Pechini-type Sol Gel Method Research Articles

Visible-light photocatalytic performance of SrTiO3 nanoparticles modified with cobalt

In this article, an experimental study on the photocatalytic performance of SrTi1-yCoyO3 nanoparticles (with y = 0.0, 0.03, 0.06, and 0.09) synthesized by the Pechini-type sol-gel method is presented. The crystalline structure analysis revealed that all the samples exhibited the cubic perovskite phase of SrTiO3. In particular, the SrTi0.91Co0.09O3 sample was found to consist of rough spherical-like particles with an average size of 26 ± 0.5 nm. Cobalt ions with 2+ and 3+ oxidation states are responsible for modifying the electronic band structure of the semiconductor and a narrowing of optical band gap from 3.1 to 1.08 eV. The resulting Co-doped SrTiO3 nanoparticles exhibited photocatalytic activity under visible light due to their enhanced light absorption, effective charge transport and effective surface chemisorption. In particular, the SrTi0.91Co0.09O3 sample exhibited the highest photocatalytic activity with 91 % degradation efficiency of methylene blue dye within 120 min of simulated solar irradiation.

Effects of Dy on structural, morphology, optical, and resistive switching properties of HfO2 thin films

This paper studies the effect of Dy on the structure, morphology, and optical properties of HfO2 thin films deposited on fused silica substrates and the optical transparency and resistive switching (RS) behavior of the thin films as an active insulator layer in Ag/active insulator layer/ITO/glass memories. Thin films were deposited by spin-coating using a precursor solution obtained by the Pechini-type sol-gel method. The structural analysis revealed that the insertion of Dy ions into the HfO2 lattice caused the phase transformation from the monoclinic to the cubic phase. Morphological analysis revealed that the thin films had thicknesses between 98 and 101 nm, and their surfaces were composed of 3D islands formed by aggregates of spherical particles ranging from 8 to 5 nm. The active insulator layers had thicknesses ranging from 235 to 218 nm, with no cavities or cracks between them. The optical transparency of the active insulator layer/ITO/glass memory structures was between 70 and 87 %. Optical transmittance, optical bandgap, and optical constants were modified incorporating Dy ions into HfO2 thin films compared to the undoped HfO2 thin films. Incorporating Dy ions into HfO2 increased oxygen vacancies in the active insulator layers. The memory with 10 w% of Dy had the highest resistance off/on ratio of 9.04 compared with undoped HfO2 memory. Also, the conduction mechanism in the high resistive state (HRS) of the memory with 10 w% of Dy was related to ohmic conduction and space charge limited conduction (SCLC).

Thermoluminescence of beta irradiated SrHfO3 powders synthesized by the Pechini-type sol-gel method

Here, we report on the thermoluminescence response of beta irradiated SrHfO3 powders synthesized by the Pechini-type sol-gel process. Powders calcined at 900 °C for 6 and 8h exhibited the orthorhombic phase of SrHfO3. The intensity TL response of SrHfO3 samples, exposed to beta irradiation doses from 0.085 to 1530 Gy, was found to increase with the irradiation dose. The TL signal of both samples showed a linear behavior in the range of 2.55–51 Gy and a sublinear behavior for higher irradiation doses. At the dose of 25.5 Gy, the TL response of the sample processed with a calcination time of 6h had the best repeatability with a standard deviation of 3.48% and the lowest fade (12.85%) in the first 48 h. The Tmax-Tstop process, initial rise method and glow curve fitting by computerized deconvolution were employed to determine the trap distribution and kinetic parameters. The TL glow curves of the samples were conveniently fitted by five glow peaks of first and second orders with activation energies ranging from 0.56 to 0.99 eV. Overall, the TL response of the samples showed to be influenced by the density and distribution of defects, mainly originated by oxygen and cation vacancies.

