Synthesis and luminescent properties of gadolinium aluminates phosphors

Article abstract of DOI:10.1016/j.ica.2011.04.026

In this work, aluminum-gadolinium oxides with different phases were prepared by the non-hydrolytic sol-gel route, using lower temperatures than those employed in methods such as solid-state reaction and Pechini method. The influence of heating treatment on sample structure was investigated. The formation process and the local structure of the samples are discussed on the basis of thermal, X-ray diffraction, photoluminescence (PL) spectroscopy, and infrared spectroscopy analyses. The quantum efficiency of Eu³⁺ in the different phases obtained in this studied was evaluated. Initial crystallization and the GdAlO₃ phase were observed at temperatures around 400 °C. PL data of all the samples revealed the characteristic transition bands arising from the ⁵D₀ → ⁵F_J (J = 0, 1, 2, 3, and 4) manifolds under maximum excitation at 275, 393, and 467 nm in all cases. The ⁵D₀ → ⁷F₂ transition often dominates the emission spectra, indicating that the Eu³⁺ ion occupies a site without inversion center.

Full text of DOI:10.1016/j.ica.2011.04.026

Inorganica Chimica Acta 375 (2011) 63–69
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis and luminescent properties of gadolinium aluminates phosphors
⇑
Marcela G. Matos, Paulo S. Calefi, Katia J. Ciuffi, Eduardo J. Nassar
Universidade de Franca, Av. Dr. Armando Salles Oliveira, 201, CEP 14404-600, Franca, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
In this work, aluminum–gadolinium oxides with different phases were prepared by the non-hydrolytic
sol–gel route, using lower temperatures than those employed in methods such as solid-state reaction
and Pechini method. The influence of heating treatment on sample structure was investigated. The for-
mation process and the local structure of the samples are discussed on the basis of thermal, X-ray diffrac-
tion, photoluminescence (PL) spectroscopy, and infrared spectroscopy analyses. The quantum efficiency
Received 9 December 2010
Received in revised form 6 April 2011
Accepted 15 April 2011
Available online 30 April 2011
3
+
of Eu in the different phases obtained in this studied was evaluated. Initial crystallization and the
Keywords:
Europium III
Sol–gel process
Optical properties
Luminescence
GdAlO
3
phase were observed at temperatures around 400 °C. PL data of all the samples revealed the char-
5
5
acteristic transition bands arising from the D
tation at 275, 393, and 467 nm in all cases. The D
indicating that the Eu ion occupies a site without inversion center.
Ó 2011 Elsevier B.V. All rights reserved.
0
? F
J
(J = 0, 1, 2, 3, and 4) manifolds under maximum exci-
5
7
0
? F
2
transition often dominates the emission spectra,
3
+
1
. Introduction
4 2 9
and Gd Al O (GAM) are chemically stable compounds that are
suitable hosts for replacement with lanthanides ion (Ln = Ce,
Nd, Er, Eu, Tb, Sm, and Dy) [7]. From a structural viewpoint, perov-
3+
Materials that emit in the UV–Vis range after absorption of high-
energy photons are known as scintillators. Based on this property,
these materials provide a myriad of applications as radiation detec-
tors in the areas of medical diagnostic imaging, industrial inspec-
tion, dosimetry, and nuclear medicine [1]. Several research
activities related to the preparation and characterization of lantha-
nides-doped phosphors for use solid-state lasers, color TV monitors,
and fluorescent lamps have been reported [2]. Materials with
specific optical and structural properties are required for different
utilizations. In general, no phosphor completely fulfills the require-
ments of all applications. Thus, improvements in one or more
properties are desirable in the quest for efficient X-ray phosphors,
which must have properties that include high density, chemical
stability, radiation hardness, high luminescent yield and, in some
cases, short lifetime. Moreover, phosphors must be inexpensive
and easily obtained [3]. Information on the properties of these
materials, such as thermal expansion coefficient, specific heat,
and thermal conductivity, as a function of temperature is essential
to evaluate the effect of temperature on their thermophysical prop-
erties under temperature gradients [4]. Gadolinium aluminate is
currently being researched as candidate material for neutron
absorption [4,5], and it is a promising candidate for optical,
magnetic, electronic, and structural applications [6]. Combinations
3
skite-type oxides (GdAlO ) score over fluoride-based oxide
systems. The former oxides offer two sites (Gd and Al) for aliovalent
doping, thereby creating vacancies in the oxygen sublattice and
aiding migration of oxygen ions through the lattice [8]. Among
these compounds, gadolinium aluminum perovskite (GAP) is an
important phosphor host material with perovskite structure [9].
