Synthesis and chain-length dependent properties of monodisperse oligo(9,9-di-n-octylfluorene-2,7-vinylene)s

A series of monodisperse oligo(9,9-di-n-octylfluorene-2,7-vinylene)s (OFVs) with fluorene units up to 11 has been synthesized following a divergent approach. Chain length was found to affect not only photophysical properties but also thermal properties. Absorption and photoluminescence spectra are red-shifted with increasing chain length. The effective conjugated length has been extrapolated to be as long as 19 fluorene vinylene units, indicative of a well-conjugated system. With the number of fluorene units > 5, the oligomers exhibit nematic mesomorphism. Glass transition temperature (T-g) and clearing point temperature (T-c) increase with increasing molecular length and with those of OFV11 up to 71 and 230 degrees C, respectively. The oligomers can form uniform films by solution casting for fabrication of light-emitting diodes. With a device structure of ITO/ PEDOT:PSS/OFV11/Ca/Al, a current efficiency of 0.8 cd.A(-1) at a brightness of 1300 cd.m(-2) along with a maximum brightness of 2690 cd.m(-2) have been realized. This performance is notably superior to that of the corresponding polymer.

Synthesis and luminescence properties of nanocrystalline Gd2O3 : Eu3+ by combustion process

The nanocrystalline Gd2O3:Eu3+ powders with cubic phase were prepared by a combustion method in the presence of urea and glycol. The effects of the annealing temperature on the crystallization and luminescence properties were studied. The results of XRD show pure phase can be obtained, the average crystallite size could be calculated as 7, 8, 45, and 23 run for the precursor and samples annealed at 600, 700 and 800 degrees C, respectively, which coincided with the results from TEM images. The emission intensity, host absorption and charge transfer band intensity increased with increasing the temperature. The slightly broad emission peak at 610 nm for smaller particles can be observed. The ratio of host absorption to O-2-Eu3+ charge transfer band of smaller nanoparticles is much stronger compared with that for larger nanoparticles, furthermore, the luminescence lifetimes of nanoparticles increased with increasing particles size. The effects of doping concentration of Eu3+ on luminescence lifetimes and intensities were also discussed. The samples exhibited a higher quenching concentration of Eu3+, and luminescence lifetimes of nanoparticles are related to annealing temperature of samples and the doping concentration of Eu3+ ions.

Two- and three-dimensional Au nanoparticle/CoTMPyP self-assembled nanotructured materials: Film structure, tunable electrocatalytic activity, and plasmonic properties

Two- and three-dimensional Au nanoparticle/[tetrakis(N-methylpyridyl)porphyrinato]cobalt (CoTMPyP) nanostructured materials were prepared by "bottom-up" self-assembly. The electrocatalytic and plasmonic properties of the Au nanoparticle/CoTMPyP self-assembled nanostructured materials (abbreviated as Au/CoTMPyP SANMs) are tunable by controlled self-assembly of the An nanoparticles and CoTMPyP on indium tin oxide (ITO) electrode. The electrocatalytic activity of the Au/CoTMPyP SANMs can be tuned in two ways. One way is that citrate-stabilized An nanoparticles are positioned first on ITO surface with tunable number density, and then positively charged CoTMPyP ions are planted selectively on these gold sites. The other way is that An nanoparticles and CoTMPyP are deposited by virtue of layer-by-layer assembly, which can also tune the amount of the as-deposited electrocatalysts. FE-SEM studies showed that three-dimensional SANMs grow in the lateral expansion mode, and thermal annealing resulted in both surface diffusion of nanoparticles and atomic rearrangement to generate larger gold nanostructures with predominant (I 11) facets.

Synthesis and luminescence properties of Gd2O3 : Eu3+ phosphors

Gd2O3: EU3+ phosphors were prepared by urea homogeneous precipitation with different surfactant and sol-gel method. XRD patterns show that all the obtained samples are in cubic Gd2O3, and the results of FTIR and fluorescent spectra conformed that OP is a good surfactant for preparing the Gd2O3: Eu3+ phosphors. The SEM photographs show that the particles prepared by urea homogeneous precipitation method are all spherical and well-dispersed, and grain morphology can be controlled by different surfactant. XRD and SEM indicate that the particle sizes prepared by sol-gel method are in the range of 5 similar to 30 nm, and the grain sizes increase with increasing of heated temperatures. Luminescence spectra indication that the main emission peaks of all samples are at 610 nm, the intensities are different from samples prepared with different surfactant and the luminescence intensities increase with increasing of annealed temperatures.

