Showing papers in "Chemistry of Materials in 2006"
TL;DR: In this paper, a model based on elemental analysis, transmission electron microscopy, X-ray dif... was proposed to unravel the chemical structure of graphite oxide (GO).
Abstract: This study contributes to the sustained effort to unravel the chemical structure of graphite oxide (GO) by proposing a model based on elemental analysis, transmission electron microscopy, X-ray dif...
1,642 citations
TL;DR: In this paper, nearly monodisperse single-crystalline Cu2O nanospheres were prepared by an effective solution method with NaBH4 as the reducing agent.
Abstract: Nearly monodisperse single-crystalline Cu2O nanospheres were prepared by an effective solution method with NaBH4 as the reducing agent. Sensors based on them have good sensitivity to some flammable gases because thin films formed by nanospheres have capacious interspaces and enough spherical surfaces to interact with gases (ppm level).
1,049 citations
TL;DR: In this paper, the synthesis of mesoporous polymers and carbon frameworks from organic−organic assembly of triblock copolymers with soluble, low-molecular-weight phenolic resin precursors (resols) by an evaporation induced self-assembly strategy has been reported.
Abstract: The syntheses of a family of highly ordered mesoporous polymers and carbon frameworks from organic−organic assembly of triblock copolymers with soluble, low-molecular-weight phenolic resin precursors (resols) by an evaporation induced self-assembly strategy have been reported in detail. The family members include two-dimensional hexagonal (space group, p6m), three-dimensional bicontinuous (Ia3d), body-centered cubic (Im3m), and lamellar mesostructures, which are controlled by simply adjusting the ratio of phenol/template or poly(ethylene oxide)/poly(propylene oxide) in the templates. A five-step mechanism from organic−organic assembly has been demonstrated. Cubic FDU-14 with a gyroidal mesostructure of polymer resin or carbon has been synthesized for the first time by using the copolymer Pluronic P123 as a template in a relatively narrow range. Upon calcination at 350 °C, the templates should be removed to obtain mesoporous polymers, and further heating at above a critical temperature of 600 °C transfor...
1,013 citations
TL;DR: In this article, the secondary dopant diethylene glycol (DEG) was added to the conducting polymer poly(3,4-ethylenedioxythiophene)− poly(styrenesulfonate) (PEDOT−PSS) to improve its electrical properties.
Abstract: The development of printed and flexible (opto)electronics requires specific materials for the device's electrodes Those materials must satisfy a combination of properties They must be electrically conducting, transparent, printable, and flexible The conducting polymer poly(3,4-ethylenedioxythiophene)− poly(styrenesulfonate) (PEDOT−PSS) is known as a promising candidate Its conductivity can be increased by 3 orders of magnitude by the secondary dopant diethylene glycol (DEG) This “secondary doping” phenomenon is clarified in a combined photoelectron spectroscopy and scanning probe microscopy investigation PEDOT−PSS appears to form a three-dimensional conducting network explaining the improvement of its electrical property upon addition of DEG Polymer light emitting diodes are successfully fabricated using the transparent plastic PEDOT−PSS electrodes instead of the traditionally used indium tin oxide
824 citations
TL;DR: In this article, the complex Zintl compound, Yb14MnSb11, was proposed for high-temperature (>900 K), p-type materials development for thermoelectric power generation.
Abstract: Thermoelectric materials provide a key solution to energy problems through the conversion of heat into electrical energy. We report that the complex Zintl compound, Yb14MnSb11, breaks a 2-decade stagnation in high-temperature (>900 K), p-type materials development for thermoelectric power generation. This material achieves quadrupled efficiency and virtually doubled figure of merit over the current state-of-the-art, SiGe, thus earmarking it superior for thermoelectric applications in segmented devices. Yb14MnSb11 represents the first complex Zintl phase with substantially higher figure of merit and efficiency than any other competing materials, opening a new class of thermoelectric compounds with remarkable chemical and physical properties.
698 citations
TL;DR: In this paper, a simple one-pot synthesis via a hydrothermal approach was proposed to synthesize a wide range of metal oxide hollow spheres, including Fe2O3, NiO, Co3O4, CeO2, MgO, and CuO hollow spheres.
