Garnet Nanoparticles Research Articles

Crystallization kinetics and densification of YAG nanoparticles from various chelating agents

Yttrium aluminium garnet (YAG, Y 3Al 5O 12) nanoparticles were prepared using sonochemical sol–gel method with three different chelating agents and the effect of crystallization kinetics was investigated with differential scanning calorimetry–thermogravimetry (DSC–TG). The activation energy values of crystallization for the as-synthesized YAG nanoparticles using citric acid (CA), glycine (G) or a mixture of citric acid–glycine (CA–G), as chelating agents were found to be 160.5, 142.2 and 140.4 kJ mol −1 and the corresponding Avarami constants were 2.2, 2.1 and 1.9, respectively. Samples produced with the mixed chelating agent under sonification, could be crystallized to single phase YAG nanoparticles (10–65 nm) after annealing at 1100 °C. Pellets made from the annealed YAG particles could be sintered to a relative density greater than 99% at 1500 °C with a grain size of 4.5 μm, made up of secondary particles formed from primary nano-crystals within the grains. Grain size and relative density increased with different chelating agents from CA to G and CA–G in the increasing order when YAG samples were sintered. Grain growth and densification occurred at a relatively low temperature of 1500 °C as compared to over 1800 °C in solid-state reactions.

Properties of sol-gel derived YAG:Eu3+ hierarchical nanostructures with their time evolution studies

Eu 3 + doped yttrium aluminum garnet (YAG) nanoparticles were synthesized by sol-gel method. The samples were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy including vacuum ultraviolet (VUV) PL spectroscopy. XRD confirmed that each and every phases of YAG were present, indicating very good quality of sample. The crystallite size, estimated by XRD, increased from 10 to 30 nm with annealing temperatures and significant changes in morphology with annealing temperature was also found in TEM study. The particles were in spherical shape initially but agglomeration of particles started at higher temperatures resulting in hierarchical nanostructures having dimension more than 50 nm. The annealed YAG:Eu3+ hierarchical nanostructures showed strong red luminescence under VUV excitation, corresponding to D50→F72 transition. PL spectra also showed significant increase in luminescence intensity with the increase in annealing temperature. Time evolution studies were also performed continuously for 150 days to check the stability of prepared hierarchical nanostructures and were found to be extremely stable, making them one of the most feasible candidate for red phosphor and seize great potential in flat panel display application that underlies the importance of the current work.

The effect of chelating copolymer additive on the yttrium iron garnet (YIG) nanoparticle formation

AbstractA series of the acrylic chelating polymer, poly(butyl acrylates‐co‐glycidyl methacrylate‐co‐2‐methylacrylic acid 3‐(bis‐carboxymethylamino)‐2‐hydroxy‐propyl ester) was prepared to act as the additive in the preparation of yttrium iron garnet (YIG) nanoparticle precursor (ACP). The ACPs and YIG nanocrystal were identified by using Fourier transfer infrared spectrophotometry (FT‐IR), inductively coupled plasma (ICP), X‐ray diffraction (XRD) spectra, and transmission electron microscope (TEM) micrograph, respectively. Compared to the traditional YIG preparation, the well‐formed YIG nanocrystal could be obtained by using this ACP precursor at a low calcination temperature of 600°C. In addition, the more amount of the chelating group was added, the higher purity of the YIG nanocrystal was obtained. Furthermore, the YIG nanocrystal obtained by using the ACP precursor had a nearly superparamagnetic behavior and their saturated magnetic property was around 5.7–41.9 emu/g after the vibrating sample magnetometer (VSM) examination. In summary, the chelating polymer additive improves not only the crystallinity of the YIG nanocrystal but also magnificently decreases the sintering temperature of the YIG nanocrystal. Copyright © 2009 John Wiley & Sons, Ltd.

