Synthesis and optical properties of non-stoichiometric lanthanide (Sm, Eu, Tm, Yb) fluorides

Article abstract of DOI:10.1134/S0036023610060045

Nonstoichiometric samarium, europium, ytterbium, and thulium fluorides were prepared by reduction of the corresponding trifluorides with the same lanthanide metal or silicon. Crystal lattice type and lattice parameters of the compounds were determined by

Full text of DOI:10.1134/S0036023610060045

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2010, Vol. 55, No. 6, pp. 841–847. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.P. Ivanenko, N.M. Kompanichenko, A.A. Omelchuk, V.F. Zinchenko, E.V. Timukhin, 2010, published in Zhurnal Neorganicheskoi Khimii, 2010,
Vol. 55, No. 6, pp. 902–908.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Synthesis and Optical Properties of Nonꢀstoichiometric
Lanthanide (Sm, Eu, Tm, Yb) Fluorides
a
a
a
b
b
A. P. Ivanenko , N. M. Kompanichenko , A. A. Omelchuk , V. F. Zinchenko , and E. V. Timukhin
a
Vernadsky Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine,
pr. akademika Palladina 32ꢀ34, Kiev, 252142 Ukraine
Bogatskii Physicochemical Institute, National Academy of Sciences of Ukraine,
b
Chernomorskaya doroga 86, Odessa, 270080 Ukraine
Received November 1, 2008
Abstract—Nonstoichiometric samarium, europium, ytterbium, and thulium fluorides were prepared by
reduction of the corresponding trifluorides with the same lanthanide metal or silicon. Crystal lattice type and
lattice parameters of the compounds were determined by powder Xꢀray diffraction. In the synthesis of ytterꢀ
bium fluoride, the formation of cubic superstructure Yb F was detected. Data reflecting the relationship
27 64
between the structure and optical characteristics of the phases (IR spectra, electronic diffuse reflectance
spectra) were obtained and the spectral bands were assigned.
DOI: 10.1134/S0036023610060045
Unique physicochemical properties of lanthanide structures and optical characteristics of the phases
fluorides account for their use as doping additives in formed (IR spectra, electronic diffuse reflectance
the manufacture of some optical materials for sensors spectra).
operating in the UV, visible, and mediumꢀIR regions,
light guides, and solar concentrators. Crystals and
glasses doped with lanthanide fluorides in low oxidaꢀ
EXPERIMENTAL
tion states are used in memory units and in the manuꢀ
The aboveꢀnoted compounds (except for EuF2 + x)
facture of fiber lowꢀtemperature lasers [1–3]. The were prepared by the reaction
design of new electrooptical materials and their appliꢀ
cation in instrument engineering require the developꢀ
(2 +
x
)LnF + (1–
3
x)Ln = 3LnF2 + x
(1)
ment and upgrading of the existing methods for the in evacuated sealed quartz ampoules. Lanthanide fluꢀ
preparation of lanthanide fluorides in various oxidaꢀ orides were prepared by dissolving reagent grade metal
tion states. Hence, optimizing the conditions for their oxides in nitric acid followed by precipitation by anaꢀ
synthesis and investigations of their physicochemical lytical grade ammonium fluoride and annealing of the
properties are topical scientific and applied problems. precipitates at 600 С. Before batch preparation, trifluꢀ
°
orides were preꢀheated in vacuum by a gas burner to
remove the sorbed water. The metals were ground,
washed with 0.1 N HCl and acetone to remove impuꢀ
The extensive scope of applications of lanthanide
fluorides, in particular, nonꢀstoichiometric fluorides
of europium, samarium, thulium, and ytterbium, in
many fields of science and technology implies the
presence of reliable methods of their identification.
