1. Introduction

The chemical and thermal stability of materials with perovskites structure (ABO₃), such as CaZrO₃ (CZ), have attracted a lot of attention to be used as a host matrix for rare earth cations, thus obtaining efficient phosphors with superior luminescent activity (T. Almeida et al., 2021; Holzapfel et al., 2020; Khan et al., 2020; Kunti et al., 2021; Tian et al., 2020). Their properties were associated to their structural arrangement, electronic structure and the possibility to control the doping sites (A or B) (Fukushima et al., 2020; Navami et al., 2020). The crystalline lattice of the CZ is composed by distorted [ZrO₆] and [CaO₈] clusters, in which the Zr atoms are coordinated by six O atoms in an octahedral symmetry, while the Ca atoms are surrounded by eight O atoms (Eglitis et al., 2020; Zeba et al., 2020).

Rare earth cations can create new defects in the forbidden region of the band gap, modifying the electronic properties that reflect in the charge transfers process and, consequently, in the optical properties (Al Boukhari et al., 2020; Chu et al., 2020). In this way, Eu³⁺ cations have a special role for obtaining efficient red phosphors, luminescent devices and lasers, for example, from the doping of several distinct semiconductor host matrices (P. Kumar et al., 2021; Mazzo et al., 2010; 2014; Ortega et al., 2019; Pinatti et al., 2015). The applications of Eu³⁺ cations are mainly related to its nondegenerate ⁷F₀ ground state and nonoverlapping ^2S+1LJ multiplets (Targonska et al., 2019). These cations are sensitive to the symmetry of the local doping site and, as a consequence, can be used to identify changes in the chemical environment (Song et al., 2010; J. Zhang et al., 2020). These advantages come from its electronic configuration which also results in a pure and strong luminescence in the red region when excited in the ultraviolet (UV) region of the electromagnetic spectrum (Saif and Abdel-Mottaleb, 2007; Smith et al., 2019; Tymiński et al., 2020). These materials have too several advantages like high Stoke displacement, defined spectrum, long lifetime and high stability (Bai et al., 2013; Lahtinen et al., 2016; van der Ziel and van Uiert, 1969; Zhou et al., 2021).

The Ca_1-xZrO₃:Eu_x (CZE) samples were studies in some previously published papers (Fukushima et al., 2020; Katyayan et al., 2017; S. Kumar et al., 2018; Shimokawa et al., 2015; Tiwari et al., 2015; H. Zhang et al., 2008). The method of obtaining these materials typically employ high-temperature strategies, such as sol-gel combustion method and solid-state reaction, that use temperatures above 1200 °C to not obtain secondary phases with ZrO₂ and nonstoichiometric oxides of Ca and Zr (Dubey and Tiwari, 2016; Khan et al., 2021; Kunti et al., 2021). These high temperatures also help to form a symmetrical chemical environment for the Eu³⁺ cations, increasing their luminescent emission and their lifetime decay (Fukushima et al., 2020; Shimokawa et al., 2015). Our research group is engaged in the investigation of the doping process with Eu³⁺ cations in different semiconductors (Fernandes et al., 2018; Lovisa et al., 2016; Pinatti et al., 2019), in particular, CZ and CZE samples were previously obtained in another experimental works (André et al., 2014; Oliveira et al., 2017; 2018; Rosa et al., 2015).

As a continuation of this research line, in this joint experimental and theoretical work, we reported the excitation-induced tunable photoluminescence (PL) properties of CZE, at different Eu³⁺ cations concentration (0.01, 0.02, 0.04, and 0.08 mol% named as CZE1, CZE2, CWZ4, and CZE8, respectively). The samples were prepared by a simple sol-gel method followed by a soft thermal treatment (600 °C) without any surfactant. This methodology enabled them to be promising materials in inorganic single-emitting component regions for optical applications. In addition, first-principles quantum-mechanical calculations, at the density functional theory (DFT) level, have been used to study and predict the structure and the PL, which would promote the development of CZE based phosphors.