Synthesis and properties of polyquinolines and polyanthrazolines containing pyrrole units in the main chain

A series of eight new polyquinolines and polyanthrazolines with pyrrole isomeric units in main chain were synthesized and characterized. The new polymers showed high glass transition temperatures (T-g = 242-339 degreesC) and excellent thermal stability (T-5% = 398-536 degreesC in air, TGA). Compared to the series of polyanthrazolines, the series of polyquinolines exhibited higher thermal stability, better solubility in common organic solvents, and lower maximum absorption wavelengths (lambda(max)(a)). Polyanthrazolines with 2,5-pyrrole linkage showed an unusually high lambda(max)(a) (565 nm) and small band gap (2.02 eV). All polymers in solution had low photoluminescence quantum yields between 10(-2%) and 10(-5%) and excited-state lifetimes of 0.28-1.29 ns. The effects of molecular structure, especially pyrrole linkage structures, on the electronic structure, thermodynamics, and some of the optical properties of the polymers were explored. A model of hydrogen bonds in the main chain of the polymers was suggested to explain the difference in the properties of the isomer polymers. In addition, a polyquinoline (PBM) was chosen to examine the proton conductivity; the result indicated that the PBM/H3PO4 complex exhibited a high conductivity of 1.5 x 10(-3) S cm(-1) at 157 degreesC.

In(OH)(3) and In2O3 nanorod bundles and spheres: Microemulsion-mediated hydrothermal synthesis and luminescence properties

Indium hydroxide, In(OH)(3), nano-microstructures with two kinds of morphology, nanorod bundles (around 500 nm in length and 200 nm in diameter) and caddice spherelike agglomerates (around 750 - 1000 nm in diameter), were successfully prepared by the cetyltrimethylammonium bromide (CTAB)/water/cyclohexane/n-pentanol microemulsion-mediated hydrothermal process. Calcination of the In(OH)(3) crystals with different morphologies (nanorod bundles and spheres) at 600 degrees C in air yielded In2O3 crystals with the same morphology. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and photoluminescence (PL) spectra as well as kinetic decays were used to characterize the samples. The pH values of microemulsion play an important role in the morphological control of the as-formed In(OH)(3) nano-microstructures from the hydrothermal process. The formation mechanisms for the In( OH) 3 nano- microstructures have been proposed on an aggregation mechanism. In2O3 nanorod bundles and spheres show a similar blue emission peaking around 416 and 439 nm under the 383-nm UV excitation, which is mainly attributed to the oxygen vacancies in the In2O3 nano-microstructures.

Seed-mediated synthesis of branched gold nanoparticles with the assistance of citrate and their surface-enhanced Raman scattering properties

We report an easy synthesis of highly branched gold particles through a seed-mediated growth approach in the presence of citrate. The addition of citrate in the growth solution is found to be crucial for the formation of these branched gold particles. Their size can be varied from 47 to 185 nm. The length of the thumb-like branch is estimated to be between about 5 and 20 nm, and changes slightly as the particle size increases. Owing to these obtuse and short branches, their surface plasmon resonance displays a marked red-shift with respect to the normal spherical particles. These branched gold particles exhibit stronger SERS activity than the non-branched ones, which is most likely related to these unique branching features.

Facile sonochemical synthesis of CePO4 : Tb/LaPO4 core/shell nanorods with highly improved photoluminescent properties

A simple, efficient and quick method has been established for the synthesis of CePO4:Tb nanorods and CePO4:Tb/LaPO4 core/shell nanorods via ultrasound irradiation of inorganic salt aqueous solution under ambient conditions for 2 h. The as-prepared products were characterized by means of powder x-ray diffraction (PXRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction ( SAED), x-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectra and lifetimes. TEM micrographs show that all of the as-prepared cerium phosphate products have rod-like shape, and have a relatively high degree of crystallinity and uniformity. HRTEM micrographs and SAED results prove that these nanorods are single crystalline in nature. The emission intensity and lifetime of the CePO4:Tb/LaPO4 core/shell nanorods increased significantly with respect to those of CePO4: Tb core nanorods under the same conditions. A substantial reduction in reaction time as well as reaction temperature is observed compared with the hydrothermal process.

Sol-gel growth of Gd2MoO6 : Eu3+ nanocrystalline layers on SiO2 spheres (SiO2@Gd2MoO6 : Eu3+) and their luminescent properties

SiO2@Gd2MoO6:EU3+ core-shell phosphors were prepared by the sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy ITEM), photoluminescence (PL) spectra as well as kinetic decays were used to characterize the resulting SiO2@Gd2MoO6:Eu3+ core-shell phosphors. The XRD results demonstrate that the Gd2MoO6:Eu3+ layers on the SiO2 spheres begin to crystallize after annealing at 600 degrees C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have a near perfect spherical shape with narrow size distribution (average size ca. 600 nm), are not agglomerated, and have a smooth surface. The thickness of the Gd2MoO6:Eu3+ shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). The Eu3+ shows a strong PL luminescence (dominated by D-5(0)-F-7(2) red emission at 613 nm) under the excitation of 307 nm UV light.

The influence of arrangement of St in MBS on the properties of PVC/MBS blends

Three series of MBS core-shell impact modifiers were prepared by grafting styrene and methyl methacrylate onto PB or SBR seed latex in emulsion polymerization. All the MBS modifiers were designed to have the same total chemical composition, and MMA/Bd/St equals 30/42/28, which is a prerequisite for producing transparent blends with PVC. Under this composition, there were three different ways of arrangement for styrene in MBS, which led to the different structure of MBS modifier. The concentration of MBS in PVC/MBS blends was kept at a constant value of 20 wt.%. The effects of arrangement of St in MBS on the mechanical and optical properties of PVC/MBS blends were studied. The notched Izod impact test results showed that the MBS with a PB homopolymer core grafted with St had a lowest brittle-ductile transition (BDT) temperature and BDT temperature increased with the amount of St copolymerized with Bd in the core of MBS. The transparency of blends also increased with the amount of St copolymerized with Bd in the core. TEM results showed that the arrangement of St in MBS influenced the deformation behavior. Two deformation modes were observed in the blends: cavitation and shear yielding.

