Luminescent and magnetic properties of YVO4:Ln@Fe3O4 (Ln = Eu or Dy) nanocomposites

A series of core-shell bifunctional magnetic-optical YVO₄:Ln³⁺@Fe₃O₄ (Ln³⁺ = Eu³⁺ or Dy³⁺) nanocomposites have been successfully synthesized via two-step method. The nanocomposites have the advantage of high magnetic responsive and unique luminescence properties. The structure, luminescent and magnetic properties of the nanocomposites were investigated by XRD, TEM, PL and VSM. The maximum emission peaks of the nanocomposites are at 618 nm (doping Eu³⁺), 574 nm (doping Dy³⁺). The special saturation magnetization of the nanocomposites is 54 emu/g. The diameter of the nanocomposites is 400-900 nm.     

Synthesis and luminescence properties of Bi-doped YVO4 phosphors

YVO₄:Bi³⁺ phosphors have been prepared by a convenient high-temperature solid-state method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) technologies are used to study the luminescence properties of YVO₄:Bi³⁺ phosphors. The emission and excitation spectra of Bi³⁺ in the YVO₄ lattice have been investigated at room temperature. The excitation band peaks at 330 nm in a region among 250-400 nm, and the emission spectrum exhibits an intense yellowish-white broad emission centered at about 543 nm covering from 400 nm to 800 nm. The full width at half maximum (FWHM) is about 144 nm. The color coordinates of the as-synthesized YVO₄:Bi³⁺ phosphors are in a range of x = 0.358-0.374, y = 0.482-0.496. The dependence of the luminescence intensity on Bi³⁺ concentrations and heat treatment condition has also been discussed. In addition, we found that a little amount of flux NH₄Cl could enhance the Bi³⁺ luminescence intensity.     

Synthesis and luminescence properties of clew-like CaMoO4:Sm, Eu

Eu³⁺ and Sm³⁺ co-doped CaMoO₄ microclews have been successfully synthesized via a facile hydrothermal method directly in surfactant-free environment. The as-prepared phosphor present clew-like agglomerates composed of 40 nm nanosheets under the moderated reaction temperature. The red phosphor CaMoO₄:Eu³⁺, Sm³⁺ can generate a strong absorption line at 405 nm, originating from ⁶H_5/2 → ⁶P_5/2 transition of Sm³⁺, which is suitable for the emission of the near-ultraviolet light-emitting diodes (∼400 nm). Energy transfer between Sm³⁺ and Eu³⁺ is detected from the varied photoluminescence spectra with different Eu³⁺ concentrations and the energy transfer mechanism is clarified via the photoluminescence spectra. When Sm³⁺ is excited (405 nm), the electron is excited from ⁶H_5/2 to ⁶P_5/2, and then relaxed to ⁴G_5/2. It jumps from ⁴G_5/2 to the lower levels corresponding to the emissions of Sm³⁺; meanwhile, the transfers from ⁴G_5/2 state of Sm³⁺ ion to ⁵D₀ state of Eu³⁺ ion come out. The transition of ⁵D₁ → ⁷F_J (J = 0, 1, 2) does not appear indicating that the transfer from ⁴G_5/2 state of Sm³⁺ to ⁵D₀ state rather than ⁵D₁ state of Eu³⁺ is the energy transfer pathway.     

Photoluminescence and thermoluminescence studies of Mg2SiO4:Eu nano phosphor

Nanoparticles of Eu³⁺ doped Mg₂SiO₄ are prepared using low temperature solution combustion technique with metal nitrate as precursor and urea as fuel. The synthesized samples are calcined at 800 °C for 3 h. The Powder X-ray diffraction (PXRD) patterns of the sample reveled orthorhombic structure with α-phase. The crystallite size using Scherer's formula is found to be in the range 50-60 nm. The effect of Eu³⁺ on the luminescence characteristics of Mg₂SiO₄ is studied and the results are presented here. These phosphors exhibit bright red color upon excitation by 256 nm light and showed the characteristic emission of the Eu³⁺ ions. The electronic transition corresponding to ⁵D₀ → ⁷F₂ of Eu³⁺ ions (612 nm) is stronger than the magnetic dipole transition corresponding to ⁵D₀ → ⁷F₁ of Eu³⁺ ions (590 nm). Thermoluminescence (TL) characteristics of γ-rayed Mg₂SiO₄:Eu³⁺ phosphors are studied. Two prominent and well-resolved TL glows with peaks at 202 °C and 345 °C besides a shoulder with peak at ∼240 °C are observed. The trapping parameters-activation energy (E), order of kinetics (b) and frequency factor (s) are calculated using glow curve shape method and the results obtained are discussed.     