2. Experimental procedures and computational details

Synthesis: CZ and CZE samples were prepared by the sol-gel method. The starting reagents used were calcium chloride dihydrate (CaCl₂·2H₂O, 99%, Synth), zirconium oxychloride (IV) octahydrate (ZrOCl₂·8H₂O, 99.5%, Sigma-Aldrich), europium oxide (Eu₂O₃, 99%, Sigma-Aldrich), ethylene glycol (C₂H₆O₂, 99.9%, J. T. Baker), and citric acid monohydrate (C₆H₈O₇·H₂O, 99.5%, J. T. Baker). The first step of the CZ synthesis consists in the zirconium citrate’s preparation. For this, 1 × 10⁻³ mol of ZrOCl₂·8H₂O was added to 25 mL (2.5 × 10⁻⁵ mol L^–1) of distilled water and add 12 × 10⁻³ mol of citric acid was added to the solution at 60 °C under stirring. After this process, 1 × 10⁻³ mol of CaCl₂·2H₂O was add to this zirconium citrate. During the previous processes, the solution was kept under N₂ bubbling to avoid the formation of unwanted phases, such as ZrO₂ and nonstoichiometric oxides of Ca and Zr. Then, ethylene glycol (in the proportion 60:40 in relation to the mass of citric acid) was added to the solution and the N₂ bubbling was removed. The temperature of the solution was changed to 80 °C to evaporate the resulting water and to form a resin. This resin was sent to the oven, undergoing three subsequent thermal processes, 110 °C/1 h, 250 °C/1 h and 400 °C/1 h. The resulting powder was taken to calcination at 600 °C for 1 h, obtaining a final white powder. For CZE samples, an identical process was performed, changing only that an acid solution of Eu³⁺ cations was added to the zirconium citrate before the CaCl₂·2H₂O. The amount of mass of Eu³⁺ cations to obtain the replacement of Ca²⁺ by Eu³⁺ cations were carried out respecting the purity of the reagents as well as the charge balance.

Characterizations: The CZ and CZE samples were characterized by X-ray diffraction (XRD) with a Rigaku DMax 2500PC (Cu Kα λ = 1.5406 Å). Element analysis of the samples was performed with a XRF 720 Shimadzu (4 kV and 80 mA). Micro-Raman spectroscopy were performed by the iHR550 spectrometer (Horiba Jobin-Yvon) coupled to a silicon CCD detector and an argon-ion laser (Melles Griot, 514.5 nm, 200 mW). Diffuse reflectance spectroscopy (DRS) measurements were performed using a Varian Cary spectrometer model 5G in the diffuse reflectance mode, with a wavelength range of 300 to 800 nm and a scan speed of 600 nm min⁻¹. Photoluminescence measurements at room temperature were performed using a 500MSpex spectrometer coupled to a GaAs photomultiplier tube (GaAs PMT). A Kimmon He-Cd laser (325 nm laser; 40mW maximum power) was used as the excitation source for PL measurements. The Fluorolog Jobin–Yvon Fluorolog III spectrofluorometer, under excitation of a xenon lamp was used to obtain the emission (394 nm) and excitation (614 nm) spectra as well the decay lifetime.

Computational details: Computational methods and theoretical procedures were utilized to study the bulk properties of CZ and CZE structures. Calculations were carried out using the periodic ab initio CRYSTAL17 package, (Dovesi et al., 2018) based on DFT using the B3LYP hybrid functional (Becke, 1993; Lee et al., 1988). In all calculations, the atomic centers were described by the standard all-electron basis set for the Zr, Ca and O atoms, consisting of (9s)-(7631sp)-(621d), (8s)-(6511sp)-(21d), (8s)-(411sp)-(1d), respectively. Basis sets for Zr, Ca and O were taken from references (De La Pierre et al., 2014; Valenzano et al., 2011), whereas an effective core potential (ECP) pseudopotential, with 11 valence electrons described by (5s5p4d)/[3s3p3d] (VTZ quality) basis sets, was used for the trivalent Eu atom. According to the f-in-core approximation, the electrons of the 4f shell of Eu³⁺ are incorporated in the pseudopotential (Oliveira et al., 2018).