Microwave-assisted synthesis and characterization of Bi-substituted yttrium garnet nanoparticles

Bi-substituted yttrium iron garnet (Bi–YIG, Bi 1.8Y 1.2Fe 5O 12) nanoparticles were prepared by microwave-assisted co-precipitation as well as conventional co-precipitation using ammonia aqueous solution as precipitant. The nanoparticles were characterized by thermal gravity-differential thermal analysis, X-ray powder diffraction, transmission electron microscopy, dynamic light scattering and vibrating sample magnetometer, respectively. The Faraday rotation of Bi–YIG modified PMMA slices was also investigated. Results demonstrate that the Bi–YIG nanoparticles prepared by microwave-assisted co-precipitation show smaller particle size and higher Faraday rotation than those prepared by conventional co-precipitation.

Magnetic studies of Bi x Y3-x Fe5O12 fabricated using conventional method

A series of Bi substituted yttrium iron garnet (Bi-YIG) nanoparticles with nominal formula of Bi x Y3 − x Fe5O12 in which x varied in steps of 0.0, 0.25 and 0.5 are prepared by conventional method. Vibration sample magnetometer (VSM) at Room temperature (RT) shows saturation magnetization decreases from 27.4 to 25.2 (emu/g) as x value increases from 0.0 to 0.5. Room temperature 57Fe Mossbauer spectra are recorded for these series. The hyperfine field value for octahedral and tetrahedral of samples increases from 484 and 390 kOe to 491 and 397 kOe respectability, as Bi replaces Y in (Bi x Y3 − x Fe5O12) atom with increasing x value. The effect of Bi3 + substitution for Y3 + on lattice constants, morphology and magnetic properties of pure YIG has been investigated.

Effect of lanthanum ions on magnetic properties of Y3Fe5O12 nanoparticles

Lanthanum ion (La3+)-substituted garnet nanoparticles Y3−x La x Fe5O12 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) were fabricated by a sol–gel method. Their crystalline structures and magnetic properties were investigated by using X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Mossbauer spectrum. The XRD results show that samples of Y3−x La x Fe5O12 (0.0 ≤ x ≤ 0.8) are all single phase and the sizes of particles range from 32 to 65 nm. Those of Y2LaFe5O12 consisted of peaks from garnet and LaFeO3 structures. Compared to pure YIG, the saturation magnetization is larger when the La concentration x = 0.2. However, with increasing La concentration (x), it decreases obviously. Meanwhile, may be due to the enhancement of the surface spin effects, the saturation magnetization rises as the particle size is increased. Different from the pure YIG, the Mossbauer spectra of Y2.8La0.2Fe5O12 and Y2.2La0.8Fe5O12 are composed of four sets of six-line hyperfine patterns. The results tell us that the substitution of La3+ ions with large ionic radius (1.061 A) will give rise to a microscopic structure distortion of the a- and d-sites to different degrees, and the Zeeman sextets from a- and d-sites begin to split into two sub-sextets, which is helpful to explain the phenomenon observed in the study of the magnetic property.

Luminescence studies on lanthanide ions (Eu 3+, Dy 3+ and Tb 3+) doped YAG:Ce nano-phosphors

Yttrium aluminum garnet nanoparticles both undoped and doped with lanthanide ions (Ce 3+, Eu 3+, Dy 3+ and Tb 3+) having average size around 30 (±3 nm) nm were prepared by glycine nitrate combustion method followed by annealing at a relatively low temperature of 800 °C. Increase in the annealing temperature has been found to improve the luminescence intensity and for 1200 °C heated samples there exists strong energy transfer from Tb 3+ to Ce 3+ ions in YAG:Ce(2%),Tb(2%) nanoparticles as revealed by luminescence studies. Co-doping the YAG:Ce nanoparticles with Eu 3+ results in significant decrease in the emission intensity of both Ce 3+ and Eu 3+ ions and this has been attributed to the oxidation of Ce 3+ to Ce 4+ and reduction of Eu 3+ to Eu 2+ ions. Dy 3+ co-doping did not have any effect on the Ce 3+ emission as there is no energy transfer between Dy 3+ and Ce 3+ ions.