Abstract: Hollow spheres of crystalline metal oxides were synthesized in a simple one-pot synthesis via a hydrothermal approach. Various metal salts were dissolved together with carbohydrates in water, and the mixtures were heated to 180 °C in an autoclave. During the hydrothermal treatment, carbon spheres are formed with metal ions incorporated into their hydrophilic shell. The removal of carbon via calcination yields hollow metal oxide spheres. Using this process, we can produce a wide range of metal oxide hollow spheres that are not accessible via sol−gel chemistry. In this paper, we report the synthesis of Fe2O3, NiO, Co3O4, CeO2, MgO, and CuO hollow spheres that are composed of nanoparticles. The surface area and thickness of the shell can be varied or controlled by the carbohydrate:metal salt concentration.
631 citations
TL;DR: In this article, a clear signal of Cu(II) carbonyl and dihydrogen complexes formed inside a crystalline microporous hosting matrix was observed for the first time.
Abstract: XRD, UV−Vis, EXAFS, XANES, and Raman techniques have been used to study the removal of water molecules coordinated to the Cu(II) framework atoms of the novel HKUST-1 metal-organic framework. The dehydration process preserves the crystalline nature of the material, just causing a reduction of the cell volume due to the shrinking of the [Cu2C4O8] cage. The removal of adsorbed H2O molecule makes the framework Cu(II) sites available for interaction with other probe molecules. In situ IR spectroscopy has evidenced the formation at liquid nitrogen temperature of labile Cu(II)···CO adducts characterized by a ν(C−O) = 2178 cm-1 and at 15 K of Cu(II)···H2 adducts characterized by a ν(H−H) = 4100 cm-1. To the best of our knowledge, we have observed for the first time a clear signal of Cu(II) carbonyl and dihydrogen complexes formed inside a crystalline microporous hosting matrix. The sinking of the oxygens of the carboxyl units, undergone by the Cu(II) framework ions in the dehydration process, is responsible for...
626 citations
TL;DR: In this article, magnetite particles with an average size of 39 nm and good monodispersity have been synthesized by coprecipitation at 70 °C from ferrous Fe2+ and ferric Fe3+ ions by a (N(CH3)4OH) solution, followed by hydrothermal treatment at 250 °C.
Abstract: Magnetite particles with an average size of 39 nm and good monodispersity have been synthesized by coprecipitation at 70 °C from ferrous Fe2+ and ferric Fe3+ ions by a (N(CH3)4OH) solution, followed by hydrothermal treatment at 250 °C. The magnetite nanoparticles before the hydrothermal step display an average size of 12 nm and are highly oxidized when they are in contact with air. Complementary microstructural and magnetic characterizations of nanoparticles after hydrothermal treatment show unambiguously that they consist of magnetite with only a slight deviation from stoichiometry (δ ≈ 0.05), leading to Fe2.95O4.
574 citations
TL;DR: In this paper, a simple, inexpensive, and high-yield synthetic route to Sr2Si5N8:Eu2+-based red nitridosilicate phosphors for white light-emitting diodes (LEDs) was reported.
Abstract: This paper reports a simple, inexpensive, and high-yield synthetic route to Sr2Si5N8:Eu2+-based red nitridosilicate phosphors for white light-emitting diodes (LEDs). Through the chemical reaction of SrCO3, Eu2O3, and Si3N4 rather than the air-sensitive Sr, Eu, Si(NH)2, Sr3N2, and EuN powders, a complex phosphor consisting of Sr2Si5N8:Eu2+ (∼64 wt %) and Sr2SiO4:Eu2+ (∼36 wt %) were obtained by firing the powder mixture at 1600 °C under 0.5 MPa N2. The structural characterization, luminescence spectra, quantum efficiency, and thermal quenching of the synthesized phosphor were investigated and compared with those of Sr2Si5N8:Eu2+ prepared by the conventional method. It shows that the emission of the existing Sr2SiO4:Eu2+ is extremely low (about 0.04% of that of Sr2Si5N8:Eu2+) under the ultraviolet-light irradiation, and it is silent under the blue-light excitation (λ = 400−480 nm); therefore, the luminescence of the complex phosphor solely arises from Sr2Si5N8:Eu2+. The Sr2Si5N8:Eu2+-based phosphor is orang...
