Modified Pechini Sol-gel Method Research Articles

Photodegradation, kinetics and non-linear error functions of methylene blue dye using SrZrO3 perovskite photocatalyst

The degradation of methylene blue dye-contaminated wastewater via photocatalysis is an efficient approach towards environmental remediation. The SrZrO3 perovskite photocatalyst was synthesized using the modified Pechini sol-gel method, and characterized using XRD, FESEM, FTIR, and UV–visible spectrophotometer. Crystallite size obtained by the Scherrer and Williamson-Hall methods were 45.56 and 44.50 nm, respectively. The sample exhibited an orthorhombic crystal structure. The optical bandgap was estimated to be 5.31 eV. Kinetic study for the degradation of methylene blue dye using SrZrO3 in the presence of H2O2 showed complete decontamination of the methylene blue dye in the time interval of 90–120 min under visible light irradiation. The degradation efficiency was above 80.1 % under illumination and less than 40.1 % in dark. Kinetic studies were performed by varying the dose of photocatalyst and initial concentration of methylene blue. It was observed that higher dose of the photocatalyst and lower concentration of the contaminant produced higher rate of degradation. The solution pH 3 and catalysts dosage of 200 mg yielded the highest rate of degradation. The experimental data fitted best into the Psuedosecond order kinetic model with the highest R2 value, indicating a strong linear relationship. The experimental data was subjected into nonlinear error functions, where the Psuedo-second order kinetic model demonstrated lower values of error functions. The results suggest that the prepared SrZrO3 photocatalyst coupled H2O2 is a promising photocatalyst for the decontamination of methylene blue dye under visible light irradiation.

Temperature sensing by means of a near-infrared luminescent Ca8NaBi(PO4)6F2:Nd3+ fluorapatite phosphor

Microrods of calcium sodium bismuth fluorapatite doped with neodymium, denoted as Ca8NaBi1-xNdx(PO4)6F2 (with x ranging from 0 to 0.5), were synthetized using a modified Pechini sol–gel method. The crystalline structure of these phosphors was refined using the Rietveld method and exhibited hexagonal symmetry with space group P63/m—C26h, where the lattice parameters were a = 9.3855(5) Å and c = 6.8998(6) Å for x = 0.2. The particles morphology was analyzed through SEM, revealing an average length of approximately 1.5 µm. When excited at 808 nm, the Ca8NaBi(PO4)6F2:0.2Nd3+ microrods emitted strongly at 872, 957 and 1055 nm, falling within the near-infrared region. These emissions correspond to the 4F3/2 → 4I9/2 (P2), 4F5/2 → 4I11/2(P3), 4F3/2 → 4I11/2(P1) transitions of Nd3+ ions, respectively, and are situated within the first and second biological windows. The luminescence lifetime of the 4F3/2 state of Nd3+ was measured to be 294.4 µs for the sample with the lowest Nd3+ concentration of x = 0.05. In addition, the luminescence intensity ratios P2/P1 and P3/P1 were found to be temperature dependent, potentially making it suitable for luminescent ratiometric thermal sensing. These findings suggest that the synthesized Ca8NaBi(PO4)6F2:Nd3+ microrod thermometers exhibit favorable characteristics in terms of relative sensitivity, temperature uncertainty, and repeatability within the temperature range of 303–403 K.

S-scheme heterojunctions based on novel Sm2CeMnO6 double perovskite oxide and g-C3N4 with excellent photocatalytic dye degradation performances.