Patterning and photolumine scent properties of perovskite-type organic/inorganic hybrid luminescent films by soft lithography

Perovskite-type organic/inorganic hybrid layered compound (C6H5C2H4NH3)(2)PbI4 was synthesized. The patterning Of (C6H5C2H4NH3)(2)PbI4 thin films on silicon substrate was realized by the micromolding in capillaries (MIMIC) process, a kind of soft lithography. Bright green luminescent stripes with different widths (50, 15, 0.8 mum) have been obtained. The structure and optical properties Of (C6H5C2H4NH3)(2)PbI4 films were characterized by X-ray diffraction (XRD), UV/Vis absorption and photoluminescence excitation and emission spectra, respectively. It is shown that the organic-inorganic layered (C6H5C2H4NH3)(2)PbI4 film was c-axis oriented, paralleling to the substrate plane. Green exciton emission at 525 nm was observed in the film, and the explanations for it were given.

Luminescent properties of rare-earth-doped CaWO4 phosphor films prepared by the Pechini sol-gel process

CaWO4 phosphor films doped with rare-earth ions (Eu3+, Dy-,(3+) Sm3+, Er3+) were prepared by the Pechini sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy, thermogravimetric and differential thermal analysis, atomic force microscopy, and photoluminescence spectra, as well as lifetimes, were used to characterize the resulting powders and films. The results of the XRD analysis indicated that the films began to crystallize at 400degreesC and that the crystallinity increased with elevation of the annealing temperature. The doped rare-earth ions showed their characteristic emissions in crystalline CaWO4 phosphor films due to energy transfer from WO42- groups to them. Both the lifetimes and PL intensities of the doped rare-earth ions increased with increasing annealing temperature, from 500 to 900degreesC, and the optimum concentrations for Eu3+, Dy3+, Sm3+, Er3+ were determined as 30, 1.5, 1.5, 0.5 at.% of Ca2+ in CaWO4 films annealed at 900degreesC, respectively.

Preparation, patterning and luminescent properties of nanocrystalline Gd2O3 : A (A = Eu3+, Dy3+, Sm3+, Er3+) phosphor films via Pechini sol-gel soft lithography

Nanocrystalline Gd2O3:A (A = Eu3+, Dy3+, Sm3+, Er3+) phosphor films and their patterning were fabricated by a Pechini sol-gel process combined with a soft lithography. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy, UV/vis transmission and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 500 degreesC and that the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free non-patterned phosphor films were obtained by optimizing the composition of the coating sol, which mainly consisted of grains with an average size of 70 nm and a thickness of 550 nm. Using micro-molding in capillaries technique, we obtained homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths (5, 10, 20 and 50 mum). Significant shrinkage (50%) was observed in the patterned films during the heat treatment process. The doped rare earth ions (A) showed their characteristic emission in crystalline Gd2O3 phosphor films due to an efficient energy transfer from Gd2O3 host to them. Both the lifetimes and PL intensity of the rare earth ions increased with increasing the annealing temperature from 500 to 900 degreesC, and the optimum concentrations for Eu3+, Dy3+, sm(3+), Er3+ were determined to be 5, 0.25, 1 and 1.5 mol% of Gd3+ in Gd2O3 films, respectively.

The VUV spectra properties of (Y,Gd)BO3 : Eu

The (Y, Gd) BO3 : Eu phosphor was synthesized by solid-state reaction, The UV spectra showed that in a certain range of Gd3+ concentration, more Gd3+ absorbed energy and transferred it to Eu3+ with its increasing concentration. From the spectra in VUV region, it was observed that both the doping and the concentrations of Gd3+, Eu3+ greatly affected the absorption of the host lattice. The absorbances at 147 nm and 170 nm increased when the Gd3+ was doped which can be explained as that Gd3+ transferred energy to BO4. The optical properties of (Y, Gd)BO3 : Eu were the best when the concentration of Eu3+ was about 0.04.

VUV excitation properties of LnAl(3)B(4)O(12): Re (Ln = Y, Gd; Re=Eu, Tb)

Vacuum ultraviolet excitation spectra of LnAl(3)B(4)O(12):Re (Ln = Y, Gd; Re = Eu, To), along with X-ray photoelectron spectra, were measured. The spectra are tentatively interpreted in terms of the optical properties of the rare earth ions and the band structure. It was found that there is an energy transfer from the hosts to the rare earth ions. It was also found that the top of the valence band in the Gd compound is mainly formed by the 2p levels of O2- and the 4f levels of Gd3+, and in the Y compound mainly by the 2p levels of O2-. (C) 2000 Elsevier Science Ltd. All rights reserved.