These methods are based on powder Xꢀray diffraction
and IR and UV/Vis spectroscopy. The synthesis of
nonꢀstoichiometric samarium, europium, ytterbium,
and thulium fluorides by reduction with the correꢀ
sponding lanthanide metal or hydrogen have been
reported [4–10]. The synthesis was carried out in vacꢀ
rities, and dried in vacuum at 200 С. The batch conꢀ
°
sisting of metal trifluoride and the metal (samarium,
thulium, ytterbium) was mixed, ground in an agate
mortar, placed in a quartz ampule, evacuated with
heating using a gas burner, and sealed. The ampoule
with the starting compounds was placed in a shaft furꢀ
nace. The synthesis was carried out at temperatures of
700–900°С for 3–6 h.
It was noted that during the synthesis, the inner
–3
–4
uum (1.33
range of 1600–1900
compounds and 800–1000 С for thulium and ytterꢀ
×
10 –1.33
×
10 Pa) in the temperature
surface of the ampoule was coated by a thin film of the
lanthanide, which prevented the reaction of quartz
with fluorides. The densest film was formed in the case
of ytterbium and thulium compounds. Depending on
°С for samarium and europium
°
bium compounds.
This communication presents the results of syntheꢀ the conditions of synthesis, the resulting fluorides had
sis of LnF2 + x, where Ln = Sm, Eu, Yb, Tm, under different colors: SmF2 + x was dark blue but soon turned
milder conditions (temperature 700–900°С; vacuum) red; YbF2 + x ranged from green to ochroid (the YbF2 + x
and the data reflecting the relationship between the phase crystallizing as a superstructure was beigeꢀcolꢀ
841

842
IVANENKO et al.
Preparation conditions, phase composition, and lattice parameters of nonstoichiometric lanthanide fluorides
Synthesis
parameters
Molar ratio LnF3 :
E
Structural type and crystal
lattice parameters, Å
Phase composition
Color in ponder
(
E is Sm, Tm, Yb, Si)
T
,
°
C
time, h
2
2
SmF2 + x
Dark blue
Not determined
(a
= 5.866 [3]) 750
750
2
2
SmF2.01 with oxyfluoride Red
impurity
Cubic = 5.777
, a
2.5
SmF2.35 with oxyfluoride Dark red
impurity
Tetragonal
= 5.856
,
a
= 4.109,
800
3
c
4
2
*
EuF2.09
TmF2.38
Light beige
Dark brown
Cubic, = 5.8252
Hexagonal
= 9.4827
Hexagonal
a
950
820
5
3
,
,
a
= 3.9546,
= 3.9449,
c
2
TmF2.42
Brown
a
750
3
c
= 9.7129
2
2
2
YbF1.91
YbF2.07
YbF2.03
Dark green
Light green
Dark green
Beige
Tetragonal
Tetragonal
Tetragonal
Tetragonal
,
,
,
,
a
a
a
a
= 5.6078
= 5.5949
= 5.5978
= 16.7304
750
890
7
1
.5
Superstructure
YbF2.37 = Yb27F64
750
750
7.5
7.5
3.26
YbF2.37
Ochroid
Beige
Tetragonal
Tetragonal
,
,
a
a
= 5.5827
Superstructure
= 16.7367
YbF2.37 = Yb27F64
*
E = Si.
ored); TmF2 + x varied from light to dark brown (table).
RESULTS AND DISCUSSION
The solidꢀstate synthesis of EuF2 + was performed in
glass carbon crucibles using silicon as the reducing
x
The conditions of synthesis and the composition
and characteristics of the compounds are summarized
in the table.
At the SmF3 : Sm molar ratio of 2.0, the reaction
gave the unstable samarium fluoride phase colored
dark blue, which was synthesized and described previꢀ
ously [4, 5] and which fast turned red. Chemical and
Xꢀray diffraction analyses of the red SmF2 + х phase
revealed the composition SmF2.01 and a cubic crystal
agent at a temperature of 950
°
С and the molar ratio
EuF3 : Si = 4 : 1 [11] according to the reaction
4
EuF + Si → 4 EuF + SiF ↑.