It has become of utmost importance to preserve marine life and human health by protecting aquatic environments from contaminants. Therefore, using photocatalytic materials in treatment of contaminated water is a promising and innovative technique. Novel double perovskite Sm2CeMnO6 was synthesized through a modified Pechini sol-gel method. Also, urea and melamine were utilized to synthesize graphitic carbon nitride (g-C3N4). Combination of Sm2CeMnO6 and g-C3N4 produced several S-scheme heterojunction materials in diverse components ratios. Average crystallite sizes of Sm2CeMnO6 and Sm2CeMnO6/g-C3N4 (20:80) samples were calculated by Debye-Scherrer and Williamson-Hall methods to be 19.77, 22.72 nm and 42.01, 43.73 nm, respectively. The coexistence of g-C3N4 (002) with a d-spacing of 0.325 nm and Sm2CeMnO6 planes of (222), (111), and (400) with spacing values of 0.314, 0.302, and 0.294 nm, respectively, was depicted in the HR-TEM image of the Sm2CeMnO6/g-C3N4 (20:80). The estimated bandgaps for the g-C3N4, Sm2CeMnO6, and Sm2CeMnO6/g-C3N4 (20:80) were 2.70, 2.60, and 2.65eV, respectively. Their application was investigated in photocatalytic degradation of methylene blue (MB) dye as typical pollutant. The estimated degradation pathway of MB was also provided through LC-MS analysis. Under the identical conditions, the best photocatalytic performance was found for Sm2CeMnO6/g-C3N4 (20:80) composite. Using response surface methodology (RSM), operational parameters of the photocatalytic degradation were modeled and optimized by the best composite through central composite design approach. Applying optimized parameters led to 96% degradation of MB (8 mg/L) at pH 10 under 120 min visible light irradiation (λ > 365 nm) using 0.15 g of Sm2CeMnO6/g-C3N4 (20:80) composite in 100 mL aqueous solution. Due to low intrinsic charge transfer resistance, modified Eg, and good performance in e‒/h+ pairs production, Sm2CeMnO6/g-C3N4 (20:80) nanocomposite was introduced as a promising S-scheme photocatalyst.

Influence of Rapid Heat Treatment on the Photocatalytic Activity and Stability of Strontium Titanates against a Broad Range of Pollutants

Strontium titanate (STO) photocatalysts were prepared via a slightly modified Pechini sol–gel method. A unique rapid calcination technique with a short exposure time was used to obtain crystalline products. The samples were characterized by X-ray diffractometry, scanning electron microscopy, diffuse reflectance spectroscopy, infrared spectroscopy, nitrogen adsorption–desorption measurements, and X-ray photoelectron spectroscopy. Their photocatalytic activity was evaluated by the photocatalytic oxidation of phenol, oxalic acid, and chlorophenol under UV light irradiation using commercial STO as a reference. These pollutants, together with glucose and propanol, were used to investigate the stability of the samples against various functional groups. All our samples exhibited higher photocatalytic activity than the commercial STO reference. With increasing calcination temperature, the crystallinity and primary crystallite sizes increased while the band gaps and specific surface areas decreased. The photocatalytic activity of the most efficient sample was explained by the presence of SrCO3 on its surface. The STO catalysts were highly stable as they largely retained their crystalline composition after exposure to chemicals with different functional groups. Finally, we compared the costs associated with the unique calcination technique with a more conventional one and found that our method is ~35% more cost-effective.

(Digital Presentation) The New 2H Hexagonal Double Perovskite Ba2CoMnO6 As a Superior OER Catalyst in Alkaline Media

