Photoluminescence properties of BaMoO4 amorphous thin films

Article abstract of DOI:10.1016/j.jssc.2005.05.024

BaMoO₄ amorphous and crystalline thin films were prepared from polymeric precursors. The BaMoO₄ was deposited onto Si wafers by means of the spinning technique. The structure and optical properties of the resulting films were characterized by FTIR reflectance spectra, X-ray diffraction (XRD), atomic force microscopy (AFM) and optical reflectance. The bond Mo-O present in BaMoO₄ was confirmed by FTIR reflectance spectra. XRD characterization showed that thin films heat-treated at 600 and 200 °C presented the scheelite-type crystalline phase and amorphous, respectively. AFM analyses showed a considerable variation in surface morphology by comparing samples heat-treated at 200 and 600 °C. The reflectivity spectra showed two bands, positioned at 3.38 and 4.37 eV that were attributed to the excitonic state of Ba²⁺ and electronic transitions within MoO^2-₄, respectively. The optical band gaps of BaMoO₄ were 3.38 and 2.19 eV, for crystalline (600 °C/2 h) and amorphous (200 °C/8 h) films, respectively. The room-temperature luminescence spectra revealed an intense single-emission band in the visible region. The PL intensity of these materials was increased upon heat-treatment. The excellent optical properties observed for BaMoO₄ amorphous thin films suggested that this material is a highly promising candidate for photoluminescent applications.

Full text of DOI:10.1016/j.jssc.2005.05.024

ARTICLE IN PRESS
Journal of Solid State Chemistry 178 (2005) 2346–2353
www.elsevier.com/locate/jssc
Photoluminescence properties of BaMoO4 amorphous thin films
Ã
Ana Paula Azevedo Marquesa, , Dulce M.A. de Meloa, Elson Longob,
Carlos A. Paskocimasa, Paulo S. Pizanic, Edson R. Leiteb
a
´ ´ ´ ´
Laboratorio de Analise Termica e Materiais, Departamento de Quımica, Universidade Federal do Rio Grande do Norte, 59072-970, Natal, RN, Brazil
b
´ ´ ˆ ˆ
Laboratorio Interdisciplinar de Eletroquımica e Ceramica, Centro Multidisciplinar de Desenvolvimento de Materiais Ceramicos, Departamento de
´
Quımica, Universidade Federal de Sa˜o Carlos, C. Postal 676, 13565-905 Sa˜o Carlos, SP, Brazil
´ ´
Laboratorio de Semicondutores, Departamento de Fısica, Universidade Federal de Sa˜o Carlos, C. Postal 676, 13565-905 Sa˜o Carlos, SP, Brazil
c
Received 10 March 2005; received in revised form 14 May 2005; accepted 22 May 2005
Abstract
BaMoO4 amorphous and crystalline thin films were prepared from polymeric precursors. The BaMoO4 was deposited onto Si
wafers by means of the spinning technique. The structure and optical properties of the resulting films were characterized by FTIR
reflectance spectra, X-ray diffraction (XRD), atomic force microscopy (AFM) and optical reflectance. The bond Mo–O present in
BaMoO4 was confirmed by FTIR reflectance spectra. XRD characterization showed that thin films heat-treated at 600 and 200 1C
presented the scheelite-type crystalline phase and amorphous, respectively. AFM analyses showed a considerable variation in
surface morphology by comparing samples heat-treated at 200 and 600 1C. The reflectivity spectra showed two bands, positioned at
3.38 and 4.37 eV that were attributed to the excitonic state of Ba2+ and electronic transitions within MoO42ꢀ, respectively. The
optical band gaps of BaMoO4 were 3.38 and 2.19 eV, for crystalline (600 1C/2 h) and amorphous (200 1C/8 h) films, respectively. The
room-temperature luminescence spectra revealed an intense single-emission band in the visible region. The PL intensity of these
materials was increased upon heat-treatment. The excellent optical properties observed for BaMoO4 amorphous thin films suggested
that this material is a highly promising candidate for photoluminescent applications.
r 2005 Elsevier Inc. All rights reserved.