Atomic positions and unit cell parameters were fully relaxed with respect to the total energy of the system for both CZ and CZE models. The convergence criteria for mono- and bielectronic integrals were set to 10⁻⁸ Hartree, while the RMS gradient, RMS displacement, maximum gradient, and maximum displacement were set to 3.0 × 10⁻⁴, 1.2 × 10⁻³, 4.5 × 10⁻⁴, and 1.8 × 10⁻³ a.u., respectively. Regarding density matrix diagonalization, the reciprocal space net was described by a dense mesh consisting of a shrinking factor set to 4×4×4 in the Monkhorst–Pack method (Monkhorst and Pack, 1976). The accuracy of the evaluation of the Coulomb and exchange series was controlled by five thresholds, whose adopted values were 10⁻⁸, 10⁻⁸, 10⁻⁸, 10⁻⁸ (ITOL1 to ITOL4), and 10⁻¹⁴ (ITOL5).

Herein, the CZ model was calculated considering the conventional unit cell with orthorhombic symmetry (Pcmn) containing 20 atoms. A supercell (2×1×2) expansion simulated the crystalline structure of the CZE model, containing 79-atoms, where two Eu³⁺ cations replaced two Ca²⁺ cations leading to the creation of one Ca²⁺ vacancy to neutralize the charges corresponding to a doping concentration of 12.5%. The neutrality in CZE model can be described as CaZrO₃ + Eu(III) → Ca_0.8125Eu_0.125ZrO₃(V_Ca), where V_Ca represents a calcium vacancy. It is worth to mention that such charge compensation mechanism is commonly used to investigate rare-earth doping in perovskites (Kunti et al., 2021).

A schematic representation in terms of component clusters, the cation replacement and vacancy formation mechanisms associated with the doping process, and the crystalline structure of CZ and CZE models are illustrated in Fig. 1. Here, it is important to point out that Eu-doping configurational tests were carried out to select the most favorable sites for Eu-doping.

3. Results and Discussion

In order to understand the modifications generated at long-range in the CZ and CZE samples, XRD diffractograms were performed. XRD shows that all materials have similar profiles linked to the orthorhombic CZ structure (Fig. 2a), according to card No. 97463 in the Inorganic Crystal Structure Database (ICSD) (Levin et al., 2003). The orthorhombic CaZrO. structure belongs to the space group Pcmn, being formed by distorted [CaO₈] and [ZrO₆] clusters. There was no secondary phase formation, indicating that the Eu³⁺ cations substitution process takes places successfully. For comparison, the theoretical lattice parameters and the unit cell volume calculated at the B3LYP level of theory were listed in Tab. 1.

An analysis of the results shows that the substitution of Ca²⁺ by Eu³⁺ cations induce variations in the atomic coordinates of the O atoms, indicating the existence of structural and electronic distortions in the [CaO₈], [ZrO₆], and [EuO₈] clusters, as well as changes in the lattice parameters and an expansion of cell parameters of ~2.86% is found in the unit cell volume.

Complementing the XRD analysis, micro-Raman measurements were performed to analyze the short-range modifications caused by the substitution of Eu³⁺ cations in the CZ structure (Fig. 2b). There are 13 active modes in the Raman spectrum, which are related to specific vibrations of the [ZrO₆] clusters (André et al., 2014; Evangeline et al., 2017; Rosa et al., 2015; Zheng et al., 2004). For the CZE samples, it was observed with the increase in the concentration of Eu³⁺ cations, there is a loss of definition in the modes located at 177, 184, 205, 221, and 229 cm⁻¹. This is due to the increase in local disorder caused by the propagation of distortions of [EuO₈] clusters in the CZ structure.