Climate change has stimulated great interest in developing clean and renewable energy conversion and storage solutions. Emerging technologies for solutions, like unitized regenerative fuel cells, metal-air batteries, and water electrolyzers, depend on the reliable catalyst materials suited for long-term application in alkaline environments[1]. In particular, the demanding reaction in these systems is the oxygen evolution reaction involving complex multielectron/proton transfer processes and thus sluggish kinetic.[2] At present, the state-of-the-art OER catalysts are IrO2 and RuO2. However, the high cost and scarcity of these materials severely prevent the wide-scale application of these systems.[3] Perovskite oxide (e.g., single perovskite expressed as ABO3) electrocatalysts are particularly considered next-generation OER catalysts due to their adjustable physicochemical properties and, as a consequence, their catalytic properties by substitution of ions in the A and B sites.[4] Via doping both at A and B site, double perovskite oxides structure can form (AA′B2O5+δ), which were shown to have stable structure during the OER due to proper O p-band center position relative to the Fermi level. The previous research shows that hexagonal perovskites exhibit enhanced catalytic activity rather than cubic or tetragonal perovskites, which is associated with the face-sharing octahedral unit. [5,6] In this work, we systematically investigate doping of parent La2CoMnO6 with Ba to tune the crystal structure and electronic structure. A series of the double perovskites with the chemical formula of La2-xBaxCoMnO6 (x = 0, 0.5, 1.5, 2) were fabricated via the modified Sol-Gel Pechini method. According to Goldschmidt tolerance factor, it is expected that when Ba amount increases in the A site, the crystal structure changes from cubic to hexagonal, which can contribute to electrocatalytic OER activity based above discussions. Furthermore, it is anticipated that increasing Ba content at the A site should result in higher valence state of transition metals due to stabilizing charge balance of the structure. It is widely reported that presence of higher valence state of transition metals is beneficial for OER.The crystal structure was confirmed by combining powder X-ray diffraction (XRD) patterns and selected area electron diffraction (SAED) patterns. The two-layer hexagonal structure of Ba2CoMnO6 (BCM) was further characterized by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The results show doping of Ba into parent La2CoMnO6 resulted in the hexagonal phase formation and BCM achieves a current density of 10 mA cm–2 at a low overpotential of 288 mV and has the highest intrinsic activity in the series of BaxLa2-xCoMnO6 (x = 0, 0.5, 1, 1.5, 2). Furthermore, BCM exhibits outstanding stability of 12 h in a 0.1 M KOH electrolyte. The electronic structure and surface work function values of the catalysts were examined with X-ray photoelectron spectroscopy (XPS). XPS analysis revealed that valence state of Co and Mn increases through Ba amount in the structure, indicating the double perovskite oxide charge balance is maintained. In addition to valence state analysis, we performed work function analysis of the catalysts tested in this work. The result shows work function of the series of BaxLa2-xCoMnO6 (x = 0, 0.5, 1, 1.5, 2) substantially decreases with Ba content. Here, we show that the high intrinsic activity of BCM is not only related with the hexagonal structure and also may be related with exhibiting lower work function value in the series. In addition, our approach presents a new strategy, air quenching method, to synthesize a phase pure 2H-hexagonal double perovskite oxide. [1] Y. Zhou, X. Guan, H. Zhou, K. Ramadoss, S. Adam, H. Liu, S. Lee, H. Shi, M. Tsuchiya, D. Fong and S. Ramanathan, Nature, 534, 231-234 (2016).[2] X. Cui, P. Ren, D. Deng, J. Deng and X. Bao, Energy & Environmental Science, 9, 123-129 (2016).[3] X. Qiu, Y. Zhang, Y. Zhu, C. Long, L. Su, S. Liu and Z. Tang, Advanced Materials, 33, 2001731 (2020).[4] W. Yin, B. Weng, J. Ge, Q. Sun, Z. Li and Y. Yan, Energy & Environmental Science, 12, 442-462 (2019).[5] L. Tang, W. Zhang, D. Lin, Y. Ren, H. Zheng, Q. Luo, L. Wei, H. Liu, J. Chen and K. Tang, Inorganic Chemistry Frontiers, 7, 4488-4497 (2020).[6] C. Chen, G. King, R. M. Dickerson, P. A. Papin, S. Gupta, W. R. Kellogg and G. Wu, Nano Energy, 13, 423-432 (2015).

Synthesis and Characterization of Fluorite-Type La2Ce2O7 Plasma Sprayable Powder for TBCs Application

This work focuses on the fabrication of lanthanum cerate (La2Ce2O7, LC) powders via two chemical routes: modified Pechini sol-gel method and solid-state synthesis. The synthesized LC powders were heat treated in the temperature range of 1000–1400 °C for 6 h and investigated as a material for thermal barrier coating (TBC) applications. For this purpose, the powder morphology, chemical composition, crystal structure and thermal stability were studied. Scanning electron microscopy (SEM) of the synthesized powders revealed an agglomerated structure consisting of fine and uniformly distributed grains. Energy-dispersive X-ray spectroscopy (EDXS) indicated that the chemical compositions of the LC powders were similar to the stoichiometric ratio of La2Ce2O7. A cubic fluorite structure was observed by X-ray diffraction analysis (XRD) after calcining the LC powder prepared by solid-state synthesis at 1300 °C. In contrast, there was always a fluorite structure in the LC powder synthesized by the Pechini sol-gel method after heat treatment over the entire temperature range. The thermal behavior of the LC powders was analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) in the temperature range of 25–1300 °C. Neither an obvious mass change nor a visible energy change was observed within the tested temperature range, indicating high phase stability of the LC powder and its suitability for TBC applications. Spheroidization on the prepared LC powders was also investigated, revealing that powder size and morphology had a significant impact on the spheroidization efficiency.

