Luminescent properties under X-ray excitation of Ba(1?x)PbxWO4 disordered solid solution

Article abstract of DOI:10.1016/j.jssc.2017.10.014

A series of polycrystalline barium-lead tungstate Ba1-xPbxWO₄ with 0 ≤ x ≤ 1 was synthesized using a classical solid-state method with thermal treatment at 1000 °C. These materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Raman (FT-Raman) spectroscopy. X-ray diffraction profile analyses were performed using Rietveld method. These materials crystallized in the scheelite tetragonal structure and behaved as quasi ideal solid solution. Raman spectroscopy confirmed the formation of the solid solution. Structural distortions were evidenced in X-ray diffraction profiles and in vibration Raman spectra. The scanning electron microscopy experiments showed large and rounded irregular grains. Luminescence experiments were performed under X-ray excitation. The luminescence emission profiles have been interpreted in terms of four Gaussian components, with a major contribution of blue emission. The integrated intensity of luminescence reached a maximum value in the composition range x = 0.3–0.6, in relation with distortions of crystal lattice.

Full text of DOI:10.1016/j.jssc.2017.10.014

Author’s Accepted Manuscript
Luminescent properties under X-ray excitation of
Ba Pb WO disordered solid solution
(1-x) x
4
B. Bakiz, A. Hallaoui, A. Taoufyq, A.
Benlhachemi, F. Guinneton, S. Villain, M. Ezahri,
J.-C. Valmalette, M. Arab, J.-R. Gavarri
www.elsevier.com/locate/yjssc
PII:
S0022-4596(17)30422-X
https://doi.org/10.1016/j.jssc.2017.10.014
YJSSC19976
DOI:
Reference:
To appear in: Journal of Solid State Chemistry
Received date: 15 July 2017
Revised date: 7 October 2017
Accepted date: 9 October 2017
Cite this article as: B. Bakiz, A. Hallaoui, A. Taoufyq, A. Benlhachemi, F.
Guinneton, S. Villain, M. Ezahri, J.-C. Valmalette, M. Arab and J.-R. Gavarri,
Luminescent properties under X-ray excitation of Ba Pb WO disordered
(1-x) x
4
solid
solution, Journal
of
Solid
State
Chemistry,
https://doi.org/10.1016/j.jssc.2017.10.014
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Luminescent properties under X-ray excitation
of Ba Pb WO disordered solid solution.
(
1-x)
x
4
B. Bakiz (a) (*), A. Hallaoui , A. Taoufyq , A. Benlhachemi , F. Guinneton (b), S.
(a)
(a)
(a)
Villain (b), M. Ezahri , J-C. Valmalette , M. Arab , J-R Gavarri
(a)
(b)
(b)
(b)
(a)
LME, Faculty of Sciences, University Ibn Zohr, 80000 Agadir, Morocco
(
b)
IM2NP, UMR CNRS 7334, University of Toulon, BP20132, 83957 La Garde- France
(
*)
To whom correspondence must be addressed: bakiz.lahcen@hotmail.fr
Abstract
A series of polycrystalline barium-lead tungstate Ba1-xPbxWO
4
with 0≤x≤1 was synthesized
using a classical solid-state method with thermal treatment at 1000°C. These materials were
characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier
Transform Raman (FT-Raman) spectroscopy. X-ray diffraction profile analyses were
performed using Rietveld method. These materials crystallized in the scheelite tetragonal
structure and behaved as quasi ideal solid solution. Raman spectroscopy confirmed the
formation of the solid solution. Structural distortions were evidenced in X-ray diffraction
profiles and in vibration Raman spectra. The scanning electron microscopy experiments
showed large and rounded irregular grains. Luminescence experiments were performed under
X-ray excitation. The luminescence emission profiles have been interpreted in terms of four
Gaussian components, with a major contribution of blue emission. The integrated intensity of
luminescence reached a maximum value in the composition range x = 0.3 to 0.6, in relation
with distortions of crystal lattice.
Key-words: Barium-Lead tungstate, solid solution, X-ray diffraction, Rietveld analysis,
Raman spectroscopy, luminescence.

