Urea Homogeneous Precipitation Method Research Articles

LiNi1/3Co1/3Mn1/3O2 coated by Al2O3 from urea homogeneous precipitation method: improved Li storage performance and mechanism exploring

Layered LiNi1/3Co1/3Mn1/3O2 has been successfully coated with a uniform Al2O3 film through an homogeneous precipitation method with urea as a precipitant. The bare and Al2O3-coated LiNi1/3Co1/3Mn1/3O2 samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and electrochemical charge/discharge tests. For the 1 % Al2O3-coated LiNi1/3Co1/3Mn1/3O2 sample, XRD results show that it possesses the best hexagonal layered crystal structure with the lowest cation mixing among all samples, and SEM and TEM images show a uniform and amorphous Al2O3 layer (~13 nm) formed on the LiNi1/3Co1/3Mn1/3O2 surface. Compared with bare sample, it exhibits superior electrochemical performance including the highest initial coulombic efficiency (92.1 %), high discharge capacity (202.6 mAh g−1 at 0.1 C), excellent cycling performance (92 % at the 100th cycle, 0.5 C), and rate performance. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) are used to aid to reveal the functional mechanism, and the results show that the improving on the electrochemical performance after Al2O3 coating can be attributed to the suppressed electrolyte (LiPF6 or solvents) decomposition reaction on the cathode/electrolyte interface and thus reduced interfacial impedance value and impedance growth speed with cycling.

Y2O3: Eu3+, Tb3+ spherical particles based anti-reflection and wavelength conversion bi-functional films: Synthesis and application to solar cells

In this study, Eu3+ and Tb3+ co-doped Y2O3 particles were prepared via the simple, cost-effective urea homogeneous precipitation method without additives. The chosen particles were added in the SiO2 sols to get anti-reflection (AR) and wavelength conversion bi-functional films. Careful investigations were carried out to find the optimum preparation conditions and proper morphology. SEM images showed that the particle sizes reduced as metal ion/urea ratio decreased. Additionally, the extracted particles turned from sphere to lamellar type when the deionized water, which was used as solvent, reduced to a certain extent. The mechanisms of the morphology formation and diversification were proposed as well. The as prepared materials can convert UV region photos to visible photons between 460nm and 640nm, which just matched the spectral response of most solar cells. The spherical sample showed better luminescence performance than the one with lamellar morphology. In addition, the optical transmittance spectra indicated that the films adding spherical particles had better anti-reflective performance, and the best adding amount was 0.08g. Finally, As a proof-of-concept application, the as prepared bi-functional films were used to test the standard monocrystalline silicon solar cell assembled with anti-reflection and wavelength conversion bi-functional films photoelectric conversion properties. As a result, the as prepared bi-functional films could effectively improve the photoelectric conversion efficiency by0.23% compared to pure SiO2 AR coating film and 0.55% compared to glass.

Luminescent core–shell Fe3O4@Gd2O3:Er3+, Li+ composite particles with enhanced optical properties

Bifunctional magneto-optical nanocomposites with Fe3O4 nanoparticles as a core and erbium and lithium codoped gadolinium (Gd2O3:Er3+, Li+) as the shell were synthesized successfully using a simple urea homogeneous precipitation method. The fabricated Fe3O4@Gd2O3:Er3+, Li+ particles were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence spectroscopy and quantum design vibrating sample magnetometry. The upconversion emission intensity was enhanced significantly comparing to that without Li+ ions. These bifunctional composites are expected to be potentially applied for drug delivery, cell separation and bioimaging.

Controlled synthesis of porous flower-like TiO2 nanostructure with enhanced photocatalytic activity

Flower-like TiO2 nanostructures were successfully synthesized via the urea homogeneous precipitation method using (NH4)2TiF6 as a titanium source in aqueous solution. This approach was simple, environmentally friendly and without using template. The flower-like TiO2 nanostructures were characterized in detail with scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV–vis spectrum, respectively. The flower-like TiO2 nanostructures, with diameters ranging from 150–300nm, were assembled by primary nanoparticles and the length of the petals was approximately 60nm. Interestingly, the surface of the flower-like TiO2 nanostructures appeared to have many pores with diameters of 10–13nm after the sample being calcined at 550°C, while the morphologies and sizes of the TiO2 samples did not change. The photocatalytic activity of the as-prepared samples was evaluated by photo-degradation of rhodamine B (RhB) from aqueous solution at ambient temperature. The flower-like porous TiO2 samples exhibited much higher photocatalytic activity than the flower-like TiO2 samples. All these advantages showed a bright future for this flower-like porous photocatalyst in environmental protection.