Keywords: BaMoO4; Photoluminescence; Thin films; Polymeric precursor method; Amorphous
1. Introduction
tional solid-state reaction [2–6]. Chang-Tai et al. [4],
showed that BaMoO4 thin films grown by an electro-
chemical method, consisted of an heterogeneous surface
and grains with sizes varying from 2 to 10 mm. Using the
polymeric precursor method, such drawbacks could be
minimized because of the immobilization of metal-
complexes in rigid organic polymeric networks. This
reduces the segregation of particular metals, thus
ensuring compositional homogeneity at a molecular
scale. Such a characteristic is essentially important for
the synthesis of multi-component oxides with compli-
cated compositions, since the chemical homogeneity
with respect to distribution of cations throughout the
entire gel system often determines the compositional
homogeneity of the final complex mixed oxides [7]. Cost-
efficient compounds with strong photoluminescence
Scheelite-type crystalline structures, such as BaMoO4,
where molybdenum atoms are arranged in tetrahedral
coordination [1,2] have recently attracted great attention
due to their approved usage as scintillating materials
and in electro-optical applications including solid-state
lasers and optical fibers [3]. In addition, numerous
investigations on their luminescent properties have been
carried out [2]. A variety of preparation techniques have
been proposed to produce these materials including
electrochemical methods, combustion synthesis, the
Chochralski technique, co-precipitation and conven-
Ã
Corresponding author.
E-mail address: apamarques@liec.ufscar.br (A.P.A. Marques).
0022-4596/$ - see front matter r 2005 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2005.05.024

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(PL) at room temperature are technologically interesting
materials for applications including solid-state optoelec-
tronic devices. Much interest has been evinced in the
study of PL in amorphous and nanostructured materials
since visible PL at room temperature was first observed
in porous silicon [8]. Several amorphous compounds
based on different metal oxianions with intense PL at
room temperature have been reported [9]. Nevertheless,
data are scarce on BaMoO4 thin films prepared by soft
chemical processing. Considering that the polymeric
precursor method has been successful in preparing oxide
thin films, this work reports on the preparation,
characterization and photoluminescent properties of
BaMoO4 thin films prepared from polymericprecursors.
barium and molybdenum cations was 1:1. The citric
acid/ethylene glycol mass ratio was set to 60:40. The
viscosity of the deposition solution was adjusted to
15 mPa/s by controlling the water content.
Si wafers were used as substrates. The substrates were
spin-coated by dropping a small amount of the
polymericprecursor solution onto them. Rotation speed
and spin time were fixed at 700 rpm for 3 s and 7200 rpm
for 30 s, using a commercial spinner (spin-coater KW-
4B, Chemat Technology). After spinning onto the
substrates, the films were heat-treated at 200 1C between
2 and 16 h or at 600 1C for 2 h in a resistive furnace
under air or, alternatively, at 600 1C for 10 min in a
microwave oven. A total of 4 layers were deposited. The
procedure was repeated for each layer.
BaMoO4 thin films were characterized by X-ray
diffraction (XRD) using CuKa radiation in order to
determine the structural evolution of the thin films upon
heat-treatment. The optical reflectance of the thin films
was measured in the wavelength range from 200 to
800 nm, using a UV-Vis-NIR (Cary 5G spectrophot-
ometer). FTIR reflectance spectra for BaMoO4 thin
films deposited on Si substrates were gathered in the
frequency range of 400–2100 cmꢀ1 at room temperature
using an Equinox/55 (Bruker) spectrometer equipped
with a 301 specular reflectance accessory. Atomic force
microscopy (AFM) was used to obtain a 3D image
reconstruction of the surface of the sample. These
images allow for accurate analysis and quantification of
highly relevant parameters such as roughness and grain
size. A Multi-Mode Nanoscope IIIa from Digital
Instruments was used.