1. Introduction
The general aim of the present work is to study and correlate structural, vibrational and
luminescence properties in the case of a solid solution based on barium and lead tungstate
phases. In fact, this study is developed within the general framework of the research of
photosensitive materials (photoluminescent or photocatalytic) that can be integrated into
radiation detection devices, or to act as photocatalysts for the conversion of pollutants into
aqueous media. In these studies, we seek to correlate properties and chemical substitution
through new series of solid solutions. In the past few years, tungstate materials have attracted
a great deal of interest, due to their broad potential to industrial application and, especially, in
the development of low cost light emitting diodes [1, 2], new optical fibers [3, 4], oxide ion
conductors [5], humidity sensors and catalysis devices [6-7]. In addition, these compounds
can be envisaged as pure or doped photocatalysts [2].
The tungstates of general formula MWO are well known for their significant luminescence
4
2
+
properties under UV or X-ray excitations. Depending on the ionic radii of M cations, they
can crystallize in two main forms: monoclinic wolframite or tetragonal scheelite-type
structures. The origin of luminescence under UV, or under X-ray excitation, was extensively
described and discussed by various authors [1, 8-13]: the main emission was generally
ascribed to charge transfer in the WO 2-
or WO
6-
oxyanions. However, some additional
4
6
emission components were also observed in relation with point defects in the crystal lattices.
It should be noted, however, that the interpretations concerning this luminescence, proposed
in the literature, remain multiple, and sometimes contradictory: the exact role of structural
defects was never clearly solved, probably because of the complexity of these systems.
One of the main objectives of our works on solid solutions would be to increase the intensity
of luminescence intensity, improving thus the sensitivity of detection in the case of sensor
applications. The presence of two cations having different sizes in a solid solution could
induce strong modifications in crystal cell parameters, strong local distortions due to the two
different Ba-O-W and Pb-O-W links, statistically distributed in the lattice. These distortions
could involve perturbations in charge transfers characteristic of the [WO4] groups, significant
modifications in electronic structures, thus in luminescent emissions. The different chemical
bonds (Ba-O, Pb-O) would also modify the crystal growth kinetics and the level of structural
defects which could be at the origin of additional luminescence centers. Within this general
framework of the properties of solid solutions, studies have already shown that, in the case of
the system Ca1-xSr
x
WO [13], synthesized by a soft chemical method and heat treated between
4

4
00 and 700 °C, the luminescence intensity resulting from UV excitation could reach a
maximum value for a strontium composition close to x= 0.4: the authors ascribed this effect to
the nature of the structural disorder induced by the thermal treatments, and to the formation of
WO clusters in the lattice.
3
Presently, we deal with tetragonal scheelite structures, with I4
units per primitive cell. The scheelite structures MWO are characterized by a juxtaposition of
WO ] tetrahedra and [MO ] hexahedra [8-12], with chemical links M-O-W. The preparation
methods of BaWO and PbWO are generally based on solid – state reaction [14 - 17],
coprecipitation [18, 19] and hydrothermal synthesis [20-22]. In our previous works, the
photoluminescence properties of solid solutions Ca1-xCd WO [23, 24], Sr1-xPb WO and
MoO [25-26] were analyzed as a function of the composition x. The general aim was
to better understand the role of substitution in the photoluminescence of tungstates, under UV
or X-ray excitations. In our previous works on the system Sr1-xPb WO [25] under X-ray
1
/a space group, two formula
4
[
4
8
4
4
x
4
x
4
Sr1−xPb
x
4
x
4
excitation, we observed a significant increase of emission intensities in the range x=0.2 to 0.4.
The maximum of emission close to x = 0.3 was attributed to a compromise between surface
states of crystals and local disorder associated with substitution.
In this work, we present a new series of substituted tungstates Ba1-xPb
x
WO
ionic radius is larger than the one of Pb , to better understand the size effect of the average
atom M = Ba1-xPb on structural and vibrational properties of the solid solution, and to
analyze the effect of substitution on luminescence properties. The series Ba1-xPb WO
0≤x≤1) has been synthesized via solid state route, and characterized using X-ray diffraction
XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM). Finally, the
4
in which Ba2+
2
+
x
x
4
(
(
luminescence properties have been analyzed under X-ray excitation.
2. Experimental section
Synthesis. Eleven samples Ba1−xPb
chemical reaction using polycrystalline precursors WO
99.5%], BaCO [Sigma-Aldrich N° 513-77-9, >99.0%] and PbO [Sigma-Aldrich N° 1317-
6-8, >99.0%]. The elaboration conditions (grinding process, temperature and time of thermal
treatment) were optimized to reach a high crystallization level.
x
WO
4
with 0≤x≤1, were prepared by classical solid state
3
[Sigma-Aldrich N° 1313-27-5,
>
3
3