The impact of microwave-assisted sintering on fabrication of cobalt ferrite nanostructure foams for gas-sensing

This study employed the Pechini-type sol-gel method to synthesize single-phase cobalt ferrite nanoparticles with almost spherical morphology and an average size of ∼50 nm. The Pechini sol-gel is based on the polysterification reaction between citric acid and ethylene glycol and the formation of colloidal nanoparticles due to the polymerization of an iron-cobalt complex. Foam samples were prepared from the obtained nanoparticles by using urea as the progenic agent and subsequent conventional or microwave sintering. The average grain size values for the microwave and conventionally sintered foam samples were 90 and 280 nm, respectively. Microwave sintering has successfully hindered grain growth regarding the initial ∼50 nm size of the cobalt ferrite nanoparticles. The microwave sintered foam sample showed an approximately two-fold increase in the surface area value compared to its conventionally sintered counterpart. The pore volume for the conventionally and microwave sintered samples was measured at 0.007 and 0.026 cc/g, respectively. Also, the pore diameter values were measured to be less than 2.5 nm in both samples. The pore size distribution within the microwave sintered sample was unimodal, while the conventionally sintered sample showed a bimodal one. The gas-sensing properties of the samples were examined in pure ethanol, acetone, and liquefied petroleum gas (LPG) atmospheres at different temperatures. The results indicated that for all the samples and in all the three atmospheres, the best working temperature is 300 °C. The microwave sintered foam sample showed the highest sensitivity and the shortest response time. This sample was more selective towards ethanol than the other two gases.

A comparison of syntheses approaches towards functional polycrystalline silicate ceramics

This study aims to shed light on processing pathways towards functional silicate ceramics, which show some promise in various emerging applications, including dielectrics and bioactive implant materials. Polycrystalline silicate ceramics of Neso-, Soro- and Inosilicate families were synthesised by three different techniques: (i) a co-precipitation method, (ii) a modified sol-gel method and (iii) standard solid-state reactions. Co-precipitated samples show increased sintering and densification behaviour compared to sol-gel and solid-state methods, with diametral shrinkage values during sintering of 28.8%, 13.3% and 25.0%, respectively. Well-controlled phase formation in these ceramics was most readily achieved through the steric entrapment of cations and shorter diffusion pathways afforded by the modified Pechini-type sol-gel method. Substituting Zn2+ for Mg2+ in enstatite samples was found to enhance the formation of orthoenstatite during cooling, which is otherwise very slow. We present guidelines for the design of synthesis methods that consider the requirements for different functional silicate ceramics in terms of phase formation and microstructure.

A facile construction of bifunctional core-shell magnetic fluorescent Fe3O4@YVO4:Eu3+ microspheres for latent fingerprint detection

Latent fingerprint recognition technique has received increasing attention because it helps to precisely identify human information for many applications. In this study, bifunctional core-shell magnetic fluorescent microspheres have been synthesized via a facile interface Pechini-type sol-gel method using citric acid and polyethylene glycol as chelating agent and cross-linking agent, respectively. The obtained Fe3O4@YVO4:Eu3+ microspheres possess a typical core-shell structure, large magnetization, and strong fluorescence emission. The surface morphology and roughness of the microspheres can be flexibly tuned by controlling the multistep interface deposition process and subsequent calcination temperatures. Due to their well-integrated bifunctionalities, these magnetic fluorescent microspheres show outstanding performance in the visualization of latent fingerprints on various substrates with high definition and excellent anti-interference, and therefore they have great potential for application in identity recognition.

Abstract P-7: NdFeCo-based Nanoparticles for Biomedical Applications

Background: The multifunctional nanoparticles can be promising antitumor materials. The results of a study of synthesized NdFeCoB oxide nanoparticles (NPs) as a basis for drug transportation systems are presented. In the next step, the NPs can be coated by a multifunctional gel shell. Methods: NPs, the composition of NdFexCo1-xB (where x =0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5), were synthesized by a Pechini-type sol-gel method. The synthesis allows tuning of NPs magnet properties by manipulating the microstructure and phase composition. NPs were studied by XRD, SEM, TEM, HRTEM, and VSM. Results: SEM images show that the average size of NPs changed from 280 nm (for x = 0) up to 416 nm (for x = 0.1 – 0.5). At TEM images the NPs of the sample without cobalt (x = 0) have an elongated shape (Fig 1a). Diffraction patterns showed that the NPs consist of single crystal or ordered crystallites. NPs with cobalt mainly consist of crystallites with a size of about 20-50 nm. There are also areas with a complex-grained microstructure. Hysteresis loops and first-order reversal curve analysis indicated that the NPs were ferromagnetic whose coercivity, squareness ratio, and magnetic interactions changed significantly with the cobalt contents.