3
(2)
2
4
The resulting europium(II) fluoride was nonꢀstoichiꢀ
ometric and colored light beige.
lattice with the parameter
oxyfluorides in the sample was noted. At SmF3 : Sm =
.5, a dark red phase was obtained corresponding to
reported compound SmF2.35 of a pseudoꢀtetragonal
system with the parameters = 4.109 = 5.856
= 4.106 = 5.825 Å [5]).
According to the results of chemical analysis, the
a = 5.777 Å. The presence of
Powder Xꢀray diffraction was carried out on a
DRONꢀ3M diffractometer (Cu
K
radiation). The
α
2
Xꢀray diffraction patterns were identified using Ident
software. Transmission IR spectra were recorded on a
a
Å
,
c
Å
–1
Specord Mꢀ80 spectrophotometer at 4000 to 200 cm
(
a
Å, c
for samples as KBr pellets and the diffuse reflectance
spectra were measured in the 200–2500 nm range on a
Lambda 9 spectrophometer (PerkinꢀElmer) in the
obtained nonꢀstoichiometric europium fluoride is
described as EuF2.09 and crystallizes in the cubic sysꢀ
coordinates
F(R) =
f(λ), where F(R) is the Kubelka–
tem with the lattice parameter
а = 5.8252 Å.
Munk function, which is analog of absorbance. The
component ratio was found from chemical analysis
data: the metals were quantified as oxides and fluorine
In the system TmF –Tm at 2 : 1 component ratio
3
and temperatures of synthesis of 750–800
°С, the
obtained compounds were TmF2.38 and TmF2.42. As in
was determined by ion selective electrode after fusing the previous study [9], stoichiometric thulium difluoꢀ
the sample with sodium potassium carbonate in the ride could not be prepared under these conditions.
presence of SiO2
.
Powder Xꢀray diffraction showed that TmF2.38 and
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010

SYNTHESIS AND OPTICAL PROPERTIES
843
TmF2.42 crystallize in the hexagonal system with the tions. The shift of the key absorption bands of the nonꢀ
unit cell parameters
a
= 3.9546
= 9.7129 Å [9]) and
= 3.9500 Å, c = 9.7076 Å [9]), respectively. uted to different symmetries of these compounds and
Å
,
c
a
= 9.4827
= 3.9449
Å
Å
(
,
a
c
=
=
stoichiometric samarium fluoride to lower frequency
with respect to the IR spectrum of SmF3 can be attribꢀ
3
.9609
.7129
Å
Å
,
(
c
a
9
The Xꢀray diffraction patterns showed also thulium the change (increase) in the Sm–F bond length. The
metal and trifluoride impurities even after longꢀterm IR spectrum of the red phase, which crystallizes in the
heating of the batches at 800
that during the synthesis, the equilibrium
°
С
. This fact indicates cubic system (Fig. 2a,
1) shows an absorption band
–1
typical of samarium oxyfluoride (470 cm ), while at
–1
2
60–400 cm , general absorption without clear peaks
TmF + Tm ↔ TmF2 + х.
3
(3)
characteristic of Sm–F bonds is observed.
was established.
The spectrum of europium difluoride (Fig. 2b)
The reactions of ytterbium trifluoride with ytterꢀ shows weak absorption bands (peaks at 270, 280, 315
–
1
–1
–1
bium metal at different component molar ratios gave
nonꢀstoichiometric fluorides described as YbF2 + х, 400 cm
where
(δ
as) cm , 350cm with a shoulder at 365 cm , 380
,
–1
(
ν
as)) characteristic of europium trifluoride
х
varied from 1.91–2.37. Figure 1 shows the with some shift.
Xꢀray diffraction patterns of these compounds.
