Influence Ca-doped SrIn2O4 powders on photoluminescence property prepared one step by ultrasonic spray pyrolysis

Article abstract of DOI:10.1016/j.jallcom.2018.03.090

Crystalline Ca-doped SrIn₂O₄ structures were prepared by a rapid and efficient Ultrasonic Pyrolysis Spray (USP) method. The Sr_1-xCa_xIn₂O₄ (x = 0, 0.1, 0.2, 0.3, 0.4 and 1 mol %) samples wer

Full text of DOI:10.1016/j.jallcom.2018.03.090

Accepted Manuscript
Influence Ca-doped SrIn O powders on photoluminescence property prepared one
2 4
step by ultrasonic spray pyrolysis
P.N. Medeiros, A.A.G. Santiago, E.A.C. Ferreira, M.S. Li, E. Longo, M.R.D. Bomio,
F.V. Motta
PII:
S0925-8388(18)30957-5
10.1016/j.jallcom.2018.03.090
JALCOM 45320
DOI:
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 30 January 2018
Accepted Date: 8 March 2018
Please cite this article as: P.N. Medeiros, A.A.G. Santiago, E.A.C. Ferreira, M.S. Li, E. Longo, M.R.D.
Bomio, F.V. Motta, Influence Ca-doped SrIn O powders on photoluminescence property prepared
2 4
one step by ultrasonic spray pyrolysis, Journal of Alloys and Compounds (2018), doi: 10.1016/
j.jallcom.2018.03.090.
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ACCEPTED MANUSCRIPT
Influence Ca-doped SrIn2O4 powders on photoluminescence property prepared
one step by ultrasonic spray pyrolysis
P. N. Medeirosa, A. A. G. Santiagoa, E. A. C. Ferreiraa, M. S. Lib, E. Longoc, M. R. D.
Bomioa, F. V. Mottaa*
aIFBA, Instituto Federal da Bahia - Campus Jacobina, 44700-000 Jacobina, BA - Brazil
bLSQM, Laboratório de Síntese Química de Materiais - DEMat, Universidade Federal
do Rio Grande do Norte - UFRN, P.O. Box 1524, 59078-970 Natal, RN, Brazil
cIFSC, USP, Av. Trabalhador São Carlense, 400, CEP 13566-590 São Carlos, SP,
Brazil
dCDMF-UFSCar, Universidade Federal de São Carlos, P.O. Box 676, 13565-905 São
Carlos, SP, Brazil
Abstract
Crystalline Ca-doped SrIn2O4 structures were prepared by a rapid and efficient
Ultrasonic Pyrolysis Spray (USP) method. The Sr1-xCaxIn2O4 (x = 0, 0.1, 0.2, 0.3, 0.4
and 1 mol %) samples were obtained by in a single step at a temperature of 1050oC for
1 min for the formation of particles. The powders were characterized by X-ray
diffraction (XRD), field emission electron microscopy (SEM-FEG), optical diffuse
reflectance and photoluminescence (PL) measurements. All diffraction peaks present in
XRD patterns could be indexed to the orthorhombic structure and that with calcium
percentage increments indicates the substitution of Ca2+ in the Sr2+ sites promotes a
decrease in its lattice parameters of the structure. MEV-FEG images show that the Sr1-
xCaxIn2O4 particles have a spherical predominance, with a porous surface in the form of
foam for x = 0 and a surface with low roughness and low porosity with an increase in

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the percentage of Ca2+ ion, especially for the 1 mol % of Ca2+. The gap energy varied
between 4.56 eV and 4.86 eV, being influenced by the structural modifications
motivated by increase of Ca2+ ion contained in the SrIn2O4 matrix. The PL emission
spectrum of the samples presents a broad band behavior with emission intensity
predominant in the blue-green region, having the sample with x = 0.1 the highest PL
intensity. The chromaticity coordinates were calculated for the sample based on the PL
spectrum and coordinates x and y show that the samples have blue emission. Ultrasonic
spray pyrolysis was an effective technique for Ca-doped SrInO4 powder production
using short production times with hold great potential for photoluminescent emitters.
Keywords: Ultrasonic spray pyrolysis, Indate, Strontium, Optical Properties,
Photoluminescence.
*Corresponding author. Tel: +55-84-3342-2512; Fax: +55-84-3342-2406 E-mail
address: fabiana@ct.ufrn.br (F. V. Motta).