GAP is normally synthesized at high temperatures by a solid-state
reaction between aluminum and gadolinium oxides. Such condi-
tions result in several problems concerning particle size, impurity,
and formation of other phases [10]. The non-hydrolytic sol–gel
route, on the other hand, involves the reaction of a metal halide
with an oxygen donor such as ether, alcohol, or another donor
under non-aqueous conditions, to form an inorganic oxide [11].
The direct advantages of this technology include the production
of novel chemical compositions with unique properties, easy
stoichiometric control, good homogeneity through mixture of the
starting materials at the molecular level in solution, relatively low
reaction temperature, shorter heating time, less potential for
cross-contamination, small size and narrow particle size distribu-
tion, excellent purity, and more convenient preparation routes that
minimize sample manipulation [12–28].
In this work, the influence of the heat treatment on the prepa-
ration of the Gd(Eu)Al oxide powder using a non-hydrolytic sol–gel
method was investigated. The powder was dried and treated at
2 3 2 3 3 3 5
of Gd O –Al O systems, such as GdAlO (GAP), Gd Al O12 (GAG),
1
00, 400, 600, 800, and 1000 °C for 4 h and structurally character-
⇑
Corresponding author. Tel.: +55 16 37118871; fax: +55 16 37213266.
E-mail addresses: mgmtos@yahoo.com.br (M.G. Matos), ejnassar@unifran.br (E.J.
ized by thermal analysis (TG/DTA), X-ray diffraction (XRD), photo-
luminescence (PL), and infrared spectroscopy (IR).
Nassar).
0
020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.04.026

6
4
M.G. Matos et al. / Inorganica Chimica Acta 375 (2011) 63–69
2
. Experimental
100
TG
9
0
DTG
DTA
2
1
.1. Preparation of solution of lanthanides ion chloride (LnCl )
3
ꢁ1
ꢁ1
3+
3+
80
ꢀ 10 mol L (Ln = Eu and Gd
)
7
0
0
The lanthanides oxides were calcined at 900 °C for 2 h. Then,
6
0
6
.9100 g Gd or 0.8798 g Eu was dissolved in H O and HCl
2
O
3
2
O
3
2
ꢁ
1
50
40
mol L . Excess HCl and H O were evaporated. The ethanol was
2
then added and evaporated three times. The final concentration
of Ln ion in the ethanolic solution was 1.0 ꢀ 10 mol L
ꢁ1
ꢁ1
.
30
20
10
0
2.2. AlCl
3
Anhydrous aluminum chloride was purchased from VetecÒ.
0
200
400
600
800
1000
2.3. Sol–gel synthesis of the Gd–Al host
Temperature (ºC)
The preparation of the gel was carried out in oven-dried glass-
ware. The material was synthesized by the non-hydrolytic method
described by us [10,24,29,30], via modification of the method
Fig. 1. TG/DTG/DTA curves for the precursors of the Gd(Eu)–Al–O samples dried at
0 °C.
5
described by Acosta et al. [31]. One gram of AlCl
nol (EtOH) were reacted with 2.5 mL EuCl solution and 22.5 mL
GdCl solution (prepared as described in Section 2.1). The mixture
3
and 20 mL etha-
3
3
⊗
was kept under reflux (the condenser was placed in a thermostatic
bath at ꢁ5 °C) for 4 h in silicon bath, at 110 °C and under argon
atmosphere. After reflux, the mixture was cooled and aged
overnight in the mother liquor at room temperature (RT), because
precipitation continues through aging in the mother liquor. The
solvent was then removed under vacuum. The powders were dried
and received heat treatment at 100, 400, 600, 800, and 1000 °C for
⊗
⊗
*
#
*
e
d
*
* *
*
º Gd O
2
3
º
# Gd Al O
4
2
9
Gd Al O
*
3
5
12
3+
º
º
º
4
h in air. The lanthanide ion dopant (Eu ) was added at a molar
º
c
⊗ Al O
2 3
3+
ratio of 1% in relation to the Gd ion.
