Liquid-Phase Synthesis of Ba2V2O7 Phosphor Powders and Films Using Immiscible Biphasic Organic-Aqueous Systems.

A liquid-phase synthesis of inorganic phosphor materials at a moderate temperature was proposed by using immiscible liquid-liquid biphasic systems. A self-activated Ba2V2O7 phosphor was actually synthesized from vanadium alkoxide dissolved in an organic solution and barium acetate in an aqueous solution. A mild hydrolysis reaction of the alkoxide started at the organic-inorganic interface, and an intermediate compound, Ba(VO3)2·H2O, was initially formed. Ba2V2O7 powders were then obtained by the conversion from Ba(VO3)2·H2O promoted in the aqueous solution. Ba2V2O7 films were obtained on surface-modified silica glass substrates through the similar chemical reactions. Factors such as the surface state of substrates, the kind of organic solvents, and the volume of aqueous solutions were examined to improve the film deposition behavior. The resultant Ba2V2O7 materials showed broad-band visible photoluminescence upon irradiation with ultraviolet light based on the charge transfer transition in the VO4(3-) units existing as dimers.

Fabrication of porous cubic architecture of ZnO using Zn-terephthalate MOFs with characteristic microstructures.

A method for synthesizing porous cubic-shaped ZnO particles a few tens of micrometers in size is described on the basis of a pyrolytic conversion of Zn-terephthalate metal-organic frameworks (MOFs). MOF crystals were initially grown in solutions containing Zn(NO3)2·6H2O and terephthalic acid as solutes and N,N-dimethylformamide (DMF) or N,N-diethylformamide (DEF) as a solvent under a solvothermal condition. It was the key to controlling the microstructure of MOF cuboids for their use as an intermediate compound for ZnO. Actually, many cracks were formed and hence the cubic microstructure was somewhat destroyed in the pyrolytic conversion from dense MOF crystals (grown in the DMF solution) to ZnO. In contrast, mesocrystal-like MOF cuboids (grown in the DEF solution) could maintain their shape during the pyrolysis because of the relaxation against a MOF-to-ZnO volume change. The resultant ZnO with a highly porous cubic structure showed intense visible photoluminescence upon irradiation with ultraviolet light.

Luminescent antireflective coatings with disordered surface nanostructures fabricated by liquid processes.

Antireflective phosphor coatings having disordered surface nanostructures were fabricated by a sol-gel dip coating method and a subsequent hot water treatment. Thin films of a Bi(3+),Eu(3+)-codoped YVO4 red phosphor were first prepared and effects of the addition of an aluminum source to precursor solutions on their microstructure and optical properties were examined. Optical transmittance of the YVO4:Bi(3+),Eu(3+) film was lower than that of a bare quartz glass substrate due to a higher refractive index of YVO4. The addition of the aluminum source and the hot water treatment resulted in a considerable increase of transmittance and its smaller angular dependence, which could generate an antireflective effect by the phosphor thin films. Observation of the microstructure revealed that the hot water treatment brought a remarkable change in the surface as well as the cross-section structure in the aluminum-added YVO4:Bi(3+),Eu(3+) film. The film density and hence the refractive index were gradually changed like a pseudo moth-eye structure, which explained the occurrence of the antireflective effect. The microstructural change was attributed to the dissolution of alumina present in the film and the reprecipitation of boehmite on the film surface during the hot water treatment. Photoluminescence of the YVO4:Bi(3+),Eu(3+) film could also be enhanced by the antireflective effect due to the suppression of surface Fresnel reflection of incident light and total internal reflection of emitted light.

Liquid-liquid biphasic synthesis of layered zinc hydroxides intercalated with long-chain carboxylate ions and their conversion into ZnO nanostructures.