Ultrasonic-assisted in situ synthesis and characterization of superparamagnetic Fe3O4 nanoparticles

Superparamagnetic Fe₃O₄ nanoparticles were synthesized via a modified coprecipitation method, and were characterized with X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Zeta potential and FT-IR, respectively. The influences of different kinds of surfactants (sodium dodecyl benzene sulfonate, polyethyleneglycol, oleic acid and dextran), temperatures and pH values on the grain size and properties were also investigated. In this method, Fe³⁺ was used as the only Fe source and partially reduced to Fe²⁺ by the reducing agent with precise content. The following reaction between Fe³⁺, Fe²⁺ and hydroxide radical brought pure Fe₃O₄ nanoparticles. The tiny fresh nanoparticles were coated in situ with surfactant under the action of sonication. Comparing with uncoated sample, the mean grain size and saturation magnetization of coated Fe₃O₄ nanoparticles decrease from 18.4 nm to 5.9-9.0 nm, and from 63.89 emu g⁻¹ to 52-58 emu g⁻¹ respectively. When oleic was used as the surfactant, the mean grain size of Fe₃O₄ nanoparticles firstly decreases with the increase of reaction temperature, but when the temperature is exceed to 80 °C, the continuous increase of temperature resulted in larger nanoparticles. the grain size decreases gradually with the increasing of pH values, and it remains unchanged when the PH value is up to 11. The saturation magnetization of as-prepared Fe₃O₄ nanoparticles always decreases with the fall of grain size.     

Preparation and luminescent properties of Eu doped Sr3La(PO4)3 phosphor

Eu²⁺-doped Sr₃La(PO₄)₃ phosphors were synthesized by solid-state reaction method. Their luminescent properties were investigated. The phosphor could be excited by ultraviolet light effectively. The emission spectra exhibit two emission peaks located at 418 nm and 500 nm, respectively. These two peaks originated from two different luminescent centers, respectively. One is nine-coordinated Eu(I) center, other is six-coordinated Eu(II) center. It was found that the doping concentration of Eu²⁺ ions affected the shape of emission spectra. As the doping concentration increasing, Eu²⁺ ions are more likely to form Eu(I) luminescent centers and emit purple light.     

Eu/Sm ions co-doped white light luminescence SrSiO3 glass-ceramics phosphor for White LED

Eu²⁺/Sm³⁺ co-doped silicate glass was prepared by high temperature melting under reducing atmosphere and the Eu²⁺/Sm³⁺ co-doped SrSiO₃ transparent glass-ceramics were obtained after heat-treatment. X-ray diffraction (XRD) and Raman spectra confirmed the formation of SrSiO₃ nano-crystals in the glass matrix. The photoluminescence excitation (PLE) spectra and photoluminescence (PL) spectra of the samples were measured. A broad emission band from 400 nm to 550 nm due to the 4f⁶5d¹ → 4f⁷ transitions of Eu²⁺ was observed, as well as several sharp emission peaks at 563 nm, 600 nm, 646 nm and 713 nm ascribed to the 4f → 4f transitions of Sm³⁺. The luminescence properties of the glass ceramics with different molar ratio of Eu²⁺/Sm³⁺ were studied and the corresponding chromaticity coordinates were calculated. The ultraviolet light-emitting diode (UV-LED) excitable glass-ceramics emitting white light were obtained by tuning the relative emission intensity of Eu²⁺ and Sm³⁺. The results indicate that the Eu²⁺/Sm³⁺ co-doped SrSiO₃ transparent glass-ceramics can be used as a potential matrix material for White LED under UV-LED excitation.     

