共查询到20条相似文献,搜索用时 406 毫秒
1.
A highly water-dispersible NaYF4:Ce/Tb (core), NaYF4:Ce/Tb@NaYF4(core/shell) and NaYF4:Ce/Tb@NaYF4@SiO2 (core/shell/SiO2) nanoparticles (NPs) were synthesized via a general synthesis approach. The growth of an inert NaYF4 and silica shell (~14 nm) around the core-NPs resulted in an increase of the average size of the nanopaticles as well as broadening of their size distribution. The optical band-gap energy slightly decreases after shell formation due to the increase the crystalline size. To optimize the influence of shell formation a comparative analysis of photoluminescence properties (excitation, emission, and luminescence decay time) of the core, core/shell, and core/shell/SiO2 NPs were measured. The emission intensity was significantly enhanced after inert shell formation around the surface of the core NPs. The Commission International de l’Eclairage chromaticity coordinates of the emission spectrum of core, core/shell, core/shell/SiO2 NPs lie closest to the standard green color emission at 545 nm. By quantitative spectroscopic measurements of surface-modified core-NPs, it was suggested that encapsulation with inert and silica layers was found to be effective in retaining both luminescence intensity and dispersibility in aqueous environment. Considering the high aqueous dispersion and enhanced luminescence efficiency of the core-NPs make them an ideal luminescent material for luminescence bioimaging and optical biosensors. 相似文献
2.
Magnetic core/shell (CS) nanocomposites (MNCs) are synthesized using a simple method, in which a magnesium ferrite nanoparticle (MgFe2O4) is a core, and an amorphous silicon dioxide (silica SiO2) layer is a shell. The composition, morphology, and structure of synthesized particles are studied using X-ray diffraction, field emission electron microscopy, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), scattering electrophoretic photometer, thermogravimetric analysis (TGA), and Mössbauer spectroscopy. It is found that the MgFe2O4/SiO2 MNC has the core/shell structure formed by the Fe?O–Si chemical bond. After coating with silica, the MgFe2O4/SiO2 MNC saturation magnetization significantly decreases in comparison with MgFe2O4 particles without a SiO2 shell. Spherical particles agglomerated from MgFe2O4 nanocrystallites ~9.6 and ~11.5 nm in size function as cores coated with SiO2 shells ~30 and ~50 nm thick, respectively. The total size of obtained CS MNCs is ~200 and 300 nm, respectively. Synthesized CS MgFe2O4/SiO2 MNCs are very promising for biomedical applications, due to the biological compatibility of silicon dioxide, its sizes, and the fact that the Curie temperature is in the region required for hyperthermal therapy, 320 K. 相似文献
3.
Li Peng Qian Li Han Zhou Heng-Phon Too Gan-Moog Chow 《Journal of nanoparticle research》2011,13(2):499-510
Gold decorated NaYF4:Yb,Er/NaYF4/silica (core/shell/shell) upconversion (UC) nanoparticles (~70–80 nm) were synthesized using tetraethyl orthosilicate and
chloroauric acid in a one-step reverse microemulsion method. Gold nanoparticles (~6 nm) were deposited on the surface of silica
shell of these core/shell/shell nanoparticles. The total upconversion emission intensity (green, red, and blue) of the core/shell/shell
nanoparticles decreased by ~31% after Au was deposited on the surface of silica shell. The upconverted green light was coupled
with the surface plasmon of Au leading to rapid heat conversion. These UC/silica/Au nanoparticles were very efficient to destroy
BE(2)-C cancer cells and showed strong potential in photothermal therapy. 相似文献
4.
