Synthesis and luminescence properties of monodisperse spherical Y2O3 : Eu3+@SiO2 particles with core-shell structure

Y2O3: Eu3+ phosphor layers were deposited on monodisperse SiO2 particles with different sizes ( 300, 500, 900, and 1200 nm) via a sol-gel process, resulting in the formation of Y2O3: Eu3+@SiO2 core-shell particles. X-ray diffraction ( XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy ( TEM), time-resolved photoluminescence ( PL) spectra, and lifetimes were employed to characterize the Y2O3: Eu3+@SiO2 core-shell samples. The results of XRD indicated that the Y2O3: Eu3+ layers began to crystallize on the silica surfaces at 600 degrees C and the crystallinity increased with the elevation of annealing temperature until 900 degrees C. The obtained core-shell particles have perfect spherical shape with narrow size distribution and non-agglomeration. The thickness of the shells could be easily controlled by changing the number of deposition cycles ( 60 nm for three deposition cycles). Under the excitation of ultraviolet ( 250 nm), the Eu3+ ion mainly shows its characteristic red ( 611 nm, D-5(0)-F-7(2)) emissions in the core-shell particles from Y2O3: Eu3+ shells.

Monodisperse and core-shell-structured SiO2@YBO3 : Eu3+ spherical particles: Synthesis and characterization

Y0.9Eu0.1BO3 phosphor layers were deposited on monodisperse SiO2 particles of different sizes (300, 570, 900, and 1200 nm) via a sol-gel process, resulting in the formation of core-shell-structured SiO2@Y0.9Eu0.1BO3 particles. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and cathodoluminescence (CL) spectra as well as lifetimes were employed to characterize the resulting composite particles. The results of XRD, FE-SEM, and TEM indicate that the 800 degrees C annealed sample consists of crystalline YBO3 shells and amorphous SiO2 cores, in spherical shape with a narrow size distribution. Under UV (240 nm) and VUV (172 nm) light or electron beam (1-6 kV) excitation, these particles show the characteristic D-5(0)-F-7(1-4) orange-red emission lines of Eu3+ with a quantum yield ranging from 36% (one-layer Y0.9Eu0.1BO3 on SiO2) to 54% (four-layer Y0.9Eu0.1BO3 on SiO2).

Luminescence properties of sol-gel derived spherical SiO2@Gd-2(WO4)(3): Eu3+ particles with core-shell structure

Monodisperse, core-shell structured SiO2@Gd-2(WO4)(3):Eu3+ particles were prepared by the sol-gel method. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy, transmission electron microscopy, photoluminescence (PL) and low-voltage cathodoluntinescence (CL). PL and CL study revealed that the core-shell structured SiO2@Gd-2(WO4)(3):Eu3+ particles show strong red emission dominated by the D-5(0)-F-7(2) transition of Eu3+ at 615 nm with a lifetime of 0.89 ins. The PL and CL emission intensity can be tuned by the coating number of Gd-2(WO4)(3):Eu3+ phosphor layers on SiO2 particles, the size of the SiO2 core particles, and by accelerating voltage and the filament current, respectively.

Radiation forces of a highly focused radially polarized beam on spherical particles

A radially polarized beam focused by a high-numerical-aperture (NA) objective has a strong longitudinal and nonpropagating electric field in the focal region, which implies that it is suitable for axial optical trapping. In this paper, we use the vectorial diffraction integral to represent the field distribution of the radially polarized beam focused by a high-NA objective and then employ the T-matrix method to compute the radiation forces on spherical particles. Effects of different parameters, such as the size of the sphere, the inner radius of the radially polarized beam, and the NA of the objective, on the radiation forces are presented.

Fabrication, characterization of spherical CaWO4:Ln@MCM-41(Ln=Eu3+, Dy3+, Sm3+, Er3+) composites and their applications as drug release systems

Spherical MCM-41 particles with a diameter of about 150 nm have been successfully coated with CaWO4:Ln (Ln = Eu3+, Dy3+, Sm3+, Er3+) phosphor layers through a simple Pechini sol-gel process. The obtained CaWO4:Ln@MCM-41 composites, which kept the mesoporous structure of MCM-41 and the luminescent properties of phosphors, were investigated as a drug delivery system using aspirin (ASPL) as a model drug.