Preparation and Structure of Oxide and Reduced Nd(Fe<sub>1-x</sub>Co<sub>x</sub>)B Nanoparticles

Nanoparticles of Nd(Fe1-xCox)B with Co concentrations ranging from x = 0 to 0.5 were prepared using a modified Pechini-type sol-gel method. We have shown the influence of Co on the morphology and size of nanoparticles, as well as on elements distribution in nanostructures. It was found that nanoparticles with increased content of Fe and Co were formed during the synthesis process. There was an interdiffusion of Nd and Fe, both after oxidation and after reduction. This study helped to define promising “bottom-up” approaches for the fabrication of nanomaterials for the advanced Nd(Fe1-xCox)B permanent magnets by chemical synthesis.

Mn-modified HfO2 nanoparticles with enhanced photocatalytic activity

Round shaped Mn-modified HfO2 nanoparticles were prepared by the Pechini type sol-gel method. The effects of Mn ions on the structure, particle growth, composition, optical properties and photocatalytic performance of HfO2 particles were investigated. The structure analysis revealed that the insertion of Mn2+, Mn3+, and Mn4+ ions inhibited the complete stabilization of tetragonal HfO2. Also, the decrease of particle size to values lower than 5 nm and the shift of optical band gap from 5.7 to 2.1 eV was obtained as effect of increasing the Mn content. HfO2 nanoparticles modified with 10 w% Mn exhibited the highest photocatalytic performance, reaching an efficiency of 91.93% in the decomposition of methylene blue, after 120 min of sunlight irradiation. The efficient trapping of photogenerated electrons on the surface of these nanoparticles generated •O2− radicals, which were the main oxidative species involved in the degradation of the dye. The improved photocatalytic performance of these nanoparticles is then attributable to their increased surface area, suitable photoactivation, and effective transport of photoexcited charge carriers. Based in studies of band gap, valence band position and active species, a mechanism of photodegradation for this photocatalyst was also proposed and discussed.

The Effect of Reduction Process Parameters on Magnetic and Structural Properties of SmCo/Co Nanocomposites

SmCo nanoplates were synthesized by a combination of Pechini type sol-gel method and reduction-diffusion process. The synthesis process started with (i) preparation of Sm-Co citrate gel, (ii) followed by annealing to obtain Sm-Co oxide powder and (iii) reduction of the powder by CaH2 at different temperatures of 870, 890, 910, 930, 950, and 970 °C for 3 h under hydrogen flow and (iv) separation of the magnetic nanoparticles through a multi-step washing process. A range of characterization techniques including XRD, TG-DTA, FE-SEM, and VSM were employed to investigate the effect of reduction temperature in terms of phase, morphology, microstructure, and magnetic properties of products. The results showed that the SmCo/Co nanocomposites were synthesized at all reduction temperatures of 870–970 °C, but by temperature increase from 930 to 950 °C, the dominant phase turned into SmCo5; the superior phase was Sm2Co17 before this step. The TG/DTA analysis indicated that at reduction temperature of 950 °C and higher, the Sm2Co17 phase is formed at the beginning, then releasing more Sm atoms results in the phase transformation to SmCo5. Meanwhile, after the temperature of 930 °C, the particle’s morphology was also changed from the nanoplates and turned into lumps. Reduced particles at 910 °C, had a maximum coercivity of 881 Oe, and the highest amount of remanence ratio (78%). However, in this sample, in spite of the presence of cobalt, as the soft phase along with SmCo, the magnetic hysteresis loop behaved like a single-phase and it proposed the hard-soft exchange coupling interaction. SmCo/Co nanocomposites were synthesized via Pechini type sol-gel method followed by reduction-diffusion process. By increasing the temperature, the dominant phase changes to SmCo5 due to the formation of excessive amount of Sm atoms. By raising reduction temperature from 930 to 950 °C, the morphology of particles changed from nanoplates to lumps. Magnetic single phase behavior as well as high remanence ratio of samples proposed the existence of exchange coupling interaction between hard and soft phases of SmCo/Co nanocomposites.