560 citations
TL;DR: In this article, three main strategies for dispersing carbon nanotubes (NTs) into a polymer matrix to get conductive nanocomposites are described, and illustrated with some appealing examples.
Abstract: The three main strategies for dispersing carbon nanotubes (NTs) into a polymer matrix to get conductive nanocomposites are described, and illustrated with some appealing examples. The direct mixing of the NTs and the polymer is the ‘simplest' concept to achieve this goal. Other approaches concern the modification of either the polymer matrix or the NT walls in order to improve the wetting of the filler with the matrix material, and thus promote the incorporation of the NTs into the polymer matrix. Most promising results seem to be obtained upon the addition of a third component. The basic concept is the generation of a stable colloidal system containing both a suspension of NTs stabilized by surfactant molecules in water, and polymer latex. After removal of the water, the resulting powder can be processed into the desired shape. This versatile and environmentally benign concept offers low percolation thresholds and relatively high conductivity levels.
512 citations
TL;DR: In this paper, a functionalized amorphous carbon material with acid catalytic activity as a solid acid replacement for sulfuric acid was used for liquid-phase acid-catalyzed reactions.
Abstract: Carbonization of d-glucose at 573−723 K followed by sulfonation produces a functionalized amorphous carbon material with acid catalytic activity as a solid-acid replacement for sulfuric acid. The carbon material contains phenolic hydroxyl, carboxylic acid, and sulfonic acid groups and exhibits high catalytic performance for liquid-phase acid-catalyzed reactions. Carbonization at higher temperature followed by sulfonation also results in amorphous carbon, but the resultant does not exhibit catalytic activity although the amorphous carbon has sufficient amount of sulfonic acid groups. Structural and active site analyses suggest that the marked difference in catalytic activity is due to the accessibility of reactants to sulfonic acid groups in the carbon structure.
TL;DR: In this paper, a detailed study of the deinsertion/insertion mechanism of the LiFePO4 insertion electrode was performed by high-resolution electron energy loss spectroscopy on thin platelet-type particles of LixFePO 4 (bPnma axis normal to the surface).
Abstract: The intriguingly fast electrochemical response of the insulating LiFePO4 insertion electrode toward Li is of both fundamental and practical importance. Here we present a comprehensive study of its deinsertion/insertion mechanism by high-resolution electron energy loss spectroscopy on thin platelet-type particles of LixFePO4 (bPnma axis normal to the surface). We find that the lithium deinsertion/insertion process is not well-described by the classical shrinking core model. Compositions of the same x value obtained by both deinsertion and insertion gave the same results, namely that the LixFePO4 so formed consists of a core of FePO4 surrounded by a shell of LiFePO4 with respective ratios dependent on x. We suggest that lattice mismatch between the two end members may be at the origin of the peculiar microstructure observed. Furthermore, because of the appearance of isosbestic points on the overlaid EELS spectra, we provide direct experimental evidence that the nanometer interface between single-phase areas...
TL;DR: In this article, a divalent salt titanate (Na2Ti2O5·H2O) with a layered structure was identified as the structure formed after the NaOH treatment, and the layered titaniate transformed into a nanotube through Na+−H+ substitution, and eventually transformed into anatase TiO2.
Abstract: We demonstrated that nanotubes synthesized from a NaOH treatment on TiO2 with subsequent acid washing could proceed with repeatable crystalline-structure transformation through a simple acid−base washing step. By providing the unit cell parameters, we identified a divalent salt titanate (Na2Ti2O5·H2O) with a layered structure as the structure formed after the NaOH treatment. With the increase in acidity during the post-treatment acid washing, the layered titaniate transformed into a nanotube through Na+−H+ substitution, and eventually transformed into anatase TiO2. Crystalline-structure analysis has shown the feasibility of this titanate−titania transformation occuring through a simple structural rearrangement. A complete scheme for the formation and transformation of nanotubes induced by the NaOH treatment and the post-treatment washing was proposed.