Finally, PL spectra of BaMoO4 thin films were
collected with a U1000 Jobin-Yvon double monochro-
mator coupled to a cooled GaAs photomultiplier and a
conventional photon counting system. The 488.0 nm
exciting wavelengths of an argon ion laser was used. The
maximum output power of the laser was 20 mW. All
measurements were taken at room temperature.
2. Experimental procedure
BaMoO4 thin films were deposited onto Si substrates
by the polymericpreucrsor method. A flow-hcart
representing the synthesis of BaMoO4 used in this study
is outlined in Fig. 1. Molybdenum citrate was formed by
the dissolution of molibidicacid (MoO 3—molybdenum
trioxide) in an aqueous solution of citric acid under
constant stirring at 60–80 1C to homogenize the
molybdenum citrate solution. After homogenization of
this solution, barium carbonate was dissolved and a
stoichiometric amount added to the molybdenum citrate
solution. The complex was well stirred for several hours
at 60–80 1C to produce a clear, homogeneous solution.
After the solution was homogenized, ethylene glycol was
added to promote the citrate polymerization by poly-
esterification. With continued heating of 80–90 1C, the
viscosity of the solution increased, albeit devoid of any
visible phase separation. The molar ratio between
3. Results and discussion
Fig. 2 shows the FTIR absorption spectra of all
BaMoO4 thin films deposited in Si(100) and heat-treated
in a resistive furnace or in a microwave oven. Measure-
ments were carried out in the reflection mode. Next
Nakamoto [10] shows that the u(CO) stretching occurs
at 2375–1100 cmꢀ1 and the u(OCO) if stretching occurs
at 1100–550 cmꢀ1. In Fig. 2a and b is clear that
undecomposed organic ligands are still present in the
film, the spectra present several bands ascribing to
carbonates groups. Vibration of around 1755 cmꢀ1
associated to the C14O stretching mode for ester
(R–COO–R) could also be observed. The vibration
around of 1680 cmꢀ1 is attributed to the vibration
Fig. 1. Flow chart of the preparation of BaMoO4 thin films from
polymericprecursors.

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Fig. 2. FTIR absorption spectra of BaMoO4 thin films deposited in
Si(100) and heat-treated at 200 1C for 2 h (a), 4 h (b), 8 h (c) and 16 h
(d) in a resistive furnace and heat-treated at 600 1C in a microwave for
10 min (e) and in a resistive furnace for 2 h (f).
Fig. 3. X-ray diffraction patterns of BaMoO4 thin films deposited in
Si(100) and heat-treated at 200 1C for 2 h (a), 4 h (b), 8 h (c) and 16 h
(d) in a resistive furnace and heat-treated at 600 1C in a microwave for
10 min (e) and in a resistive furnace for 2 h (f).
asymmetricCOO. The bands of around 1540 and
1430 cmꢀ1 are attributed to the vibration symmetric
COO (Fig. 2a and b) [1]. The band at 2350 cmꢀ1 refers to
the CO2 atmosphericadsorbed. The spectra of Fig. 2c
and d do not present these bands referent to carbonates
groups, which prove that an treatment at 200 1C for 8 h
is sufficient to eliminate the organic components and
that the resulting phase is indeed a carbon-free inter-
mediate inorganicamorphous phase. The spectrum of
crystalline BaMoO4 thin films (heat-treated at 600 1C)
displays a very broad absorption band from 800 to
820 cmꢀ1 (Fig. 2e and f). This band is attributed to the
Mo–O bonds of a solid oxide network [10]. The
representation for the tetrahedral symmetry is
GTd ¼ A1ðn1Þ þ Eðn2Þ þ F2ðn3Þ þ F2ðn4Þ, but only the
F2ðn3; n4Þ modes are IR active. The F2ðn3Þ vibrations
are antisymmetricstrethces, whereas the F2ðn4Þ vibra-
tions are bending modes. Therefore, the bands at 809
and 820 cmꢀ1 were assigned to F2ðn3Þ antisymmetric
stretching vibrations of BaMoO4 thin films heat-treated
at 600 1C in a resistive furnace or microwave, respec-
tively. These bands have been reported to correspond to
the Mo–O stretching vibration in the MoO24ꢀ tetrahe-
dron [10].