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1. Introduction
Indium-based oxides have been constantly investigated, due to their probable
applications in photocatalysis [5], solar cells [6], gas sensors [7,8], anode lithium ion
batteries [9] and phosphors [10,11].
SrIn2O4 is a semiconductor that has an orthorhombic structure of the CaFe2O4
ͥͪ
ʚ
ʛ
space group [12]. In the SrIn2O4 structure, there are octahedral
type with Pnam ̾
ͦ#
chains of InO6, which give this material good photocatalytic and luminescent properties
due to a possible mobility of charge carriers [13]. Kang et al [14] obtained SrIn2O4
doped with Eu3 + and studied the photoluminescent properties in the application of red
phosphors to white LED's. Wang and Tian [15] investigated the photoluminescent
properties of SrIn2O4:Eu3+,Gd3+e SrIn2O4:Eu3+,Sm3+. Li et al [16] synthesized SrIn2O4
4: Eu3+, Sm3+ and observed some red emission in the photoluminescent spectrum. Kao
[17] obtained yellow-green phosphors from SrIn2O4 powders:xTb. Photocatalytic
properties and luminescent upconversion of SrIn2O4 are also reported in the literature
[18-20].
CaIn2O4 is a semiconductor that presents an orthorhombic crystal structure also of
the CaFe2O4 type but with space group Pca21 or Pbcm. [21] Studies on the
photoluminescent properties of CaIn2O4 have been reported in the literature, such as
obtaining orange-red [21] and white- hot [22] and effective upconversion [23-25].
The solid-state reaction method is commonly used to obtain the indates (MIn2O4,
M = Ca, Sr, Ba), but it is a method that uses very high temperatures and long furnace
periods [13-15,26,27]. Other more energy-efficient methods of obtaining indates are

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reported in the literature, such as combustion method [16,28], coprecipitation [29],
electrospinning [30], pechini sol-gel [31] and spray pyrolysis [32,33].
The ultrasonic pyrolysis spray (USP) method consists of atomising or nebulizing a
precursor solution by ultrasound, then the droplets undergo thermal treatment,suffering
physicochemical phenomena such as solvent evaporation, precipitation and drying of
the solutes for the formation of fine powders, occurring the need for decomposition or
chemical alteration by reduction or oxidation of these fine powders with morphology of
non-agglomerated microspheres [34,35].
In this work, Sr1-xCaxIn2O4 powders (x = 0, 0.1, 0.2, 0.3, 0.4 and 1 mol %) were
obtained in a single step by ultrasonic pyrolysis spray method (USP). The time for
particle formation inside the reactor was approximately 1 min. The correlation of the
photoluminescent properties with doped Ca ions are substituted for the Sr ions in the
SrIn2O4 crystal structure was investigated.
2. Experimental
2.1. Materials
Sr1-xCaxIn2O4 (x = 0, 0.1, 0.2, 0.3, 0.4 and 1 mol %) powders were prepared by
the ultrasonic spray pyrolysis method (USP) [36,37]. Indium nitrate [In (NO3)2. (Alfa
Aesar, 99% purity), and calcium nitrate tetrahydrate [Ca(NO3)2] (Alfa Aesar, 99%
purity). 4H2O] (Synth, 99% purity) were used as precursors.
2.2. Preparation of Sr1-xCaxIn2O4 particles
The precursor solution was prepared by dissolving 9 mmol of strontium nitrate
and 18 mmol of indium nitrate in 190 ml of distilled water. The precursor solution was