Facile synthesis, magnetic and microwave absorption properties of Fe3O4/polypyrrole core/shell nanocomposite

Fe₃O₄/polypyrrole (PPy) core/shell nanocomposite, with Fe₃O₄ nanoparticle as core and PPy as shell, could be facilely synthesized via in situ chemical oxidative polymerization of pyrrole monomers on the surface of Fe₃O₄ nanoparticles. The results indicate that core/shell nanocomposite consists of Fe₃O₄ core with the mean diameter of 100 nm and adjacent PPy shell with a thickness of about 70 nm. The as-prepared Fe₃O₄/PPy core/shell nanocomposite exhibits a saturated magnetization of 20.1 emu/g and coercivity value of 368.3 Oe, respectively. The electromagnetic characteristics of Fe₃O₄/PPy core/shell nanocomposite were also investigated with a vector network analyzer in the 2-18 GHz range. The absorbing peak position moves to lower frequency with increasing the thicknesses of samples. The value of the minimum reflection loss is −22.4 dB at 12.9 GHz for Fe₃O₄/PPy core/shell nanocomposite with a thickness of 2.3 mm, and a broad peak with a bandwidth lower than −10 dB is about 5 GHz. Such strong absorption is attributed to better electromagnetic matching due to the existence of PPy and the special core/shell structure.     

Luminescence properties of SrIn2O4:Eu incorporated with Gd or Sm ions

The photoluminescence (PL) properties of SrIn₂O₄:Eu³⁺,Gd³⁺ and SrIn₂O₄:Eu³⁺,Sm³⁺ are investigated in this work. When the Gd³⁺ ions are introduced in this compound, the average distance metal-oxygen is increased, and then the vibration of lattice is decreased. It results in that the nonradiation of Eu³⁺ is decreased. Therefore, the emissions of SrIn₂O₄:Eu³⁺ are increased. However, little of energy transfer occurs from Gd³⁺ to Eu³⁺ ions. When the Sm³⁺ ions are introduced into SrIn₂O₄:Eu³⁺, the energy transfers occur from the CTS of O²⁻-Sm³⁺ to Sm³⁺ and Eu³⁺ ions, from the host absorption to Eu³⁺ ions, and from Sm³⁺ to Eu³⁺ ions, but not from the host absorption to Sm³⁺ ions.     

Preparation and properties of multifunctional Fe@C@Y2O3:Eu nanocomposites

Multifunctional Fe@C@Y₂O₃:Eu³⁺ nanocomposites were prepared by the solvo thermal method, and their structure, magnetic and luminescent properties were characterized by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and scanning electron microscope (SEM). Results show that the nanocomposites are spherical with a mean diameter of 700 nm and there are high special saturation magnetization (47.4 emu/g) and strong red emission under UV-light. Even dispersed in water solution, the nanocomposites also exhibit a strong red emission under ultraviolet light radiation, and it could be manipulated using an external magnet. Thus it looks promising for application in biomedicine field, especially in drug targeting and fluorescence label. And we also discussed the effect of the electron transfer process between the Fe magnetic core and Y₂O₃:Eu³⁺ shell.     

Luminescence studies of Ba1−xMg2−y(PO4)2:xEu, yMn phosphor

The phosphors BaMg₂(PO₄)₂ doped with Eu²⁺ and Mn²⁺ solely or doubly were prepared by solid state reaction, and their luminescent properties were also investigated. Under the excitation of 322 nm, it has been observed a broad blue emission band centered at 417 nm and a red emission band centered at about 665 nm, resulting from Eu²⁺ and Mn²⁺, respectively. Resonance-type energy transfers from Eu²⁺ to Mn²⁺ were discovered by directly overlapping the emission spectra of Eu²⁺ and the excitation spectra of Mn²⁺. According to the changes of relative intensities of Eu²⁺ and Mn²⁺ emission, efficiencies of energy transfer were calculated. Based on the principle of energy transfer, the relative intensities of blue and red emission could be tuned by adjusting the contents of Eu²⁺ and Mn²⁺.     

