Thermal decomposition of lanthanide(III) complexes with 4,4,4-trifluoro-1-phenyl-1,3-butanedione : PPPPPPPPPPPPPhotoluminescent properties and kinetic study

Article abstract of DOI:10.1007/s10973-006-7502-9

The complexes of general formula Ln(btfa)₃L, where Ln=Eu or Tb, btfa=4,4,4-trifluoro-1-phenyl-1,3-butanedione, L=1,10-phenanthroline (phen) or 2,2-bipyridine (bipy), were synthesized by reacting the corresponding metal chloride with the proper β-diketone and the other ligand. The complexes were obtained in the powder form and were characterized by photoluminescence and TG. Their thermal decomposition was studied by non-isothermal thermogravimetric techniques. The Eu(btfa)₃bipy complex presented the highest thermal stability and it melts before being decomposed. The complex Eu(btfa) ₃phen presented the largest activation energy for a heating rate of 5°C min^-1. Springer-Verlag 2007.

Full text of DOI:10.1007/s10973-006-7502-9

Journal of Thermal Analysis and Calorimetry, Vol. 87 (2007) 3, 887–891
THERMAL DECOMPOSITION OF LANTHANIDE(III) COMPLEXES
WITH 4,4,4-TRIFLUORO-1-PHENYL-1,3-BUTANEDIONE
Photoluminescent properties and kinetic study
Crislene R. S. Morais1*, C. G. Gameiro2, P. A. Santa-Cruz2, S. Alves Jr.2, L. E. B. Soledade3
and A. G. Souza3
1Departamento de Engenharia de Materiais, CCT, Universidade Federal de Campina Grande, Campina Grande, PB
CEP 58.109-970, Brazil
2Departamento de Química Fundamental, CCEN, Universidade Federal de Pernambuco, Cidade Universitária, Recife, PE
CEP 50.670-901, Brazil
3Departamento de Química, CCEN, Universidade Federal da Paraíba, , Jo±o Pessoa, PB, CEP 58.059-900, Brazil
The complexes of general formula Ln(btfa)3L, where Ln=Eu or Tb, btfa=4,4,4-trifluoro-1-phenyl-1,3-butanedione, L=1,10-phenan-
throline (phen) or 2,2-bipyridine (bipy), were synthesized by reacting the corresponding metal chloride with the proper β-diketone
and the other ligand. The complexes were obtained in the powder form and were characterized by photoluminescence and TG. Their
thermal decomposition was studied by non-isothermal thermogravimetric techniques. The Eu(btfa)3bipy complex presented the
highest thermal stability and it melts before being decomposed. The complex Eu(btfa)3phen presented the largest activation energy
for a heating rate of 5°C min–1.
Keywords: lanthanide, photoluminescence, thermal decomposition kinetics
Introduction
submitted to such thermoevaporation process without
any significant thermodecomposition. Therefore, a
kinetic and thermodynamic study is necessary in
order to predict whether the complex is stable enough
to be successfully heated and thermoevaporated.
Several properties of these complexes have been
studied, such as synthesis, luminescence, quantum
yields, spectroscopic characteristics and structure,
including also the production of thin films, but not
much is known about their thermal decomposition
kinetics [6, 9, 10].
There has been a large research activity on coordina-
tion compounds of the lanthanide ions with organic
ligands including β-diketones, which can act as excel-
lent light conversion molecular device (LCMD) [1–5].
However, several aspects are to be considered [6–8], in
order to obtain a highly luminescent complex: (i) molar
absorbance of the ligands, (ii) energy transfer from the
ligands to the metal, (iii) photoluminescence of the
metal ion and (iv) non-radioactive decay processes due
to OH and CH oscillators.
In the present work, it is proposed to study the
photoluminescent properties and the thermal decompo-
sition kinetics, using non-isothermal heating meth-
ods [7, 8, 11] of Ln(btfa)3L, in which Ln stands for
Eu3+ or Tb3+, btfa stands for 4,4,4-trifluoro-1-phenyl-
1,3-butanedione and L stands for phen and bipy.
The use of these compounds ranges from radia-
tion sensors to a variety of photonic and integrated op-
toelectronic devices [4], as well as probes in bio-
inorganic systems [5, 9, 10] and luminescent labels in
fluoroimmunoassays [5, 9]. In addition, these materials
may also be applied in the development of ultraviolet
dosimetry technology. An ultraviolet dosimeter, highly
sensitive and selective to UV cumulative measure-
ments, was developed from thin films of these com-
plexes [11]. These thin films were prepared by a
thermoevaporation process, in which the powder com-
plex was heated under high vacuum, volatilized and
deposited on a substrate.
Experimental
Starting materials
The starting materials used to synthesize the com-
plexes were high purity Eu2O3 (99%) and
Tb2O3 (99%), btfa (99%), phen (99%) and bipy (99%)
supplied by Aldrich Chemical Co. Here, btfa stands
for 4,4,4-trifluoro-1-phenyl-1,3-butanedione, phen
Nevertheless, in order to obtain high quality thin
films for such application, these compounds must be
*
Author for correspondence: crislene@dema.ufcg.edu.br
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2007 Akadémiai Kiadó, Budapest