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atomized using an ultrasonic nebulizer with a frequency of 2.4 MHz. The nebulizer was
coupled in a quartz aerosol reactor of laminar flow (50 mm in diameter and 1.2 m in
length). The reactor was inserted into a horizontal electric double tubular heating
furnace. The atomized droplets were transported inside the reactor by an air flow, at an
air flow rate of 3 L min-1. The heating temperatures were 700 ºC for zone 1 and 1050
ºC for zone 2. The resulting particles were collected by means of electrostatic
precipitation at the end of the reactor by a copper tube. The other precursor solutions (x
= 0.1, 0.2, 0.3, 0.4 and 1 mol %) were performed according to stoichiometry.
2.3 Characterization of Sr1-xCaxIn2O4 particles
The Sr1-xCaxIn2O4 powders (x = 0, 0.1, 0.2, 0.3, 0.4 and 1 mol %) were
characterized by XRD 7000, 30 kV and 30 mAh XRD (Shimadzu, model XRD 7000)
with CuKα radiation (λ = 1.5406 Å), 2θ 10º to 80º and step speed of 1º min-1. The
morphology was analyzed using field emission scanning electron microscopy (SEM-
FEG) (Carl Zeiss, model Supra 35-VP) operating at 6 kV. The Uv-vis reflectance
spectrum was obtained using Uv-Vis spectrometer (Shimadzu, model UV-2600).
Photoluminescence (PL) spectra were obtained using a 27 Thermal Jarrell-Ash
Monospec monochromator and an R446 Hamamatsu photomultiplier. The excitation
source used in the samples was a laser with a wavelength of 350.7 nm with krypton ions
(Coherent Innova) with an output of approximately 13.3 mW.
3. Results and discussion
Figure 1 shows the XRD patterns of the Sr1-xCaxIn2O4 (x = 0, 0.1, 0.2, 0.3, 0.4
and 1 mol %) powders obtained by the ultrasonic pyrolysis spray method. The samples

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were indexed in a unit cell with orthorhombic structure with the space group Pnam (66)
according to JCPDS 33-1336. While the samples with x = 1 were indexed in a unit cell
with orthorhombic structure with the space group Pca (57) according to JCPDS 17-
0643. The presence of SrCO3 peaks was observed. The formation of SrCO3 is attributed
by the reaction between SrO and carbon dioxide under a low oxygen partial pressure
and at high temperatures [31]. No other peaks were observed regarding possible
secondary phases of calcium, thus indicating that the indates were well crystallized by
the Ultrasonic Pyrolysis Spray (USP) method and that the Ca2+ were well incorporated
in the SrIn2O4 structure, forming a solid solution. With the increase of the calcium
percentage in the orthorhombic phase of SrIn2O4obtained by UPS (Figure 1II), it was
verified that a small displacement of the diffraction peaks occurs to larger angles (2θ),
indicating a decrease in the network parameters of the material, which is attributed to
the substitution of Ca2+ ions at the
Sr2+ sites. Ramarao et al [38] replaced Ca2 + for
Sr2 + ions in a Mo matrix and observed similar behavior, with shifting to smaller angles
and increasing network parameters.
[Insert Fig. 1]
In order to explain possible modifications of the differences in the structural
arrangements induced by the processing of Sr1-xCaxIn2O4 particles the Rietveld
refinement method [39] was performed using the General Structure Analysis System
(GSAS) program with the EXPGUI graphical interface [40]. Since no correct ICSD or
JCPDS file is available for CaIn2O4, all peaks Sr1-xCaxIn2O4 were indexed by
orthorhombic cells (Pnma) with parameters close to 16241 ICSD (SrIn2O4) [20]. The

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refined parameters were as follows: scale factor and phase fraction; background, which
was modeled using a displaced Chebyshev polynomial function; peak shape, which was
modeled using Thomson-Cox-Hasting pseudo-Voigt; change in network constants;
fractional atomic coordinates; and isotropic thermal parameters. The results of the
Rietveld refinement are shown in Figure 2.
[Insert Fig. 2]
For the samples the diffraction patterns are well adapted to 16241 ICSD. As
shown in the Obs-Calc line, the differences between the experimentally observed
diffraction patterns and the theoretically calculated data are close to zero. Table 1 and 2
present the results of the structural parameters and atomic positioning, crystallite size of
Sr1-xCaxIn2O4, obtained by refinement. For x = 0 and 1, the values found for the network
parameters, a, b and c, are in agreement with the literature. Lakshminarasimhan and
Varadaraju [41] synthesized SrIn2O4 by the solid state reaction method at 1200oC for 24
hours and obtained the values for the network parameters a = 9.8082 Å, b = 11.4578Å
and c = 3.2581Å. Guan et al [20] obtained CaIn2O4 via a solid state reaction at 1300 ° C
for 3 hours, resulting in the values of a = 9.6485 Å, b = 11.2953 Å and c = 3.2144 Å. In
this work, the Ca2+ ions that substitute the Sr2+ ions, show a decrease in the ionic radius
in the following sequence: Sr2+(0.126 nm) > Ca2+(0.112 nm). Thus, the network
parameters decrease with the increase of the Ca2+ ion contained in the SrIn2O4 matrix
(Table 1), according to the literature [38].
The Sr1-xCaxIn2O4 crystallite size decreased from 41 nm (x = 0) to 23 nm (x = 0.4)
(Table 1). This behavior can be explained by the fact that the increase in the Ca