The choice of the thermal treatment of the barium lead tungstates resulted from a systematic
WO tungstates (A=Ca, Sr, Ba; B = Pb, Cd) developed in previous works [23
study on A1-x
B
x
4
to 26]. It was necessary to determine optimized synthesis conditions allowing comparing
these compounds between them. It was shown that the times and temperatures of thermal
treatments could have some influence on crystallinity and luminescence properties. The
objective of our studies was to clearly correlate structure and properties, thus it was necessary
to have samples sufficiently crystallized to be correctly characterized through crystallographic
analyses (presently the Rietveld procedure). The correlation between thermal treatment and
crystallinity can be generally established through the study of the broadening of X-ray
diffraction profiles but also the study of the broadening of Raman spectra.
For these A1-x
compromise allowing a sufficient crystallization of samples. In the specific case of A1-x
Pb WO series, a classical difficulty resided in PbO loss during thermal treatment. To avoid
B
x
WO
4
scheelite-like families, a treatment in two steps was found to be a good
x
4
this PbO loss, the first step was as follows: the reagents in stoichiometric proportions were
first thoroughly mixed and milled in an agate mortar for 15 min, then thermally treated at 600
°C for 3 h, in pure alumina crucible, under air. The second step consisted in milling the
samples again, thoroughly for 2 h, and then heating the powders at 1000 °C for 6 h, under air.
This last step ensured the formation of the crystallized solid solution without significant
deficiency of PbO. In the case of barium lead tungstate family, studies with various times of
thermal treatments were carried out and the results are not reported here. The optimized time
chosen was the one ensuring a sufficient crystallinity of samples, allowing a correct structural
determination. With longer times of thermal treatments, the improvement of crystallinity is
associated with crystal growth, not with significant improvement of luminescence emission
intensities.
The various structural parameters of each sample were refined using Rietveld procedure [27-
3
0]. The FULLPROF program [31] was used to characterize the evolutions of the diffraction
profiles and determine the crystallographic parameters (profile parameters, cell parameters,
atom coordinates, Debye-Waller (DW) factors). In the space group I4 /a, the atom positions
1
of Ba and W occupy special Wyckoff positions. Having regard to the weak diffusion factor of
oxygen interacting with X-ray, the atom coordinates of oxygen cannot be determined or
refined from X-ray diffraction on polycrystalline materials with accuracy. Consequently, the
oxygen coordinates were calculated by assuming that they can be obtained by interpolation

from the coordinates (x, y, z) of oxygen atoms O(BaWO
BaWO [32] and PbWO [34]. The following relation was applied:
O(x)> = (1-x).O(BaWO ) + x. O(PbWO ).
4
) and O(PbWO ), respectively in
4
4
4
<
4
4
[1]
In this relation, the coordinates of O(BaWO4) and O(PbWO4) are successively x = 0.2310,
y = 0.1235, z = 0.0587 and x = 0.2388, y = 0.1141, z = 0.0429.
Scanning electron microscopy. A systematic analysis of grain sizes and morphologies was
performed using a Supra 40 Vp Column Gemini Zeiss scanning electron microscope (SEM),
with a maximum voltage of 20 kV. Local chemical analysis using an Oxford EDS X-Max
system, with a spatial resolution of 0.1 µm was carried out to control the homogeneity of
powders.
Raman spectroscopy analyses. Raman spectroscopy was used to characterize the evolution
of the observed phases and to try to connect vibrational modes with these structural
evolutions. The equipment used to perform the various vibrational spectra was a spectrometer
Horiba Jobin-Yvon HR800 LabRam, spatially resolved to 0.5 microns, by means of an optical
microscope with a 100X objective. The latter has a dual function: it allows firstly focusing the
laser beam on a small area, and, secondly, visualizing the area of the sample. The 514.5 nm
line of an Ar-ion laser was used as the excitation source; the photonic power applied to the
samples was limited to 5 μW with an acquisition time of 30 seconds. Each Raman emission
-1
band was characterized by its wavenumber (in cm ).
Luminescence experiments. The copper X-ray source of the diffractometer Empyrean
(Panalytical) was used to irradiate the samples and perform luminescence experiments. The
nominal emission conditions (voltage VRX / current IRX) were 45 kV/35 mA. The resulting
excitation energies ranged between 0 and 45 000 eV, with a maximum located at about 20 000
eV. It should be noted that the X-ray source also delivered the classical transition energies of
copper source. All samples were in form of 2 mm thick cylindrical pellets, compacted under a
pressure of 5 kbars, placed at a constant distance of the X-ray source, set with a fixed
inclination relative to the incident X-ray beam of about 10 cm. The luminescence emissions of
samples were recorded using a UV – visible spectrophotometer MicroHR (Jobin Yvon)
equipped with an optical fiber of 400 ꢀm in diameter. The fiber was set at a fixed distance of
the sample surfaces (1 mm), with a fixed inclination of 55 degrees with respect to the sample
surface. The constant dimensions of the rectangular surfaces of irradiated grains were of about