According to Xꢀray diffraction data of ytterbium comꢀ
pounds close to stoichiometry, the samples crystallize
with the cubic system and their lattice parameters
In the IR absorption spectrum of thulium fluoride
Fig. 2c), the most intense bands occur at 460–
(
–1
–1
2
60 cm . At 200–300 cm , the spectrum shows a
–1
band with a peak at 290 cm (Fig. 2c, 2) attributable to
antisymmetric bending vibrations. At 300–500 cm , the
spectrum of thulium trifluoride exhibits four absorpꢀ
tion peaks at 330, 345, 355, 390, 405, and 425 cm
and two shoulders at 455 and 500 cm . The spectrum
of TmF2.38 (Fig. 2c, ) differs from the trifluoride specꢀ
–1
(
table) almost coincide with the values reported previꢀ
ously [8]. Note that the reactions of the starting reacꢀ
tants at molar ratios of 2.5 or 3.26 are distinguished by
the formation of two phases, colored green to ochroid
–1
–1
(
major) and beige. According to Xꢀray diffraction
1
data, the major phase crystallizes with the cubic sysꢀ
tem and is the basis structure for the second phase
whose crystal structure can be described by three basis
trum by the presence of feebly defined principal charꢀ
acteristic peaks; in addition, no absorption band is
–
1
present at 425 cm and a band with a maximum at
–
1
formulas, a(Yb F ) = 3a ) (Fig. 1). These
(YbF2.37
27 64
315 cm appears. For TmF2.42, in the range of 325–
–
1
phases are separated rather easily when taken out of
the reactor. The phase that forms the superstructure is
a powder located in the upper part of the ampoule,
while the major phase, the cake, is in the lower part of
the ampoule.
According to chemical analysis data, the obtained
nonꢀstoichiometric europium fluoride has the compoꢀ
5
00 cm , broadening of the principal band with a
–
1
ν
vague maximum at 400 cm
( as) is observed. The
bending vibrations of these compounds shift to lower
–1
frequency (the peak at 275 cm ).
–1
In the region of 550–320 cm , no absorption
bands typical of ytterbium trifluoride are observed in
the IR spectra of nonꢀstoichiometric ytterbium comꢀ
pounds with the cubic structure (Fig. 2d). The region
sition EuF2 and crystallizes in the cubic system with
.09
–1
the lattice parameter а = 5.8252 Å.
of 250–320 cm contains an absorption band with a
–1
IR absorption spectra of samarium, europium, and peak at 260–280 cm , which is shifted to lower freꢀ
ytterbium trifluorides coincide with the reported data quency with respect to the trifluoride. This band is
[
12]. No data on the spectra of thulium trifluoride and attributable to bending vibrations of the F–Yb–F
nonꢀstoichiometric lanthanide fluorides were found in bond. Note that the spectra of nonꢀstoichiometric
the literature. The fundamental vibration frequencies ytterbium fluorides that crystallize in the cubic system,
calculated theoretically for europium and ytterbium which were obtained and described above, are similar
difluorides were reported [13]. The absorption freꢀ to the IR spectrum of BaF2 [15]. The spectrum of the
quencies of nonꢀstoichiometric compounds (Fig. 2) nonꢀstoichiometric compound Yb F crystallizing in
27 64
occur approximately in the same range as for trifluoꢀ a superstructure approaches more closely the specꢀ
rides; however, the peaks are less pronounced, broadꢀ trum of ytterbium trifluoride. The line intensities
ened, and somewhat shifted to lower wavelengths. decrease and the peaks shift to the nearꢀIR range relaꢀ
According to publication [14], the absorption bands at tive to those of the trifluoride (280 sh at 275, 300, 350,
–
1
–1
4
00–500 cm refer to antisymmetric stretching vibraꢀ 380, 425, 510 cm for the superstructure; 290, 355,
–1
–1
tions and the bands at 200 to 400 cm are due to Ln–F 370, 385, 395 sh at 400, 430 cm for ytterbium trifluꢀ
bending vibrations.