Bifunctional Gd2O3:Er3+ particles with enhanced visible upconversion luminescence

This study examined the enhanced upconversion luminescence emission of bimodal Gd2O3:Er3+ particles by codoping with a trace amount of Li+ ions. Gd2O3:Er3+/Li3+ composite particles with enhanced upconversion luminescence emission were synthesized by using a simple urea homogeneous precipitation method. The effect of the particle size and Er3+/Li+ concentration ratio on the structural, morphological and optical properties of Gd2O3:Er3+/Li+ particles were studied systematically by X-ray powder diffraction, field emission scanning electron microscopy and room temperature photoluminescence. Strong upconversion eye-visible green light emission was observed from the Gd2O3:Er3+/Li+ particles under continuous near-infrared pump excitation from a commercially available diode laser. Monodisperse bimodal Gd2O3:Er3+/Li+ particles show a good potential for biomedical and solid state lighting applications.

Facile fabrication and luminescent properties enhancement of bimodal Y2O3:Eu3+ particles by simultaneous Gd3+ codoping

Recently, lanthanide doped bifunctional phosphor materials have begun to play important roles in biomedical applications. On the other hand, little effort has been made to develop systems with paramagnetic and luminescent properties combined in a single particle. In this study, nearly-uniform versatile bifunctional yttria Y2O3 codoped with luminescent Eu3+ and paramagnetic Gd3+ systems (∼150–200nm in diameter) were synthesized using a facile urea homogeneous precipitation method. We demonstrated that partial replacing of Y3+ with Gd3+ linearly improves the strongest red 612nm emission associated with 5D0→7F2 transition of Eu3+. Therefore, codoping yttria based red luminescent phosphors with Gd3+ resulted to enhancement of red luminescent emission together with paramagnetic functionality of the prepared composite particles. The uniform and well-dispersed particles obtained in this study are expected to find promising applications in a range of areas.

Contrasting behaviour of the co-activators in the luminescence spectra of Y2O2S:Tb3+,Er3+nanometre sized particles under UV and red light excitation

Nanometre sized particles of terbium and erbium co-doped yttrium oxysulfide up-converting phosphors were prepared by a urea homogeneous-precipitation method. Results from X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and photoluminescence spectroscopy studies on the microstructure and luminescent properties of the materials are reported. Upconversion emission was observed from the Er(3+) cations when particles were excited with laser light of 632.8 nm wavelength. Under these conditions no interactions between the Er(3+) cations and the Tb(3+) cations were observed. In contrast there was evidence from the Stokes emission of the Er(3+) cations under 254 nm excitation for an interaction between the Er(3+) and Tb(3+) cations reducing intensity of the latter's blue and green emission bands by cross relaxation processes.

Synthesis and luminescence properties of nanocrystalline Gd3Ga5O12:Eu3+ by a homogeneous precipitation method

Nanocrystalline Gd3Ga5O12:Eu3+ with cubic phase was prepared by a urea homogeneous precipitation method. X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric and differential thermal analysis (TG-DTA) and photoluminescence spectra were used to characterize the samples. The effects of the initial solution pH value and urea content on the structure of the sample were studied. The XRD results show that pure phase Gd3Ga5O12 can be obtained at pH =6 and pH =8 of the initial solution. The average crystallite size can be calculated as in the range of 24∼33 nm. The average crystallite size decreases with increasing molar ratio of urea to metal ion. The results of excitation spectra and emission spectra show that the emission peaks are ascribed to 5D0→7FJ transitions of Eu3+, and the magnetic dipole transition originated from 5D0 →7F1 of Eu3+ is the strongest; the broad excitation bands belong to change transfer band of Eu-O and the host absorption of Gd3Ga5O12. An efficient energy transfer occurs from Gd3+ to Eu3+.