2
mm/20 mm. Experiments with voltages VRX varying from 10 to 45 kV and filament current
I
RX varying between 10 to 35 mA, were also performed.
3. Results and discussion
3
.1. X-ray diffraction
Figures 1a and 1b show the X-ray diơraction patterns of the Ba(1−x)Pb
x
WO samples with x
4
varying between 0 and 1. As composition x increases, the 2ꢁ angles of Bragg peaks shift
slightly to largest 2ꢁ angles. All Bragg peaks were indexed in the scheelite tetragonal
structure. Figure 1b represents a zoom of diffraction patterns showing the cell parameters
modifications and the distortions of Bragg peaks as a function of composition x, which is
clearly visible for 0.2<x<0.8.
The refinement results were obtained using the space group I4
observed in Bragg peaks were supported by the Rietveld procedure. The results of XRD
analysis reported in Table 1 indicate that the Ba(1−x)Pb WO solid solution was formed and
corresponded to the unique scheelite structure. No residual oxide phase was detected by XRD.
1
/a. The structural distortions
x
4
Fig. 1. (a) XRD patterns of the tetragonal Ba(1−x)Pb
x
WO powders, 0 ≤ x ≤ 1.;
4
(
b) Zoom in the 2ꢁ angle range 40 to 60 °
Table 1 gives the refined structural parameters associated with the solid solution, as a
function of composition x: lattice parameters, cell volumes, DW factors and the different
factors of agreement between the observed and calculated profiles. The results for pure
barium and lead tungstate BaWO
4
[32] and PbWO [24]), reported in this Table, agree with
4
the ones found in the literature. In Figure 2, the linear variations of a and c parameters and of
cell volume V, as a function of composition x (Figures 2), clearly show that the solid solution
is quasi-ideal. No variation of the DW factor of tungsten atom was observed in our
refinements. The Debye-Waller factor of average atom M=Ba1-xPb increased with x slightly.
x

Table 1: Structural parameters for tetragonal solid solutions MWO
Space group: I 4 /a
4
.with M=Ba1-xPb .
x
1
Fig. 2: (a) Variations of: (a) cells parameters a and c; (b) cell volume V as a function of
composition x.
Figure 3 allows comparison between the observed and calculated profiles of x=0.5 sample.
The difference curve shows a good agreement between the observed and calculated patterns.
Fig. 3. Calculated and observed diffraction profiles from Rietveld analyses for the
Ba0.5Pb0.5WO phase. Ycalc: calculated profile and Yobs: observed profile.
4
In the expanded patterns of Figure 1b, a systematic broadening of Bragg peaks is observed:
we have reported in Figure 4 the variations of FWHM of Bragg peaks as a function of x:
except the samples at compositions x=0, 0.1, 0.8, 0.9 and 1, the substitution clearly involved
distortions in the lattices. The maximum of distortion is observable in the composition range
x=0.35 to 0.55 (close to x=0.4). It should be noted that these distortions are also depending on
the unique thermal process chosen to elaborate the samples at 1000°C. These lattice
distortions could be associated with stacking faults, non-stoichiometry (loss of BaO, PbO,
oxygen and cation vacancies, appearance of WO
gradients due limited thermal treatment.
3
clusters…), and small composition

Fig. 4: FWHM of Bragg peaks as a function of composition x.
3
. 2. Raman spectra
Considering the Raman active modes of scheelite-type MWO
types of vibration modes, belonging to the internal and external vibrations. The first mode
4
compounds, there are two
2
-
corresponds to the normal motion of atoms inside the [WO
4
] tetrahedrons, and the second
one involves the vibration of WO tetrahedrons against the divalent M atoms.
4
The group theory shows that the scheelite structures have 26 distinct vibration modes [33]
Raman and infrared), as indicated in equation:
+5A
Thirteen of these vibration modes noted as 3A +5B
34-36].
Figure 5 reports the Raman spectra of Ba(1−x)Pb
(
ꢂꢃRaman + Infrared) = 3A
g
u
+5B
g
+3B
u
+5E
g
+5E
u
g
g
+5E
g
belong to the Raman active modes
[
x
WO 0 ≤ x ≤ 1 samples.
4
Figure 5: Raman spectra (λ = 514.5 nm) of the Ba1-xPb
x
WO solid solutions.
4
In Table 2 we have reported the various vibration modes observed as x increases. The
continuous decrease of the wavenumbers of Raman active modes confirms the substitution
effect of Ba by Pb cations: this wavenumber shift is mainly due to the mass effect associated
with the substitution of Ba by Pb.
Table 2: Raman spectroscopy data of Ba(1−x)Pb
x
WO solid solution with 0 ≤ x ≤1.
4
Figure 6a represents the variation of the Ag strongest wavenumber decreasing with x. This
vibration mode is generally attributed to the symmetrical vibrations of WO group (breathing
4

mode) interacting with Ba or Pb through Ba-O-W and Pb-O-W links. A typical feature resides
-
1
-1
in the evolution of two Raman bands close to 800 cm : the Eg (796 cm , doubly degenerated)
-1
and Bg (832 cm ) modes. The disorder of atom distributions can be evidenced from the
appearance of a doublet in place of the doubly degenerated Eg mode. This feature was
classically observed in the two other series SrPb(W,Mo)O
of these Eg and Bg modes. We clearly observe a perturbation of these Raman bands as x
increases: the doubly degenerated Eg mode of BaWO (or PbWO ) is transformed into an
4
. Figure 6b reports a magnification
4
4
expanded doublet corresponding to the rise of degeneracy of this Eg mode, coupled with the
modification of links M-O-W as x varies. Due to the disorder of Ba and Pb distributions, all
new modes are broadened. The maximum of perturbation occurs in the composition range
x=0.3 to 0.6 i.e. close to x=0.5, in good agreement with the maximum of distortions of Bragg
peaks observed in the composition range 0.35<x<0.55.
-1
Figure 6: (a) Variation vs. composition x of the wavenumber of Ag (926 cm ) mode;
-1
-1
(
b) Evolution vs. x of the Eg (795 cm ) and Bg (832 cm ) vibration bands: a doublet in
place of unique Eg band.
3
.3. Scanning electron microscopy.
The scanning electron analyses reported in Figure 7a-k show that the as prepared powders,
with compositions x varying between 0 and 1, are generally constituted of a complex
distribution of different grain sizes. The grains have increasing sizes as x increases, with
irregular morphologies: small crystallites for x = 0, large grains for x = 1 and a rounded
appearance for all compositions. The local EDX statistical chemical analysis (not reported
here) is in good agreement with nominal composition x.