The average crystallite size (D) obtained through the Scherrer’s equation (Eqs. 1 and 2) and the lattice strain (ε) (Eq. 3) value are shown in Tab. 2.

where D is the average crystallite size, λ is the X-ray wavelength (0.15406 nm), θ is the Bragg angle, β_obs is the experimental full width at half maximum (FWHM) of the sample, and β_st is the FWHM of LaB₆ standard (Muniz et al., 2016). These parameters, D and ε, were also obtained by the Williamson-Hall (WH) plot obtained through Eq. 4:

where β is the FWHM of the peak, D is the crystallite size, λ is the 0.154056 nm, K is 0.89, and ε is the lattice strain (Manohar et al., 2021; Mesquita et al., 2021).

For the CZE samples, a tendency to decrease the D value is observed in reference to the CZ sample. This behavior is due to the low concentrations of the rare earth that can inhibit the growth of CZ crystallite (El-Bahy et al., 2009; Jayachandraiah et al., 2015). In general, the doping process induces a structural and electronic strain in the crystalline lattice, evidenced by the increase in the ε value (W. Liu et al., 2017). To confirm the amount of Eu³⁺ cations in the CZE samples (spectral line Lα, energy 5.849 keV), X-ray fluorescence (XRF) measurements (S4 Pioneer, Bruker) were performed (Tab. 2). It is observed that the real concentration Eu³⁺ cation is very close to the nominal one, confirming the replacement of Ca²⁺ by Eu³⁺ cations.

The calculated band structure and density of states (DOS) projected for the atoms and orbitals of CZ and CZE models are displayed in Fig. 3. An analysis of the band structure and projected DOS presented here reveals that the direct transition is produced along the k-points Γ-Γ (000 to 000) and U-Γ (101 to 000) from the top of the VB to the bottom of the CB of pure and doped models, respectively. The E_gap values is 6.23 eV to CZ and 5.09 eV to CZE 12.5% model. As regard the obtained E_gap values, experimental and theoretical values were compared evidencing a good agreement.

An analysis of the DOS, the main contribution to the valence band maximum (VBM) region is due to the 2p (p_x, p_y, and p_z), orbitals from the O atoms and a predominance of the 4d (d_z², d_x²_-y², d_xy, d_xz, d_yz) and 4f (f³, f_xz², f_{yz2, fz(x}²_-y²₎, f_xyz, f_x(x²_-3y²₎, f_y(3x²_-y²₎) states formed by Zr and Eu atoms is found in the conduction band minimum (CBM) region, situated from 6.23 to 9 eV (CZ) and from 5.09 to 6.5 eV (CZE 12.5%) and with a small contribution from Ca orbitals.

Additionally, the Fig. 4 summarizes the electronic density maps of the CZ and CZE (12.5%) models obtained from the optimized wavefunction, where the electronic density matrix was resolved as isolines that describe the density in an area. These electronic density maps were described along the Ca−O, Zr−O, and Eu−O bonds direction of the models, which corresponds more specifically to the diagonal (110) plane (Fig. 4).

To observe the possible application of CZE samples as a red emitter, the samples were first excited with a laser at 325 nm (Fig. 5). The CZ sample has a broadband emission profile, characteristic of a multiphonic process, involving several intermediate energy states (Gupta et al., 2015b). The maximum emission of the CZ sample is found in approximately 447 nm, in the blue region, which is the result of internal charge transfers of O 2p to Zr 4d orbitals (Oliveira et al., 2017). For CZE samples, the broadband emission characteristic of the CZ sample is no longer observed, giving space to the specific emission of Eu³⁺ cations. The characteristic emission bands of the Eu³⁺ cations are located at 584, 596, 615, 659, and 705 nm can be assigned to the transitions ⁵D₀→⁷F_J, J = 0, 1, 2, 3, and 4, respectively (D’Achille et al., 2021; Gnanam et al., 2021; M. Liu et al., 2021; Riul et al., 2021). The intensity of the CZE samples is proportional to the concentration of Eu³⁺ cations, being the CZE1 sample the least intense and CZE8 sample the most intense. The maximum emission of CZE samples was attributed to the ⁵D₀→⁷F₂ transitions (615 nm). The appearance of these transitions confirms the CZ structure as a good host matrix for sensitizing the red emission of Eu³⁺ cations.