GdAlO3
Y O
b
2
3
2.4. Characterization techniques
a
Thermal analysis (TG/DTG/DTA) was carried out (Thermal
Analyst 2100 – TA Instruments SDT 2960 simultaneous DTA–TG)
10
20
30
40
50
60
in nitrogen atmosphere at a heating rate of 20 °C/min, from 25 to
2θ (degree)
1
000 °C.
The X-ray diffraction (XRD) measurements were performed at
room temperature using a Rigaku Geigerflex D/max-c diffractome-
ter with monochromated Cu K radiation (k = 1.54 Å). Diffracto-
Fig. 2. X-ray diffraction patterns of the Gd(Eu)–Al–O precursor gels treated at (a)
00, (b) 400, (c) 600, (d) 800, and (e) 1000 °C for 4 h.
1
a
grams were recorded in the 2h range from 4° to 80° at a
resolution of 0.05°.
Photoluminescence (PL) data were obtained under continuous
Xe lamp (450 W) excitation with a spectrofluorometer (SPEX – Flu-
orolog II) at room temperature. The emission was collected at 90 °C
from the excitation beam. The slits were placed at 1.0 and 0.2 mm
for excitation and emission, respectively, giving a bandwidth of 3.5
and 0.5 nm. Oriel 58916 (exc.) and Corning 97612 (em.) filters
were used.
The infrared absorption spectra (FTIR) were acquired on a Per-
kin-Elmer 1739 spectrophotometer with Fourier transform, using
the KBr pellet technique, with a sample/KBr ratio of 1:300,
approximately.
5
D
2
5
L6
CTB
2
76
5
D
4
5
L
7
5
D3
e
d
c
b
3
08
314
a
350
400
450
e
d
c
3
. Results and discussion
b
3.1. Thermal analysis (TG/DTA/DTA)
a
Fig. 1 shows the TG/DTG/DTA curves obtained for the precursors
250
300
350
400
450
500
of the Gd(Eu)–Al–O samples prepared by the non-hydrolytic
method and dried at 50 °C.
Wavelength (nm)
The TG/DTG/DTA curves reveal peaks accompanied by mass
Fig. 3. Excitation spectra of the Eu3+ ion in the Gd(Eu)–Al–O host treated at (a) 100,
losses at 70, 120, 170, and 270 °C, attributed to the loss of water
(b) 400, (c) 600, (d) 800, and (e) 1000 °C for 4 h, kem = 616 nm.

M.G. Matos et al. / Inorganica Chimica Acta 375 (2011) 63–69
65
5
7
D0
- F2
5
7
D0
-
F0
5
7
D0
-
F1
5
7
D0
- F4
5
7
D0
- F3
500
550
600
650
700
500
550
600
650
700
Wavelength (nm)
Wavelength (nm)
a
b
500
550
600
650
700
500
550
600
650
700
Wavelength (nm)
Wevalength (nm)
c
d
500
550
600
650
700
wavelength (nm)
e
Fig. 4. Emission spectra of the Eu3+ ion in the Gd(Eu)–Al–O samples treated at (a) 100, (b) 400, (c) 600, (d) 800, and (e) 1000 °C for 4 h, excited at CTB.
molecules weakly bound to the oxide and solvent molecules.
Another mass loss appears at 400 °C, ascribed to pyrolysis of organ-
ic matter remaining from the synthesis.
The thermogravimetric analysis shows that most of the weight
loss, around 40% (w/w), is associated with the loss of water and
weakly bound solvent molecules in the sample, which takes place
mainly between 70 and 250 °C.
The DTA curve displays small exothermic peaks around 400 and
9
70 °C, due to phase transition. The exothermic peak around 400 °C
can be due to crystallization of different phases, as observed in the
XRD patterns. The crystallization temperature of the sample
obtained by the non-hydrolytic route is low compared with those
of materials obtained by Cizauskaite et al. (1000 °C) and by other
methods such as Pechini (850 °C) and solid-state reactions
3.2. X-ray diffraction (XRD)
Fig. 2 presents the XRD patterns of the powders obtained after
treatment at 100, 400, 600, 800, and 1000 °C for 4 h.
The XRD pattern of the precursor powder of Gd(Eu)–Al–O
prepared by the non-hydrolytic sol–gel process and dried at
100 °C reveals the presence of several peaks that can be due to a
mixture of the precursors in the sample (Fig. 2). Crystallization of
(
1450 °C) [3,4,6]. The other peak at approximately 970 °C is
characteristic of a second crystallization, as can be seen from the
formation of different phases in the XRD patterns.