MORAIS et al.
stands for 1,10-phenanthroline and bipy stands for
danan (MD) [13], and the approximation methods
proposed by Horowitz–Metzger (HM) [14] and
Van Krevelen (VK) [15].
2,2-bipyridine. The complexes Eu(btfa)3L and
Tb(btfa)3L were synthesized by reacting the corre-
sponding metal chlorides with the β-diketone and the
other ligands as reported [6].
The kinetic parameters in the dynamic heating
method were determined according to the Coats–Red-
fern [12] equation, using the thermal decomposition
model that better fits the data obtained in the
isothermal experiments.
The complexes were synthesized in the form of
powder and were placed inside an alumina crucible,
placed inside the deposition chamber. The thin films
were later deposited over a boron silicate glass target,
previously cleaned and degreased to assure proper
film adhesion, by thermo-evaporation. For the mixed
complex thin film presented in Fig. 1, the two
compounds (Tb(btfa)3phen and Eu(btfa)3bipy) were
vigorously blended in order to obtain homogeneity,
and they were later thermally co-evaporated.
Results and discussion
Luminescence results
Figure 1 illustrates the emission spectrum of a 600 
thick-mixed 5:95 Eu(btfa)3bipy/Tb(btfa)3phen thin
film under 315 nm excitation. This spectrum presents
sharp and narrow lines and also the overlapping of the
transitions corresponding to the emissions associated
to the Eu(III) and Tb(III) ions mixed in the film. The
two main transitions 5D0→7F2 for Eu(III) and
5D4→7F5 for Tb(III) are highlighted in the figure. As
can be noticed, these are two very sharp and high
intensity peaks, allowing promising applications in
optical devices.
The films were photolitographically defined to
form a rectangular structure of about 1 cm2. The
depositions were monitored in real time by a 6 MHz
quartz crystal thickness-meter model STM-100/MF
from Sycon Instruments, which measures the film
thickness by the shift of frequency of the quartz
oscillator. Ellipsometric measurements, with a model
Rudolph Research AutoEL-IV ellipsometer, were
also performed at several wavelengths to assure film
high quality and uniformity.
Methods
Thermal measurements
The thermogravimetric curves were obtained using a
Shimadzu model TGA-50 thermobalance with an
alumina crucible, and with heating rates of 5, 10, 15
and 20°C min–1 at a temperature range of 25–900°C
and under a nitrogen atmosphere with a flow rate
of 50 mL min–1. The sample mass was 2.0 0.5 mg.
TG curves were analyzed with the aid of the TASYS
software from Shimadzu.
Fig. 1 Emission spectrum of a 600  thick-mixed
5:95 Eu(btfa)3bipy/Tb(btfa)3phen 60 nm thick thin film
under 315 nm excitation
Photoluminescence
The photoluminescence spectra were obtained at
room temperature using a double Jobin-Yvon
Ramanor U-1000 monochromator, coupled to a
RCAC31034-RF photomultiplier tube. The excitation
source was a 150 W Xe–Hg lamp emitting at 315 nm
with a Corning 7-54 filter. The photoluminescence
spectra were obtained with the aid of a Spectralink
interface connected to a microcomputer.
Thermal behavior
Figures 2a and b show the overlapping of the thermo-
gravimetric curves for the complexes Eu(btfa)3bipy
and Tb(btfa)3phen, at different heating rates. The
profile of these TG curves indicates that the different
decomposition steps correspond to thermal decompo-
sition reactions of the complexes. The thermal de-
composition curves of the complexes Eu(btfa)3bipy,
Eu(btfa)3phen, Tb(btfa)3bipy and Tb(btfa)3phen
displayed three, four, five and six decomposition
steps, respectively (Fig. 3).
Other measurements
The kinetic parameters, activation energy, reaction
order and frequency factor were obtained from the
thermogravimetric data by the integral methods pro-
posed by Coats–Redfern (CR) [12] and Madhusu-
The characteristic temperatures and mass losses
of these reactions are listed in Table 1. In order to
888
J. Therm. Anal. Cal., 87, 2007