Structural and optical properties of Bi-and-Pr-doped ZnO

The effect of Bi substitution (up to 2 wt%) on the structural and optical properties of Pr0.01Zn0.97O materials synthesized by a modified sol–gel Pechini method has been investigated. The as-synthesized powders Pr0.01Zn0.97O and Pr0.01Bi0.01Zn0.97O are characterized by X-ray diffraction (XRD), Photoluminescence spectroscopy (PL) and UV–Vis diffuse reflectance spectroscopy (UV–visDRS). The structure refinement of the sample was performed in the hexagonal and monoclinic setting of the (P63mc) and (P21/c) space group. The microstructural effects in terms of crystallite size and lattice strain of these materials were pointed using the Scherrer method, Williamson-Hall (W-H) analysis and size-strain plot (SSPM) method. We found that the incorporation of Bi ion in the Pr0.01Zn0.97O structure caused an increase in the size and the band gap energy of nanocrystals as compared to Pr0.01Zn0.97O. The interesting evolution of PL emission in the UV, visible and continuous deep level emission further, resulted by introducing Bi3+ in the nanocomposites, demonstrates the potential application of this material in optoelectronics devices.

Preparation and Characterization of Ni/ZrTiAlOx Catalyst via Sol-Gel and Impregnation Methods for Low Temperature Dry Reforming of Methane

Recently, the dry reforming of methane (DRM) has received much attention as a conversion technology of greenhouse gases. Ni-based catalysts supported on ternary metal oxide composite (ZrTiAlOx) were prepared to improve the coke resistance properties in the DRM (CH4:CO2 = 1) at low temperature. The ZrTiAlOx supports with different ratios of Zr/Ti were prepared through the modified Pechini sol-gel method, and then the Ni was impregnated on the synthesized support via the incipient wetness impregnation method. Considering the Zr/Ti ratios, different catalytic activity and durability in the DRM were identified. The Ni/ZrTiAlOx catalyst with Zr/Ti of 2 exhibited enhanced coke inhibition property compared to the others at low temperature DRM for 50 h. The catalysts with a high Zr/Ti ratio under the same condition were rapidly deactivated, while the catalyst with a low Zr/Ti ratio showed deficient activity. It was found from temperature-programmed surface reactions (TPSR) and DRIFTS (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) analysis that the addition of Ti has led in to higher catalytic stability at Zr/Ti = 2, which could be as a result of oxygen vacancies generated by the ternary metal oxides. Ni/ZrTiAlOx catalyst with ratio of Zr/Ti = 2 showed high stability and good catalytic activity towards DRM for the production of syngas.

Critical Exponent Analysis and Evidence of Long-Range Ferromagnetic Order in Lightly Pr-Doped Nanocrystalline (La1-xPrx)0.67Ba0.33MnO3 (x = 0.15 and 0.22) Manganites

We investigate the effect of lightly Pr3+ doping ions on the critical behavior of (La1-xPrx)0.67Ba0.33MnO3 (x = 0.15–0.22) perovskite synthesized by the modified sol–gel Pechini method. The obtained critical exponents (beta, gamma and delta) have been investigated by measuring the magnetization around the Curie temperature, TC. Based on the modified Arrott plot and Kouvel–Fisher techniques, scaling hypothesis, and critical isotherm analysis, we have determined the critical exponent values characteristic of magnetic order of (La1-xPrx)0.67Ba0.33MnO3 (x = 0.15–0.22), with β = 0.55–0.49, γ = 1.06–1.01, and δ = 2.702–3.299. These values indicate that the magnetic order due to lightly Pr3+ doping exhibits long-range ferromagnetic ordering. This fact is in good agreement with the mean-field model. In addition, the exchange interaction is obtained as J(r) ~ r4.56 and ~ r4.49 for 15-at. % Pr and 22-at., respectively. We argue that the range of interaction extends beyond the nearest neighbors.