Fig. 3 shows X-ray patterns of BaMoO4 thin films
deposited onto Si substrates after heat-treatment at 200
and 600 1C for different times. They correspond to the
crystalline BaMoO4 scheelite-type phase. In Fig. 3a–d,
BaMoO4 thin films heat-treated at 200 1C between 2 and
16 h were amorphous and no crystallized phases were
observed. The diffraction peak (112) is the 100% peak, it
is absent in Fig. 3a–d, indicating that these films were
amorphous. Above 600 1C (Fig. 3e and f), the thin films
consisted uniquely of BaMoO4 phases, confirming
results published elsewhere [2,11]. The intensity of
substrate peak changes according to thin film thickness:
thin films with bigger thickness present minor substrate
peak than thin films with smaller thickness. All
diffraction peaks were indexed with the JCPDS data-
base [12] and indicated the tetragonal symmetry. From
the peak positions displayed in Fig. 3, the lattice
parameters were calculated using a least-square refine-
ment REDE93 program. The lattice parameters a and c
for these BaMoO4 thin films were found to be as a ¼
(
(
5:582ð2Þ A and c ¼ 12:775ð8Þ A for the thin film heat-
(
treated in a furnace and a ¼ 5:581ð2Þ A and c ¼
(
12:805ð13Þ A heat-treated in microwave. These values
are in good agreement with those corresponding to the
(
structure of the bulk material (a ¼ 5:5802 A and
(
c ¼ 12:821 A) [12].
Fig. 4 shows the transversal cross-section micrographs
of the BaMoO4 thin film on Si substrate by SEM. The
BaMoO4 thin films treated at 200 1C for 2, 4, 8 and 16 h
have thicknesses of about 164, 308, 105 and 146 nm,
respectively, and for thin films treated at 600 1C for 2 h
in a furnace and 10 min in a microwave have of about
484 and 164, respectively, measured by transversal
cross-section by SEM.
A detailed AFM analysis revealed differences in terms
of surface morphology for BaMoO4 thin films heat-
treated at 200 1C and 600 1C (Fig. 5). The AFM analysis
showed a considerable variation in the surface morphol-
ogy between samples submitted to heat-treatment at 200
and 600 1C. It was clear from AFM analyses that the
BaMoO4 thin films heat-treated at 200 1C showed
homogeneous surface morphology with very low rough-
ness (2.2 nm). There was no evidence of granular

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2349
structure. Conversely, the surface morphology signifi-
cantly changed upon heat-treatment at 600 1C. At this
stage, nuclei coalescence took place accompanied by the
formation of a granular structure thus increasing the
roughness of the film (213.5 nm). This result was in good
agreement with XRD data, which revealed significant
crystallization after heat-treatment at 600 1C. The AFM
analysis also showed that the BaMoO4 thin films heat-
treated at 600 1C presented homogeneous nucleation
resulting in grain sizes between 280 and 320 nm.
Reflectivity spectra recorded in the 2.0–6.0 eV range
for BaMoO4 thin films are presented in Fig. 6. Two
bands at 3.38 (367 nm) and 4.37 eV (284 nm) were
observed for BaMoO4 thin film crystalline treated at
600 1C. The band at 4.37 eV was attributed to electronic
transitions within the MoO24ꢀ complex according to
Spassky [13]. The band at 4.25 eV (292 nm) was
attributed to electronic transitions within the MoO42ꢀ
Fig. 4. SEM micrograph of BaMoO4 thin films heat-treated at 200 1C
for 4 h (a), heat-treated at 600 1C in a microwave for 10 min (b) and in
a resistive furnace for 2 h (c), where S ¼ substrate and T ¼ thickness.