Synthesis and photoluminescence of Eu by co-doping Eu and Cl in Sr2P2O7 under air atmosphere

A novel phosphor Sr₂P₂O₇ co-doped with europium ion and chlorine ion was firstly synthesized by solid state reaction under air atmosphere. Its properties were systematically analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fluorescence spectra. The introduction of chlorine into the system was helpful and necessary to Eu³⁺ substitute Sr²⁺ site and subsequently to reduce Eu³⁺ to Eu²⁺, XPS results confirmed that some amount of Eu³⁺ ions could be reduced to Eu²⁺ ions under air atmosphere at high temperature. The reduction tendency of Eu³⁺ depends not only on the doping Cl⁻ content, but also on the sintering temperature and time. Photoluminescence spectra also revealed that europium ions were present in divalent as well as trivalent oxidation states, the emission peak at 415 nm is ascribed to the typical 5d-4f transition of Eu²⁺, 592 nm and 613 nm assigned to the characteristic transitions of ⁵D₀-⁷F_1,2 of Eu³⁺. Such abnormal reduction was attributed to the electronegative defects formed by nonequivalent substitution of Eu³⁺ on the Sr²⁺ sites in the investigated phosphors.     

Combustion synthesis of CaSc2O4:Ce nano-phosphors in a closed system

The CaSc₂O₄:Ce³⁺ nano-phosphors were successfully prepared by a single-step combustion method at an ignition temperature as low as 200 °C in a closed autoclave using glycine as a fuel and PEG4000 as a dispersant. The samples were characterized by X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscope (TEM). The results revealed that CaSc₂O₄:Ce³⁺ nano-phosphors can be conveniently prepared at an ignition temperature as low as 200 °C, which was much lower than that in the ordinary combustion methods. The optimized ignition temperature was 220 °C. The CaSc₂O₄:Ce³⁺ nano-phosphors give a uniform particle size in the range of 15-20 nm. The low ignition temperature and the addition of PEG4000 dispersant play important roles in the formation of small sized nanoparticles. The as-prepared nano-phosphors were incompact aggregates, but highly dispersed nano-phosphors can be obtained after further ultrasonic treatment. The CaSc₂O₄:Ce³⁺ nano-phosphors give satisfactory luminescence characteristic benefiting from the closed circumstance, in which cerium atoms can be isolated from the oxidizing atmosphere and non-fluorescent Ce⁴⁺ ions can be ruled out. The present highly dispersed CaSc₂O₄:Ce³⁺ nano-phosphors with efficient fluorescence are promising in the field of biological labeling, and the present low temperature combustion method is facile and convenient and can be applied as a universal process for preparing non-aggregate oxide nano-phosphors, especially those being sensitive to air at high temperature.     

Vacuum ultraviolet spectroscopic properties of KSrPO4:Tb

KSrPO₄:Tb³⁺ phosphors were prepared by a solid-state method and their photoluminescence properties were investigated under vacuum ultraviolet excitation. In the excitation spectrum monitoring at 544 nm, the band in the region of 120-162 nm can be attributed to be the overlap of host absorption and charge transfer transition of O²⁻ → Tb³⁺, and the band ranging from 162 to 300 nm was assigned to the f-d transition of Tb³⁺. The photoluminescence spectrum shows that the phosphors exhibited a strong green emission around 544 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺ under the excitation of 147 nm. Optimal emission intensity was obtained when x = 7% in KSr_1-xPO₄:xTb³⁺ and the luminescent chromaticity coordinates were calculated to be (x = 0.317, y = 0.522) for KSr_0.93PO₄:7%Tb³⁺.     

Direct synthesis and characterization of mesoporous Fe3O4 through pyrolysis of ferric nitrate-ethylene glycol gel

Mesoporous magnetite (Fe₃O₄) was successfully synthesized on a large scale by direct pyrolysis of ferric nitrate-EG (EG = ethylene glycol) gel in a one-end closed horizontal tube furnace in the air without using any template, additions, and carrier gas. The as-synthesized mesoporous Fe₃O₄ were characterized by powder X-ray diffraction (XRD), infrared spectra (IR), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), and thermal gravimetric analysis (TGA). Results from TEM showed that the as-obtained Fe₃O₄ has mesoporous structure formed by the loose agglomeration of nanoparticles with diameter of about 6 nm, which was also confirmed by small-angle XRD and nitrogen adsorption analysis. Furthermore, vibrating sample magnetometer (VSM) measurements indicated that the saturated magnetization of the as-obtained mesoporous Fe₃O₄ was ferromagnetic with the saturation magnetization (Ms) and coercivity (Hc) of 46 emu/g and 136 Oe, respectively. In addition, a possible growth mechanism of mesoporous Fe₃O₄ was also discussed.     