Crystallization kinetics of binary Yb2O3–Al2O3 glass

The ytterbium aluminum garnet composition YbAG (62.5 mol.% Al2O3, 37.5 mol.% Yb2O3) was prepared in the form of glass microspheres by flame synthesis. Precursor powder for flame synthesis with high homogeneity was prepared by modified sol–gel Pechini method. XRD pattern of prepared glass microspheres indicated predominantly amorphous nature of the sample. Detailed study of morphology of the microspheres by scanning electron microscopy revealed the presence of a small fraction of partially or fully crystallized microspheres. The high-temperature X-ray powder diffraction analysis (HT XRD) was carried out in the temperature interval 750–1450 °C: The temperature dependence of phase composition was determined. Crystallization of Yb3Al5O12—ytterbium aluminum garnet phase—was observed in the temperature range 900–1200 °C. The DSC analysis with heating rates 2, 4, 6, 8, 10 °C min−1 in temperature interval 25–1200 °C was performed in N2 atmosphere to study thermal behavior and crystallization kinetics of prepared glass microspheres. The two exothermic effects at 918 and 939 °C were observed, which were attributed to Yb3Al5O12 crystallization. The crystallization kinetics of prepared sample was examined with the use of JMAK model, and the kinetic triplet—frequency factor A = (1.8 ± 2.2) 10+28 min−1 (for the first peak), A = (1.2 ± 1.6) 10+55 min−1 (for the second peak), apparent activation energy Eapp = (6.4 ± 0.1) 10+02 kJ mol−1 (for the first peak), Eapp = (1.3 ± 0.1) 10+03 kJ mol−1 (for the second peak) and the Avrami coefficient m = 3 (for the first peak) and m = 2 (for the second peak)—was determined using RSS, Radj2 , AIC and WAIC criteria.

Structure, morphology and adsorption properties of titania shell immobilized onto cobalt ferrite nanoparticle core

A magnetic core-shell adsorbent was synthesized by immobilization of titanium dioxide nanoclusters on the cobalt ferrite nanoparticles. The synthesis was carried out using a modified Pechini sol-gel method with citric acid and ethylene glycol as chelating agents. The structure and morphology of reference TiO2, pristine CoFe2O4 and resulting nanocomposite CoFe2O4@TiO2 were thoroughly characterized using XRD, XRF, BET, SEM, IR spectroscopy and Mössbauer spectroscopy. The obtained spectral data indicate that a shift of electron density from titanium to oxygen atoms takes place. Antistructure modeling suggests that some titanium atoms are entered into the CoFe2O4 spinel structure resulting in defects of crystalline structure. In this way additional adsorption centers arise. The adsorption efficiency of the CoFe2O4@TiO2 nanocomposite was found to be more than twice as high as compared to TiO2 and CoFe2O4 alone. The observed synergistic effect is associated just with the formation of distorted titania nanocrystals. The obtained magnetic nanoadsorbent proved to be efficient in water purification from dichromate anions (83% removal) and Congo Red dye (61% removal).

Role of non-magnetic dopants on the room temperature ferromagnetism and optical properties of BaSnO3 perovskite

In this study, room temperature ferromagnetism was induced in diamagnetic BaSnO3 ceramic through light doping with non-magnetic elements composed of Tl, Bi, Ce, Zr and Y. Pure BaSnO3 powders were synthesized via a modified sol gel Pechini method. XRD measurements and Rietveld refinement confirmed the formation of cubic BaSnO3 structure with effective incorporation of dopants into BaSnO3 host lattice. A relation between the ionic radius and valence states of the dopants with the occupation sites and defect states in BaSnO3 crystal lattice was noticed. The SEM micrographs of doped BaSnO3 showed an improvement in the grain shape accompanied by grain size reduction, as compared to the characteristics of pure BaSnO3. EDX analysis verified the presence of Ba, Sn and O as main elements besides Tl, Bi, Ce, Zr or Y as dopants in BaSnO3 samples. From Kubelka-Munk plots, the dopants prompted red and blue shifts in the optical band gap of BaSnO3 (3.22 eV) range from 0.04 to 0.06 eV. As based on photoluminescence (PL) measurements, pure and doped BaSnO3 revealed luminescence peaks in the near infrared and visible regions. Interestingly, Tl, Bi, Ce, Zr and Y as non-magnetic dopants stimulated remarkable room temperature ferromagnetism in BaSnO3 structure. The hysteresis loops shape, saturation magnetization (Ms) and coercivity (Hc) value were found to depend on dopant type. Among all dopants, the BaSn0.98Zr0.02O3 composition revealed perfect room temperature ferromagnetism with the highest Ms and Hc values of 0.106 emu/g and 3212 Oe respectively, which draws attention of utilizing it as spintronic material. A correlation between the grain size, oxygen vacancies, ionic radii, oxidation state of dopants and the emerged ferromagnetism was discussed in details.