Anees A. Ansari A. K. Parchur M. Alam J. Labis Abdallah Azzeer 《Journal of fluorescence》2014,24(4):1253-1262
CaMoO4:Pr(core), CaMoO4:Pr@CaMoO4 (core/shell) and CaMoO4:Pr@CaMoO4@SiO2 (core/shell/shell) nanoparticles were synthesized using polyol method. X-ray diffraction (XRD), thermogravimatric analysis (TGA), UV–vis absorption, optical band gap energy analysis, Fourier transform infrared (FTIR), FT-Raman and photoluminescence (PL) spectroscopy were employed to investigate the structural and optical properties of the synthesized core and core/shell nanoparticles. The results of the XRD indicate that the obtained core, core/shell and core/shell/shell nanoparticles crystallized well at ~150 °C in ethylene glycol (EG) under urea hydrolysis. The growth of the CaMoO4 and SiO2 shell (~12 nm) around the CaMoO4:Pr core nanoparticles resulted in an increase of the average size of the nanopaticles as well as in a broadening of their size distribution. These nanoparticles can be well-dispersed in distilled water to form clear colloidal solutions. The photoluminescence spectra of core, core/shell and core/shell/shell nanoparticles show the characteristic charge transfer emission band of MoO4 2? (533 nm) and Pr3+ 4f2?→?4f2, with multiple strong 3H4?→?3P2, 1D2?→?3H4 and 3P0?→?3?F2 transitions located at ~490, 605 and 652 nm, respectively. The emission intensity of the CaMoO4:Pr@CaMoO4 core/shell and CaMoO4:Pr@CaMoO4@SiO2 core/shell/shell nanoparticles increased ~4.5 and 1.7 times,respectively, with respect to those of CaMoO4:Pr core nanoparticles. This indicates that a significant amount of nonradiative centers existing on the surface of CaMoO4:Pr@CaMoO4 core/shell nanoparticles can be eliminated by the shielding effect of CaMoO4 shells. 相似文献
5.
Although Gd2O3 (gadolinia) nanoparticle is the subject of intense research interest due to its magnetic property as well as controllable
emission wavelengths by doping of various lanthanide ions, it is known to be difficult to prepare monodisperse crystalline
gadolinia nanoparticles because it requires high temperature thermal annealing process to enhance the crystallinity. In this
article, we demonstrate the synthesis of hollow nanoparticles of crystalline Gd2O3 by employing poly(N-vinylpyrrolidone) (PVP) to stabilize the surface of Gd(OH)CO3·H2O nanoparticles and to successively form SiO2 shell as a protecting layer to prevent aggregation during calcinations processes. Silica shells could be selectively removed
after calcinations by a treatment with basic solution to give hollow nanoparticles of crystalline Gd2O3. The formation mechanism of hollow nanoparticles could be suggested based on several characterization results of the size
and shape, and crystallinity of Gd2O3 nanoparticles by TEM, SEM, and XRD. 相似文献
6.
ZnO nanoparticles were prepared by a simple chemical synthesis route. Subsequently, SiO2 layers were successfully coated onto the surface of ZnO nanoparticles to modify the photocatalytic activity in acidic or alkaline solutions. The obtained particles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS) and zeta potential. It was found that ultrafine core/shell structured ZnO/SiO2 nanoparticles were successfully obtained. The photocatalytic performance of ZnO/SiO2 core/shell structured nanoparticles in Rhodamine B aqueous solution at varied pH value were also investigated. Compared with uncoated ZnO nanoparticles, core/shell structured ZnO/SiO2 nanoparticles with thinner SiO2 shell possess improved stability and relatively better photocatalytic activity in acidic or alkaline solutions, which would broaden its potential application in pollutant treatment. 相似文献
7.
A general facile synthesis approach was used for fabrication of highly emissive aqueous dispersible hexagonal phase upconversion luminescent NaGdF4:Yb/Er nanorods (core NRs) through metal complex decomposition process. An inert NaGdF4 and porous silica layers were grafted surrounding the surface of each and every NRs to enhance their luminescence efficiency and colloidal dispersibility in aqueous environment. Optical properties in terms of band gap energy of core, core/shell, and silica-coated core/shell/SiO2 nanorods were observed to investigate the influence of surface coating, which was gradually decreased after surface coating because of increase crystalline size after growth of inert and silica shells. The inert shell formation before silica surface grafting, upconversion luminescence intensity was greatly improved by about 20 times, owing to the effective surface passivation of the seed core and, therefore, protection of Er3+ ion in the core from the nonradiative decay caused by surface defects. Moreover, after silica coating, core/shell nanorods shows strong upconversion luminescence property similar to the hexagonal upconversion core NRs. It is expected that these NaGdF4:Yb/Er@NaGdF4@SiO2 (core/shell/SiO2) NRs including highly upconversion emissive and aqueous dispersible properties make them an ideal materials for various photonic-based potential applications such as in upconversion luminescent bioimaging, magnetic resonance imaging, and photodynamic therapy. 相似文献
8.
In this paper, a facile co-precipitation process for preparing mono-dispersed core–shell structure nanoparticles is reported.
The 110 nm SiO2 cores coated with an yttrium aluminum garnet (Y3Al5O12) layer doped with Er3+ were synthesized and the influence of the concentration ratio of [urea]/[metal ions] on the final product was investigated.