Fig. 5. AFM 2D images for the surfaces of BaMoO4 thin films heat-treatment at 200 1C for 8 h (a), at 600 1C for 10 min in a microwave (b) and AFM
3D image of BaMoO4 thin films at 600 1C in a microwave (c).

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Fig. 7. Reflectivity spectra recorded in the 2.0–6.0 eV range of
BaMoO4 thin films heat-treated at 200 1C for 8 h (K) and 600 1C for
2 h in a resistive furnace (K) and plots of (ahn)2 vs. photon energy hn
The band gap energy (Eg) is deduced from extrapolation of the straight
Fig. 6. Reflectivity spectra recorded in the 2.0–6.0 eV range of
BaMoO4 thin films heat-treated at 200 1C for 2 h (a), 4 h (b), 8 h (c)
and 16 h (d) in a resistive furnace and heat-treated at 600 1C in a
microwave for 10 min (e) and in resistive furnace for 2 h (f).
2
line up to ðahnÞ ¼ 0.
Table 1
Eg data of BaMoO4 thin films
Samples
Eg (eV)
complex without noticeable contribution from cationic
states by Spassky et al. [13]. A peak at 3.6 eV was
observed in the PbMoO4 but no in the CaMoO4 and the
BaMoO4. Kolobanov [14] observed similar situation for
lead tungstate where at the edge of the fundamental
absorption region reflectivity peak was observed that
has no analogues in calcium and barium tungstates
reflectivity spectra. Spassky et al. [13] showed that the
dependence on sample orientation and comparison with
excitons in lead halides was noticed after a study on the
shift that peak as a function of the temperature. They
were supposed that the peak at 3.6 eV in PbMoO4 is also
due to the creation of excitonic state in Pb2+. Therefore,
although Spassky has not observed this peak in
BaMoO4 and the excitonic state between Pb2+ and
Ba2+were different, it is reasonable to assume that the
peak observed at 3.38 eV in BaMoO4 can also corre-
BaMoO4—200 1C/2 h
BaMoO4—200 1C/4 h
BaMoO4—200 1C/8 h
BaMoO4—200 1C/16 h
BaMoO4—600 1C/2 h (furnace)
BaMoO4—600 1C/10 min (microwave)
4.77
4.73
4.22
4.82
4.88
5.11
[18] show the a values major at 104, confirm the
existence of direct band gaps. One similarity between
CaMoO4 and BaMoO4; therefore, the same comport-
ment is expected for both compounds. Zhang et al. [17]
also showed that the valence and conduction bands near
the band gap are dominated by molecular orbitals
associated with the MoOꢀ4 ions, where a ꢂ 2. The value
a
spond to the creation of the excitonic state on Ba2+
.
for CaMoO4 of band gap calculated for Zhang et al. [17]
were underestimated and the value was 3.41 eV. In this
work the calculated Eg values for BaMoO4 starting from
experimental dates were 4.22 and 5.11 eV for amorphous
and crystalline films, respectively. In spite of differences
in these values calculated experimentally and theoreti-
cally, this value obtained experimentally is acceptable
because the value theoretically is one value under-
estimated [17]. The gap value for CaWO4 obtained
experimentally was 5.27 eV [7] and by calculated
theoretically was 4.09 eV [17], showing that the differ-
ence between the value obtained by plotting (ahn)2 as a
function of (hn2Eg) starting from the experimental
dates and the value theoretical using the linearized-
augment-plane-wave method is acceptable. The band
One large band around 4.8 eV (258 nm) was observed for
BaMoO4 thin film amorphous treated at 200 1C for 2
and 4 h (Fig. 6a and b). This peak around 4.8 eV was
attributed to organicligands undecomposed present in
the film [15].