Figure 6a shows the excitation spectra of CZE samples under 614 nm emission band. At 280 nm a broad band related to the CZ matrix is observed. According to Dorenbos (2003), this emission related to the charge transfer band (CTB) of O²⁻ to Eu³⁺. It is also observed the emissions referring to the transitions of the Eu³⁺ cations for CZE samples. These transitions are ⁷D₀→⁵D_J (J = 2, 3 and 4), ⁷F₀→⁵L_J (J = 6, 7 and 8) and ⁷F₀→⁵G_J (J = 4, 5 and 6) (Vieira et al., 2019). The most intense is located at 394 nm referring to the ⁷F₀→⁵L₆ transition. This transition inspecific is useful for applications in near-UV and LEDs (Hou et al., 2012; Singh et al., 2021). The emission spectra of CZE samples excited at 394 nm was shown in Fig. 6b. It is observed that the transitions ⁵D₀→⁷F_J, J = 0, 1, 2, 3, and 4, become more defined, locating at 565, 592, 616, 655, and 703 nm (Chen et al., 2000; X. Liu et al., 2007; Song et al., 2010). The red emission at 616 nm is due to the ⁵D₀→⁷F₂ electric-dipole transition that is parity forbidden and hypersensitive by the crystalline field (Baig et al., 2021; Bharathi et al., 2021; Wu et al., 2021). The ⁵D₀→⁷F₁ magnetic-dipole transition is located at 592 nm it is not affected by the environment (Kalu et al., 2021; Lakde et al., 2021; Peipei et al., 2021). So, the integrated area ratio of the peaks corresponding to ⁵D₀→⁷F₂ and ⁵D₀→⁷F₁ transitions provides information on the changes in the environment around the Eu³⁺ cations (Parchur and Ningthoujam, 2012). The values obtained for the samples are 4.92, 4.91, 4.81, and 4.66 for the samples CZE1, CZE2, CZE4, and CZE8. These values are very close and indicate that the Eu³⁺ environment changes to a higher symmetry site with the increase in the concentration of Eu³⁺ cations, since the ratio of the relative areas decreases with the increase of the Eu-doping. (P. Almeida et al., 2021; Mazzo et al., 2010; Pinatti et al., 2015).

Figure 7a depicts the decay behavior of the ⁵D₀→⁷F₂ transition for Eu³⁺ cations in the CZE samples, using the emission and excitation wavelengths fixed at 614 and 394 nm, respectively (He et al., 2018; Parchur et al., 2011). These life times were fitted using a monoexponential function (Eq. 5):

where y is the intensity; y₀ is the intensity at the 0 ms; A₁ is the amplitude and τ is the lifetime of the ⁵D₀→⁷F₂ transition (Nyein et al., 2003).

Excited state τ values determined were 1.16, 1.14, 1.12, and 1.06 ms to CZE1, CZE2, CZE4, and CZE8, respectively. The excited state τ values of Eu³⁺ cations decreased with increasing doping concentration due the exchange interactions between activated ions pairs and the higher concentration of the activated ions density around quenching center. Figure 7b shows the monoexponential decay of the samples fitted with an exponential function as the Eq. 5. The energy transfer rate between Eu³⁺–Eu³⁺ (η_Eu-Eu) was calculated by the Eq. 6:

where τ_CZE is the lifetime of CZE samples and τ_CZEH is the lifetime of the sample with higher τ (in this case, 1.16 ms to CZE1) (Kunti et al., 2021).