The structure and morphology of samples were characterized by the X-ray powder diffraction, Fourier transform IR spectroscopy
and transmission electron microscopy, respectively. The results indicate that a layer of well-crystallized garnet Y3Al5O12:Er3+ were successfully coated on the silica particles with the thickness of 20 nm. The near infrared and upconversion luminescent
spectra of the SiO2@Y3Al5O12:Er3+ powders further confirm that a Y3Al5O12:Er3+ coating layer has formed on the surface of silica spherical particles. 相似文献
9.
Arjen Didden Philipp Hillebrand Markus Wollgarten Bernard Dam Roel van de Krol 《Journal of nanoparticle research》2016,18(2):35
Conductive TiN shells have been deposited on SiO2 nanoparticles (10–20 nm primary particle size) with fluidized bed atomic layer deposition using TDMAT and NH3 as precursors. Analysis of the powders confirms that shell growth saturates at approximately 0.4 nm/cycle at TDMAT doses of >1.2 mmol/g of powder. TEM and XPS analysis showed that all particles were coated with homogeneous shells containing titanium. Due to the large specific surface area of the nanoparticles, the TiN shells rapidly oxidize upon exposure to air. Electrical measurements show that the partially oxidized shells are conducting, with apparent resistivity of approximately ~11 kΩ cm. The resistivity of the powders is strongly influenced by the NH3 dose, with a smaller dose giving an order-of-magnitude higher resistivity. 相似文献
10.
Given the importance of the optical properties of Au and Au/SiO2 core/shell nanoparticles, in this article we focus our attention on the light scattering properties of such systems and on a relative comparison. In particular, we report theoretical results of angle-dependent light scattering intensity and scattering efficiency for Au and Au/SiO2 core/shell nanoparticles increasing the Au particle radius from 30 to 130 nm, and for Au/SiO2 core/shell particles changing the core-to-shell sizes ratio. Finally, a comparison between the scattering efficiency of the Au and Au/SiO2 core/shell nanoparticles is drawn. The results of this work can be used in the design of tunable efficiency light scattering devices (biological and molecular sensors, solar cells). 相似文献
11.
Synthesis of water dispersible boron core silica shell (B@SiO<Subscript>2</Subscript>) nanoparticles
Nathan I. Walton Zhe Gao Yulia Eygeris Hamidreza Ghandehari Ilya Zharov 《Journal of nanoparticle research》2018,20(4):112
Water dispersible boron nanoparticles have great potential as materials for boron neutron capture therapy of cancer and magnetic resonance imaging, if they are prepared on a large scale with uniform size and shape and hydrophilic modifiable surface. We report the first method to prepare spherical, monodisperse, water dispersible boron core silica shell nanoparticles (B@SiO2 NPs) suitable for aforementioned biomedical applications. In this method, 40 nm elemental boron nanoparticles, easily prepared by mechanical milling and carrying 10-undecenoic acid surface ligands, are hydrosilylated using triethoxysilane, followed by base-catalyzed hydrolysis of tetraethoxysilane, which forms a 10-nm silica shell around the boron core. This simple two-step process converts irregularly shaped hydrophobic boron particles into the spherically shaped uniform nanoparticles. The B@SiO2 NPs are dispersible in water and the silica shell surface can be modified with primary amines that allow for the attachment of a fluorophore and, potentially, of targeting moieties. 相似文献
12.
Y.C. Wu C. Garapon R. Bazzi A. Pillonnet O. Tillement J. Mugnier 《Applied Physics A: Materials Science & Processing》2007,87(4):697-704
Terbium doped Y2O3 planar waveguides were fabricated by sol–gel process and dip-coating using yttrium acetate as precursor. Two different doping
modes were compared, i.e. introduction in the sol of dispersed Tb3+ions from dissolved Tb(NO3)3, or of nanoparticles of Tb2O3 or [Y2O3:50% Tb] from an alcoholic suspension. The chemical and nanostructural properties were analyzed by infrared spectroscopy,
transmission electron microscopy and X-ray diffraction. The Tb3+ fluorescence properties were studied as a function of temperature and atmosphere of the thermal treatments, and of the Tb3+ concentration. The fluorescence properties are discussed in relation to the quenching mechanisms induced by Tb4+ transformation, residual OH groups, and crystallites size and structure. Optical propagation losses of the Tb doped Y2O3 planar waveguides related to the doping modes and Tb3+ concentration are presented. Doping sol–gel films by nanoparticles is shown to be a valuable alternative to the conventional
doping from dissolved terbium salt.