The band gap (Eg) was estimated by plotting (ahn)2 as
a function of (hn2Eg), as it can be seen in Fig. 7. The
optical absorption coefficient, a may be obtained by
a ¼ ½1=dðln ð1=TÞꢁ, where d is the thickness of the film
and T the transmittance [16]. Zhang et al. [17] calculate
the density-functional for CaMoO4 using the linearized-
augment-plane-wave method and the results indicate
that CaMoO4 have direct band gaps. The a value
obtained for BaMoO4 was major at 104, and Sian et al.

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Fig. 8. Room-temperature PL spectra of BaMoO4 thin films excited with the 488 nm line of an argon ion laser: I—heat-treated at 200 1C for 2 h (a),
II—heat-treated at 200 1C for 4 h (b), III—heat-treated at 200 1C for 8 h (c), IV- heat-treated at 200 1C for 16 h (d), V—heat-treated at 600 1C in a
microwave for 10 min (e) and in a resistive furnace for 2 h (f) and VI—PL spectra of all BaMoO4 thin films.

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Table 2
Evolution of the PL red fraction with the structural disorder
gap decreases in the amorphous material with relation
of the crystalline because the amorphous materials have
the crystal orbital not degenerated due which there has
been a loss of symmetry that is crystalline. In the crystal
orbital of the amorphous material were formed news
levels of energy, and this news levels were responsible for
the band gap change. The cause of band gap change will
be studied more deeply in a new paper that is being
prepared. Fig. 7 showed for the BaMoO4 thin film
crystalline two bands around of 3.4 and 4.4 eV, this
band are the same presented for this material in the
reflectivity spectra. The Eg data of the BaMoO4 thin
films are given in Table 1.
Samples
Peak 1 (eV)
Peak 2 (eV)
RA/FA
BaMoO4—200 1C/2 h
BaMoO4—200 1C/4 h
BaMoO4—200 1C/8 h
BaMoO4—200 1C/16 h
2.06
2.07
2.05
1.96
2.31
2.31
2.28
2.14
0.75
0.76
0.79
0.66
RA, FA are areas of the red decomposed band and fitted band,
respectively.
Fig. 8 illustrates PL spectra recorded at room
temperature for BaMoO4 thin films heat-treated at 200
or 600 1C for different periods of time. The samples were
excited by the 488 nm line of an argon ion laser. The
band emission wavelength of BaMoO4 thin films was
around 2.13 eV. The bands were broad and intense,
mostly for the amorphous thin film heat-treated at
200 1C for 8 h (Fig. 8c). The intensity of the PL emission
significantly increased (about 660 times) comparing the
film heat-treated at 200 1C for 8 h with that heat-treated
at 600 1C. The PL emission of BaMoO4 crystalline thin
films heat-treated in a resistive furnace or microwave
oven was virtually null comparing to that of amorphous
films heat-treated at 200 1C/8 h (Fig. 8c). The PL
intensity of the thin film heat-treated at 200 1C for 8 h
was 1.4, 2.2 and 93.5 times higher comparing to the
intensity of films heat-treated at 200 1C for 4, 2 and 16 h,
respectively. The PL intensity is linked to the thermal
treatment history of the films, and therefore, to their
structural disorder. The best PL emission was obtained
from the structure that was neither completely amor-
phous (200 1C/2 h) nor fully ordered (600 1C). Although
crystalline samples are not photoluminescent under
excitation by the 488 nm line of an argon ion laser used
in this study, similar compounds exhibit luminescence
with different light sources [13].
Orhan et al. [19] showed that the emission bands from
SrWO4 can be decomposed into two components, two
broadbands. In this case, molybdenum is similar to
tungsten, therefore yours emission bands also are
decomposed in two components with their maxima
around 2.07 eV (600 nm) (orange-red), peak 1, and
2.34 eV (530 nm) (green), peak 2, as illustrated on Fig.