Color-tunable properties of Eu3+- and Dy3+-codoped Y2O3 phosphor particles

Rare-earth phosphors are commonly used in display panels, security printing, and fluorescent lamps, and have potential applications in lasers and bioimaging. In the present study, Eu3+- and Dy3+-codoped uniform-shaped Y2O3 submicron particles were prepared using the urea homogeneous precipitation method. The structure and morphology of the resulting particles were characterized by X-ray diffraction, field emission scanning electron microscope, and field emission transmission electron microscope, whereas their optical properties were monitored by photoluminescence spectroscopy. The room-temperature luminescence color emission of the synthesized particles can be tuned from red to yellow by switching the excitation wavelength from 254 to 350 nm. The luminescence intensities of red and yellow emissions could be altered by varying the dopant concentration. Strong quenching was observed at high Eu3+ and Dy3+ concentrations in the Y2O3 host lattice.

Synthesis and optical properties of Gd2O3:Pr3+ phosphor particles

Abstract Spherical-shaped Gd 2 O 3 :Pr 3? phosphor parti-cles were prepared with different concentrations of Pr 3? using the urea homogeneous precipitation method. Theresulting Gd 2 O 3 :Pr 3? phosphor particles were character-ized by X-ray diffraction, field emission scanning electronmicroscope, and photoluminescence spectroscopy. Theeffects of the Pr 3? doping concentration on the luminescentproperties of Gd 2 O 3 :Pr 3? phosphors were investigated.Photoluminescence measurements revealed the Gd 2 O 3 :1 %Pr 3? phosphor particles to have the strongest emission. Theluminescence properties of Gd 2 O 3 :Pr 3? particles arestrongly affected by the phosphor crystallinity and X-raydiffraction measurements confirmed that the crystallinity ofGd 2 O 3 cubic structure could be enhanced by increasing thefiring temperature. The luminescent Gd 2 O 3 :Pr 3? phosphorparticles have potential applications in areas, such asoptical display systems, lamps and etc.Keywords Gd 2 O 3 Particles Pr 3? doped Phosphor Luminescence1 IntroductionThe synthesis and precise manipulation of phosphor mate-rials on the submicron and nanoscale regime have attractedconsiderable attention for display and lighting technology.Phosphor particles with different luminescence emissionspectra can be fabricated by the controlled doping of somespecific lanthanide ions into a suitable host material. On theother hand, for each host material, there is an optimumconcentration of dopant rare-earth (RE) ions. Moreover, theluminescent behavior of all RE-doped phosphors dependson the morphology, size and synthetic route. Phosphorscomprised of small and ideally spherical particles are ofinterest because of their high packing densities and lowlight scattering, which can result in high brightness and ahigh resolution [1, 2]. Therefore, the ideal morphology ofphosphor particles includes a perfect spherical shape, nar-row size distribution and no agglomeration.Gadolinium oxide (Gd

Tailoring the luminescent properties of Gd2O3:Tb3+ phosphor particles by codoping with Al3+ ions

Spherical-shaped, Tb3+/Al3+ codoped Gd2O3 phosphor particles were synthesized using a urea homogeneous precipitation method. Field emission scanning electron microscopy measurements confirmed the formation of nearly-uniform spherical particles with sizes in the range, 250±50nm. In this study we examined the effects of the Al3+ codoping concentration on the photoluminescence emission of Tb3+ doped Gd2O3 phosphor particles. The results confirmed that incorporating Al3+ into Gd2O3:Tb3+ phosphor is highly favorable for improving the emission of the synthesized Gd2O3:Tb3+ phosphor particles. In addition, the simple approach for the luminescence enhancement given here can be extended to the other phosphor systems.

The <i>h</i>-BN Protective Method Used for the Synthesis of Highly Uniform Spherical Si-Based Oxynitride Phosphors

The highly uniform spherical Si-based oxynitride core-shell structured phosphors with narrow size distribution and non-aggregation were successfully fabricated by the h-BN protective method for the first time. Firstly, the raw metallic ions (rare earth and alkaline earth ions) were coated on the surface of SiO2 templates via the urea homogeneous precipitation method. Then the core-shell precursor particles were coated with a H3BO3 layer, which was transformed to a h-BN protective film in the reduction condition. At last, the spherical core-shell structured oxynitride phosphors were synthesized through a gas reduction and nitridation method. The as-received phosphors show excellent luminescence properties due to the 4f65d-4f7 transition of Eu2+ under the excitation of UV and blue lights. The homogeneous spherical phosphors are expected to have excellent dispersing and coating properties, which are very important for LED and PDP applications.