TL;DR: In this paper, the formation and luminescence of a new garnet phosphor for light emitting diode (LED) based lighting, Lu2CaMg2(Si,Ge)3O12:Ce3+.
Abstract: In this paper, we describe the formation and luminescence of a new garnet phosphor for light emitting diode (LED) based lighting, Lu2CaMg2(Si,Ge)3O12:Ce3+. The regions for garnet phase formation are initially described with respect to larger rare earth substitution and show reasonable correlation to previous crystal chemistry studies for the garnet parent structure. While the pure silicate phosphor also has apatite second phases, a significant amount of Ce3+ enters the garnet phase, giving Ce3+ luminescence that is significantly redder when compared to typical Al3+ garnet phosphors with quantum efficiencies comparable to commercial Ce3+ garnet phosphors. Potential reasons for the emission red shift and the high quantum efficiency are discussed. Finally, the performance of these new phosphors is tested within LED based lamps. Lamps using these phosphors can reach color temperatures required for general illumination lighting and also have comparable phosphor conversion efficiencies when compared to lamps us...
TL;DR: In this article, the authors highlight the lithium ion intercalation properties of nanostructured vanadium oxides for energy storage as well as other applications in sensors, actuators, and transistors.
Abstract: Nanomaterials lie at the heart of the fundamental advances in efficient energy storage/conversion and other types of nanodevices in which the surface process and transport kinetics play determining roles. This review describes some recent developments in the synthesis and characterizations of various vanadium oxide nanostructures including nanowires, nanorolls, nanobelts, and ordered arrays of nanorods, nanotubes, and nanocables for significantly enhanced intercalation properties. The major topic of this article is to highlight the lithium ion intercalation properties of nanostructured vanadium oxides for energy storage as well as other applications in sensors, actuators, and transistors.
TL;DR: In this paper, the results obtained in a base and an aprotic electrolyte, KOH and TEABF(4)/PC, respectively, were evaluated with cycling voltammetry, a galvanostatic charge/discharge technique, and electrochemical impedance spectroscopy.
Abstract: Carbon materials with significant nitrogen contents were investigated as the electrode materials of supercapacitors. The preparation procedure involved the polymerization of melamine in the interlayer space of template fluorine mica and carbonization at 750, 850, and 1000 degrees C. Some samples were also stabilized prior to carbonization. We have shown previously that these carbons possess very interesting capacitive behavior in an acidic medium despite small surface areas. High capacitance values in H2SO4 were attributed to the pseudocapacitive interactions between the protons and nitrogen atoms. This paper further discusses the results obtained in a base and an aprotic electrolyte, KOH and TEABF(4)/PC, respectively. Electrochemical properties were evaluated with cycling voltammetry, a galvanostatic charge/discharge technique, and electrochemical impedance spectroscopy. High capacitance values were obtained in proton-free KOH, and the presence of pseudocapacitive interactions between the ions of the electrolyte and the nitrogen atoms of the carbon matrix is proposed. Compared to those in sulfuric acid, greater capacitances of nonstabilized samples were obtained in KOH, i.e., for the sample carbonized at 1000 degrees C, the capacitance was 84.61 F/g in KOH vs 47.92 F/g in H2SO4. On the other hand, less porous but more nitrogen-rich stabilized samples gave better performances in H2SO4, i.e., 62.24 F/g in H2SO4 compared to 49.86 F/g in KOH for the sample stabilized and carbonized at 1000 degrees C. The sample heat-treated at 750 degrees C with a surface area of ca. 400 m(2)/g performs similarly in both electrolytes, i.e., similar to 200 F/g. Significantly lower gravimetric capacitances were obtained in TEABF(4)/PC from the samples carbonized at 750 degrees C. On the other hand, the almost nonporous sample subjected to stabilization prior to carbonization at 1000 degrees C gave a capacitance of similar to 20 F/g. Hence, we suggest that the faradaic interactions between the carbon electrode material and the electrolyte, although much less significant than those in H2SO4 and KOH, play an important role in the nonaqueous electrolyte as well. Narrow micropores were detected by CO2 adsorption/desorption, and their importance to the interpretation of capacitive behavior is also discussed.