Pechini sol-gel synthesis of Cu2O/Li3BO3 and CuO/Li3BO3 nanocomposites for visible light-driven photocatalytic degradation of dye pollutant

Cu2O/Li3BO3 and CuO/Li3BO3 nanocomposites were prepared by a modified Pechini sol-gel method. This study indicates that by controlling the process parameters such as type of chelating agent, gelling agent and mole ratio of chelating agent to total metal salts, the various sizes and morphologies of the Cu2O/Li3BO3 nanocomposites can be prepared. The properties of Cu2O/Li3BO3 product were evaluated by using SEM, EDS, XRD, DRS, FT-IR, BET, TEM, HRTEM and VSM analysis. Furthermore, the Cu2O/Li3BO3 nanocomposites exhibited excellent photocatalytic activity for degradation of acid violet 7 as azo dye pollutant under visible light irradiation. Also, the radical trapping test illustrated that the superoxide radicals and holes were the prevailing active species in the photocatalytic performance.

Synthesis and magnetocaloric properties of La0.67Ca0.29Sr0.04MnO3 obtained from modified sol-gel Pechini method

This work deals with the study of the physical properties of substituted lanthanum manganite, La0.67Ca0.29Sr0.04MnO3, prepared by using a modified sol-gel Pechini method. The manganite was obtained following the traditional Pechini method, but starting from an unusual mixture of precursors wherein manganese sulfate replaces the manganese nitrate. This single change induces variations on the physical properties of the compound. The phase crystallization was analyzed using X-ray diffraction along with the Rietveld method of refinement of the structure. Morphological analysis showed particle sizes around 0.5 µm organized in porous structures and forming cubic clusters. The manganite exhibits high crystallinity and second-order ferromagnetic–paramagnetic transition near room temperature. Also, the magnetocaloric effect and the maximum entropy change (ΔSMmax) were calculated by using a phenomenological model. The associated magnetic entropy change |ΔSM| and the relative cooling power have been determined from the phenomenological parameters as a function of the applied magnetic field. In the vicinity of the Curie temperature (TC), ΔSM reached a maximum value of 2.44 J/kgK when 3 T of magnetic strength was applied.

From nanomelting to nanobeads: nanostructured SbxBi1−x alloys anchored in three-dimensional carbon frameworks as a high-performance anode for potassium-ion batteries

A modified Pechini sol–gel method was developed to synthesize three-dimensional pomegranate-like SbxBi1−x@C composites as anode materials for advanced potassium-ion batteries.

Processing of high performance composite cathodes for protonic ceramic fuel cells by exsolution

La0.5Ba0.5CoO3−δ–BaZrO3 (LB–BZ)-based composite materials were prepared by a modified Pechini sol–gel method combined with exsolution.

On the roles of HEC in Pechini sol-gel method: Enhancement of stability, wettability of the sol and surface roughness of Bi2212 film

Bi2212 superconducting thin film was prepared through a modified Pechini sol-gel method called surfactant assisted Pechini. Nitrates were used as reactors, ethylenediamine tetraacetic acid (EDTA) and hydroxyethyl cellulose (HEC) was adopted as chelating agent and surfactant respectively to prepare sol for Bi2212 film. The effects of HEC on the phase formation, crystallization behavior, morphology and superconductivity of the samples were characterized using X-ray diffraction, field emission scanning electron microscope, atomic force microscope and the standard four-probe method. C-axis epitaxial Bi2212 thin film with high Bi2212 phase purity was obtained through the modified method, and the sample had good crystallization properties, smooth surface and excellent electrical transport properties. Furthermore, a model is proposed to clarify the roles of surfactant in the preparation of Bi2212 films.