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percentage was accompanied by the increase in the number of defects of the crystalline
strontium-induced lattice, which increased the network tension (Ca2+ and Sr2+ cations
and O2-interstitial anions, respectively). This behavior is a reminiscent of Vegard's law,
which for two-component metal solid solutions, predicts that the unit cell dimensions of
the solid solution vary linearly with the concentration of the solute component [42,43].
[Insert Table 1]
[Insert Table 2]
The reliability parameters X², Rwp and Rp, shown in Table 1, indicate a good
quality of structural refinements and numerical results. These data confirm that the Sr1-
xCaxIn2O4 samples (with x = 0, 0.1, 0.2, 0.3, 0.4 and 1) show a crystalline structure
which is suitably described by an orthorhombic structure, with symmetry described by
the Pnam space group. In addition, it was also observed the presence of SrCO3
secondary phase for all compositions investigated. The percentages of each phase are
shown in Table 3.
[Insert Table 3]
With the network parameter data and atomic coordinate data obtained in the
Rietveld refinement (Table 1 and 2), the VESTA program [44] was used to model the
unit cells of each sample, as shown in Figure 3.

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[Insert Fig. 3]
The Sr1-xCaxIn2O4 orthorhombic structure (Pnma) is formed of two different
octahedron clusters of [InO6] and one octahedrode cluster [SrO8] and / or [CaO8] [12]. It
can be seen that the substitution of Ca2+ in the Sr2+ sites promotes small changes in the
positioning Sr / Ca, In and O atoms and the distance of the Sr-O / Ca-O and In-O atomic
bonds , resulting in small distortions in the clusters of [InO6] and in the cluster of [SrO8]
and / or [CaO8]. Figure 4 shows the difference of the distances of the chemical bonds
between the Sr-O and Ca-O atoms of the samples.Schenck and Müller-buschbaum [12]
presented values close to the distances between the Sr-O atoms of SrIn2O4shown in
Figure 4 , which were 2.53Å (2x), 2.55Å (2x), 2.61Å, 2.69Å, 2.75Å and 3.76Å. The
small changes at these distances is a result of the synthesis method used, its temperature
and time conditions, and the changes promoted by the substitution of Ca2+ in the Sr2+
sites.
[Insert Fig. 4]
The morphology of Sr1-xCaxIn2O4 particles (Figure 5) is microspheres formed by
nanoparticles. Figure 5(a) shows the morphology of SrIn2O4, it is seen that the
microspheres have porous surfaces, such as foam. On the other hand, in Figure 5(f), the
CaIn2O4 microspheres have a less porous surface. Messing et al [45] reported some
simultaneos physical phenomena during the pyrolysis spray process as the evaporation
of the solvent on the surface of the droplet, diffusion of solvent vapors away from the
drop in the gas phase, shrinkage of the drop, change in the drop temperature and