Figure 7: Scanning electron microscopy analysis of the Ba1-xPb
x
WO phase (a) x=0, (b)
4
x=0.1, (c) x=0.2, (d) x=0.3, (e) x= 0.4, (f) x= 0.5, (g) x=0.6, (h) x=0.7, (i) x=0.8, (j) x=0.9
and (k) x= 1.
3. 4. Luminescence properties
The luminescence spectra obtained under X-ray excitation (excitation energies ranged
between 0 and 45 000 eV) are presented in Figure 8. Each luminescence spectrum was
decomposed into several spectral components: four gaussian spectral components noted G1
(
≈2 eV, orange-red), G2 (≈2.5 eV, light blue), G3 (≈2.9 eV, dark blue) and G4 (≈3.2 eV,
purple)) were necessary to correctly fit the experimental profiles.
Figures 9 a,b,c,d,e report the values of the intensities of fitted components IG1-4(x),
corresponding to the calculated surfaces of gaussian components, with the associated energies
EG1-4(x) corresponding to the maximum of the calculated curves.
Fig. 8: Luminescence under X-Ray excitation (45kV; 35A): Experimental emission
bands of the Ba(1−x)Pb
x
WO polycrystalline phases with 0 ≤ x ≤ 1. Four Gaussian
4
components fitted to the experimental emission profile are shown for each composition.
Fig.9a: Luminescence under X-ray excitation. Energies of G1, G2, G3, G4 fitted
components and global spectra as a function of composition x.

Fig. 9b: Luminescence under X-ray excitation. Intensities of G1, G2, G3, G4 fitted
components and global spectra as a function of composition x. Maximum of emission
close to x=5.
The G
6, 37-39], the low energy G
centers associated with oxygen atoms, such as Frenkel defects on the grain surfaces as well as
Schottky defects (local clusters WO ). Other authors [40-41] attributed this low energy
1
to G4 components present energies quasi invariant with x. According to authors [23-
2
1
component (orange component) could be ascribed to defect
3
emission to oxygen or cation vacancies. These specific defects are generally due to
elaboration conditions, crystal growth and extrinsic defects, and are not directly depending on
substitution. Recently, the high energetic G
4
component (purple component) was attributed to
spin allowed transitions 1T1,2 ꢀ A
1
of the tungstate groups by authors [23-25, 42-44].
1
The two G
2
and G components (light and dark blue components) are invariant in energy and
3
their intensities exhibit a large maximum in the range x=0.40 to x=0.7. These two G
components were classically ascribed to the basic transitions 3T1, 2 ꢀ A, allowing describing
2
and G
3
1
the luminescence emissions of WO 2-
oxyanions in scheelite structures. Their intensity
4
enhancement may be due to several factors: optical quality of grains, nature of surfaces, and
presence of defects allowing increase of the number of luminescence centers.
Several effects must be considered in the whole range of composition: (i) increase of the
number of luminescence centers due to the increasing of proportion of Pb atoms (additional
Pb(6s) levels below the O(2p) orbitals), (ii) increase of structural disorder and point defects
resulting from substitution and thermal process; and (iii) contribution of the optical nature of
surfaces associated with crystal growth. The broad maximum of luminescence intensity
observed in the range of composition x = 0.4 to 0.6 (close to x=0.5) can be ascribed, for a
large part, to a maximum of distortion due to the maximum disorder of M atoms in the lattice,
observed through the broadening of Bragg peaks and Raman spectra (Eg modes).
It should be remarked that the observation of four components could also be interpreted in
3
terms of splitting of the T levels into three or four levels due to Jahn-Teller distortion of the
WO groups [45, 46].
4