A method for synthesizing layered zinc hydroxide compounds in high yields is developed using an immiscible liquid-liquid system in one pot. Long-chain carboxylate ions such as heptanoate, decanoate, and dodecanoate were successfully intercalated between zinc hydroxide layers in one process starting from a xylene-water system. Typically, a xylene phase dissolving the respective carboxylic acids was allowed to stand in contact with an aqueous phase dissolving zinc nitrate hexahydrate and urea. During keeping the resultant biphasic system at 80 °C, urea was thermo-hydrolyzed to supply OH(-) in the aqueous phase while the carboxylic acids were continuously transferred from the xylene phase under the distribution law. The aqueous phase was then supersaturated, and a solid phase of layered basic zinc carboxylate was precipitated as films on glass substrates through heterogeneous nucleation and subsequent two-dimensional crystal growth. Crystal structures and morphology of the films were modulated by the kind of the carboxylic acids employed. The layered basic zinc carboxylate films could be converted to nanostructured, mesoporous ZnO films by heating at 450 °C in air. The relationship between the initial solution compositions and the final solid products was systematically examined to discuss reaction mechanisms in the biphasic systems.

Synthesis of inorganic-organic layered compounds using immiscible liquid-liquid systems under the distribution law.

A method for synthesizing inorganic-organic layered compounds is proposed using a biphasic liquid-liquid system in one pot. Layered basic zinc benzoate (LBZB) compounds were chosen, and their formation was investigated starting from a xylene-water system. In a typical synthesis, a xylene phase dissolving benzoic acid was allowed to stand in contact with an equal amount of an aqueous phase dissolving zinc nitrate hexahydrate and urea. A role of urea is to supply OH(-) gradually by hydrolysis at an elevated temperature. The biphasically separated solutions were maintained at 80 °C, and then LBZB was obtained in the aqueous phase. Two kinds of layered structures with a basal spacing of 27.14 and 14.77 Å were formed by changing a C(6)H(5)COOH/Zn molar ratio. Chemical compositions of the 27.14 and the 14.77 Å layered phases were estimated to be Zn(OH)(1.74)(C(6)H(5)COO)(0.26)·0.29H(2)O and Zn(OH)(1.12)(C(6)H(5)COO)(0.88)·0.21H(2)O, respectively. The 27.14 Å phase could also be deposited as a film on substrates by heterogeneous nucleation. The film consisted of standing platelike particles and exhibited a two-dimensional structure, which could be converted to ZnO by heating. The relationship between the initial solution compositions and the final solid products was systematically examined on the basis of distribution law for benzoic acid in the xylene-water system.

Synthesis of Pt-Loaded Y2WO6:Eu3+ Microspheres and Their Hydrogen-Sensitive Turn-Off Luminescence.

Pt nanoparticles were loaded on Y2WO6:Eu3+ phosphor microspheres to enhance hydrogen sensitivity at low temperatures through turn-off luminescence. Mesoporous Y2WO6:Eu3+ microspheres were synthesized first by a hydrothermal method. Pt loading on the surface of the Y2WO6:Eu3+ microspheres was then carried out by a method of the self-regulated reduction of surfactants using aqueous K2PtCl4 solutions. Structural and morphological properties of unloaded and Pt-loaded Y2WO6:Eu3+ microspheres were investigated by various techniques such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The relative photoluminescence intensity of the Pt-loaded Y2WO6:Eu3+ microspheres, due to 5D0 → 7F J (J = 0, 1, 2, 3, 4) electronic transitions of doped Eu3+ ions, was found to decrease as low as 22% after the microspheres were kept in the hydrogen gas atmosphere at a low temperature of 150 °C for 15 min. Meanwhile, mechanisms underlying this turn-off luminescence of the Pt/Y2WO6:Eu3+ microspheres in response to hydrogen gas are illustrated in detail.

Biphasic Sol-Gel Synthesis of Microstructured/Nanostructured YVO4:Eu3+ Materials and Their H2O2 Sensing Ability.

Microstructured/nanostructured YVO4:Eu3+ powders and films were synthesized through a biphasic sol-gel method, aiming at their application as H2O2 sensing materials based on the turn-off luminescence of Eu3+ ions. The synthesis was typically carried out at temperatures of 80 °C or lower by using organic solutions to dissolve vanadium alkoxide and aqueous solutions to dissolve yttrium and europium salts together with sodium carboxylates. The resultant crystalline YVO4:Eu3+ powders and films were characterized as containing micrometer-sized particles comprising primary nanoparticles with high specific surface areas. A comparative study was performed on the H2O2-responsive turn-off luminescence properties for the above samples and those synthesized by a single-phase sol-gel or a conventional solid-state reaction method. The results indicated that the microstructural feature of the samples from the biphasic sol-gel method was effective for detecting H2O2 through its adsorption on the particle surface and quenching of the Eu3+ luminescence. The film samples showed repeatable and quantitative turn-off luminescence, thereby demonstrating their suitability as solid-state H2O2 sensors.

