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A facile one-pot synthetic approach, using oleic acid and oleylamine as composite stabilizers combined with high-temperature treatment in 1-octadecene, has been developed for the preparation of monodisperse and uniform lanthanum phosphate and europium-doped lanthanum phosphate nanocrystals. In particular, with the present synthetic approach, the size of the resulting nanocrystals could be tuned precisely and continuously from 3.5 to 6.5 nm by seed-mediated epitaxial growth. The as-obtained uniform nanocrystals with hydrophobic surfaces, which show efficient photoluminescence, could be easily dispersed in nonpolar solvents. More importantly, these nanocrystals can also be easily modified to water-dispersed ones with hydrophilic surfaces for potential use in in vitro imaging in bioanalysis. In addition, a synthetic mechanism for these monodisperse nanocrystals is presented and discussed.
Dopamine covalently chelated ZnO nanoparticles were synthesized by a nonaqueous one-step chemical process at a temperature as low as 60 °C. The formation of ZnO/dopamine hybrid structure was proved by x-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) techniques. Detailed absorption, luminescence, and time-resolved decay studies were performed for these ZnO/dopamine hybrid nanoparticles. We observed an enhanced green emission, which could be assigned to a new band-gap emission based on the fast of nanosecond lifetime of the green emission. Our results demonstrated that the change of optical properties of ZnO nanoparticles after covalently chelated by dopamine ligands is closely associated with the formation of new band structure.
Three different strategies, wet impregnation, in situ reduction, and grafting with silane coupling agents, have been used to introduce CoNi nanoparticles with different existing forms into mesoporous silica. These composites were used as catalysts to grow nanostructured carbons by catalytic chemical vapor deposition using ethene. Carbon nanotubes (CNTs) with different inner diameters can grow out of mesoporous silica particles incorporated with CoNi nanoclusters. Many fewer CNTs could be found in the pore channels of the sample prepared by using silane coupling agents than in those of the sample synthesized via wet impregnation. No CNTs formed in the pore channels of the sample prepared by in situ reduction. After the removal of silica, different carbon nanostructures have been obtained in the pore channels. Ordered graphite carbon mesostructure was obtained from the sample prepared by in situ reduction. Highly dispersed metal catalysts inside mesopore channels are favorable for the formation of graphite carbons with ordered mesostructures.
Well-structured and monodisperse nanocomposite spheres with a magnetic core/mesoporous silica shell structure (MCMS) were obtained. The effects on the structure and morphology of the MCMS spheres were investigated under various synthesis conditions, including reaction time, quantity of silicate sources of tetraethoxysilane (TEOS) and n-octadecyltrimethoxysilane (C18TMS), ratio of TEOS/C18TMS, and ratio of H2O/EtOH in the starting solution. The particle size of the MCMS spheres and pore diameter are tunable in a certain range with 100% yield. A synthesis mechanism of the mesoporous silica shell was proposed that proceeds via three main stages. The silica shell proved to be effective on protecting the cores from leaching out in acidic conditions.
In this paper, we report a facile route, the tin vapor treatment method, to prepare tin oxide containing mesoporous silica composites (TOMS), which display room-temperature photoluminescence (RT-PL). Among them, TOMS-1 and TOMS-2 were synthesized from mesoporous silica SBA-15 and KIT-6, respectively. They are composed of amorphous SiO2 and tin oxide species and they display strong emission near ultraviolet (UV) when excited by UV light. By increasing the preparation temperature, their Sn content can be increased and subsequently their photoluminescence (PL) intensities can be greatly enhanced. Besides, their PL properties are revealed to be closely related to 2-fold-coordinated tin oxygen-deficient centers.
A simple solution combustion synthesis technique was explored to produce Tb3+-doped Lu3Al5O12 (LuAG:Tb) phosphor with particle size in the range from about 25 to 900 nm by using glycine, urea, and the mixture of them as fuels. The effects of processing parameters such as type of fuel, fuel-to-oxidizer ratio and the composition of the complex fuel were studied. An increase in phosphor brightness and a decrease in crystallization temperature with increasing urea content in the fuel were observed. The integrated emission intensity ratio of the 5D3–7Fj transition to the 5D4–7Fj transition as a function of Tb concentration in LuAG was also investigated. It is very interesting that the growth process of the particles exhibited two steps when the content of urea in the complex fuel increased from 0 to 1.0. By tailoring the glycine-to-urea ratio in the fuel, an excellent fuel was found and high performance phosphors were obtained.
A stable mesoporous multilamellar silica vesicle (MSV) was developed with a gallery pore size of about 14.0 nm. A simulative enzyme, hemoglobin (Hb), was immobilized on this newly developed MSV and a conventional mesoporous silica material SBA-15. The structures and the immobilization of Hb on the mesoporous supports were characterized with x-ray diffraction, transmission electron microscopy, N2 adsorption-desorption isotherms, Fourier transform infrared, ultraviolet-visible spectroscopy, and so forth. MSV is a promising support for immobilizing Hb due to its large pore size and high Hb immobilization capacity (up to 522 mg/g) compared to SBA-15 (236 mg/g). Less than 5% Hb was leached from Hb/MSV at pH 6.0. The activity study indicated that the immobilized Hb retained most peroxidase activity compared to free Hb. Thermal stability of the immobilized Hb was improved by the proctetive environment of MSV and SBA-15. Such an Hb-mesoporous support with high Hb immobilization capacity, high activity, and enhanced thermal stability will be attractive for practical applications.