PACS 81.21.Fw; 84.40.Az; 78.67.Bf 相似文献
13.
The sandwich structure core–shell–shell nanospheres SiO2@(Y,Gd)BO3:Eu3+@SiO2 (SiO2@YGB@SiO2) have been synthesized by depositing YGB nanoparticles on silica core surface through the precipitation method, followed by sol–gel processing of tetraethoxysilane (TEOS) to form smooth silica shell over the surface of YGB. The phosphors were characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), transmission electronic microscope (TEM) and photoluminescence spectra. The results showed that the phosphors with spherical morphology can be produced easily by assembling the core–shell or core–shell–shell structure, and the XRD patterns indicated that the crystallinity of YGB is weakened due to the core–shell structure, which resulting from the local site symmetry of Eu3+ was decreased. The photoluminescence properties of the product are compared with those of the pure YGB, the core–shell structure SiO2@YGB and YGB@SiO2. The emission intensity, relative luminous efficiency and Red/Orange values of phosphors are increased in the order SiO2@YGB@SiO2>SiO2@YGB>YGB@SiO2>YGB; and the chromaticity coordinates of the phosphors are shifted from orange of pure YGB to red of SiO2@YGB@SiO2. 相似文献
14.
K. A. Petrovykh V. S. Kortov N. V. Gaponenko A. A. Rempel’ M. V. Rudenko L. S. Khoroshko S. S. Voznesenskii A. A. Sergeev V. A. Pustovarov 《Physics of the Solid State》2016,58(10):2062-2067
The photoluminescence properties of a composite material prepared by the introduction of the nanosized phosphor Zn2SiO4:Mn2+ into porous anodic alumina have been investigated. Scanning electron microscopy studies have revealed that Zn2SiO4:Mn2+ particles are uniformly distributed in 70% of the volume of the pore channels. The samples exhibit an intense luminescence in the range of 2.3–3.0 eV, which corresponds to the emission of different types of F centers in alumina. After the formation of Zn2SiO4:Mn2+ nanoparticles in the pores, an intense photoluminescence band is observed at 2.4 eV due to the 4T1–6A1 electronic transition within the 3d shell of the Mn2+ activator ion. It has been found that the maximum of the photoluminescence of Zn2SiO4:Mn2+ xerogel nanoparticles located in the porous matrix is shifted to higher energies, and the luminescence decay time decreases significantly. 相似文献
15.
Jing Sun Jiaqi Zhuang Shaowei Guan Wensheng Yang 《Journal of nanoparticle research》2008,10(4):653-658
Water-soluble Mn doped ZnS (ZnS:Mn) nanocrystals synthesized by using 3-mercaptopropionic acid (MPA) as stabilizer were homogeneously
coated with a dense silica shell through a multi-step procedure. First, 3-mercaptopropyl triethoxy silane (MPS) was used to
replace MPA on the particle surface to form a vitreophilic layer for further silica deposition under optimal experimental
conditions. Then a two-step silica deposition was performed to form the final water-soluble ZnS:Mn/SiO2 core/shell nanoparticles. The as-prepared core/shell nanoparticles show little change in fluorescence intensity in a wide
range of pH value. 相似文献
16.
E. G. Bagryanskaya O. A. Krumkacheva A. E. Belikov V. A. Mal’tsev S. A. Novopashin 《Journal of Engineering Thermophysics》2011,20(1):55-63
Measurements of proton nuclear spin-spin and spin-lattice relaxation times are applied for determining the concentration of
solid-phase nanoparticles in nanofluids. This approach is tested for metal oxides SiO2, TiO2, Al2O3 and metal-carbon nanoparticles of 3d-metals Fe and Cu. It is shown that the sensitivity of the method for determining concentrations
of 3d-metals is much higher than for oxides (by 2–4 orders of magnitude). It is revealed that measurement of the proton spin-spin
relaxation time allows one to determine the concentration of Cu nanoparticles to 0.0001 mg/ml and that of Fe nanoparticles
to 0.00001 mg/ml. 相似文献
17.
