
3+
GdF :Eu samples are shown in Fig. 4. The excitation peaks at
3
3
16 nm, 360 nm, 373 nm and 393 nm originate from the transitions
7
3+
from F0 ground state to different excited states of Eu , and the
excitation peaks at 272 nm, 296 nm, 304 nm and 310 nm originate
8
6
8
6
8
6
from the transitions of S7/2 → I7/2, S7/2 → P3/2, S7/2 → P 5/2,
8
6
3+
Fig. 3. Configuration of Gd3+ ions in hexagonal and orthorhombic GdF3:Eu3+ struc-
ture according the Rietveld refinement results.
and S7/2 → P 7/2 of Gd . Stronger excitation peaks at 272–310 nm
3+
based on the intratransition of Gd than at 316–393 nm based on
3+
the intratransition of Eu indicate that an efficient energy transfer
from Gd3+ to Eu in GdF :Eu occurs, as reported previously for
3+
3+
3
as follows [20,21]:
3+
LiGdF :Eu [22].
4
PAB = 1
.4 × 10
24fAfBS
Fig. 5 shows the emission spectra of polytype GdF :Eu sam-
3+
3
,
(2)
2
6
ꢀ
E R
ples excited at 393 nm and 272 nm. They are dominated by the
5
7
peaks located at 592 nm and 619 nm, corresponding to D → F
0
1
where
5
7
3+
and D → F transitions, respectively, in Eu , which are typical
0
2
magnetic and electronic dipole transitions [23]. Since the excita-
PAB: probability of energy transfer,
fA, fB: oscillator strengths of the donor and acceptor, respectively,
S: overlap of donor emission and acceptor absorption,
8
6
3+
tion of 272 nm corresponds to the transition S7 → IJ of Gd , and
/2
7
5
3+
3
93 nm excitation corresponds to the transition F → L of Eu
0
6
3+
ions, it can be concluded that both the energy transfer from Gd
ꢀE: transition energy,
to Eu3+ and the intratransition in Eu can excite PL (592 nm and
3+
R: distance between the donor and acceptor.
3+
6
19 nm). Hexagonal GdF :Eu emitted a stronger luminescence
3
Table 2
Gdx → Gd0 distance in polytype GdF3:Eu3+. X denotes the ion site in Fig. 3.
8
6
S7/2- I
7/2
X
Interatomic distance Gdx → Gd0 (nm)
272nm
6
6
6
6
8
6
4
2
.0x10
.0x10
.0x10
.0x10
A:hexagonal
B:orthorhombic
Hexagonal
Orthorhombic
1
2
3
4
5
6
7
8
9
0.385532
0.385532
0.385532
0.385532
0.406382
0.406382
0.421907
0.421907
0.421901
0.421901
0.421901
0.421901
0.393070
0.393070
0.394006
0.394006
0.394006
0.394006
0.437152
0.437152
0.437152
0.437152
0.439695
0.439695
8
6
S7/2- P
8
6
7/2
7
5
S7/2- P 310nm
F - L
5/2
0
J
3
16nm
304nm
7
5
8
6
F - L
S7/2- P
0
6
3/2
3
93nm
296nm
7
5
7
5
F - D
F - G
0
6
0
4
3
60nm 373nm
1
1
1
0
1
2
0.0
2
80
300
320
340
360 380
400
Wavelength (nm)
Fig. 4. Excitation spectra of hexagonal (solid line) and orthorhombic (dashed line)
GdF3:Eu nanophosphors at 592 nm.