Nd-doped Y3ScxAl5−xO12(Nd:YSAG) powder were prepared with a chemical combustion method. The powders were nano-sized and had a pure cubic phase when calcined at 900 °C. Transparent Nd:YSAG ceramics with up to 40% scandium substitution for aluminum were successfully fabricated by sintering the powder compact at 1800 °C under H2 atmosphere. The synthesis process and optical properties were investigated in detail. It was found that the light emission intensity at 1064 nm of the Nd:YSAG with 40% scandium substitution for aluminum can be enhanced by 2–3 times over that of Nd:YAG single crystal when pumped with the same 808-nm diode laser. In addition, the material was found to have prolonged fluorescence lifetime. This highly enhanced light emission intensity is fundamentally important for obtaining higher light output together with suppressed self-heating than Nd:YAG ceramic and single crystals.
Eu3+-doped Lu2O3 phosphors were synthesized through a novel solution combustion route using glycine as the fuel. The influence of the glycine-to-nitrate (G/N) mole ratio on the crystallite size, specific surface area, morphology, and photoluminescence of the synthesized phosphors was investigated. The ignition temperature on the properties of the products was also studied. With G/N ratio increasing from 1.0 to 1.7, the grain size increased from 35 to 118 nm accordingly, resulting in the obvious changes of the photoluminescence properties. Concentration dependence of the emission intensity revealed that the quenching concentration of europium dopant was around 5 mol% for G/N- 1.7. The intensity of the peak emission due to the 5D0 → 7F2 transition of the Eu3+ ions dropped as the grain size decreased. The charge transfer band position of Eu3+-doped lutetia phosphors shifted toward lower energy (red shift) with the reduction of crystallite sizes and also with the increase of Eu3+ concentrations.
Transparent ceramic scintillators of La2Hf2O7:Ti4+ were developed by a novel combustion synthesis method. The optical transmittance for a 1.0-mm-thick specimen is about 60% of the incident light, and the x-ray stopping power is also quiet high. The broad emission band centered at 475 nm originates from the oxide-Ti4+ charge-transfer transitions, which renders fast decay time on the order of 10 μs. The highest relative light output has reached about 1.5 times that of Bi4Ge3O12 (BGO) single crystal when excited by 120 kV x-rays.
Nano-sized (Y,Gd)2O3:Eu powders were synthesized by a novel co-precipitation processing in which a mixture of ammonium hydroxide and ammonium hydrogen carbonate was adopted as a complex precipitant. Evolution behaviors of precursors during calcinations were studied by means of thermogravimetry-differential scanning calorimetry-mass spectrum, Fourier transform infrared, x-ray diffraction, scanning electron microscopy, and transmission electron microscopy in detail. Nano-sized (Y,Gd)2O3:Eu powder as prepared possessed a primary grain size of about 30 nm and specific surface area of 38 m2/g after being calcined at 850 °C for 2 h, showing much finer grains and less agglomeration. The as prepared nanopowder shows intense luminescence at 611nm under x-ray or ultraviolet excitation. Transparent (Y,Gd)2O3:Eu ceramics can also be fabricated using this high sinterable nanopowder.
A simple approach has been developed for the synthesis of Au@CdS core-shell nanoparticles by a direct self-assembling process. Stable Au@CdS composite colloids were prepared by thiourea, as a double-functional reagent that acted as the linkage agent between Cd2+ ions and gold nanoparticles. The CdS-capped gold composite nanoparticles were successfully integrated into BaTiO3 films. A significant enhancement of third-order nonlinear optical susceptibility in the Au@CdS nanoparticles with core-shell structure is reported. To compare the effect of enhanced nonlinear response, single gold or CdS nanoparticles embedded in BaTiO3 films were also prepared.
PbS/ZrO2 optical films were prepared by the dip-coating method from a mixed sol containing two precursors, Zr(OC3H7)4 and Pb(CH3COO)2. The phase structure and size of PbS nanoparticles were characterized by x-ray diffraction and transmission electron microscopy, respectively. Optical absorption and fluorescence spectra were taken on the PbS/ZrO2 films. Larger blue shifts of band edge and weak fluorescence emission of PbS were observed. The third-order nonlinear properties of PbS/ZrO2 films were studied. The calculated values of nonlinear refractive indexes n2 varied between 10−8 and 10−9 cm2/W.
Using lithography, and selective etching the Si1-xGex/Si multiple quantum well wires are fabricated. The characteristics of the selective chemical etching of Si1-xGex and Si are investigated, and high-performance etchants are developed. The etchant composed of HF:NH4F:H202:NH4OH is used for the etching of the epitaxial Si1-xGex films, the selectivity is better than 250 for Si0.76Ge0.24, and increases with the increase of the mole fraction x of Ge. Another etchant composed of NH4NO3:NH4OH is used for the etching of Si, the selectivity is higher than 1000 ( x ≥ 0.1 ). A preliminary photoluminescence (PL) result obtained from the Si0.76Ge0.24 multiple quantum well wires is presented. As the linewidth of the wires is reduced down to 50 nm, an intense complicated PL spectrum in the wavelength range of 500∼800 nm is observed at liquid nitrogen temperature. The origin of such spectrum is unclear.
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