Photoluminescence and energy transfer studies on Eu and Ce co-doped SrCaSiO4 for white light-emitting-diodes

The luminescence of SrCaSiO₄:Eu²⁺, Ce³⁺ is studied as a potential ultraviolet light-emitting diodes (UV-LEDs) phosphor that is capable of converting the ultraviolet emission of a UV-LED into green light with good luminosity. There are two emissions peaks peaking at 420 and 500 nm, respectively. The two emissions come from d-f transitions of Ce³⁺ and Eu²⁺, respectively. Effective energy transfer occurs in Ce³⁺/Eu²⁺ co-doped SrCaSiO₄ due to a part of spectral overlap between the emission of Ce³⁺ and excitation of Eu²⁺. Co-doping of Ce³⁺ enhances the emission intensity of Eu²⁺ greatly by transferring its excitation energy to Eu²⁺. The Ce³⁺/Eu²⁺ energy transfer, thoroughly investigated by the diffuse reflection emission and excitation spectra, photoluminescence decay curves, is demonstrated to be in the mechanism of electric dipole-dipole interaction.     

In situ synthesis of Co3O4/graphene nanocomposite material for lithium-ion batteries and supercapacitors with high capacity and supercapacitance

Co₃O₄/graphene nanocomposite material was prepared by an in situ solution-based method under reflux conditions. In this reaction progress, Co²⁺ salts were converted to Co₃O₄ nanoparticles which were simultaneously inserted into the graphene layers, upon the reduction of graphite oxide to graphene. The prepared material consists of uniform Co₃O₄ nanoparticles (15-25 nm), which are well dispersed on the surfaces of graphene nanosheets. This has been confirmed through observations by field emission scanning electron microscopy, transmission electron microscopy and atomic force microscopy. The prepared composite material exhibits an initial reversible lithium storage capacity of 722 mAh g⁻¹ in lithium-ion cells and a specific supercapacitance of 478 F g⁻¹ in 2 M KOH electrolyte for supercapacitors, which were higher than that of the previously reported pure graphene nanosheets and Co₃O₄ nanoparticles. Co₃O₄/graphene nanocomposite material demonstrated an excellent electrochemical performance as an anode material for reversible lithium storage in lithium ion cells and as an electrode material in supercapacitors.     

One-step solvothermal approach for preparing soft magnetic hydrophilic PFR coated Fe3O4 nanocrystals

The hydrophilic phenol formaldehyde resin coated Fe₃O₄ nanocrystals are prepared via a novel one-step solvothermal approach at 160 °C for 6-9 h without inert gas protection. Water-glycol mixture is used as solvent in common air surrounding. FeSO₄·7H₂O, hexamethylenetetramine and phenol are used as resource materials without any others additives or surfactants. The transmission electronic microscope images show the samples are composed of sphere-like particles with sizes about 10-20 nm. The X-ray diffraction data indicate cube-phase Fe₃O₄ nanocrystals are obtained at given conditions. Fourier transform infrared spectra further reveal the samples are consisted of Fe₃O₄ and PFR. Without modified pH and added surfactants, the solubility of the obtained sample is over 1% in water, which is far more than its solubility in toluene. Room-temperature hysteresis loop indicate that the as-obtained nano-crystals possess soft magnetic properties with high saturated mass magnetization (50.6 emu/g) and negligible coercivity.     

Synthesis and phosphorescence properties of Mn, La and Ho in MgAl2Si2O8

Mn⁴⁺, La³⁺ and Ho³⁺ doped MgAl₂Si₂O₈-based phosphors were first synthesized by solid state reaction. They were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X-ray powder diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). The phosphors were obtained at about 1300 °C. They showed broad red and fuchsia-pink emission bands in the range of 610-715 nm and had a different maximum intensity when activated by UV illumination. Such a fuchsia-pink emission can be attributed to the intrinsic d-d transitions of Mn⁴⁺.