TL;DR: In this article, a set of ionogels with different ionic liquid content was studied by DSC and 1H NMR spectroscopy, and it was shown that the nanometric level of the confinement of the ionic liquids significantly modify the phase transitions, while still allowing some molecular mobility.
Abstract: A simple nonaqueous sol−gel processing led to ionogels, resulting in the confinement of an ionic liquid within a silica-like network. In the case of a non-water-soluble ionic liquid, ionogels were made stable toward water immersion by the presence of hydrophobic methyl groups in the solid network. A set of ionogels with different ionic liquid content was studied by DSC and 1H NMR spectroscopy. The nanometric level of the confinement of the ionic liquid turned out to significantly modify the phase transitions, while still allowing some molecular mobility. Moreover, ionogels were found to keep the high conducting performances of the ionic liquid.
TL;DR: In this paper, a method for controlled and homogeneous silica coating of low-aspect-ratio CTAB-stabilized gold nanorods has been developed through the combination of the LBL technique and the Stober method.
Abstract: A method for controlled and homogeneous silica coating of low-aspect-ratio CTAB-stabilized gold nanorods has been developed through the combination of the LBL technique and the Stober method. Hydrophobation of the gold nanoparticles was achieved via surface functionalization with a hydrophobic silane coupling agent.
TL;DR: A few types of crystalline hollow structures, such as crystalline carbon hollow spheres (750 nm), crystalline Carbon hollow spheres with encapsulated or decorated 1−3 nm SnO2 nanoparticles, and crystalline...
Abstract: A few types of crystalline hollow structures, crystalline carbon hollow spheres (750 nm), crystalline carbon hollow spheres with encapsulated or decorated 1−3 nm SnO2 nanoparticles, and crystalline...
TL;DR: In this article, the direct relationship between the electronic conductivity of the nanostructured spinel LiMn2-xNixO4 and its lattice parameter is reported.
Abstract: The direct relationship between the electronic conductivity of the nanostructured spinel LiMn2-xNixO4 and its lattice parameter is reported. Within the 8.167−8.183 A range studied, there was a systematic 2.5 orders of magnitude difference between the highest electronic conductivity (cation disordered Fd3m spinel) to lowest conductivity (ordered P4332 spinel). The underlying reason behind the higher conductivity of the former was the presence of Mn3+ (nonexistent in ordered) and Mn4+ sites. The impact of the observed electronic conductivity on electrochemical performance is discussed with respect to morphological impact on ion diffusion and power delivery in various electrode formulations.
TL;DR: In this paper, reverse microemulsion techniques combined with templating strategies have led to the synthesis of four types of nanoparticles: homogeneous SiO2-coated Fe2O3 (SiO2/Fe 2O3) nanoparticles with controlled SIO2 shell thickness (1.8−30 nm) were synthesized by reverse micro-emulsion.
Abstract: Reverse microemulsion techniques combined with templating strategies have led to the synthesis of four types of nanoparticles. First, homogeneous SiO2-coated Fe2O3 (SiO2/Fe2O3) nanoparticles with controlled SiO2 shell thickness (1.8−30 nm) were synthesized by reverse microemulsion. These nanocomposite particles were used as templates for the deposition of a mesoporous silica shell. The iron oxide core in SiO2/Fe2O3 could be partially and completely etched to produce rattle-type SiO2/Fe2O3 nanoballs and hollow SiO2 nanoballs, respectively. These facile synthetic methods led to the formation of different nanoparticle architectures with tailored silica shell thickness and porosity.
TL;DR: In this paper, transition metal nanoclusters are used for the hydrogenation of nitrobenzene and showed excellent reactivity, with a conversion rate that was ∼5 times higher than commercial Pd/C catalyst.
Abstract: Transition metal nanoclusters are highly selective and active catalysts. To allow for ease of recycling, Pd nanoclusters were supported on SiO2/Fe2O3 magnetic nanocomposites. Pd/HS-SiO2/Fe2O3 and Pd/H2N-SiO2/Fe2O3 were examined for the hydrogenation of nitrobenzene. Pd/H2N-SiO2/Fe2O3 showed excellent reactivity, with a conversion rate that was ∼5 times higher than commercial Pd/C catalyst.