Fabrication of highly porous and micropatterned SnO2 films by oxygen bubbles generated on the anode electrode.

The fabrication process of highly porous SnO(2) thick film by reaction between tin ions and oxygen gas generated by an anodic applied potential on substrates in SnCl(2) aqueous solution is reported; moreover, we succeeded in forming porous SnO(2) micropatterns through site-selective deposition on a Pt-patterned F-doped SnO(2)(FTO) coated substrate .

Fabrication and photoluminescence of chemically stable La2O3:Eu3+-La2Sn2O7 core-shell-structured nanoparticles.

Core-shell-structured La2O3:Eu3+-La2Sn2O7 nanoparticles were fabricated through SnO2-coating of LaOF:Eu3+ in an aqueous solution and subsequent heat treatments at a higher temperature. The nanoparticles exhibited high chemical stability under an ambient atmosphere and intense red photoluminescence upon irradiation with ultraviolet light.

Growth of layered basic zinc acetate in methanolic solutions and its pyrolytic transformation into porous zinc oxide films.

Layered basic zinc acetate (LBZA), Zn(5)(OH)(8)(CH(3)COO)(2).2H(2)O, was deposited on glass substrates by a chemical bath deposition (CBD) method using methanolic solutions of zinc acetate dihydrate. The substrates were put into bottles filled with the solutions and sealed up and were kept at 60 degrees C in a drying oven. Immersion time necessary for the deposition of LBZA films was typically more than 28 h. This was a key to inducing heterogeneous nucleation of LBZA through control over a degree of supersaturation in the evolution of a unique, nest-like morphology. Hydration water contained by zinc acetate dihydrate was quantitatively enough to promote hydrolysis of zinc acetate. The LBZA films were transformed into nanocrystalline, porous ZnO films without morphological deformation by heating at 150 degrees C in air. A mechanism of the formation of the nest-like morphology was discussed based on nonaqueous solution reactions, nucleation, and crystal growth during the CBD process.

Synthesis of New RE3+ Doped Li1+xTa1-xTixO3 (RE: Eu, Sm, Er, Tm, and Dy) Phosphors with Various Emission Colors.

New phosphors with various emission colors for RE3+ doped Li1+xTa1-xTixO3 (LTT) (RE: Eu, Sm, Er, Tm, and Dy) were synthesized by electric furnace at 1423 K for 15 h. The microstructure of the host material and the photoluminescence (PL) property were determined and compared to those of RE3+ doped Li1+xNb1-xTixO3 (LNT). In the LTT phosphor, the highest PL intensity was achieved for the mixture composition Li1.11Ta0.89Ti0.11O3 with a LiTaO3 structure, although it has an M-phase superstructure. In the LTT host material, the effective activators were Eu3+ and Sm3+ ions, in contrast to the LNT host material. Here, we discuss the relationship between PL property and the host material's structure.

One-step synthesis of nano-micro chestnut TiO2 with rutile nanopins on the microanatase octahedron.

The solution synthesis of large single crystals of octahedron-like anatase TiO2 is reported, although this novel result is unexpected in the light of reported theoretical calculations. Moreover, systematic control of the crystal growth of rutile nanopins on the microanatase octahedron single crystal results in a nano-micro chestnut-like TiO2 structure. The control of the formation of rutile nanopins on the large single crystals of anatase in the same solution is an interesting and useful technique, based on thermodynamics and surface chemistry.

Layered single-metal hydroxide/ethylene glycol as a new class of hybrid material.