Site-Bi3+ and Eu3+ dual emissions in color-tunable Ca2Y8(SiO4)6O2:Bi3+, Eu3+ phosphors prepared via sol-gel synthesis for potentially ratiometric temperature sensing

A series of Ca2Y8(SiO4)6O2 (CYSO):Bi3+, Eu3+ phosphors were prepared via a Pechini-type sol-gel reaction method. The refinement results for CYSO:Bi3+, Eu3+ phosphors implied that they had a pure phase. The blue-green emission ascribed to Bi3+ 3P1→1S0 transition was generated upon UV excitation in Bi3+ singly-doped CYSO samples. Spectral analysis indicated that two main emission bands around 414 and 494 nm correspond to two kinds of Bi3+ occupying the crystal lattices of 4f and 6 h available for Y3+ in CYSO, denoted as Bi3+(2) and Bi3+(1), respectively. A broad spectral overlap between Bi3+ emission and Eu3+ excitation spectra implied the existence of energy transfer from Bi3+ to Eu3+ ions in CYSO:Bi3+,Eu3+, which resulted in the tunable emission color from blue-green to red. The energy transfer mechanism from Bi3+ to Eu3+ ions was determined to be a dipole-quadrupole interaction. Moreover, the quite different luminescence thermal quenching behaviors between Bi3+(2) and Eu3+ showed good temperature sensing properties with a temperature range of 298–523 K by analyzing the temperature sensitivity of the fluorescent intensity ratio [Bi3+(2)/Eu3+(612)]. The maximum absolute and relative sensitivities reached as high as 0.07174 K-1 (523 K) and 0.958% K−1 (423 K), which can be compared to the highest values of 0.015 K-1 and 1.1%K−1 in reported optical thermometric materials before, respectively, based on the thermally coupled level (TCLs) of Er3+. Meanwhile, the luminescence thermal quenching mechanism in this system was investigated in detail. Results inspire that a feasible method based on site-Bi3+ and Eu3+ emissions is potential as one of candidate strategies for developing novel ratiometric optical thermometry materials.

Synthesis of Sm–Co nanoparticles by sol–gel method

Sm–Co nanoparticles have promising applications in both scientific and industrial fields. In this paper, Sm–Co single-crystal nanoparticles were prepared using respective metal salts and complexing agents, such as citric acid by Pechini-type sol–gel method. The mixture solution was heated to form a highly viscous gel, and then heated at different temperatures to achieve SmCo-oxide. And then Sm–Co particles were yielded by reductive annealing of the precursors. Phase analysis, microstructural investigation and magnetic properties were performed by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Fourier transform infrared (FT-IR) and VSM. TGA trace analysis of the gel determined the heat treatment temperature. XRD results showed that SmCoO3 and Co3O4 were obtained at 800[Formula: see text]C, FT-IR spectrometry analysis also verified the results. In the calcium-thermal reduction process, Sm2O3 and Co were obtained after reductive annealing at 800[Formula: see text]C, meanwhile Sm–Co nanoparticles were formed at 850[Formula: see text]C. FESEM analysis revealed that the Sm–Co nanoparticles were composed in the form of spherical granules and exhibited well distribution with size in the range of 100 nm. The room temperature saturation magnetization and coercivity of the Sm–Co nanoparticles were 49.61 emu/g and 3.53 kOe, respectively.