Average
0.40959
0.41585
3
+

X. Zhang et al. / Journal of Alloys and Compounds 509 (2011) 2076–2080
2079
5
7
2
3
72nm
93nm
D - F
0
1
5
A:hexagonal
6
4
2
.0x10
A:hexagonal
592nm
619nm
5
5
7
.0x10
D - F
I272nm/393nm=4.4
0
2
4
1.0x10
5
.0x10
λex = 396nm
5
7
D - F
1
J
0
.0
5
40
560
580
600
620
640
3
5
7
1.0x10
5
D - F
2
4
6
8
10
12
14
16
3
2
1
.0x10
0 1
272nm
93nm
3
B:orthorhombic
B:orthorhombic
5
.0x10
592nm
4
I272nm/393nm=3.6
5
7
1.0x10
619nm
D - F
0
2
5
.0x10
5
7
D - F
1
J
0
.0
λex = 396nm
5
40
560
580
600
620
640
Wavelength (nm)
3
1.0x10
Fig. 5. Emission spectra of hexagonal (upper) and orthorhombic (lower) GdF3:Eu3+
0
2
4
6
8
10
12
14
16
nanophosphors excited at 272 nm and 396 nm.
Time (ms)
Fig. 6. Decay curves of 5D0 → 7F1,2 emissions (592 and 619 nm) are shown by open
triangles and open circles, respectively. The solid curves are fitting result to two
exponential functions by a least-square fitting method. Left and right panels indicate
than orthorhombic GdF :Eu3 under both excitation wavelengths.
+
3
More remarkably, the luminescence intensity of the nanocrys-
tals excited at 272 nm is in both cases stronger than that of the
nanocrystals excited at 393 nm. The intensity ratio of the 592 nm
emission peaks under different excitation at 272 nm and 393 nm
was estimated to be 4.4 for the hexagonal structure. Similarly,
the ratio of the 592 nm emission intensity at 272 nm and 393 nm
excitation was estimated to be 3.6 for the orthorhombic struc-
ture. Therefore, the energy transfer probability from the Gd ion
to the Eu ion in the hexagonal structure is higher than that in
the orthorhombic structure if we assume that the absorption cross
3
+
hexagonal and orthorhombic GdF3:Eu nanophosphors, respectively.
clarity, the average lifetimes of 5D → F
7
emissions were also
1,2
0
calculated with Eq. (4) using the fitted results and are given in
Table 4.
3+
˛ꢁ + ˇꢁ2
2
f
s
3
+
ꢁ = ˛
(4)
ꢁf + ˇꢁs
7
5
3+
3+
sections of the transition F → L in Eu ions are the same.
It is very clear that hexagonal GdF :Eu exhibits a longer life-
3
0
6
5
3+
3+
Fig. 6 shows the decay curves of D → F emissions for poly-
time than orthorhombic GdF :Eu , supporting the notion that Eu
0
1,2
3
3
+
type GdF :Eu nanophosphors. Luminescence decay curves can
ions are positioned in hexagonal systems with a higher symmetric
structure.
3
be well fitted with a double-exponential function using the least-
squares fitting method:
As mentioned above, the 5D → F emission peak at 592 nm
7
0
1
from Eu3+ indicates a magnetic dipole transition in nature, which
is insensitive to the atomic coordination around Eu ions, how-
ꢀ
ꢁ
ꢀ
ꢁ
I(t)
I0
−t
−t
ꢁs
3
+
=
˛ exp
+ ˇ exp
(3)
ꢁ
f
5
7
ever, the electric dipole transition of the D → F peak at 619 nm
0
2
where ꢁ is the decay time of the fast component, ꢁs is the decay
from Eu3+ is quite sensitive to the atomic coordination. Since the
f
3+
3+
time of the slow component, and ˛ and ˇ are the amplitude ratios
of the fast and slow components, respectively (˛ + ˇ = 1)[17]. The
results fitted to the decay curves are summarized in Table 3. For
atomic coordination around Eu ions or the site symmetry of Eu
3+
ions is strongly dependent on the location of Eu in the GdF3
matrix, that is, interstitial, surface-state, or substitutional Eu3+ in
Table 3
5
7
5
7
3+
Lifetimes and amplitude ratio obtained by fitting the decay curves of D0→ F1 and D0→ F2 emission for GdF3:Eu nanocrystals.