In this study, FeNi3/Al2O3 core-shell
nanocomposites, where individual FeNi3 nanoparticles were coated with a
thin layer of alumina, were fabricated by a modified sol-gel method. Several physical characterizations were performed on the samples of FeNi3/Al2O3 nanocomposites with different thickness of Al2O3 shell. The encapsulation of FeNi3 nanoparticles with
alumina stops FeNi3 agglomeration during heat treatment, and prevents
interaction among the closely spaced magnetic FeNi3 nanoparticles. The
Al2O3 insulating shell improves the soft magnetic properties of FeNi3. The study of the complex permeability of the samples shows that the real part μ’ of the permeability of the sample with Al molar content of 20% (Al/(Fe+Ni)) is as high as 12, and independent of frequency up to at least 1 GHz. The tunneling magnetoresistance arising from the presence of the Al2O3 shell have also been studied. 相似文献
18.
Fei Qi Anna Moiseev Joachim Deubener Alfred Weber 《Journal of nanoparticle research》2011,13(3):1325-1334
Anatase is the low-temperature (300–550 °C) crystalline polymorph of TiO2 and it transforms to rutile upon heating. For applications utilizing the photocatalytic properties of nanoscale anatase at
elevated temperatures (over 600 °C) the issue of phase stabilisation is of major interest. In this study, binary TiO2/SiO2 particles were synthesized by a flame aerosol process with TiCl4 and SiCl4 as precursors. The theoretical Si/Ti ratio was varied in the range of 0.7–1.3 mol/mol. The synthesized TiO2/SiO2 samples were heat treated at 900 and 1,000 °C for 3 h to determine the thermostability of anatase. Pyrogenic TiO2 P25 (from Evonik/Degussa, Germany) widely applied as photocatalyst was used as non-thermostabilized reference material for
comparison of photocatalytic activity of powders. Both the non-calcinated and calcinated powders were characterized by means
of XRD, TEM and BET. Photocatalytic activity was examined with dichloroacetic acid (DCA) chosen as a model compound. It was
found that SiO2 stabilized the material retarding the collapse of catalyst surface area during calcination. The weighted anatase content
of 85% remains completely unchanged even after calcination at 1,000 °C. The presence of SiO2 layer/bridge as spacer between TiO2 particles freezes the grain growth: the average crystallite size increased negligibly from 17 to 18 nm even during the calcination
at 1,000 °C. Due to the stabilizing effect of SiO2 the titania nanoparticles calcinated at 900 and 1,000 °C show significant photocatalytic activity. Furthermore, the increase
in photocatalytic activity with calcination temperature indicates that the titania surface becomes more accessible either
due to intensified cracking of the SiO2 layer or due to enhanced transport of SiO2 into the necks thus releasing additional titania surface. 相似文献
19.
A method to prepare a core–shell structure consisting of a Pt metal core coated with a silica shell (Pt(in)SiO2) is described herein. A silica shell was grown on poly(vinylpyrrolidone) (PVP)-stabilized Pt nanoparticles 2–3 nm in size through hydrolysis and condensation reactions of tetraethyl orthosilicate (TEOS) in a water/ethanol mixture with ammonia as a catalyst. This process requires precise control of the reaction conditions to avoid the formation of silica particles containing multiple Pt cores and core-free silica. The length of PVP molecules, water content, concentration of ammonia and Pt nanoparticles in solution were found to significantly influence the core–shell structure. By optimizing these parameters, it was possible to prepare core–shell particles each containing a single Pt nanoparticle with a silica layer coating approximately 10 nm thick. 相似文献
20.
Jingyu Si Jianfeng Zhang Jinyu Duan Huajian Xu Qunling Fang 《Journal of nanoparticle research》2018,20(11):299
This work reported a novel kind of CdTe quantum dot (QD) decorated mesoporous SiO2 (m-SiO2/QD) hybrid hollow nanoparticles for carrying photodynamic therapy (PDT) reagent. Both rod-like and spherical nanoparticles were prepared by using different shaped templates. Due to the porous shell and hollow interior, the hybrid m-SiO2/QD hollow nanorod with 360 nm long and 120 nm in diameter was selected for carrying zinc(II) phthalocyanine (ZnPc) photosensitizing molecules (61 mg/g) since the generated reactive 1O2 could be easily delivered out of the hollow particles through the porous shell (BET area 251 cm2/g). It was found that the m-SiO2/QD-ZnPc hollow nanorods exhibited a good PDT activity and showed effective photocytotoxicity for the cancer cells. Because of the porous nature, fluorescence characteristic, and excellent storage ability, the m-SiO2/QD hybrid hollow particles possessed broad potential in the fluorescent labeled PDT. 相似文献