Neutral ethylene glycol (EG) molecules have been intercalated into zinc hydroxide layers to produce a new hybrid material in which only one kind of metal ion is included. Initially, layered basic zinc acetate (LBZA, Zn(5)(OH)(8)(CH(3)COO)(2).2H(2)O) was prepared from a methanolic zinc acetate dihydrate solution. The immersion of LBZA in EG resulted in its intercalation, which was accompanied by an interlayer expansion of 7.12 A, as revealed by X-ray diffractometry. A Fourier transform infrared spectroscopic study indicated that the new compound contained both the acetate groups and the EG molecules. Together with thermogravimetry-differential thermal analysis, a composition of the new compound was estimated to be Zn(5)(OH)(8)(CH(3)COO)(2)(HOC(2)H(4)OH)(2).2H(2)O. The EG intercalation was found to increase the dehydration temperature of the zinc hydroxide layers from 130 to 180 degrees C. So the thermally stable material is then promising as a new class of precursors in creating organic-inorganic nanocomposites.

Superhydrophobic perpendicular nanopin film by the bottom-up process.

We first fabricated the superhydrophobic film with a water contact angle of 178 degrees based on a perpendicular nanopin fractal structure by a bottom-up process. Until now, only materials with an original water contact angle larger than 90 degrees , which is classified as hydrophobicity, could be used to fabricate the superhydrophobic film (>170 degrees ) according to the possible fractal structure by a top-down process. Now, in this work, a water contact angle of about 178 degrees can be achieved using a lauric acid-coated film with an original contact angle of 75 degrees , which is classified as hydrophilicity, based on an ideal fractal structure for the superhydrophobic surface which is fabricated by the nanosize pin with 6.5 nm diameter.

Fabrication of nanoparticulate porous LaOF films through film growth and thermal decomposition of ion-modified lanthanum diacetate hydroxide.

This paper first reports fabrication of macro/nanotextured rare-earth oxyfluoride films. Usage of ion-modified lanthanum diacetate hydroxide (LDAH) as self-templates was successful in producing nanoparticulate lanthanum oxyfluoride (LaOF) films. LDAH template films were deposited on glass substrates through a chemical bath deposition in solutions composed of lanthanum acetate sesquihydrate, methanol, trifluoroacetic acid, and aqueous ammonia. The LDAH films had a unique, nestlike morphology owing to a two-dimensional hexagonal crystal growth. Modification of LDAH with trifluoroacetate ions led to formation of LaOF after pyrolyzing the template films at temperatures of 400-600 degrees C in air. The resultant LaOF films had a nanoparticulate porous microstructure, maintaining the morphology of the original LDAH template films. It was also successful to incorporate Eu3+ ions into LaOF through deposition of the LDAH film in a solution containing europium acetate tetrahydrate. The characteristic photoluminescence from Eu(3+) was observed with an ultraviolet-light excitation at 273 nm, indicating that Eu3+ was homogeneously distributed in LaOF host crystals. Thus the ion-modification of LDAH was also demonstrated to be a useful method for preparing nanostructured rare-earth oxyfluoride materials havingvarious cationic compositions.

Growth of submicrometer-scale rectangular parallelepiped rutile TiO2 films in aqueous TiCl3 solutions under hydrothermal conditions.

Evolution of a new morphology of rutile TiO2 films consisting of nearly single-crystalline parallelepipeds was achieved through hydrothermal treatments of aqueous TiCl3 solutions in the presence of NaCl.

Hydrothermal routes to prepare nanocrystalline mesoporous SnO2 having high thermal stability.

We report simple hydrothermal routes to prepare thermally stable SnO2 particles having high specific surface areas and mesoporosity. The preparation method includes a new combination of synthetic processes: hydrolysis of tin(IV) chloride at 95 degrees C in the absence of alkaline solutions (aqueous NH3 or NaOH), formation of nanocrystalline SnO2, and subsequent hydrothermal treatments at temperatures between 100 and 200 degrees C. After annealing treatments of the hydrothermally treated SnO2 particles at 400 or 500 degrees C, their crystallite sizes remained smaller than 7.7 nm and their specific surface areas were still higher than 110 m2/g, indicative of the high thermal stability against particle growth and sintering. Furthermore, mesoporosity evolved with a relatively narrow pore size distribution typically in the range of 3.0-4.3 nm. The effects of the hydrothermal treatment were explained by uniformization of the particle size that was beneficial to the suppression of particle growth.