5D0 → 7F1 emission (592 nm)
5D0 → 7F2 emission (619 nm)
Fast component
Slow component
Fast component
Slow component
Hexagonal GdF3:Eu3+(A)
ꢁf = 4.6 ms ˛ = 0.57
ꢁf = 1.28 ms ˛ = 0.25
ꢁf = 14.97 ms ˇ = 0.43
ꢁf = 7.06 ms ˇ = 0.75
ꢁf = 1.84 ms ˛ = 0.36
ꢁf = 4.6 ms ˛ = 0.4
ꢁf = 8.29 ms ˇ = 0.64
ꢁf = 5.2 ms ˇ = 0.6
Orthorhombic GdF3:Eu3+(B)
Table 4
Average lifetimes of Eu ions 5D07→F1 and D0→ F2 emission and fractional number located in higher symmetry sites in polytype GdF3 nanocrystals.
3
+
5
7
Average luminescence lifetime (ms)
Fraction of Eu3+ occupied
symmetric site
5D07 → F1 (592 nm)
5D07 → F2 (619 nm)
Hexagonal GdF3:Eu3+(A)
11.8
6.7
7.5
4.8
71%
69%
Orthorhombic GdF3:Eu3+(B)

2
080
X. Zhang et al. / Journal of Alloys and Compounds 509 (2011) 2076–2080
GdF3 nanocrystals, the decay behavior owing to electric-dipole
and magnetic-dipole transitions includes information on the Eu
location. The observed nonexponential decay curves (see Fig. 6),
in the hexagonal structure was shorter than that in the orthorhom-
bic structure. A higher PL intensity owing to more efficient PL
3+
3+
excitation via energy transfer from Gd to Eu in hexagonal
3+
3+
expressed by Eq. (3), mean that at least two sites for Eu ions
GdF :Eu nanophosphors was demonstrated. This was explained
3
3
+
exist in GdF :Eu nanocrystals for both hexagonal and orthorhom-
by the energy transfer probability, taking account of the inter-
atomic distance. The polytype control (hexagonal–orthorhombic)
3
bic structures. As previously reported [17], luminescence with a
short lifetime can be observed from Eu3 ions positioned in very
asymmetric sites (e.g., surface-state and interstitial sites), whereas
luminescence with a long lifetime was observed from Eu3 ions in
a highly-symmetric site. Considering the crystal structures of GdF3,
the latter site is considered to be a crystallographic position in the
+
of matrix LnF enabled us to enhance the energy transfer probabil-
3
ity from Gd3+ to Eu by varying the interatomic distance.
3+
+
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core of GdF nanocrystals. The former must be a surface-state site
3
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3
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f
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3
[
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systems can be estimated using the theory of transition probabil-
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[
[
[
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3
+
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refinement, most Eu ions could substitutionally be positioned at
3
the Gd3+ site in hexagonal and orthorhombic GdF :Eu nanocrys-
3+
3
[11] D.H. Allan Zalkin, templeton, J. Am. Chem. Soc. 75 (1953) 2453–2458.
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3
+
tals. The similarity between the dispersibility of Eu ions in the
3+
cores of hexagonal and orthorhombic GdF :Eu nanocrystals indi-
3
1431–1446.
cates that the stronger Eu3 luminescence of hexagonal GdF :Eu
+
3+
3
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nanocrystals is a consequence of the highly symmetric hexagonal
3+
structure and the shorter interatomic distance between Gd and
[
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3+
Eu ions and, that the polytype structure is the main factor for
determining the luminescence properties of these samples.
1
[
[
[
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4
. Conclusions
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In this study, we succeeded in effectively characterizing hexag-
3+
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onal and orthorhombic GdF :Eu nanophosphors synthesized by
3
[
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the precipitation method. It was estimated by the Rietveld fitting of
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replaced Gd in both polytypes. In addition, Rietveld analysis indi-
cated that the interatomic distance between Gd and substituted Eu
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[