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diffusion of solute towards the center of the drop. Furthermore, it is described that metal
nitrate derivatives generally form porous or irregular particles, because the metal
nitrates melt before the solvent is completely removed, and the molten salt formed will
inhibit the solvent removal [45].
[Insert Fig. 5]
Thus, the use of strontium nitrate favors phenomena that result in the formation of
particles with a porous surface, while the use of a higher percentage of calcium nitrate
favors the formation of particles with a less rough surface. Kang et al [46] obtained
SrTiO3 particles via spray pyrolysis with spherical morphology and porous surface.
While, Lanfredi et al [47] synthesized CaTiO3 using the pyrolysis spray method, but the
particles showed spherical morphology and non-porous surface. Thus, with the increase
of x value of Sr1-xCaxIn2O4, there is a decrease in the surface porosity of the particles,
due to the stoichiometric increase of calcium and the reduction of strontium, as shown
in Figure 6.
[Insert Fig. 6]
The diffuse reflectance spectroscopy in the visible ultraviolet region was used to
determine the gap band of the samples. The reflectance data were converted to
absorbance data using the Kubelka-Munk function [48], and the optical gap band value
(Egap) was estimated using the Wood and Tauc method [49]. In the Wood and Tauc's
method, the optical gap energy is given by αhv α (hv-Egap) k, where h is the Planck

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constant, v is the frequency, α is the absorbance and k is indicated for different
transitions (k = 1/2, 2, 3/2 or 3 for direct allowed, indirect allowed, direct forbidden and
indirect forbidden, respectively). For the Sr1-xCaxIn2O4 samples, k = 2 was allowed, that
is, indirect allowed, indicating an indirect allowed electronic transition. Absorbance
versus photon energy plot (eV) was plotted and the linear portion of the curve was
extrapolated for zero absorption to estimate Egap. Figure 7 and Table 4 present the
estimated values for the gap energy of Sr1-xCaxIn2O4 samples (x = 0, 0.1, 0.2, 0.3, 0.4
and 1 mol %). The verified band gap values of the samples are in agreement with the
values found in the literature (Table 4). Dali et al [50] synthesized SrIn2O4 and CaIn2O4
using solid state reaction at 900 ° C for 24 hours and found that Egap values were 3.60
eV and 3.90 eV, respectively.
[Insert Fig. 7]
[Insert Table 4]
The small differences observed in the gap band of the samples can be attributed to
the use of the synthesis method, as well as reagents, temperature, time and morphology.
It was observed that the substitution of Sr2+ cations for Ca2+ cations resulted in a slight
decrease in the gap energy, being more evident when x = 0.1. It is believed that the
slight decrease in gap energy is related to defects introduced by cationic substitution, as
well as displacement of Sr-O / Ca-O and In-O bonds, and distortion of [InO6] and
[SrO8] clusters / [CaO8] (Figures 3 and 4).

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Figure 8 shows the photoluminescent emission (PL) spectra of the Sr1-xCaxIn2O4
(x = 0.1, 0.2, 0.3, 0.4 and 1 mol %) powders obtained by the USP method at room
temperature, when excited at 350.7 nm. Spectra are typical of broadband systems where
relaxation processes occur by multiphonon and multilevel processes, that is, a system in
which relaxation occurs by several paths and involving the participation of numerous
intermediate states within the gap band of the materials investigated [51].
[Insert Fig. 8]
A proper structural disorder can result in a better photoluminescent emission
compared to a fully ordered structure. In general, structurally disordered materials
exhibit oxygen vacancies, network defects, impurities and / or distorted local bonds that
give rise to electronic levels in the band gap. These electronic levels are responsible for
improving the PL emission process [52].
In the PL emission, each electronic transition is represented by a color and
associated with a structural arrangement, the lower the order of this structural
arrangement, the more the spectrum tends to decrease in the areas of blue-green and to
increase in the areas of yellow-orange-red. Therefore, the emission in the blue-green is
associated with an orderly structure with shallow defects, while the emission in red-
yellow is associated with a disordered structure with deep defects [52]. Using the
Gaussian method, PL curves of the samples were decomposed into five components,
referring to the region in the visible spectrum. PL curves were analyzed using the
PeakFit deconvolution program [53]. The features extracted from deconvolution curves
and the areas under the curve of respective transitions are illustrated in Fig. 9(a-f).