Mesoporous silica coated CeF3 : Tb3+ particles for drug release

CeF3:Tb3+ nanoparticles were successfully prepared by a polyol process using diethylene glycol ( DEG) as solvent. After being coated with dense silica, these CeF3:Tb3+ nanoparticles can be coated with mesoporous silica using nonionic triblock copolymer EO20PO70EO20 ( P 123) as structure-directing agent. The composite can load ibuprofen and release the drug in the PBS. The composite was characterized by X-ray diffraction ( XRD), transmission electron microscopy ( TEM), nitrogen absorption/desorption isotherms, fluorescence spectra, and UV/Vis absorption spectra, respectively.

Synthesis and photoluminescent properties of silica-coated LaCeF3 : Tb nanocrystals

La0.45Ce0.45F3:Tb (10 mol% Tb) nanoparticles was synthesized via sonochemical method and then coated with silica (SiO2) shells through a microemulsion process, resulting in the formation of core/shell structured LaCeF3:Tb/SiO2 nanoparticles. The obtained core/shell LaCeF3:Tb/SiO2 nanoparticles are spherical and uniform in size (average size about 60 nm), strongly fluorescent, and long fluorescence lifetime (1.87 ms). This kind of nanoparticles was water-soluble, which could be applied in biological labeling and other fields.

Coating Gd2O3 : Eu phosphors with silica by solid-state reaction at room temperature

Silica coating on Gd2O3:Eu particles was obtained by a simple method, e.g. solid-state reaction at room temperature. The urea homogeneous precipitation method was used to synthesize the Gd2O3:Eu cores. Transmission electron microscopy (TEM) shows that the core particles are spherical with submicrometer size which is the soft agglomerates with nanometer crystallites. The TEM morphology of coated particles shows that a thin film is coated on the surface of Gd2O3:Eu cores. Scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS) analysis indicate that the coating of silica can be used to avoid agglomeration of Gd2O3:Eu particles to obtain smaller particles. X-ray photoelectron spectra (XPS) show that silica is coated on the surface of core particles by forming the chemical bond. Photoluminescence (PL) spectra conform that Gd2O3:Eu phosphors remain well-luminescent properties by the silica coating.

Fabrication and photoluminescence properties of core-shell structured spherical SiO2@Gd2Ti2O7 : Eu3+ phosphors

A sol-gel technique was used to prepare Gd2Ti2O7:Eu3+-coated submicron silica spheres (SiO2@Gd2Ti2O7:Eu3+). The resulted SiO2@Gd2Ti2O7:Eu3+ core-shell particles were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive x-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, as well as kinetic decays. The XRD results demonstrate that the Gd2Ti2O7:Eu3+ layers begin to crystallize on the SiO2 spheres after annealing at 800 degrees C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have perfect spherical shape with narrow size distribution (average size similar to 620 nm), non-agglomeration, and smooth surface. The thickness of the Gd2Ti2O7:Eu3+ shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (60 nm for four deposition cycles). Under the irradiation of 310 nm ultraviolet, the SiO2@GdTi2O7:Eu3+ samples show strong emission of Eu3+.

Sol-gel fabrication and photoluminescence properties of SiO2@Gd2O3 : Eu3+ core-shell particles

A uniform nanolayer of europium-doped Gd2O3 was coated on the surface of preformed submicron silica spheres by a Pechini sol-gel process. The resulted SiO2@Gd2O3:Eu3+ core-shell structured phosphors were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as kinetic decays. The XRD results show that the Gd2O3:Eu3+ layers start to crystallize on the SiO2 spheres after annealing at 400 degrees C and the crystallinity increases with raising the annealing temperature. The core-shell phosphors possess perfect spherical shape with narrow size distribution (average size: 640 nm) and non-agglomeration. The thickness of the Gd2O3:Eu3+ shells on the SiO2 cores can be adjusted by changing the deposition cycles (70 nm for three deposition cycles). Under short UV excitation, the obtained SiO2@Gd2O3:Eu3+ particles show a strong red emission with D-5(0)-F-7(2) (610 nm) of Eu3+ as the most prominent group.The PL intensity of Eu3+ increases with increasing the annealing temperature and the number of coating cycles.