4. Conclusions
In this study, we have established clear correlations between structural disorder coupled with
local distortions and vibrational properties. The structural modifications are directly induced
by substitution and they can be clearly correlated with the increase in the luminescence
intensities emitted under X-ray excitation.
The four components (G1 to G4) observed in our luminescence experiments are characteristic
of solid solution and of its defects: the G1 and G4 components are currently observed in
tungstate based solid solutions and can result from defects involved in the thermal process at
1
000°C. The intensities of G2 and G3 “blue” components increase in a composition range
2
-
close to x = 0.3 to 0.7. These components are characteristic of charge transfers in WO
4
oxyanions, in relation with local distortions, oxygen vacancies and Pb-O-W and Ba-O-W
links. The maximum of emission close to the composition x = 0.5 differs slightly from the
maximum observed in the other series Sr1-xPb
0.3). In these previous studies, the significant variations of crystal sizes and morphologies
played probably a significant role in emission intensities, which would not be the case for the
present series Ba1-xPb WO . However, it is not possible to dismiss a moderate influence on
x
WO
4
and Sr1-x Pb
x
MoO
4
(maximum close to x
=
x
4
optical properties of grain surfaces.
These evolutions in luminescence signals show that chemical substitution could be used to
master and optimize the luminescence under X-ray excitation, at least in polycrystalline
materials. This approach differs from the doping by a rare earth, because it allows using
enhanced intrinsic luminescence. Now, it should be interesting to analyze the luminescence
properties resulting from coupling of chemical substitution and doping by specific
luminescence centers, to combine different types of emissions, for example in radiation
sensors or in new enhanced light emitting diodes.

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Table 1: Structural parameters for tetragonal solid solutions MWO
Space group: I 4 /a
4
.with M=Ba1-xPb
x
.
1
Composition x
0
0.1
0.2
0.3
0.4
0.5
-
10
a (10 m)
5.61353 (4)
5.61353 (4)
12.71985 (3)
5.59346 (4)
5. 59346 (4)
12.65344 (3)
5.58014 (3)
5. 58014 (3)
12.59743 (3)
5.56532 (4)
5. 56532 (4)
12.53540 (6)
5.55034 (3)
5. 55034 (3)
12.48154 (4)
5.53704 (5)
5. 53704 (5)
12.41453 (6)
-
10
b=a (10 m)
c (10- m)
10
Volume Cell
10- m ) : V
30
3
400.824 (4)
395.885 (2)
392.258 (3)
388.256 (5)
384.510 (3)
380.614 (5)
(
2
2
B (M)= (8ꢄ /3).<ꢅr >
2
(
Å )
0.28(1)
0.49(2)
0.21 (4)
0.51 (1)
0.24 (3)
0.47 (3)
0.26 (2)
0.48 (3)
0.25 (3)
0.51 (2)
0.32 (2)
0.47 (1)
B (W) (Å2)
Atom coordinates
M (x, y, z)
Fixed values : x = 0.00000 ; y = 0.25000 ; z= 0.12500 (*)
Fixed values : x = 0.00000 ; y = 0.25000 ; z= 0.62500 (*)
W (x, y, z)
O (x, y, z)
x =
y =
z =
0.23100
0.12350
0.05870
0.23178
0.12256
0.05712
0.23256
0.12162
0.05554
0.23334
0.12068
0.05396
0.23412
0.11974
0.05238
0.2349
0.1188
0.0508
Reliability factors (*)
R
R
R
B
%
6.91
5.23
7.33
6. 96
5.56
7.05
6.87
5.35
6.94
7.11
6.15
7.24
7.14
6.43
6.88
7.43
6.48
6.96
F
(%)
exp (%)
Composition x
0.6
0.7
0.8
0.9
1
-
10
a (10 m)
5.52852 (5)
5. 52852 (5)
12.35184 (3)
5.51663 (3)
5. 51663 (3)
12.28865 (4)
5.49286 (2)
5. 49286 (2)
12.20954 (3)
5.47862 (4)
5. 47862 (4)
12.12852 (3)
5.46432 (3)
5.46432 (3)
12.06212 (5)
-
10
b=a (10 m)
c (10- m)
10
Volume Cell
10- m ) : V
30
3
377.528 (4)
373.983 (5)
368.381 (3)
364.041 (4)
360.161 (3)
(
2
2
B (M) = (8ꢄ /3).<ꢅr >
2
(
Å )
0.34(3)
0.50 (1)
0.38 (3)
0.49 (3)
0.38 (1)
0.48 (2)
0.36 (2)
0.53 (1)
0.45 (2)
0.52 (2)
B (W) (Å2)
Atom coordinates
O (x, y, z)
x =
y =
z =
0.23568
0.11786
0.04922
0.23646
0.11692
0.04764
0.23724
0.11598
0.04606
0.23723
0.11504
0.04448
0.23880
0.11410
0.04290
Reliability factors (**)
R
R
R
B
%
7.82
6.51
7.14
7. 44
6.22
6.31
7.54
6.15
6.45
8.55
6.32
6.97
9.14
6.87
7.91
F
(%)
exp (%)
Notes: (*) Ba, Pb. W coordinates from authors [24, 32] have been fixed.
obs
calc
obs
obs
- Fkicalc│/ ∑ │F obs│}; Rexp=100.{[ (N-P+C) / ∑
(**) R
B
= 100.{∑│I
k
- Iki │/ ∑ │I
k
│}; R
F
= 100.{∑ │F
k
k
obs 2 1/ 2
w
i
│y
i
│ ] } where N, P and C are the number of observations, parameters and constraints respectively.
(
***) Atom coordinates of oxygen calculated from interpolation.