Enhancement of the up-conversion luminescence in LaVO4 nanomaterials by doping with M2+, M4+ (M2+ = Sr2+, Ba2+, Mg2+; M4+ = Sn4+) ions

In this paper, we demonstrate the enhancement of up-conversion luminescence of LaVO4:Yb3+/Ln3+ (Ln = Ho, Er and Tm) nanoparticles by co-doping this material with alkaline ions M2+ (M = Mg, Sr and Ba) and Sn4+ ions. The samples were synthesised by a Pechini-type sol-gel method and annealed at 600 °C for 2 h in an air atmosphere. Their structure and morphology were characterised by powder X-ray diffraction, transmission electron microscopy and inductively coupled plasma atomic emission spectroscopy, revealing that the nanomaterials were single-phase and homogeneous with the dimensions of about 20 nm and co-doped ions were successfully incorporated in LaVO4 lattice. Laser spectroscopy measurements (emission and excitation spectra, luminescence lifetimes and luminescence intensity dependences on power density) indicated that under NIR excitation (about 980 nm) nanoparticles showed bright up-conversion luminescence. After co-doping with M2+/Sn4+ ions, the phase structure of the host lattice remained unaltered, but the cell parameters slightly changed, as these ions can occupy La3+ sites or interstitial positions and change local crystal field. As a result, spectroscopic properties were changed, and emission intensity was enhanced in all samples, making these nanoparticles more attractive in, for instance, photonics or electronic industry.

Effect of Ce doping on the structure and optical properties of HfO2 films by the Pechini-type sol–gel method

HfO2 and Ce-doped HfO2 thin films were deposited by the spin coating of Pechini-type sol–gel solutions on silica-fused substrates. The effect of Ce doping on the structure and optical properties of the HfO2 thin films were studied. The microstructure analysis of the resulting films revealed that the insertion of Ce ions into the HfO2 lattice caused a phase transformation from the monoclinic to the metastable tetragonal t′ form. The surface morphology studies revealed the homogeneous deposition of HfO2 and Ce-doped HfO2, with thicknesses ranging from 515 to 590 nm, formed by the aggregation of spherical particles with sizes <10 nm. X-ray photoelectron spectroscopy revealed the insertion of both Ce3+ and Ce4+ ions in the structure of the Ce-doped HfO2. Although all films were optically transparent, the presence of Ce3+ ions (oxygen vacancies) induced color centers related to the yellowish coloration of the Ce-doped HfO2 films and a red-shift of the optical band gap from 5.67 to 4.02 eV.

Influence of $$\hbox {TiO}_{2}$$ TiO 2 particle size and conductivity of the CuCrO $$_{2}$$ 2 nanoparticles on the performance of solid-state dye-sensitized solar cells

Solid-state dye-sensitized solar cells have been fabricated with mesoporous \(\hbox {TiO}_{2 }\) photoanode and N719 dye as photosensitizer. First, \(\hbox {TiO}_{2}\) and non-doped, Zn- and Mg-doped CuCrO\(_{2}\) nanoparticles have been synthesized by sol–gel method. In addition, the \(\hbox {TiO}_{2}\) pastes have been prepared through Pechini-type sol–gel method. The effect of \(\hbox {TiO}_{2}\) particle size, mesoporous \(\hbox {TiO}_{2}\) photoanode thickness and solid-state electrolyte thickness on the efficiency of the fabricated devices has been investigated. Our results show that in spite of the low amount of dye loading for photoanode with large \(\hbox {TiO}_{2}\) nanoparticles (80–180 nm), the dye-sensitized solar cell made from it has higher efficiency than that constructed from the photoanode comprising of small particles about 10–15 nm in size. The higher efficiency is attributed to the longer diffusion length of electrons because of a better electron transport and penetration of a large amount of \(\hbox {CuCrO}_{2 }\) nanoparticles in the porous structure of \(\hbox {TiO}_{2}\) photoanode. By using the doped \(\hbox {CuCrO}_{2}\) nanoparticles, the efficiency has been increased from 0.027% for \(\hbox {TiO}_{2}\)/N719 dye/CuCrO\(_{2}\) to 0.033% for \(\hbox {TiO}_{2}\)/N719 dye/CuCrO\(_{2}\):Zn and further increased to 0.042% for \(\hbox {TiO}_{2}\)/N719 dye/CuCrO\(_{2}\):Mg. The efficiency enhancement by doping is ascribed to the conductivity improvement due to the presence of impurity atoms.