Synthesis and optical properties of Dy3+-doped Y2O3 nanoparticles

In the present study, nearly-uniform spherical-shaped dysprosium-doped cubic yttrium-oxide nanoparticles were prepared by using the urea homogeneous precipitation method. X-ray diffraction patterns of synthesized particles confirmed the formation of a pure cubic phase of Y2O3. The morphology and the elemental analysis measurements were carried out using a transmission electron microscope and a field-emission scanning electron microscope. The particles were observed to have average sizes of around 110 nm. In order to select the optimum concentration of the Dy3+ dopant in the samples, we measured the strongest yellow emission peak intensity due to the strong 4F9/2-6H13/2 transition (573 nm) as a function of the Dy-ion dopant concentration under a constant 349 nm excitation. The PL results showed that the strongest yellow emission at 573 nm occurred when the dopant concentration was about 1% in mol equivalent. Y2O3:Dy3+ phosphor can be used for applications in security printing, biolabel technology, lamps for illumination purposes, etc.

Synthesis and luminescence properties of Ho 3+ doped Y 2O 3 submicron particles

This paper presents comprehensive results of the eco-friendly, large scale fabrication of nearly spherical Ho 3+-doped Y 2O 3 submicron particles, synthesized using the urea homogeneous precipitation method. The dependence of the photoluminescence emission on the doping concentration was examined to determine the optimum Ho 3+ concentration in the samples. X-ray diffraction data of the Y 2O 3:Ho 3+ particles revealed a cubic Y 2O 3 structure. Field emission scanning electron microscopy confirmed the formation of nearly spherical shape particles with a mean diameter of 200±50 nm. The luminescence emission intensity significantly increased with increasing calcination temperature due to the improved crystallinity of the synthesized particles. Strong visible green-yellowish emission due to 5F 4; 5S 2– 5I 8 Stokes transitions was observed under constant 450 nm excitation. Simple large scale fabrication along with the strong visible green-yellowish emission might give these particles wide area of applications.

Submicron Y2O3 particles codoped with Eu and Tb ions: Size controlled synthesis and tuning the luminescence emission

Eu3+ and Tb3+ codoped Y2O3 submicron particles were prepared using the simple urea homogeneous precipitation method. X-ray diffraction patterns revealed the synthesized particles to have a pure cubic Y2O3 structure. Field-emission scanning electron microscopy and field-emission transmission electron microscopy showed that the synthesized particles had almost uniform spherical shapes. The luminescence color emission of the synthesized particles could be tuned from red due to the effective 5D0→7Fj (j=0, 1, 2 and 3) transitions within Eu3+ to green due to the 5D4→7F5 transition within Tb3+ by switching the excitation wavelength from 255 to 310nm. Luminescence quenching was observed at high dopant concentrations. Strong and effective color-tunable emission is expected to find a wide range of applications in industry.

Synthesis of nano-sized and highly sinterable Nd:YAG powders by the urea homogeneous precipitation method

Neodymium-doped yttrium aluminum garnet (Nd:YAG) nanopowders were synthesized via the urea homogeneous precipitation method. The morphology and sintering property controlling effects of ammonium sulfate and urea during the synthesis process were discussed. Spawn-like and fibrillar precipitates were obtained without and with sulfate ions, respectively. Dispersive Nd:YAG nanopowder with proper sintering property was obtained with 1273K calcination for 2h from the precursor with 4.56wt.% ammonium sulfate. Combined with the influence of the [urea]/[metal ions]([U]/[M]) concentration ratio, the dispersion, composition and morphology of the Nd:YAG nanopowders could be controlled via homogeneous precipitation process. A transparent Nd:YAG ceramic was achieved from the Nd:YAG powders obtained with 4.56wt.% ammonium sulfate and a [U]/[M] concentration ratio of 40.