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The Sr1-xCaxIn2O4 PL curves for all samples are composed of four PL components
with the following nm maxima: blue = 450 nm, green = 525 nm, orange = 607.5 nm and
red = 682.5 nm. The PL deconvolution (Fig. 9) shows the Sr1-xCaxIn2O4 disordered to
ordered structure, favoring the green and blue light emission for the all samples.
[Insert Fig. 9]
The x and y coordinates were determined to verify the light emission. The CIE
color coordinates can be calculated by integrating the X, Y and Z values [54]. The CIE
is one of the important factors to evaluate the performance of phosphors. Figure 10
shows the CIE (x, y) coordinates of the samples, while Table 5 lists the CIE coordinate
values, color temperature correlation (CCT) values and the emitted color of each
sample.
[Insert Fig. 10]
[Insert Table 5]
All samples showed light emission in the blue color. However, for samples with
x = 0, 0.1 and 0.2 the CCTs were colder than for samples with x = 0.3, 0.4 and 1. This
occurs because the samples with x = 0.1 and 0.2 show a predominant emission in the

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blue region, while the samples with x = 0.3, 0.4 show the largest emission contribution
in the green region.
4. Conclusion
The Sr1-xCaxIn2O4 powders (x = 0, 0.1, 0.2, 0.3, 0.4 and 1 mol %) were obtained,
in a single step by the ultrasonic pyrolysis spray process. The XRD patterns showed that
the samples have an orthorhombic crystal structure, with the network parameters and
crystallite size which decreases as the cationic substitution of Sr2 + for Ca2 + increases.
The particles obtained are predominantly spherical, with a porous surface in the form of
foam for x = 0 and a slightly rough surface for x = 1, observing a decrease of the surface
porosity as the values of x increase, that is, with an increase in the replacement of Sr2 +
ions for Ca2+ ions. The gap energy varied between 4.56 eV and 4.86 eV, presenting the
lowest energy for the sample with x = 0.1. The spectra of PL emission of the all samples
have broadband behavior, with predominant emission in the blue-green region.
According to the CIE diagram, the samples have emission in the blue region. These
optical properties exhibited by disordered Sr1-xCaxIn2O4 suggest that this material is a
highly promising candidate for photoluminescent applications.
Acknowledgment
The authors thank the financial support of the Brazilian research financing institutions:
CAPES/PROCAD 2013/2998/2014, CNPq.No 307546/2014-4, FAPESP2013/07296-2
and INCTMN 2008/57872-1.

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Figure Captions
Figure 1. XRD patterns of Sr1-xCaxIn2O4 obtained by USP with (a) x=0, (b) x=0.1, (c)
x=0.2, (d) x=0.3, (e) x=0.4 and (f) x=1. [*: SrCO3 (JCPDS 84-1778)]
Figure 2. Rietveld refinement of Sr1-xCaxIn2O4 with (a) x=0, (b) x=0.1, (c) x=0.2, (d)
x=0.3, (e) x=0.4 and (f) x=1.
Figure 3. Model of orthorhombic structure of the (a) SrIn2O4, (b) Sr0.9Ca0.1In2O4, (c)
Sr0.8Ca0.2In2O4, (d) Sr0.7Ca0.3In2O4, (e) Sr0.6Ca0.4In2O4 and (f) CaIn2O4.
Figure 4. Distances of the chemical bonds between Sr-O and Ca-O atoms of the (a)
SrIn2O4, (b) Sr0.9Ca0.1In2O4, (c) Sr0.8Ca0.2In2O4, (d) Sr0.7Ca0.3In2O4, (e) Sr0.6Ca0.4In2O4
and (f) CaIn2O4.
Figure 5. SEM micrographs of (a) SrIn2O4, (b) Sr0.9Ca0.1In2O4, (c) Sr0.8Ca0.2In2O4, (d)
Sr0.7Ca0.3In2O4, (e) Sr0.6Ca0.4In2O4and (f) CaIn2O4.