Multichannel Luminescence Properties of Mixed-Valent Eu2+/Eu3+ Coactivated SrAl3BO7 Nanocrystalline Phosphors for Near-UV LEDs.

Up to now, orchestrating the coexistence of Eu2+ and Eu3+ activators in a single host lattice has been an extremely difficult task, especially for the appearance of the characteristic emission of Eu2+ and Eu3+ in order to generate white light. Nevertheless, here we demonstrate a new Eu2+/Eu3+ coactivated SrAl3BO7 nanocrystalline phosphor with abundant and excellent multichannel luminescence properties. A series of Eu2+/Eu3+ coactivated SrAl3BO7 nanocrystalline phosphors were prepared through a Pechini-type sol-gel method followed by a reduction process. With excitation of UV/NUV light, the prepared SrAl3BO7:Eu2+,Eu3+ phosphors show not only the characteristic f-f transitions of Eu3+ ion (5DJ → 7FJ,J', J, J' = 0-3), but also the 5d → 4f transitions of Eu2+ ion with comparable intensity from 400 to 700 nm in the whole visible spectral region. The luminescence color of the SrAl3BO7:Eu2+,Eu3+ phosphor can be tuned from blue, blue-green, white, and orange to orange-red by changing the excitation wavelength, the overall doping concentration of europium ions (Eu2+, Eu3+), and the relative ratio of Eu2+ to Eu3+ ions to some extent. A single-phase white-light emission has been realized in SrAl3BO7:Eu2+,Eu3+ phosphor. The obtained SrAl3BO7:Eu2+,Eu3+ phosphor has potential application in the area of NUV white-light-emitting diodes.

Study of magnetic properties of NiZnCu ferrite synthesized by Pechini method and solid-state reactions

Ni-Zn-Cu ferrites are exhibiting excellent magnetic properties at large frequencies and are consequently produced as low-loss magnetic materials used for magnetic components in power electronics. Here we present an experimental study of (Ni0.31Zn0.49Cu0.20)0.979Co0.021Fe1.9-dO4 ferrites synthesized by the Pechini type sol-gel method. Their structural and magnetic properties are characterized and compared to the ones of reference ferrites synthesized by classical solid-state reactions. Optimized parameters for Pechini method allow obtaining comparable low magnetic core-losses for both synthesis methods. The cores obtained by this sol-gel method present higher static permeability and lower coercive field than the ones obtained by classical solid-state reactions. Results suggest that the microstructure of ferrites synthesized by Pechini method can be considered as a promising alternative route for the design of low-loss magnetic components.

Highly Stable and Recyclable Graphene Layers Protected Nickel–Cobalt Bimetallic Nanoparticles as Tunable Hydrotreating Catalysts for Phenylpropane Linkages in Lignin

Nickel–cobalt bimetallic nanoparticles coated with several layers of graphene were developed through direct heating treatment of bimetallic oxide precursor prepared by the modified Pechini-type sol–gel method. These nanomaterials were demonstrated to be versatile catalysts for lignin depolymerization. The catalysts showed unexpectedly tunable selectivity that directly depends on the composition of bimetallic nanoparticles. Dimeric lignin model compounds can be converted totally and the hydrogenolysis selectivities above 85% over Ni–Co@C (Ni:Co = 1:3). During the recycling test, the nanocatalyst showed excellent recyclability in the ten-batch investigation. The deposition of graphene layers over bimetal nanoparticles fosters a subtle balance between protecting effects and surface accessibility to catalytic reactions and significantly improves their stability to air and moisture. Ni–Co@C catalysts were readily separated from the liquid mixtures with high recycling ratio due to their magnetic properties. Ni–Co bimetallic nanoparticles are coated with graphene layers. Graphene layers over the nanoparticles protect them from deactivation. Ni–Co@C shows tunable selectivity in the hydrogenolysis of dimeric lignin linkage. The non-precious metal catalyst showed excellent recyclability and can be reused ten times without significant loss of activity.