Table 2: Raman spectroscopy data of Ba(1−x)Pb
x
WO
4
solid solution with 0 ≤ x ≤1.
Bg Eg (*) Bg
Ag
-1
ꢆꢇꢃ cm )
x=0
Eg
Bg
Eg
Eg
Ag
Eg
Ag+Bg
** 63.85 75.74 102.12 151.33 192.33 333.58 346.42 795.79 831.74 926.24
** 64.04 76.50 101.98 154.27 193.86 332.82 346.94 783.82 830.22 925.54
** 64.40 77.15 99.36 157.82 195.02 331.58 348.74 783.06 826.48 923.93
x=0.1
x=0.2
x=0.3
x=0.4
x=0.5
x=0.6
x=0.7
x=0.8
x=0.9
x=1
**
64.3 77.32
**
**
**
**
**
**
**
**
158.06 195.71 331.04 348.83 782.83 825.61 923.50
164.30 196.98 329.56 350.84 779.69 806.00 920.42
166.27 197.03 329.02 351.45 776.29 801.00 919.23
169.78 195.72 328.35 353.07 767.60 790.00 916.95
172.13 195.61 327.81 354.53 764.41 775.00 914.32
174.41 194.73 328.35 355.98 756.4 772.17 912.37
176.88 194.10 328.15 357.33 754.61 769.09 909.44
179.29 193.70 328.38 358.64 753.46 767.03 906.59
** 64.89 80.38
60.51 67.22 79.87
60.83 69.48 85.71
62.39 72.45 87.65
64.05 74.96 89.13
65.23 76.54 90.69
65.41 78.26 91.83
-
1
Note: ꢆ = wavenumber (Raman shift) in cm ; (*) Eg mode: only one underlined wavenumber (in
italic) is given to represent the new doublet resulting from the rise of degeneracy.
Highlights
Ba(1-x)Pb
x
WO
X-ray diffraction and Rietveld method characterize disorder of solid solution
Raman spectroscopy confirms the structural disorder of Ba(1-x)Pb WO compounds
4
compounds are elaborated from a two-step solid state route
x
4
Luminescence under X-ray excitation characterizes the solid solution
Luminescence intensity reaches a maximum for composition x=0.5

Figure(s)
(
a)
x=0
x=0.1
x=0.2
x=0.3
x=0.4
x=0.5
x=0.6
x=0.7
x=0.8
x=0.9
x=1
0
1
0
20
30
40
50
60
70
80
2ꢁꢇꢃꢈꢉ
(
b)
x=0
x=0.1
x=0.2
x=0.3
x=0.4
x=0.5
x=0.6
x=0.7
x=0.8
x=0.9
x=1
0
4
0
50
60
2ꢁꢇꢃꢈꢉ
Fig. 1. (a) XRD patterns of the tetragonal Ba(1−x)Pb
x
WO powders, 0 ≤ x ≤ 1. ;
4
(b) Zoom in the 2ꢁ angle range 40 to 60 °

Figure(s)
1
2.8
a=b
c
(b)
5
5
5
5
5
5
.61
.58
.55
.52
.49
.46
(
a)
4
3
00
90
12.6
1
1
1
2.4
2.2
2.0
380
3
3
70
60
0.0
0.2
0.4
0.6
0.8
1.0
0
.0
0.2
0.4
0.6
0.8
1.0
x (Pb) fraction
x (Pb) fraction
Fig. 2: (a) Variations of: (a) cells parameters a and c; (b) cell volume V as a function of
composition x.

Figure(s)
Fig. 3. Calculated and observed diffraction profiles from Rietveld analyses for the
phase. Ycalc: calculated profile and Yobs: observed profile.
Ba0.5Pb0.5WO
4

Figure(s)
0
0
0
0
0
.24
.20
.16
.12
.08
0
.0
0.2
0.4
0.6
0.8
1.0
x (Pb) fraction
Fig. 4: FWHM of Bragg peaks as a function of composition x.

Figure(s)
A
g
B
g
A +B
g
g
B
A
g
E
E
E
g
g
B
g
g
E
g
g
x=0
E
g
x=0.1
x=0.2
x=0.3
x=0.4
x=0.5
x=0.6
x=0.7
x=0.8
x=0.9
x=1
2
00
400
600
800
1000
-1
Raman Shift (cm )
Figure 5: Raman spectra (λ = 514.5 nm) of the Ba1-xPb
x
WO solid solutions.
4

Figure(s)
9
9
9
9
9
9
30
25
20
15
10
05
(
a)
0,0
0,2
0,4
0,6
0,8
1,0
x (Pb) fraction
E
g
B
(
b)
g
x=0
x=0.1
x=0.2
x=0.3
x=0.4
x=0.5
x=0.6
x=0.7
x=0.8
x=0.9
x=1
8
00
-
1
Raman Shift (cm )
-1
Figure 6: (a) Variation vs. composition x of the wavenumber of Ag (926 cm ) mode;
-1
-1
(
b) Evolution vs. x of the Eg (795 cm ) and Bg (832 cm ) vibration bands: a doublet in
place of unique Eg band.