The obtained η_Eu-Eu values were 1.72, 3.44 and 8.62, for CZE2, CZE4 and CZE8, respectively. The distance between Eu³⁺ cations decrease with increasing concentration of these cations in the CZ host matrix, causing an energy transfer more efficient and allowing new decay channels (Kunti et al., 2021). These extra channels provide new radiative and nonradiative transition probabilities decreasing the lifetime (İlhan and Keskin, 2018). The efficiency of energy transfer (η_ET) (Eq. 7).

where τCZE is the lifetime of CZE samples and τ_CZ is the lifetime of the CZ sample (2.57 in this case) (Li et al., 2007).

The obtained η_ET values were 0.5486, 0.5564, 0.5642, and 0.5875 for the CZE1, CZE2, CZE4, and CZE8, respectively. As expected, the energy transfer efficiency (η_ET) goes hand in hand with the increase in the concentration of Eu³⁺ cations.

Figure 8 shows the color variations of the characteristic emissions of the samples according to the Commission Internationale de L’Éclairage (CIE) (Du et al., 2013). As a characteristic emission, for the CZ sample its emission in blue region is observed at 325 and yellow at 394 nm. However, for the CZE samples, with the increase in the amount of Eu³⁺ cations in the CZ host matrix, a displacement towards the red region is observed, reaching almost pure red emission in both excitations.

In addition, theoretical methodology can contribute to an explanation for the optical properties, since a reduction in the band gap value and the PL emissions of CZ and CZE models. In order to clarify the effect of Eu³⁺ cations on the PL emissions of CZ, it was proposed a general scheme combining the DOS and band structure calculations for CZ and CZE models, as shown in Fig. 9.

Doping with Eu³⁺ cations generate a new electron density distribution, being located on the oxygen-mediated [EuO₈]–[ZrO₆] interaction, to which is trapped in empty Zr (4d) and Eu (4f) orbitals. Initially, the Eu³⁺ cations doping process induces the formation of V_Ca sites that perturb the VB energy levels and promotes the insertion of 4f orbitals in the CBM; in other words, intermediate energy levels are introduced in the E_gap region, reducing the energy required for electron transfer (Fig. 9a). The next step is the photoinduced electron transfer from the VB to the CB, generating an electron–hole pair within the CZE electronic structure (Fig. 9b). This step is crucial because it offers a new interpretation of the optical properties of a material.

In addition, a deeper insight into the PL emission of pure and Eu-doped structures, based on the effective mass of electrons (m_e*) and holes (m_h*), following the procedure reported in a previous study is presented in Tab. 3 (Silva et al., 2020). Such an approach is effective in discussing the photoinduced properties of solid-state materials once the effective mass allows one to ascertain the mobility of the charge carriers.

The calculated values reported in Tab. 3 for CZ and CZE indicates that excited electrons are lighter than generated holes. Also, it was observed that Eu-doping induces a heavier (lighter) electron (hole) effective mass in comparison to CZ, increasing the hole mobility that contributes to increase the electron–hole recombination rate, explaining the superior PL properties of CZE. This fact can be associated with the bonding character of Eu−O interactions in comparison to Ca−O summed to the presence of V_Ca in the doped crystalline structure due to the electron density redistribution that governs the band gap narrowing for doped samples, as confirmed in Fig. 9. Once the Eu−O bonds are more covalent than Ca−O, the band curvature is affected, and the effective mass of electrons and holes is controlled from doping.