Magnetic properties and magnetization reversal mechanism of Nd-Fe-B nanoparticles synthesized by a sol-gel method

Nd–Fe–B oxide powders with various pH were prepared using chloride and nitrate precursors including NdCl3·6H2O, FeCl3·6H2O, H3BO3, Nd2O3, Fe(NO3)3·9H2O, HNO3, citric acid (CA), ethylene glycol (EG) by Pechini type sol–gel method. The pH of chloride and nitrate base sols were 0 and 2.2, respectively. Mixed oxide powders were obtained by calcination and annealing the gels. These oxides by using a reduction-diffusion process under high vacuum and employing CaH2 as reducing agent at 800°C were hated to prepare Nd2Fe14B nanoparticles. The role of pH on phase, morphologies, microstructure, and magnetic properties of the powders were investigated. The results show that with a decrease in pH, the average particle size and coercivity of Nd–Fe–B oxide powders were decreased and increased, respectively. Nd2Fe14B nanoparticles were formed successfully after reduction process. The average particle size of reduction treated products were 30 and 65nm for powders which made of chloride and nitrate base metal salts, respectively. Final powders which made of chloride and nitrate base metal salts had a saturation magnetization of 127.7emu/g and 122.8emu/g while the coercivity of samples were 3.32kOe and 1.82kOe, respectively. The experimental results in the angular dependence of coercivity indicated that the normalized coercivity of the permanent magnets Hc(θ)/Hc(0) obeys the 1/cosθ law and intermediate between the 1/cosθ law and Stoner-Wohlfarth formula for different Nd2Fe14B magnets which made of nitrate and chloride base metal salts, respectively. Also, the results show that different Nd2Fe14B magnets which made of nitrate and chloride base metal salts had the maximum energy product of 5 and 16 MGOe, respectively. The Henkel plot showed that magnetic phases in synthesized NdFeB magnets which made of chloride and nitrate base metal salts were coupled by exchange and dipolar interactions, respectively. Different average particle size, morphology and microstructure were the reasons for variation of magnetic properties.

Facile pechini synthesis of Sr3Y2Ge3O12:Bi3+/Eu3+ phosphors with tunable emissions and energy transfer for WLEDs

A series of Sr3Y2Ge3O12 (SYGO), SYGO:Bi3+, SYGO:Eu3+ and SYGO:Bi3+/Eu3+ phosphors were synthesized by a facile pechini type sol-gel method. X-ray diffraction patterns exhibited a characteristic cubic lattice structure with a space group of la3¯d(230) after annealing at 1200 °C for 8 h. The morphological properties of the SYGO host lattice were studied by a field-emission scanning electron microscope, which displayed nearly spherical-shaped particles. Under ultraviolet (UV) or near-UV excitations, the SYGO:Bi3+ phosphors showed the blue emission of Bi3+ (3P1 → 1S0) at 467 nm and the SYGO:Eu3+ phosphors exhibited orange red emission of Eu3+ (5D0 → 7F1) at 594 nm, respectively. The energy transfer process was investigated in between the Bi3+ and Eu3+ ions by the wide spectral overlap of Bi3+ emission spectrum and Eu3+ excitation spectrum. The efficient energy transfer phenomenon from Bi3+ to Eu3+ ions was studied by adjusting the Eu3+ ion concentration in SYGO:Bi3+/Eu3+ phosphors and it was strongly confirmed by their luminescence decay curves. The critical distance was calculated for the energy transfer process from Bi3+ to Eu3+ ions due to the concentration quenching effect and it was further demonstrated to be a resonance type of quadrupole-quadrupole interactions. The obtained photoluminescence results revealed tunable emissions from blue to cool white, depending on the Eu3+ ion concentration. Furthermore, the thermal properties and quantum yield of the optimized cool white-light emitting SYGO:0.02Bi3+/0.05Eu3+ phosphor sample were studied and it exhibited good thermal stability with 20.5% quantum yield. Commission International de I'Eclairage chromaticity coordinates were calculated for all the prepared samples. Therefore, all these results indicate that the SYGO:0.02Bi3+/0.05Eu3+ is a promising phosphor for the application of white light-emitting diodes.