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Figure 6. Illustration of the morphology variation of Sr1-xCaxIn2O4 particles according to
the value of x.
Figure 7. UV-Vis absorbance spectra of (a) SrIn2O4, (b) Sr0.9Ca0.1In2O4, (c)
Sr0.8Ca0.2In2O4, (d) Sr0.7Ca0.3In2O4, (e) Sr0.6Ca0.4In2O4and (f) CaIn2O4.
Figure 8. PL emission spectra of (a) SrIn2O4, (b) Sr0.9Ca0.1In2O4, (c) Sr0.8Ca0.2In2O4, (d)
Sr0.7Ca0.3In2O4, (e) Sr0.6Ca0.4In2O4 and (f) CaIn2O4.
Figure 9. Deconvolute the PL curves of (a) SrIn2O4, (b) Sr0.9Ca0.1In2O4, (c)
Sr0.8Ca0.2In2O4, (d) Sr0.7Ca0.3In2O4, (e) Sr0.6Ca0.4In2O4 and (f) CaIn2O4.
Figure 10. CIE diagram ofSr1-xCaxIn2O4 (x=0, 0.1, 0.2, 0.3, 0.4 and 1).

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Table Captions
Table 1. Rietveld refined structural parameters for theSr1-xCaxIn2O4 (with x = 0, 0.1, 0.2,
0.3, 0.4 and 1 mol %).
Table 2. Position of the atoms in the unit cell.
Table 3. Percentage of each phase obtained by Rietveld refinement.
Table 4. Comparative results between the Egap values ofSr1-xCaxIn2O4 (x = 0, 0.1, 0.2,
0.3, 0.4 and 1 mol %) obtained in this work and those reported in the literature.
Table 5. Chromaticity coordinates (CIE) and correlated temperature color (CCT) for
Sr1-xCaxIn2O4 (x = 0, 0.1, 0.2, 0.3, 0.4 and 1 mol%).

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Table 1. Rietveld refined structural parameters for theSr1-xCaxIn2O4 (with x=0, 0.1, 0.2,
0.3, 0.4 and 1).
Compoun
Sr0.9Ca0.1In2O
SrIn2O4
Orthorhombic
Pnam
Sr0.8Ca0.2In2O4 Sr0.7Ca0.3In2O4 Sr0.6Ca0.4In2O4
CaIn2O4
ds
4
Crystal
system
Orthorhombic Orthorhombic
Orthorhombic Orthorhombic Orthorhombic
Space
Group
Pnam
Pnam
Pnam
Pnam
Pnam
Lattice parameters (Å)
a
b
9.8430
9.8312
11.5089
3.2728
90°
9.8157
11.4895
3.2689
90°
9.8051
11.4819
3.2675
90°
9.7901
11.4508
3.2607
90°
9.6538
11.3005
3.2197
90°
11.5178
3.2740
90°
c
α
V(ų)
X²
371.179
1.229
370.316
1.210
368.672
1.203
367.867
1.203
365.553
1.224
351.242
1.946
Rwp (%)
Rp (%)
D (nm)
ε (x10-3)
18.75
17.96
18.30
19.41
19.34
17.84
13.77
13.06
13.39
14.38
14.43
13.91
41.4762
1.1083
31.0655
1.5590
24.8951
1.0904
26.2382
2.6944
22.8719
2.2348
35.2113
1.5213