4. Conclusions

In this paper, a simple sol-gel method followed by a soft thermal treatment without any surfactant was applied to investigate the influence of Eu³⁺ cations in the host matrix of CZ. The Ca_1-xZrO₃:Eu_x crystals (x = 0.01, 0.02, 0.04, and 0.08 mol%) were characterized by XRD and the patterns confirms that the Eu-doped samples present an orthorhombic structure as the CZ pure. However, the results shows that the replacement of Ca²⁺ by Eu³⁺ cations induce local defects in the lattice causing distortions in the [CaO₈], [ZrO₆], and [EuO₈] clusters, as well as changes in the lattice parameters and an expansion of cell parameters. The micro-Raman results disclosure that the presence of Eu³⁺ cations in the host matrix of CZ caused a loss of definition in the modes located at 177, 184, 205, 221, and 229 cm⁻¹ due to the increase in local disorder. The real amount of Eu³⁺ cations in the CZE samples was verified by XRF and the results confirms the presence of Eu³⁺ cations in the host matrix. The substitution of Ca²⁺ by Eu³⁺ cations also affected the Egap value in which a decrease with the increase of Eu³⁺ cations amount in the host matrix was observed, and this result was endorsed by the first-principles calculations. According to the DOS analysis, the electronic density in the VBM is due to the O 2p orbitals and a predominance of the Zr 4d and Eu 4f orbitals is observed in the CBM. The luminescence profile of the sample was investigated, and the results show that the intensity of the CZE samples is proportional to the concentration of Eu³⁺ cations, being the CZE1 sample the least intense and CZE8 the most intense. The appearance of the ⁵D₀→⁷F₂ transitions (615 nm) confirms that the CaZrO₃ structure is a good host matrix for sensitizing the red emission of Eu³⁺ cations. From the experimental and theoretical results, it was proposed a general luminescence scheme for the CZE samples.

Authors’ contribution

Conceptualization: Assis, M.; Oliveira, M. C.; Gouveia, A. F.; Ribeiro, R. A. P.

Data curation: Assis, M.; Ribeiro, R. A. P.; Bort, J. M. A.; Longo, E.

Formal Analysis: Assis, M.; Oliveira, M. C.; Gouveia, A. F.; Ribeiro, L. K.; Ribeiro, R. A. P.

Funding acquisition: Rosa, I. L. V.; Ribeiro, R. A. P.; Bort, J. M. A.; Longo, E.

Investigation: Assis, M.; Oliveira, M. C.; Gouveia, A. F.; Ribeiro, L. K.; Ribeiro, R. A. P.

Methodology: Assis, M.; Oliveira, M. C.

Project administration: Bort, J. M. A.; Longo, E.

Resources: Rosa, I. L. V.; Ribeiro, R. A. P.; Bort, J. M. A.; Longo, E.

Software: Oliveira, M. C.; Gouveia, A. F.; Ribeiro, R. A. P.; Bort, J. M. A.

Supervision: Rosa, I. L. V.; Ribeiro, R. A. P.; Bort, J. M. A.; Longo, E.

Validation: Assis, M.; Oliveira, M. C.; Gouveia, A. F.; Ribeiro, R. A. P.

Visualization: Assis, M.; Oliveira, M. C.; Gouveia, A. F.; Ribeiro, R. A. P.

Writing – original draft: Assis, M.; Oliveira, M. C.; Gouveia, A. F.; Ribeiro, L. K.; Ribeiro, R. A. P.

Writing – review & editing: Assis, M.; Oliveira, M. C.; Gouveia, A. F.; Ribeiro, L. K.; Ribeiro, R. A. P.

Data availability statement

The data will be available upon request.

Funding

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP). Grant No: 2013/07296-2; 2019/01732-1.

Universitat Jaume I. Project: UJI-B2019-30.

Acknowledgments

The authors acknowledge the support of institutes: CDMF (Centro de Desenvolvimento de Materiais Funcionais), Universidade Federal de São Carlos/FAPESP and Universitat Jaume I. M.A. was supported by the Margarita Salas postdoctoral contract MGS/2021/21(UP2021-021) financed by the European Union-NextGenerationEU. J.A. acknowledges Universitat Jaume I (project UJI-B2019-30), the Generalitat Valenciana (Project AICO/2020/329), and the Ministerio de Ciencia, Innovación y Universidades (Spain) (project PGC2018094417-B-I00) for financially supporting this research. A.F.G acknowledges the Universitat Jaume I for the postdoctoral contract (POSDOC/2019/30).

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Notas de autor

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