LANTHANIDE(III) COMPLEXES WITH 4,4,4-TRIFLUORO-1-PHENYL-1,3-BUTANEDIONE
Fig. 2 TG curves of the complexes, at different heating rates; a – Eu(btfa)3bipy and b – Tb(btfa)3phen
analyze these effects, one should consider all thermal
decomposition steps, which possibly refer to the loss
of the β-diketone ligands. According to the results
presented, the following order of thermal stabilities
can be suggested:
Eu(btfa)3bipy>Tb(btfa)3bipy>
Eu(btfa)3phen>Tb(btfa)3phen
Kinetic studies of the non-isothermal decompositions
A kinetic study was undertaken for the thermal
decomposition reactions of complexes. This study
correlates the thermogravimetric profiles and the
heating rate, taking into account only the values of the
decomposed fraction (α) from 0.10 to 0.90.
Fig. 3 TG curve of the Ln(btfa)3L complexes obtained using a
heating rate of 10°C min–1
The kinetic parameters in the dynamic heating
method were determined according to the Coats–Red-
Table 1 Thermal decomposition data for the Ln(btfa)3L complexes heated at 10°C min–1
Mass loss/%
Decomposition
step
Temperature
range/°C
Complex
Lost species
experimental
theoretical
first
24–74
5.5
48.0
9.5
5.5
48.5
10.5
4.0
1/3 phen
2/3 phen+1 4/7 btfa
3/7 btfa
second
third
fourth
fifth
210–384
384–457
497–577
718–823
823–910
Tb(btfa)3phen
4.0
1/5 btfa
6.0
6.0
1/5 btfa+1/10 btfa
1/5 btfa
sixth
5.0
6.5
first
27–70
2.5
43.5
17.5
2.5
2.5
44.5
17.0
2.5
1/6 bipy
5/6 bipy+1 1/3 btfa
2/3 btfa+1/8 btfa
1/8 btfa
second
third
169–383
383–503
503–578
657–904
Tb(btfa)3bipy
fourth
fifth
11.5
12.0
4/8 btfa
first
25–88
9.0
53.5
4.0
9.0
53.0
4.0
1/2 phen
1/2 phen+2 btfa
2/10 btfa
second
third
216–460
460–684
715–899
Eu(btfa)3phen
Eu(btfa)3bipy
fourth
9.0
9.0
4/10 btfa
first
158–358
358–583
697–941
40.0
24.5
27.5
39.5
24.5
27.5
1 bipy+1 btfa
1 btfa+1/12 btfa
9/12 btfa
second
third
J. Therm. Anal. Cal., 87, 2007
889