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Table 2. Position of the atoms in the unit cell.
Sample
Atom
x
y
z
Occ
Sr1 0.7548 0.6523 0.2500 1.0000
In1 0.4183 0.1070 0.2500 1.0000
In2 0.4291 0.6113 0.2500 1.0000
O1 0.2151 0.1651 0.2500 1.0000
O2 0.1308 0.4769 0.2500 1.0000
O3 0.5214 0.7800 0.2500 1.0000
O4 0.4066 0.4188 0.2500 1.0000
Sr1 0.7536 0.6533 0.2500 0.9288
In1 0.4195 0.1075 0.2500 1.0000
In2 0.4295 0.6119 0.2500 1.0000
O1 0.1290 0.1675 0.2500 1.0000
O2 0.1290 0.4655 0.2500 1.0000
O3 0.5275 0.7761 0.2500 1.0000
O4 0.4054 0.4256 0.2500 1.0000
Ca1 0.7536 0.6533 0.2500 0.1032
SrIn2O4
Sr0.9Ca0.1In2O4
Sr0.8Ca0.2In2O4
Sr0.7Ca0.3In2O4
Sr1 0.7529 0.6535 0.2500 0.8457
In1 0.4179 0.1086 0.2500 1.0000
In2 0.4285 0.6123 0.2500 1.0000
O1 0.2114 0.1684 0.2500 1.0000
O2 0.1347 0.4623 0.2500 1.0000
O3 0.5504 0.7634 0.2500 1.0000
O4 0.4074 0.4274 0.2500 1.0000
Ca1 0.7529 0.6535 0.2500 0.2112
Sr1 0.7533 0.6541 0.2500 0.7798
In1 0.4190 0.1082 0.2500 1.0000
In2 0.4282 0.6122 0.2500 1.0000
O1 0.2094 0.1674 0.2500 1.0000
O2 0.1304 0.4704 0.2500 1.0000
O3 0.5236 0.7824 0.2500 1.0000
O4 0.3985 0.4247 0.2500 1.0000
Ca1 0.7533 0.6541 0.2500 0.3344
Sr1 0.7504 0.6509 0.2500 0.6589
In1 0.4168 0.1087 0.2500 1.0000
In2 0.4283 0.6129 0.2500 1.0000
O1 0.2056 0.1685 0.2500 1.0000
O2 0.1435 0.4415 0.2500 1.0000
O3 0.5596 0.7605 0.2500 1.0000
O4 0.4106 0.4354 0.2500 1.0000
Ca1 0.7504 0.6509 0.2500 0.4396
Ca1 0.7540 0.6487 0.2500 1.0000
Sr0.6Ca0.4In2O4
CaIn2O4

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In1 0.4182 0.1086 0.2500 1.0000
In2 0.4269 0.6124 0.2500 1.0000
O1 0.2080 0.1942 0.2500 1.0000
O2 0.1450 0.4591 0.2500 1.0000
O3 0.5090 0.7964 0.2500 1.0000
O4 0.3890 0.4143 0.2500 1.0000

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Table 3. Percentage of each phase obtained by Rietveld refinement.
Sample
SrIn2O4 (ICSD 16241) SrCO3 (ICSD 202793)
SrIn2O4
89.98%
87.15%
85.64%
88.11%
82.38%
10.02%
12.85%
14.36%
11.89%
17.62%
Sr0.9Ca0.1In2O4
Sr0.8Ca0.2In2O4
Sr0.7Ca0.3In2O4
Sr0.6Ca0.4In2O4

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Table 4. Comparative results between the Egap values ofSr1-xCaxIn2O4 (x=0, 0.1, 0.2, 0.3,
0.4 and 1) obtained in this work and those reported in the literature.
Sample
SrIn2O4
E
gap (eV) Synthesis Method
Ref.
[This work]
[This work]
[This work]
[This work]
[This work]
[This work]
[This work]
[51]
3.66
3.56
3.61
3.61
3.61
3.62
3.82
3.60
3.90
3.66
3.46
3.82
SPU
SPU
Sr0.9Ca0.1In2O4
Sr0.9Ca0.1In2O4
Sr0.8Ca0.2In2O4
Sr0.7Ca0.3In2O4
Sr0.6Ca0.4In2O4
CaIn2O4
SPU
SPU
SPU
SPU
SPU
SrIn2O4
State Solid
State Solid
Combustion
Combustion
SPU
CaIn2O4
[51]
SrIn2O4
[18]
CaIn2O4
[28]
CaIn2O4
[32]

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Table 5. Chromaticity coordinates (CIE) and correlated temperature color (CCT) for
Sr1-xCaxIn2O4 (x=0, 0.1, 0.2, 0.3, 0.4 and 1).
Code
A
B
C
D
Sample
x
y
CCT (K)
10831
14108
16643
8883
Color
SrIn2O4
0.2503 0.3282
Overcast sky (Blue)
Sr0.9Ca0.1In2O4 0.2496 0.2904
Sr0.8Ca0.2In2O4 0.2434 0.283
Sr0.7Ca0.3In2O4 0.2706 0.3379
Sr0.6Ca0.4In2O4 0.2823 0.3472
Beginning dusk (Blue)
Beginning dusk (Blue)
Cloudy sky (Blue)
E
F
7952
7420
Average summer shade (Blue)
Light summer shade (Blue)
CaIn2O4
0.286 0.3703

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