8 I–IV. The orange-red band represents 75%, 76%, 79%
and 66% of the total PL band area for the thin films
heat-treated at 200 1C for 2, 4, 8 and 16 h, respectively
(see Table 2). This decomposition of the broad PL
emission band indicates that with the degree of
structural disorder, the fraction of the red emission
band increases. The thin film treated at 200 1C/8 h
possesses the biggest red area because it is a transition
between completely amorphous structures and comple-
tely ordered one, similar to SrWO4 showed for Orhan
[19]. The components of the PL emission bands are
probably linked to specific atomic arrangements. Similar
to SrWO4, as studied by Orhan [19], the structural
transformations of the BaMoO4 occurring from dis-
ordered to ordered phases start from the early stage of
the polyesterification of the citrate solution contain the
molybdenum and barium ions. The molybdenum, who
is the lattice former, tends ideally to bond with four
oxygens, but before it reaches this ideal configuration
there exist various coordination numbers for Mo in the
structure. When the crystallization is reached, only
MoO4 clusters exist and the PL vanishes, showing that a
complete order is not suitable for a good PL emission.
Before the crystallization, the structure is a mixture of
MoOx clusters (x ¼ mostly 3 and 4) intercalated by Ba
atoms. The higher the heat treatment temperature, the
more frequent the MoO4 conformation and the more
ordered the structure, confirmed by FTIR and reflectiv-
ity spectra. The PL spectra show that a complete
disorder is not favorable for a high PL emission, as the
spectrum of the 200 1C/8 h sample is much higher than
one of the 200 1C/2 h sample.
According to Pontes et al. [20], if the photolumines-
cent signal is related to the amorphous structure, as the
system is organized, the signal fades away as confirmed
by Fig. 8d. This conclusion is a good indication that the
PL of BaMoO4 thin films obtained by the polymeric
precursor method originates from inorganic amorphous
phases with photoluminescent properties.
4. Conclusions
Intense visible PL at room temperature was observed
in highly amorphous BaMoO4 thin films prepared by
the polymericpreucrsor method and heat-treated at
relatively low temperatures (200 1C/8 h). Processing thin
films in such a manner does not require expensive
equipment or reagents, deposition in high vacuum
chambers or special atmospheric control. The results
revealed that BaMoO4 is a highly promising candidate
material for PL applications.

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2353
Acknowledgments
[9] E.R. Leite, F.M. Pontes, E.J.H. Lee, R. Aguiar, E. Longo, D.S.L.
Pontes, M.S.J. Nunes, P.S. Pizani, F. Lanciotti Jr., et al., J. Mol.
Struct.-THEOCHEM 668 (2–3) (2004) 87.
The authors gratefully acknowledge the financial
support granted by the Brazilian Research Financing
Institutions FAPERN, CEPID, CNPq and PRONEX.
The authors gratefully acknowledge the Miryam R.
Joya, of Departamento de Fisica—Universidade Feder-
al de Sao Carlos for the collaboration in the article
accomplishing the measures of PL.
[10] K. Nakamoto, Infrared and Raman Spectra of Inorganic
and Coordination Compounds, fourth ed, Wiley, New York,
1986.
[11] V. Thangadurai, C. Knittlmayer, W. Weppner, Mater. Sci. Eng.
B-Solid 106 (2004) 228.
[12] JCPDS No. 29-0193.
[13] D.A. Spassky, S.N. Ivanov, V.N. Kolobanov, V.V. Mikhailin,
V.N. Zemskov, B.I. Zadneprovski, L.I. Potkin, Radiat. Meas. 38
(2004) 607.
[14] V.N. Kolobanov, I.A. Kamenskikh, V.V. Mikhailin, I.N.
Shpinkov, D.A. Spassky, B.I. Zadneprovsky, L.I. Potkin, G.
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