Synthesis of Nanosized Ce3+,Eu3+-Codoped YAG Phosphor in a Continuous Supercritical Water System

Luminescent yttrium aluminum garnet (Y3Al5O12) nanoparticles codoped with Ce3+ and Eu3+ (YAG:Ce3+,Eu3+) were continuously synthesized by directly feeding potassium hydroxide solution and a metal salt solution to supercritical water (SCW). The effects of the Ce3+-to-Eu3+ concentration ratio on the photoluminescence of the synthesized nanoparticles were studied using a continuous SCW tubular reactor. At 20-s reaction time and a pH of 9.10 in the SCW reactor, the average size of the prepared phosphor nanoparticles was 60−150 nm and cubic or hexagonal particles coexisted with the spherical particles. The phosphor nanoparticles presented a broad emission band in the green-yellow spectral region due to Ce3+, as well as a sharp emission peak at around 610 nm in the red spectral region due to Eu3+. Without further thermal treatment, the YAG:Ce3+,Eu3+ phosphor synthesized in the continuous reactor under SCW conditions showed strong luminescence properties. Simultaneously, enhancement of the red spectral emission i...

Preparation and Characterization of Nanostructured Ferrite Materials by a Nitrate-Citrate Self-Combustion Sol–Gel Synthesis

New chemical synthesis procedure for the preparation of nickel zinc doped W-type hexagonal barium ferrite and aluminium doped yttrium-iron garnet nanoparticles has been developed, using the nitrate-citrate sol-gel auto-combustion method (NCSAM). The crystalline phase attributes, microstructure, morphology, specific surface area, Curie temperature (TC), permeability, thermal behavior of the as-burnt phase and the heat treated powders were characterized using XRD, SEM, FT-IR, BET, TG-DTA and AC magnetic permeability with frequency shift. In the case of the hexaferrite, the pure W-type ferrite phase is formed during 4 hour annealing at a temperature of 1200 °C, the garnet phase is formed at a lower temperature i.e. 1000 °C. Furthermore it has been confirmed, that the AC magnetic permeabilities of the garnet materials are strongly depending on the chemical composition.

Preparation and Faraday rotation of Bi-YIG/PMMA nanocomposite

Bismuth-substituted yttrium iron garnet (Bi-YIG) nanoparticles (NPs) were prepared by coprecipitation and subsequent heating treatment. Thermal gravity-differential thermal analysis was performed to investigate the thermal behavior of the Bi-YIG precursors and to decide the best annealing temperature. Phase formation of garnet NPs was investigated by X-ray powder diffraction. The size of Bi-YIG NPs was investigated by transmission electron microscopy, and the magnetic properties of Bi-YIG NPs were measured using a vibrating sample magnetometer. The results show that the temperature needed for the transformation of Bi-YIG from the amorphous phase to the garnet phase decreases with increasing Bi content, and Bi-YIG NPs with sizes of 28–78 nm are obtained after heating treatment at 650–1000 °C. The saturation magnetization of Bi-YIG NPs increases as the Bi content increases. Moreover, the Faraday rotation of polymethyl methacrylate (PMMA) slices doped with Bi-YIG NPs was investigated. The results indicate that the angle of Faraday rotation increases with increasing Bi content in PMMA composites, and the maximum value of the figure of merit is 1.46°, which is comparable to the value of a sputtered film. The Bi-YIG NPs-doped PMMA slices are new promising materials for magneto-optical devices.

A simple process to synthesize sphere-shaped gadolinium gallium garnet nanoparticles for transparent ceramic

Abstract The citrate sol–gel method has been developed for the synthesis of sphere-shaped cubic-phase Gd 3 Ga 5 O 12 (GGG) nanoparticles, which were obtained at low temperatures and dispersed uniformly. NH 2 OH·HCl was used as chelator, Ga(NO 3 ) 3 ·6H 2 O, Gd(NO 3 ) 3 and citric acid were used as starting materials, respectively. X-ray powder diffraction (XRD) patterns were used to identify the GGG phase structure. Transmission electron microscopy (TEM) investigations indicated that the as-synthesized products were composed of a large number of sphere-shaped nanoparticles with diameters of 40 nm. High-resolution transmission electron micrography (HRTEM) images showed that the as-synthesized sphere-shaped GGG were single-phase nanoparticles, whose interlayer spacing observed was 0.3087 nm. Also, the formation mechanism of sphere-shaped GGG nanoparticles in this work is provided.