Multicolor-tunable emissions of YOF: Ln3+/Yb3+ (Ln3+ = Ho3+, Er3+, Tm3+) nanophosphors

Color tuning of down-shifting and up-conversion emissions of YOF:Ln3+/Yb3+ (Ln3+ = Ho3+, Er3+, Tm3+) nanophosphors is demonstrated. Nanophosphors were prepared by the modified sol-gel Pechini method and characterized by the X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. Samples consist of 20 nm particles crystallized in the rhombohedral crystal structure. Depending on the Ln3+/Yb3+ concentration ratio and the type of excitation (UV/VIS or NIR) color of the particle's emission varied from the blue to red. Commission Internationale de L'Eclairage chromaticity coordinates of emission colors are given for the range of Ln3+/Yb3+ concentration ratios for both down-shifting and up-conversion luminescence. We showed that the emission color of these nanophosphors may be additional tuned by simultaneous excitation with UV-VIS and NIR radiation (in different proportion) which yields unique color labels for the anti-counterfeit and security applications.

Bifunctional ferromagnetic Eu-Gd-Bi-codoped hybrid organo-silica red emitting phosphors synthesized by a modified Pechini sol-gel method

Red phosphor, composed of Eu-Gd-Bi-codoped hybrid organo-silica glass, has been synthesized via a modified Pechini sol-gel process. The synthesized hybrid glass was analyzed with powder X-ray diffraction (XRD), differential thermal analysis coupled with thermogravimetry (DTA-TG) and Fourier transform infrared (FTIR) spectroscopy. XRD and DTA-TG confirmed its amorphous structure up to 1000 °C. Magnetic behavior of the produced phosphor was investigated using vibrating specimen magnetometer (VSM) and the obtained results revealed its unsaturated ferromagnetic behavior. Photoluminescence (PL) properties of the obtained phosphor have been investigated under near-UV excitation at 395 nm. The influence of calcination temperature on the PL intensity and its decay behavior as well as on the ferromagnetic characteristics has been studied to determine the optimal reaction temperature of the phosphor. The PL emission spectra show the characteristic emission bands of Eu3+ ions in the wavelength range from 580 to 700 nm. These emission spectra have been dominated by the electric dipole 5D0→7F2 transition of the Eu3+ peaked at 610–620 nm producing the red light emission of the phosphors. It was found that the phosphor performance, expressed by its PL intensity and life time, could be significantly improved by increasing of the heat treatment temperature up to 900 °C. Also, calcination at 900 °C for 6 h greatly increased both of the magnetization and retentivity, while decreased the coercivity value. The organic phenomenon of metal citrate-ethylene glycol chelation and its degradation by calcination were well followed by FTIR spectroscopy. The obtained results are promising and could afford a basis for designing of efficient red phosphors for displays, lighting and bifunctional biosensors for biomedical applications.

Influence of magnetic ion doping on structural, optical, magnetic and hyperfine properties of nanocrystalline SnO2 based dilute magnetic semiconductors

This article reports the structural, optical and magnetic properties of transition metal (Ni, Co, Mn and Fe) doped SnO2 nanoparticles prepared by modified Pechini sol–gel method. From the X-ray diffraction studies, it is obvious that all the synthesized samples show a phase purity of rutile tetragonal crystal structure of SnO2. The morphology was studied and the particle sizes were estimated from the field emission scanning electron microscopy. From photoluminescence spectra, we observed emission due to the presence of singly ionized oxygen vacancies. Raman spectroscopy shows dominant peaks at 644 and 782 cm−1 which were ascribed to A1g and B2g modes of the rutile structure. Isomer shifting due to dopant addition and large quadrupole splitting due to surface defects were observed in Mossbauer spectra. All the samples show ferromagnetic ordering up to 1 T. The relatively stronger ferromagnetic nature in Fe and Co doped SnO2 is due to the strong p–d exchange interaction. In case of Ni and Mn doped SnO2 samples, the lack of carrier-mediated interaction due to its inherent semiconducting nature reduces the total magnetic moment observed in these samples. The exchange coupling depends on the dopant type and its concentration.