6
6
M.G. Matos et al. / Inorganica Chimica Acta 375 (2011) 63–69
500
550
600
650
700
500
550
600
650
700
Wavelength (nm)
Wavelength (nm)
a
b
500
550
600
650
700
500
550
600
650
700
Wavelength (nm)
Wavelength (nm)
c
d
500
550
600
650
700
Wavelength (nm)
e
Fig. 5. Emission spectra of the Eu3+ ion in the Gd(Eu)–Al–O samples treated at (a) 100, (b) 400, (c) 600, (d) 800, and (e) 1000 °C for 4 h, excited at 393 nm (5L
level).
6
the materials becomes evident with increasing temperatures of
heat treatment. An amorphous phase appears in the case of the
powders treated at 400, 600, and 800 °C, but the amount of this
phase decreases with increasing temperature. The onset of crystal-
lization is observed at 400 °C. Several phases can be observed for
the samples treated at 400 and 600 °C, such as GdOCl (JCPDF No.
vertex and a Gd3+ ion displaced slightly within the x–y plane in
the center [33]. The larger A cation is situated in the void formed
by eight octahedra and, in the ideal cubic structure, this cation is
surrounded by the 12 nearest neighboring oxygens at equal dis-
0
tances [34]. The angle of the monoclinic unit cell is 90°–27 in this
3
+
material, so twinning readily takes place during growth [35]. Gd
3
+
1
2-718, EuOCl JCPDF No. 12-163), Gd
Eu JCPDF No. 12-393), and the oxide mixture of Gd and Al,
namely GdAlO (GAP, JCPDF No. 9-85). The orthorhombic GdA-
lO -type perovskites (Pbnm), with general stoichiometry ABO
are derived from the ideal cubic structure (Pm3m) via the tilting
and distortion of the BO octahedra [32]. Its framework can be
regarded as a cube with a distorted oxygen octahedron at each
2
O
3
(JCPDF No. 43-1014,
and Eu
have the same valence and similar ion radius
(rGd = 0.94 Å, rEu = 0.95 Å) [36]. At 800 and 1000 °C, the XRD
3
+
3+
2
O
3
3
patterns evidence new crystalline phases that can be ascribed to
3
3
,
Gd
No. 30-14). Also, there are phases of Al
and Gd (Eu ). Gd Al (GAM) is monoclinic and its structure
is related to that of the mineral cuspidine, whereas Gd Al
3
5
Al O
12 (GAG, JCPDF No. 18-517), and Gd
4 2 9
Al O (GAM, JCPDF
2 3
O (JCPDF No. 2-1373)
6
2
O
3
2
O
3
4
2 9
O
3
5 12
O

M.G. Matos et al. / Inorganica Chimica Acta 375 (2011) 63–69
67
500
550
600
650
700
500
550
600
650
700
Wavelength (nm)
Wavelength (nm)
b
a
500
550
600
650
700
500
550
600
650
700
Wavelength (nm)
Wavelength (nm)
c
d
500
550
600
650
700
Wavelength (nm)
e
Fig. 6. Emission spectra of the Eu3+ ion in the Gd(Eu)–Al–O samples treated at (a) 100, (b) 400, (c) 600, (d) 800, and (e) 1000 °C for 4 h, excited at 467 nm ( D
5
level).
2
(
GAG) belongs to the garnet structure type [4]. Gadolinium alumi-
3.3. Photoluminescence (PL)
Fig. 3 depicts the excitation spectra of Eu ion-doped Gd(Eu)–
num garnet (GAG) is one of the most important phosphors host
materials with cubic structure [7]. The phase transition was
observed by DTA analysis.
3
+
5
7
0 2
Al–O host samples monitored at the D ? F transition.
The peaks at 2h = 23.05° (GdAlO
3
), 28.89°, 39.05°, 42.93°, 50.52°,
The excitation spectra of the samples were recorded by fixing
the emission wavelength at the Eu : D ? F transition. The
0 2
3
+
5
7
and 56.06° (Gd or Eu ) appear in the samples treated at 400
2
O
3
2
O
3
and 600 °C. When the precursor is heated at 800 and 1000 °C,
there is a new crystalline phase of the material with peaks at
bands can be assigned to different excitation processes. The sharp
lines observed in the 350–475 nm range (f–f transitions) are attrib-
7
5
5
5
2
5
h = 16.96° (Gd
4
Al
2
O
9
), 20.71°, 27.16°, 30.01°, 36.11°, 54.60°,
).