Comparison of YAG: Eu phosphors synthesized by supercritical water in batch and continuous reactors

Luminescent yttrium aluminum garnet (YAG, Y3Al5O12) nanoparticles doped with Eu (10 at%) were synthesized in batch-type and continuous-type supercritical water (SCW) reactors. In the case of the continuous-type SCW method, the particles of YAG: Eu phosphors were much smaller and demonstrated a uniform spherical-like shape. Inversely, in the case of the batch-type SCW method, a needle-like or elliptical-like shape was formed because a finite amount of time was required to reach SCW conditions from ambient conditions. However, the emission intensity of YAG: Eu phosphors synthesized by using the batch-type SCW method was stronger. Therefore, it is concluded that the continuous-type SCW method is superior to the batch-type SCW method from the viewpoint of the particle size and shape, but the luminescence property of phosphors in the continuous-type SCW method needs to be improved. In addition, a calcination process slightly improved the luminescence intensities of YAG: Eu phosphors generated by using either the batch-type or continuous-type SCW methods.

Effect of erbium oxide on synthesis and magnetic properties of yttrium-iron garnet nanoparticles in organic medium

Yttrium iron garnet doped with the erbium oxide using a conventional complex agent (citric acid) in organic medium (CH3COOH) was synthesized by sol-gel technique. The obtained samples were characterized by X-ray powder diffraction superconducting quantum interference device, scanning probe microscopy and transmission electron microscope. The influences of the pH value,quantities of citric acid and the initial concentration of the solution on the final product were studied. At the same time, the crystallite size and magnetic properties were observed and studied in detail.

Saturation magnetic properties of Y3−x Re x Fe5O12(Re: Gd, Dy, Nd, Sm and La) nanoparticles grown by a sol–gel method

Re3+-substituted garnet nanoparticles Y3−xRexFe5O12 (Re = Gd, Dy, Nd, Sm and La) were fabricated by a sol–gel method .The XRD patterns of all samples have only peaks of the garnet structure and the sizes of nanoparticles rang from 34 to 69 nm. Results of VSM show that the saturation magnetization of Y3−xGdxFe5O12, Y3−xDyxFe5O12 and Y3−xSmxFe5O12 nanoparticles decrease evidently as the Re3+ concentration (x) is increased. The saturation magnetization of Y3−xNdxFe5O12 and Y3−xLaxFe5O12 increases firstly and then decreases as the Re3+ concentration (x) is increased. In the meanwhile, it is observed that may be due to the enhancement of the surface spin effects, the saturation magnetization rises as the nanoparticle size is increased.

Glycothermal Synthesis and Magnetic Properties of YIG/YAG Nanoparticles

Yttrium aluminum garnet (YAG) nanoparticles of 14.5±3.2 nm in diameter are synthesized from yttrium acetate and aluminum isopropoxide in 1,4-butanediol by autoclave treatment at 300oC for 2h. Yttrium iron garnet (YIG) / YAG composite nanoparticles of 21.1±4.9 nm in diameter are synthesized from yttrium acetate and iron(III) acetylacetonate in 1,4-butanediol by autoclave treatment at 300oC for 2h using YAG nanoparticles as the seed. In contrast, YIG is not formed by the same procedure in the absence of the YAG seed. The saturation magnetizations of nanoparticles with different YIG/YAG ratios range from 11.9 to 17.8 emu/g. YIG/YAG nanoparticles dispersed in the agarose gel are observed by magnetic resonance imaging (MRI). The degree of the negative MRI contrast depends on the concentration of YIG/YAG nanoparticles.