Fabrication and optical properties of core-shell structured spherical SiO2@GdVO4 : Eu3+ phosphor via sol-gel process

Europium-doped nanocrystalline GdVO4 phosphor layers were coated on the surface of preformed submicron silica spheres by sol-gel method. The resulted SiO2@Gd0.95Eu0.05VO4 core-shell particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, low voltage cathodoluminescence (CL), time resolved PL spectra and kinetic decays. The XRD results demonstrate that the Gd0.95Eu0.05VO4 layers begin to crystallize on the SiO2 spheres after annealing at 600 C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have spherical shape, narrow size distribution (average size ca. 600 nm), non-agglomeration. The thickness of the Gd0.95Eu0.05VO4 shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). PL and CL show that the emissions are dominated by D-5(0)-F-7(2) transition of Eu3+ (618 nm, red).

Effective nonlinear AC response to composite with spherical particles

An effective nonlinear alternative-current (AC) response to granular nonlinear-composite with spherical inclusions embedded in a host medium under the action of an external AC field is investigated by using a perturbation approach. The local potentials of composite at higher harmonics are derived both in a region of local inclusion particles and in a local host region under the action of a sinusoidal field E-1 sin ω t + E-3 sin 3ω t. An effective nonlinear-response to composite and the relationship between the effective nonlinear-responses at the fundamental frequency and the third harmonics are also studied for the spherical inclusions in a dilute limit.

Ultrasonic synthesis of silica-alumina nanomaterials with controlled mesopore distribution without using surfactants

A novel sol-gel process has been developed for the synthesis of amorphous silica-aluminas with controlled mesopore distribution without the use of organic templating agents, e.g., surfactant molecules. Ultrasonic treatment during the synthesis enables production of precursor sols with narrow particle size distribution. Atomic force microscopy analysis shows that these sol particles are spherical in shape with a narrow size distribution (i.e., 13-25 nm) and their aggregation during the gelation creates clusters containing similar sized interparticle mesopores. A nitrogen physiadsorption study indicates that the mesoporous materials containing different Si/Al ratios prepared by the new synthesis method has a large specific surface area (i.e., 587-692 m(2)/g) and similar pore sizes of 2-11 nm. Solid-state Al-27 magic angle spinning (MAS) NMR shows that most of the aluminum is located in the tetrahedral position. A transmission electron microscopy (TEM) image shows that the mesoporous silica-alumina consists of 12-25 nm spheres. Additionally, high-resolution TEM and electron diffraction indicate that some nanoparticles are characteristic of a crystal, although X-ray diffraction and Si-29 MAS NMR analysis show an amorphous material.

Combined Effects of Silica Filler and Its Interface in Epoxy Resin

In this paper, mechanical properties of silica-filled epoxy resin are tested. The tests show that at elevated temperatures, the material’s properties (e.g. yield stress, flow stress, etc.) vary immonotonically with filler volume fraction. Nanoindentation test results suggest that an interface region, stronger than the matrix, is formed in the materials. The formation of the interface has positive effects on the yield strengths of materials. The addition of particles in the matrix produces a large disturbance in stress distribution, leading to stress concentration in the matrix. The stress concentration has negative effects on the yield strengths of materials. The calculation demonstrates that the maximum stress in samples varies immonotonically with particulate concentration. So, the immonotonic variation of mechanical behavior of materials may be rooted in the contradictory effects of the interface region and the stress concentration caused by particulate addition.

An Energy-Based Method for Analyzing Instrumented Spherical Indentation Experiments

Using dimensional analysis and finite element calculation, we studied spherical indentation in elastic-plastic solids with work hardening. We report two previously unknown relationships between hardness, reduced modulus, indentation depth, indenter radius, and work of indentation. These relationships, together with the relationship between initial unloading stiffness and reduced modulus, provide an energy-based method for determining contact area, reduced modulus, and hardness of materials from instrumented spherical indentation measurements. This method also provides a means for calibrating the effective radius of imperfectly shaped spherical indenters. Finally, the method is applied to the analysis of instrumented spherical indentation experiments on copper, aluminum, tungsten, and fused silica.