oride), which is related to the coordination of similar
Figure 2a shows the IR spectra of samarium fluoꢀ structural groups.
rides. The blueꢀblack phase of nonꢀstoichiometric fluꢀ The electronic diffuse reflectance spectra of nonꢀ
oride is responsible, at 300–600 cm , for two absorpꢀ stoichiometric fluorides were also studied (Fig. 3). The
tion bands with maxima at 375 and 325 cm , which spectrum of samarium difluoride we prepared (Fig. 3a)
can be attributed to antisymmetric stretching vibraꢀ can be divided into two ranges of interest: UV (200–
tions. The absorption band at 200–300 cm with a 400 nm) and near IR (800–2200 nm) ranges. The
–1
–1
–1
–1
maximum at 250 cm is attributable to bending vibraꢀ region of 270–400 nm shows a band with a maximum
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010

844
IVANENKO et al.
(а)
(b)
20
40
60
80
, deg
20
40
60
80
, deg
2
θ
2
θ
(c)
(d)
20
40
60
80
, deg
20
40
60
80
, deg
2
θ
2
θ
(
e)
20
40
60
80
, deg
2
θ
Fig. 1. XꢀRay diffraction patterns of the nonꢀstoichiometric compounds: (a) SmF2 + х; (b) EuF2.09; (c) TmF2 + х; (d) basis strucꢀ
ture YbF2 + х, (e) superstructure Yb F64.
27
4f–4f
electron transitions typical of Sm3+ ions. The
at about 300 nm corresponding to the principal charꢀ the
acteristic bands of divalent samarium [16] caused by diffuse reflectance spectra of EuF2 + x [17] (Fig. 3d)
–5 electron transitions; the intensity of other charꢀ have two strong absorption bands in the UV range: at
acteristic peaks is negligibly low. The region of 800– 210–220 and at 390–400 nm caused by the
–5
200 nm exhibits a series of absorption peaks related to electron transitions in the Eu(II) ion. In the nearꢀIR
4f
d
4f
d
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010

SYNTHESIS AND OPTICAL PROPERTIES
a) (b)
845
(
4
3
2
2
1
1
ν
, cm–1 1000
800
600
400
200
ν
, cm–1 1000
800
600
400
200
(
d)
6
5
(c)
4
3
3
2
1
2
1
ν
, cm–1 1000
800
600
400
200
ν
, cm–1 1000
800
600
400
200
Fig. 2. IR spectra of fluoride compounds of (a) samarium: (
pseudotetragonal SmF2.35 phase; (b) europium: ( ) EuF2.09, and (
) cubic YbF2.03 and YbF2.37 phases, respectively, (
1
) SmF , (
2
) blueꢀblack SmF2 + x phase, (
) EuF ; (c) thulium: ( ) TmF2.38, (
) superstructure Yb F , (
3
2
) cubic SmF2.01, and (
) TmF2.42, and ( ) TmF3;
) YbF , and ( ) BaF2
4)
3
1
2
1
3
6
3
(
d) ytterbium: (
1,
3
2
,
4
5
27
64
3
(reagent grade).
region (1800–2200 nm), the spectrum shows weak intensity of these peaks is 10–20 times lower than
broadened absorption peaks related to the intracenter observed for initial EuF ; however, their presence
–4
electron transitions typical of Eu(III) ions. The attests to incomplete reduction of EuF to EuF . The
3
4f
f
3
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010

846
IVANENKO et al.