Reduced magnetization in magnetic oxide nanoparticles

Magnetic oxide nanoparticles have been studied to elucidate the effects of nanoscale finite size on the magnetic behavior of the particles. Magnetite nanoparticles synthesized by coprecipitation show superparamagnetism at room temperature with reduced saturation magnetization MS. The MS value decreases and approaches zero with decreasing particle size. Yttrium iron garnet (YIG) nanoparticles also show a similar trend. The magnetization of nanoparticles estimated using the Langevin function with the particle size distribution indicates that the reduced magnetization can be consistently explained by the existence of a spin-disordered surface layer with the thickness of 1–2nm. The results found in magnetite and YIG nanoparticles suggest that the reduced magnetization can be commonly observed among magnetic oxide nanoparticles due to the existence of spin disordered surface layer.

Synthesis and magnetic properties of Sm–Y 3Fe 5O 12 nanoparticles

Garnet nanoparticles Y 3− x Sm x Fe 5O 12 were fabricated by a sol–gel method. The XRD patterns of all the samples have only peaks of the garnet structure and the sizes range from 34 to 67 nm. Results of VSM show that the saturation magnetization of Y 3− x Sm x Fe 5O 12 (0< x⩽3) decreases on increasing the Sm concentration x evidently. Meanwhile, it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the nanoparticle size is increased.

Magnetic properties of Bi-doped Y3Fe5O12 nanoparticles

Abstract Bi3+ substituted garnet nanoparticles Y3−xBixFe5O12 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2 and 1.3) were fabricated by a sol–gel method and their crystalline structures and magnetic properties were investigated by using X-ray diffraction (XRD), IR spectroscopy, thermal gravity analysis–differential thermal analysis (TG-DTA), transmission electron microscope (TEM), Mossbauer spectroscopy and vibrating sample magnetometer (VSM). The XRD patterns of Y3−xBixFe5O12 have only peaks of the garnet structure. From the results of VSM, it is shown that the saturation magnetization of sample is decreased with increasing the content of Bi ions. Meanwhile, it is observed that with the enhancement of the single magnetic domains surface spin effects, the saturation magnetization is raised as the particle size of samples is increased.

Magnetic properties of Nd-Y3Fe5O12 nanoparticles

Nb3+-substituted garnet nanoparticles Y3−xNdxFe5O12 (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were fabricated by a sol-gel method and their crystalline structures and magnetic properties were investigated by using X-ray diffraction (XRD), thermal analysis (DTA/TG), and vibrating sample magnetometer (VSM). The XRD patterns of Y3−xNdxFe5O12 have only peaks of the garnet structure and the sizes of particles range from 34 to 70 nm. From the results of VSM, it is shown that when the Nd concentration x ( 1.0, the saturation magnetization of Y3−xNdxFe5O12 increases as the Nd concentration (x) is increased, and gets its maximum at x = 1.0, but when x ( 1.0, the saturation magnetization decreases with increasing the Nd concentration (x), this may be due to the distortion of the microstructure of Y3−xNdxFe5O12, which leads to the decrease of the effective moment formed by Fe3+. Meanwhile, it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the particle size is increased.

Synthesis of nano-sized YAG:Eu 3+ phosphor in continuous supercritical water system

Luminescent yttrium aluminum garnet (Y 3Al 5O 12) nanoparticles doped with Eu (YAG:Eu 3+) were continuously synthesized by directly feeding potassium hydroxide solution and metal salt solution to supercritical water (SCW). Effects of Eu concentration, pH, and residence time on photo-luminescence were studied using a continuous tubular reactor. Residence time played a key role in producing single-phase YAG:Eu 3+ nanoparticles. The residence time of 20 s under SCW conditions (400 °C and 280 bar) was enough to form YAG:Eu 3+ phosphor without any intermediate phases. At this residence time, the Eu concentration and pH condition under SCW contributed to improving the size, morphology and luminescent property of YAG: Eu 3+ nanoparticles. The average size of the prepared phosphor nanoparticles at 10 at.% and pH of 9.10 was 74 nm and the morphology was identified as nearly uniform and spherical-like in shape. Without further thermal treatment, the phosphor YAG:Eu 3+ synthesized in the continuous reactor under SCW conditions showed strong luminescence properties and red emission spectra.