TL;DR: In this paper, the bulk preparation of nanocrystalline Si−SiO2 composites via straightforward reductive thermal annealing of a well-defined molecular precursor, hydrogen silsesquioxane, is reported.
Abstract: We report the bulk preparation of nanocrystalline Si−SiO2 (nc-Si/SiO2) composites via straightforward reductive thermal annealing of a well-defined molecular precursor, hydrogen silsesquioxane. The presented method affords quantitative yields of composite powders in large quantities. Freestanding, hydride-surface-terminated silicon nanocrystals that photoluminesce throughout the visible spectrum are readily liberated from nc-Si/SiO2 composite powders upon etching in ethanol−water solutions of hydrofluoric acid. Composites and freestanding particles were characterized using transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy, Fourier transform infrared spectroscopy (FT−IR), and thermogravimetric analysis (TGA).
TL;DR: In this article, temperature variations of the electron magnetic resonance (EMR) spectra and magnetization measurements are used to show that Ce3+ ions in concentration ≃18% are present in 3 nm CeO2 nanoparticles supported on silica aerogel.
Abstract: Temperature variations of the electron magnetic resonance (EMR) spectra and magnetization measurements are used to show that Ce3+ ions in concentration ≃18% are present in 3 nm CeO2 nanoparticles supported on silica aerogel. It is argued that the presence of Ce3+ implies the defect structure CeO2-x for ceria nanoparticles due to oxygen vacancies. This transformation of Ce4+ to Ce3+ driven by oxygen vacancies may be the key to understanding the catalytic properties of ceria.
TL;DR: In this article, a strategy for the synthesis of multifunctional mesoporous silica nanoparticles is presented, which simultaneously possess magnetic, luminescent, and porous properties.
Abstract: We demonstrate a strategy for the synthesis of multifunctional mesoporous silica nanoparticles. These uniform tumblerlike nanocomposites, which simultaneously possess magnetic, luminescent, and porous properties, have great potential in biomedical applications.
TL;DR: In this paper, the structure, oxygen stoichiometry, and chemical and thermal expansion of Ba0.5Sr 0.5Co0.8Fe0.2O3-δ (BSCF) between 873 and 1173 K and oxygen partial pressures of 1 × 10-3 to 1 atm were determined by in situ neutron diffraction.
Abstract: The structure, oxygen stoichiometry, and chemical and thermal expansion of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) between 873 and 1173 K and oxygen partial pressures of 1 × 10-3 to 1 atm were determined by in situ neutron diffraction. BSCF has a cubic perovskite structure, space group Pm3m, across the whole T−pO2 region investigated. The material is highly oxygen deficient with a maximum oxygen stoichiometry (3 − δ) of 2.339(12) at 873 K and a pO2 of 1 atm and a minimum of 2.192(15) at 1173 K and a pO2 of 10-3 atm. Good agreement is obtained between oxygen stoichiometry data determined by neutron diffraction and thermogravimetry. In the range covered by the experiments, the thermal and chemical expansion coefficients are 19.0(5)−20.8(6) × 10-6 K-1 and 0.016(2)−0.026(4), respectively.
TL;DR: In this article, a series of ordered mesoporous SiO2−CaO−P2O5 sol−gel glasses which are highly bioactive has been synthesized through evaporation-induced self-assembly in the presence of a nonionic triblock copolymer, EO20PO70EO20 (P123), template.
Abstract: A series of ordered mesoporous SiO2−CaO−P2O5 sol−gel glasses which are highly bioactive has been synthesized through evaporation-induced self-assembly in the presence of a nonionic triblock copolymer, EO20PO70EO20 (P123), template. By keeping constant the SiO2 + P2O5/P123 ratio, the influence of the CaO precursor, Ca(NO3)2·4H2O, on the mesostructure has been determined. After calcination at 700 °C, ordered mesoporous glasses are obtained, showing structures that evolve from 3D-cubic to 2D-hexagonal when the CaO content increases. The mesoporous glasses are highly bioactive compared with conventional ones, due to the increased textural characteristics supplied by the template. The bioactivity tests point out that the surface area, porosity, and 3D-structure become more important than chemical composition during the apatite crystallization stage in these materials, due to the very high textural parameters obtained.