MORAIS et al.
Table 2 Kinetic parameters of the first and second decomposition steps of the lanthanide complexes calculated from the
dynamic thermogravimetric data at 10°C min–1 heating rate
Methods
Decomposition
Parameter
step
CR
MD
HM
VK
Eu(btfa)3bipy
Eu(btfa)3phen
Tb(btfa)3bipy
Tb(btfa)3phen
Ea/kJ mol–1
A/s–1
62
1.2⋅103
62
1.2⋅103
87
3.2⋅105
73
5.1⋅109
First
n
0.40
0.36
0.69
0.52
Ea/kJ mol–1
A/s–1
112
1.6⋅105
0.54
112
1.9⋅105
0.54
142
3.2⋅107
0.77
126
1.0⋅1012
0.64
Second
n
Ea/kJ mol–1
A/s–1
129
1.0⋅109
1.93
124
4.2⋅108
1.83
156
3.2⋅1011
2.30
140
4.0⋅1015
2.04
First
n
Ea/kJ mol–1
A/s–1
121
1.1⋅105
0.86
120
1.1⋅105
0.82
160
3.7⋅107
1.18
138
1.1⋅1012
1.00
Second
n
Ea/kJ mol–1
A/s–1
111
2.3⋅107
0.69
111
2.9⋅107
0.70
132
3.0⋅109
0.86
117
3.6⋅1013
0.74
First
n
Ea/kJ mol–1
A/s–1
243
1.5⋅1015
1.13
241
1.1⋅1015
1.11
277
4.8⋅1017
1.30
265
3.1⋅1013
1.22
Second
n
Ea/kJ mol–1
A/s–1
107
2.8⋅106
0.57
104
1.9⋅106
0.51
127
1.9⋅108
0.67
115
6.9⋅1012
0.63
First
n
Ea/kJ mol–1
A/s–1
156
3.3⋅107
0.26
168
2.5⋅108
0.44
189
5.7⋅109
0.42
174
3.6⋅1014
0.35
Second
n
fern [12] equation, using the thermal decomposition
model suggested by the data obtained in the isothermal
experiments.
Therefore, the comparison of these values of
activation energy suggests the following decreasing
order of thermal stability for the first steps:
The evaluation of the kinetic parameters:
reaction order (n), apparent activation energy (Ea) and
frequency factor (A) for the first and second steps,
which are considered as the most significant steps, are
listed for each complex in Table 2. The apparent
activation energy for the Horowitz–Metzger (HM)
and Van Krevelen (VK) approximation methods are
higher than those for the Coats–Redfern (CR) and
Madhusudanan (MD) integral methods.
Eu(btfa)3phen>Tb(btfa)3phen>
Tb(btfa)3bipy> Eu(btfa)3bipy
The kinetic models that best described the
thermal decomposition reaction for the Ln(btfa)3L
complexes were F1 and R2 (Table 3).
The F1 model indicates that the mechanism is con-
trolled by reaction order and is defined by the function
g(α)= –ln(1–α), indicating a first order reaction. The R1
Table 3 Kinetic parameters determined using dynamic thermogravimetric method of Coats–Redfern’s equation for φ=10°C min–1
Complex
Decomposition
Parameter
step
Tb(btfa)3phen
Tb(btfa)3bipy
Eu(btfa)3phen
Eu(btfa)3bipy
Ea/kJ mol–1
A/s–1
103
7.5⋅106
0.999
R2
127
9.4⋅108
0.996
F1
98
1.2⋅106
0.984
F1
65
1.1⋅103
0.999
R2
First
r
model
Ea/kJ mol–1
A/s–1
172
2.1⋅109
0.999
R2
229
1.3⋅1014
0.999
F1
131
5.4⋅105
0.999
F1
140
2.2⋅107
0.998
F1
Second
r
model
890
J. Therm. Anal. Cal., 87, 2007

LANTHANIDE(III) COMPLEXES WITH 4,4,4-TRIFLUORO-1-PHENYL-1,3-BUTANEDIONE
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by the function g(α)=2[1–(1–α)1/2], corresponding to a
one half reaction order [16].
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Received: January 10, 2006
Accepted: July 21, 2006
DOI: 10.1007/s10973-006-7502-9
Acknowledgements
The authors acknowledge CAPES and CNPQ for scholarship
and financial support of this work.
J. Therm. Anal. Cal., 87, 2007
891