0 6 7
uted to transitions from the F level to the L , L , and D2-4 levels,
7.63° (Gd Al 12), 44.50° and 53.34° (Al O
3
5
O
2 3
for all the treated samples. The excitation spectra of the powders

6
8
M.G. Matos et al. / Inorganica Chimica Acta 375 (2011) 63–69
5
0 1
ion occupies a site without inversion center. The D transi-
? 7F
Table 1
Number of bands observed for all the samples, excited at different wavelengths: CTB,
tion (591 nm) is purely magnetic-dipole allowed, and not
restricted by any symmetry [11,18].
3
93, and 467 nm.
5D
Samples kexc. = CTB
? 7
F
(nm) 5D
? 7
F
(nm)
5D
? 7
F
(nm)
3+
0
0
0
1
0
2
Emission of Eu -doped samples obtained at 100 °C present
broad peaks or no peaks at all, typical of the emission profile of
non-crystalline compounds or highly disordered systems (Figs. 4
and 6). In Fig. 5, the emission spectrum can be ascribed to halide
precursors.
By applying the section rules for electric dipole (ED) and mag-
netic dipole (MD) transitions, the number of lines depends on
the Eu symmetry site, which can be determined by the allowed
0 J
transitions. Usually, the splitting number of D ? F transitions
can provide information about the Eu ions surrounding and
depends on the J value and the site symmetry around Eu , with
a maximum line number of ‘‘2J + 1’’ for each lattice site [11,14].
A clear change in the symmetry of Eu can be noted, since the
samples present different numbers of emission lines. This indicates
different symmetries for the Eu ion. Table 1 lists the number of
bands present in the emission spectra of the Eu ion when excited
1
4
6
8
1
00 °C
00 °C
00 °C
00 °C
a
579
579
579
587; 595
586; 595
586; 591; 597
614; 619 ; 629
614; 619 ; 629
610 ; 614; 628
a
a
a
000 °C 579
586; 589; 591; 597 610 ; 614; 617; 626; 628
Samples kexc. = 393 nm
3
+
a
1
4
6
8
1
00 °C
00 °C
00 °C
00 °C
578
578
579
579
582; 585; 588; 592 611 ; 617
586; 595
587; 595
586; 592; 598
a
5
7
614; 619 ; 626; 629
610; 614; 619 ; 625; 629
610 ; 613; 618; 629
a
3+
a
3+
a
000 °C 579
586; 589; 591; 597 610 ; 614; 616; 622; 628
Samples kexc. = 467 nm
3+
1
4
6
8
1
00 °C
00 °C
00 °C
00 °C
614; 618a
610; 614; 618 ; 621; 628
579
579
579
586; 594
586; 594
3
+
a
a
3+
586; 592; 594; 597 610 ; 613; 622; 628
586; 589; 591; 597 610 ; 613; 616; 627; 629
a
000 °C 579
at CTB, 393, and 467 nm, respectively.
5
7
a
0 0
The D ? F transition appears at the same wavelength for all
Emission maxima.
the samples, independent of the excitation wavelength. There is a
difference concerning the relative intensity with relation to the
5
7
0 1
D ? F transition. The latter transition presents different
display a broad band between 250 and 330 nm, ascribed to charge
transfer band (CTB) transitions in the Eu3+–O bond lying in the
band gap region of the Gd–Al mixed oxide host [29]. For the sam-
ples treated at 400 and 600 °C, the CTB is located at 290 nm,
whereas the CTB of the materials treated at 800 and 1000 °C is
located at 265 nm. The CTB energy of Eu3 depends on the anion
type, the binding strength of valence band electrons, and the size
numbers of bands, depending on the excitation wavelength and
2ꢁ
temperature. The samples treated at 400 and 600 °C display a
3+
similar number of bands, thus indicating that Eu occupies the
same symmetry site in the host, as observed by XRD. For the
powders heated at 800 and 1000 °C, a new profile emission spec-
trum is observed. This is due to the fact that a different symmetry
+
3+
site is occupied by the Eu ion, also seen in the XRD. The sample
3+
of the site occupied by the Eu ions [3]. In the case of lanthanide
aluminates in which the Eu3 ion occupies a small site, the energy
of the CTB tends to increase, so this band appears at a shorter
wavelength [37]. Therefore, the symmetry of the samples treated
at 800 and 1000 °C is lower than that of powders treated at 400
and 600 °C. The CTB is a measure of the covalent character of the
Eu–ligand bond. The higher energy of this band indicates stronger
metal–ligand interactions [38], thus the samples treated at 800 and
5
7
treated at 1000 °C has four peaks in the case of the
0 1
D ? F
+
transition, more than the number allowed by 2J + 1. This is further
evidence that the ion has a new surrounding.