Figure(s)
Figure 7: Scanning electron microscopy analysis of the Ba1-xPb
x
WO phase (a) x=0, (b) x=0.1, (c) x=0.2,
4
(d) x=0.3, (e) x= 0.4, (f) x= 0.5, (g) x=0.6, (h) x=0.7, (i) x=0.8, (j) x=0.9 and (k) x= 1.

Figure(s)
450
300
150
0
x=0
Global
G1
x=0.1
Global
G1
x=0.2
Global
G1
7
20
660
G2
G2
540
G2
G3
G4
G3
G4
4
40
20
0
G3
G4
3
60
80
0
2
1
1
.5
2.0
2.5
3.0
3.5
1.5
2.0
2.5
3.0
3.5
1
.5
2.0
2.5
3.0
3.5
4.0
Energy (eV)
Energy (eV)
Energy (eV)
2800
2100
1400
x=0.3
Global
G1
x=0.4
Global
G1
6000
4500
x=0.5
2
100
400
Global
G1
G2
G2
G2
G3
G4
G3
G4
1
G3
G4
3000
7
00
7
00
1500
0
0
0
1
.5
2.0
2.5
3.0
3.5
1.5
2.0
2.5
3.0
3.5
1
.5
2.0
2.5
3.0
3.5
Energy (eV)
Energy (eV)
Energy (eV)
x=0.6
Global
G1
x=0.7
Global
G1
7
50
00
x=0.8
Global
G1
4
500
000
500
0
3200
6
G2
G2
2
400
600
G2
G3
G4
G3
G4
3
1
G3
G4
450
1
3
00
50
0
800
1
0
1
.5
2.0
2.5
3.0
3.5
1
.5
2.0
2.5
3.0
3.5
1
.5
2.0
2.5
3.0
3.5
Energy (eV)
Energy (eV)
Energy (eV)
1
20
x=1
x=0.9
Global
G1
Global
G1
2
40
60
90
G2
G2
G3
G3
G4
1
6
0
0
0
G4
3
80
0
2
.0
2.5
3.0
3.5
1.5
2.0
2.5
3.0
3.5
4.0
Energy (eV)
Energy (eV)
Fig. 8: Luminescence under X-Ray excitation (45kV; 35A): Experimental emission
bands of the Ba(1−x)Pb WO polycrystalline phases with 0 ≤ x ≤ 1. Four Gaussian
components fitted to the experimental emission profile are shown for each composition
x
4

Figure(s)
2.20
2.15
2.10
2.05
2.00
1.95
1.90
G1
2
.70
G2
2.65
2.60
2.55
2.50
2.45
2.40
2.35
2.30
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Fraction x(Pb)
Fraction x(Pb)
3
3
3
3
.6
.4
.2
.0
G3
G4
3
3
2
2
2
.1
.0
.9
.8
.7
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Fraction x(Pb)
Fraction x(Pb)
3
3
2
2
2
2
2
2
2
.1
.0
.9
.8
.7
.6
.5
.4
.3
Global
0.0
0.2
0.4
0.6
0.8
1.0
Fraction x(Pb)
Fig.9a: Luminescence under X-ray excitation. Energies of G1, G2, G3, G4 fitted
components and global spectra as a function of composition x.

Figure(s)
200
150
100
G1
G2
3
000
2400
1
800
200
1
50
600
0
0
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Fraction x(Pb)
Fraction x(Pb)
1
800
200
G3
120
00
G4
1
1
8
6
4
2
0
0
0
0
0
6
00
0
0.0
0.2
0.4
0.6
0.8
1.0
0
.0
0.2
0.4
0.6
0.8
1.0
Fraction x(Pb)
Fraction x(Pb)
5600
4200
2800
1400
0
Global
0
.0
0.2
0.4
0.6
0.8
1.0
Fraction x(Pb)
Fig. 9b: Luminescence under X-ray excitation. Intensities of G1, G2, G3, G4 fitted
components and global spectra as a function of composition x. Maximum of emission
close to x=5.

.
) i t n . U r b A ( y t i s n e I n
)
. u ( a i t s y n t e I n

*Graphical Abstract Legend (TOC Figure)
Graphical Abstract Legend
System Ba1-xPb
x
WO (0≤x≤1). Correlation between disordered structure and luminescence
4
under X-ray excitation. Left: Structural disorder from Raman spectra. Right: maximum of
luminescence under X-ray excitation.