F(R)
F(R)
2
1
0
.0
0.5
0.3
0.1
(a)
(b)
2.4
1.8
1.2
0.6
0.3
.2
0
.2
.1
0
.4
2
00 400
)
400
1.0
800 1100 1500
1.0
1900
λ
, nm
200
F(R)
400 16002100 2600
λ
, nm
F
(R
4
.0
4.0
0.5
0.4
(
c)
(d)
3
.2
0.8
0.6
0.4
0.2
0.8
0.6
0.4
0.2
3.2
2
1
0
.4
.6
.8
2.4
1.6
0.8
0.3
0.2
0.1
200
400 400
800 1100 1500 1900
λ
, nm
200
400 8001000 1400
1800
λ, nm
Fig. 3. Electronic diffuse reflectance spectra of nonꢀstoichiometric compounds LnF2 + x, where Ln = (a) Sm, (b) Eu, (c) Tm, (d) Yb.
2+
electronic spectra of thulium (Fig. 3b) and ytterbium reflectance spectra confirm the presence of Ln and
3
+
(
Fig. 3d) fluorides can be split into analogous regions: Ln ions in these compounds [6].
in the case of nonꢀstoichiometric ytterbium fluorides,
the region of 200–400 nm contains absorption bands lium, and ytterbium fluorides with like lanthanides in
with maxima at 220, 275, and 350 nm related to the the temperature range of 700–900 in a vacuum of
10 Pa affords nonꢀstoichiometric lanꢀ
Thus, the contact interaction of samarium, thuꢀ
°С
–1
4
f–5
d
transition, while the 900–1100 nm region 1.33–1.33 ×
thanide compounds in low oxidation states.
shows a peak at ~1000 nm due to the 4f–4f transition
of Yb . The thulium spectra show, in the 200–450 nm
range, reflection bands with maxima at 215, 220, 260,
3
transitions of Tm . The visible region shows a weak
reflection band with a maximum at 560 nm, which can
be assigned to the Tm
3+
The composition of the phases formed depends on
the ratio of the initial components of the batch in the
following way: an increase in the LnF3 : E molar ratio
E = Sm, Tm, Yb, Si) results in an increase in the fluꢀ
orine content in the resulting compounds LnF2 + x. In
the case of ytterbium, the molar ratios YbF3 : Yb =
40, 360, and 430 nm caused by the 4f–5d electron
(
2+
2+
3+
Tm transition, while the
2
.5–3.26 and keeping the batch at 750
bands with maxima at 1380, 1670, 1900, and 2130 nm resulted in a superstructure.
°С for 7.5 h
3+
correspond to Tm characteristic bands and are
The electronic diffuse reflectance spectra (intense
described by the
4f–4
f
transition. Thus, the diffuse absorption bands in the UV region) confirm the presꢀ
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010

SYNTHESIS AND OPTICAL PROPERTIES
847
ence of lanthanide ions in lower oxidation states in the
samples.
7. T. Petzel and O. Greis, Z. Anorg. Allg. Chem. 396, 95
1973).
(
The IR spectra of nonꢀstoichiometric fluorides like
LnF2 + x (Ln = Sm, Eu, Tm, Yb) were reported for the
first time. For the ytterbium fluoride with the basic
8. O. Greis, Z. Anorg. Allg. Chem. 430, 175 (1977).
9. O. Greis and T. Petzel, Z. Anorg. Allg. Chem. 434, 89
(1977).
cubic structure, no absorption bands in the frequency 10. O. Greis, J. Solid State Chem. 24, 227 (1978).
–
1
range of 400–4000 cm were detected.
1
1. V. F. Zinchenko, O. G. Eremin, N. P. Efryushina, et al.,
Zh. Neorg. Khim. 50 (5), 748 (2005) [Russ. J. Inorg.
Chem. 50 (5), 676 (2005)].
Owing to the aboveꢀpresented characteristics, the
obtained compounds can be recommended as doping
additives for the synthesis of fluorineꢀcontaining 12. E. N. Yurchenko, G. N. Kustova, and S. S. Batsanov,
glassy materials.
Vibrational Spectra of Inorganic Compounds (Nauka,
Novosibirsk, 1981) [in Russian].
1
1
1
3. N. V. Filippenko, et al., Izv. Vyssh. Uchebn. Zaved.,
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010