The Enhanced Low-Voltage Cathodoluminescent Properties of Spherical Y2O3:Eu3+ Phosphors Coated with In2O3 and its Application to Field-Emission Displays

Dispersed and spherical Y2O3:Eu3+ red phosphor particles were prepared by the urea homogeneous precipitation method. In2O3 nanoparticles were successfully coated on the surface of the phosphor. Phase compositions, morphologies, photoluminescence (PL) spectra, and cathodoluminescence (CL) properties of Y2O3:Eu3+ phosphors before and after In2O3 coating were examined. It was found that CL properties such as luminous efficiency, lifetime, and stability of In2O3-coated phosphor screen were improved significantly, even though its PL intensity decreased compared with that of the uncoated sample. The reason is attributed to the increase of the electrical conductivity and the decrease of the charge accumulating effect. The present results prove that Y2O3:Eu3+ phosphor coated with an appropriate amount of In2O3 is more suitable to the requirement for low-voltage field-emission displays.

Effect of Yb 3+ concentration on the structures and upconversion luminescence properties of Y 2O 3:Er 3+ ultrafine phosphors

Y 2O 3:Er 3+ ultrafine phosphors with a varying Yb 3+ ion concentration were prepared by a urea homogeneous precipitation method. The results of XRD show that all the samples are of a pure cubic structure and the average crystallite sizes can be calculated as 45, 34, and 28 nm for Y 2O 3:Er 3+ ultrafine phosphors with Yb 3+ ion concentrations of 0, 10%, and 20%, respectively. The lattice constant and cell volume of the ultrafine phosphors decrease with enhancing Yb 3+ ion concentration. The upconversion luminescence spectra of all the samples were studied under 980 nm laser excitation. The strong green and red upconversion emission were observed, and attributed to the 2H 11/2 → 4I 15/2, 4S 3/2 → 4I 15/2 and 4F 9/2 → 4I 15/2 transitions of Er 3+, respectively. The intensity of red emission increases with increasing Yb 3+ ion concentration. The effect of Yb 3+ ion concentration on the structures and upconversion luminescence mechanism were discussed.

Alpha-particle-induced luminescence of rare-earth-doped Y 2O 3 nanophosphors

The feasibility of utilizing Y 2O 3:Tb 3+ and Y 2O 3:Eu 3+ as radioluminescent nanophosphors under alpha-particle excitation is investigated. Materials synthesized by the urea homogeneous precipitation method were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The XRD analysis of as-produced precipitates and nanophosphors fired at temperatures ranging from 950 to 1100 °C indicated the presence of highly crystalline cubic Y 2O 3 with crystallite sizes of ∼40 nm. SEM and TEM analysis revealed that particles with average diameters of ∼200 nm and comprised of ∼40 nm grains were obtained. High-resolution radioluminescence and photoluminescence spectra were used to investigate the unwanted radioluminescence saturation effects associated with the high ionization rate of alpha-particles. Additionally, the radioluminescence intensity as a function of rare-earth ion dopant concentration is investigated for these materials under alpha-particle excitation. The prospect for utilizing these materials as intermediate absorbers in indirect-conversion radioisotope batteries is discussed.

Cerium-Doped Lutetium Aluminum Garnet Phosphors and Optically Transparent Ceramics Prepared from Powder Precursors by a Urea Homogeneous Precipitation Method

Nanosized, purified crystalline-phase cerium-doped lutetium aluminum garnet (LuAG:Ce) phosphors were prepared by the urea homogeneous precipitation method. The obtained phosphors showed much higher dispersivity, a fairly uniform size of about 30 nm, and higher luminescence intensity than those synthesized by a sol–gel combustion process. The radioluminescence spectrum of the phosphors consisted of two emission bands owing to the transitions from the lowest 5d excited state to the 4f ground state of Ce3+. The transmittance in the visible light region of the transparent ceramics fabricated at 1800 °C for 10 h under a higher vacuum of 1.5×10-3 Pa using the prepared powders reached 70% and the attenuation coefficient decreased to 0.116 mm-1, which caused much higher luminescence intensity. Compared with those reported previously, the optical properties of the LuAG:Ce transparent ceramics fabricated in the present work improved markedly.