3+
3+
Because Gd and Eu are very similar in terms of ionic radius,
3+
3+
the doped Eu ion occupies the Gd sites, thereby resulting in the
5
7
3+
hypersensitive red emission transition D
0 2
? F of Eu , the most
prominent group in the emission of this ion [13].
5
The emission quantum efficiency (
state was determined by balance between radiative and
non-radiative processes, as described in Ref. [41].
0 2
g) of the D ? 7F emission
1
3
000 °C have higher covalence. The sharp lines at 276, 308, and
a
14 nm observed in the spectra of the materials treated at 800
3
+
and 1000 °C can be attributed to energy transfer from Gd ions
to Eu and correspond to the 8
3
+
6
8
6
g
¼
s
rad
=s
rad
þ
s
nrad
S
7/2 ? I3/2
,
S
7/2 ? P
J
transitions
Table 2 presents the lifetime of emissive CTB, L , and 5D2 to
5
[
3,39,40].
6
Figs. 4–6 correspond to the emission spectra of the Eu3 ion in
+
5
ground F states for the samples treated at different temperatures
2
5
the Gd(Eu)–Al–O host, monitored at CTB, 393 nm ( L
4
6
level), and
for 4 h.
5
67 nm ( D
2
level), respectively.
The samples excited at CTB have one lifetime only, indicating
3
+
The emission spectra of the phosphors, obtained by excitation
that energy transfer occurs in only one kind of Eu site.
The biexponential decay behavior of the activator is frequently
observed when the excitation energy is transferred to different
5
7
at CTB, 393, and 467 nm, consist of
lines of Eu dominated by the D
D
0
? F
J
(J = 0–4) emission
3
+
5
7
0 2
? F
(ꢂ610 nm) electric dipole
3+
Eu sites from the donor. The samples excited at the L6 and 5D2
3+
5
transition, which is strongly dependent on the Eu surroundings.
3
+
When the Eu ion is situated in a low symmetry site (without
levels have two lifetimes, which is one more indication of the pres-
inversion center), the hypersensitive transition 5
D ? F is often
7
3+
0 2
ence of different Eu sites in the host, as demonstrated by the XRD
3
+
dominating in the emission spectra. This indicates that the Eu
and PL techniques.
Table 2
2 6 2 2 2
s F L F D F , and quantum efficiency (%) for the samples annealed at 100, 400,
) of the samples containing Eu3+ when excited at different levels: CTB ? 7 , 5 ? 7 and 5 ? 7
Lifetime (
00, 800, and 1000 °C for 4 h.
6
CTB ? 7
Quantum efficiency (%)
F
5L
Quantum efficiency (%)
? 7
F
5D
? 7
F
2 2
2
6
2
Lifetime (ms)
Lifetime (ms)
Quantum efficiency (%)
Lifetime (ms)
g
1
s
1
g
1
g
2
s1
s
2
g
1
g
2
s
1
s2
1
4
6
8
1
00 °C
00 °C
00 °C
00 °C
25.38
35.75
43.15
62.32
55.83
1.46
1.25
1.31
1.98
2.20
2.28
19.20
42.79
31.44
45.40
0.13
0.38
0.49
0.27
1.57
1.12
1.30
1.39
1.60
1.80
8.93
22.58
51.39
5.41
36.59
25.29
0.14
0.49
1.05
1.55
0.19
2.80
1.39
12.36
11.18
7.28
000 °C
39.62
43.67
1.53

M.G. Matos et al. / Inorganica Chimica Acta 375 (2011) 63–69
69
In general, excitation within the f-manifold promotes high
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