TL;DR: A new family of homoleptic iridium(III) complexes that emit blue phosphorescence at room temperature was reported in this article, consisting of phenyltriazole ligands and were easily prepared via short synthetic routes.
Abstract: We report a new family of homoleptic iridium(III) complexes that emit blue phosphorescence at room temperature. The iridium( III) complexes are comprised of phenyltriazole ligands and were easily prepared via short synthetic routes. The parent fac-tris(1-methyl-5-phenyl-3-propyl-[1,2,4]triazolyl)iridium(III) complex exhibits blue photoluminescence (PL) with emission peaks at 449 and 479 nm and has a solution PL quantum yield of 66%. The emission was sequentially blue-shifted by the attachment of one and two fluorine atoms to the ligand phenyl ring with the fac-tris{1-methyl-5-(4,6-difluorophenyl)-3-propyl-[1,2,4]triazolyl} iridium( III) complex having the 1931 Commission Internationale de l'Eclairage coordinates of (0.16, 0.12) at room temperature. In contrast, when the phenyl ring of the ligands was substituted by trifluoromethyl, the PL spectrum was red-shifted when compared to the parent compound whereas if the trifluoromethyl group was attached to the triazole ring, the emission was blue-shifted. The radiative rates of these new blue iridium( III) complexes were found to be in the range of 2-6 x 105 s(-1), indicating that the emission had varying amounts of metal-to-ligand charge-transfer character. Molecular orbital calculations showed that for the fluorinated complexes the contribution of the ligand triplet character to the emissive energy state increased with the hypsochromic shift in emission. This was confirmed by time-resolved PL measurements, which showed that the complex with the deepest blue emission had the slowest radiative decay rate.
TL;DR: In this paper, a covalent organic framework (COF-18A) based on poly(boronate ester)s has been successfully synthesized through a facile dehydration process in 85−95% isolated yield.
Abstract: A covalent organic framework (COF-18A) based on poly(boronate ester)s has been successfully synthesized through a facile dehydration process in 85−95% isolated yield. Spectroscopic characterization confirms formation of the intended ester linkages as the key structural motif forming infinite 2D hexagonally porous sheets. Powder X-ray diffraction studies were used to determine the stacking orientation between the ester-linked sheets, such that atoms in adjacent layers lie directly over each other, resulting in a hexagonal array of 1D, 18 A pores. COF-18A exhibits rigid, thermally stable (to 500 °C) pores with high surface area (1260 m2/g) and a micropore volume of 0.29 cm3/g.
TL;DR: CeF3, CeF3:Tb3+ and Tb3/LaF3 (core/shell) nanoparticles were obtained by the polyol method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-Ray photoelectron spectra (XPS), UV−vis absorption spectra, photoluminescence (PL) spectra and lifetimes as mentioned in this paper.
Abstract: CeF3, CeF3:Tb3+, and CeF3:Tb3+/LaF3 (core/shell) nanoparticles were prepared by the polyol method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), UV−vis absorption spectra, photoluminescence (PL) spectra, and lifetimes. The results of XRD indicate that the obtained CeF3, CeF3:Tb3+, and CeF3:Tb3+/LaF3 (core/shell) nanoparticles crystallized well at 200 °C in diethylene glycol (DEG) with a hexagonal structure. The TEM images illustrate that the CeF3 and CeF3:Tb3+ nanoparticles are spherical with a mean diameter of 7 nm. The growth of the LaF3 shell around the CeF3:Tb3+ core nanoparticles resulted in an increase of the average size (11 nm) of the nanopaticles as well as in a broadening of their size distribution. These nanocrystals can be well-dispersed in ethanol to form clear colloidal solutions. The colloidal solutions of CeF3 and CeF3:Tb3+ show the characteristic emission of Ce3+ 5d−4f (320 nm) and Tb3+ 5D4−7FJ (J = 6−3, with 5D4−7F...