Toshio Torikai

Highly efficient NIR–NIR upconversion in potassium substituted CaMoO4:Tm3+, Yb3+ phosphor for potential biomedical applications

We obtained highly efficient NIR to NIR (excitation by 980 nm, emission at 800 nm) upconversion in CaMoO4:Tm3+, Yb3+, M+ (M = Li, Na, K, Rb) nanocrystals synthesized by a hydrothermal method. The XRD patterns show that they are all of tetragonal structure despite a small amount of RE3+ and M+ ion doping. The solid solubility of lithium, sodium, potassium and rubidium ions in the CaMoO4 were found to be 30 mol%, 20 mol%, 10 mol% and 5 mol%, respectively. The doped M+ ions affect the crystal field symmetry around Tm3+ ions in the CaMoO4 host, which results in the change of the irradiation transition probabilities between their transition levels and intensifies the UC intensities. Compared with CaMoO4:Tm3+, Yb3+, the NIR to NIR upconversion emission intensity of CaMoO4:Tm3+, Yb3+, 0.10M+ nanocrystals increases 2.2, 3.3, 47 and 10 fold for Li, Na, K and Rb, respectively. The K substituted CaMoO4:Tm3+, Yb3+ phosphor exhibited intense UC emission pumped by less than 1 mW laser power and can have potential application in NIR to NIR photodynamic diagnosis.

Synthesis and controllable wettability of micro- and nanostructured titanium phosphate thin films formed on titanium plates.

The hydrothermal treatment of a titanium plate in a mixed aqueous solution of hydrogen peroxide and aqueous phosphoric acid under different conditions results in the formation of various titanium phosphate thin films. The films have various crystal structures such as Ti2O3(H2PO4)2·2H2O, α-titanium phosphate (Ti(HPO4)2·H2O), π-titanium phosphate (Ti2O(PO4)2·H2O), or low-crystallinity titanium phosphate and different morphologies that have not been previously reported such as nanobelts, microflowers, nanosheets, nanorods, or nanoplates. The present study also suggests the mechanisms behind the formation of these thin films. The crystal structure and morphology of the titanium phosphate thin films depend strongly on the concentration of the aqueous hydrogen peroxide solution, the amount of phosphoric acid, and the reaction temperature. In particular, hydrogen peroxide plays an important role in the formation of the titanium phosphate thin films. Moreover, controllable wettability of the titanium phosphate thin films, including superhydrophilicity and superhydrophobicity, is reported. Superhydrophobic surfaces with controllable adhesion to water droplets are obtained on π-titanium phosphate nanorod thin films modified with alkylamine molecules. The adhesion force between a water droplet and the thin film depends on the alkyl chain length of the alkylamine and the duration of ultraviolet irradiation utilized for photocatalytic degradation.

Chemical modification of carbonized wheat and barley straw using HNO3 and the adsorption of Cr(III)

The effects of oxidation using HNO(3) on the properties of the carbonized wheat and barley straw were investigated by measuring different properties such as specific surface area, PZC, total surface acidic groups as well as FTIR and TG-DTA. A small decrease in the specific surface area due to pore blockage was observed after oxidation. After oxidation, the acidity was increased considerably and the point of zero charge shifted from approximately pH 9 to pH 2 in both types of carbon. By the oxidation of the carbon with nitric acid, carboxylic groups were produced as shown by absorption peaks at 1750 cm(-1) in the FTIR spectra. Boehm titration results showed that the number of carboxyl groups increased by approximately 11-fold after oxidation. The oxidized carbon samples were compared with the unoxidized original carbon samples for Cr(III) adsorption. It was observed that the oxidized carbons exhibit high adsorption efficiencies for Cr(III) ions compared to the original carbonized straws and this can be correlated to the decrease in PZC which is mainly due to the increase in carboxylic functional groups in the oxidized carbonized straws and these are responsible for their cation ion exchange phenomenon.

Apatite-forming ability of titanium compound nanotube thin films formed on a titanium metal plate in a simulated body fluid.

We compared the apatite-forming ability of a sodium titanate nanotube thin film, an anatase-type titanium dioxide nanotube thin film, and a silver nanoparticle/silver titanate nanotube nanocomposite thin film, in simulated body fluid. The ability of the silver nanoparticle/silver titanate nanotube nanocomposite thin film is slightly higher than that of the anatase-type titanium dioxide nanotube thin film and significantly higher than that of the sodium titanate nanotube thin film. The high ability of the silver nanoparticle/silver titanate nanotube nanocomposite thin film is a newly observed phenomenon, which is probably due to the crystal structure of silver titanate--specifically, to the surface atomic arrangement, the large amount of Ti-OH formed on the nanotube surface, or both. The anatase-type titanium dioxide nanotube thin film and the silver nanoparticle/silver titanate nanotube nanocomposite thin film may have bright prospects for future use in implant materials such as artificial joints. The silver nanoparticle/silver titanate nanotube nanocomposite thin film is particularly promising for its antibacterial properties.

Rare Earth Free Phosphor with Controlled Microstructure and Its Photocatalytic Activity

Microsphere of rare earth free phosphor, , with broadband yellowish white emission was synthesized by combustion route and compared with the hydrothermal, sol-gel, and solid state reaction methods. The phosphor samples were characterized by X-ray diffraction and scanning electron microscopy. UV-visible absorption and photoluminescence (PL) emission and excitation spectra were investigated for these phosphors. phosphor containing 10 mol% of H3BO3 flux exhibited enhanced PL emission showing broadband from 450 nm to 750 nm. Effect of stoichiometry of Zn and V on the host lattice and its effect on the PL emission spectra were studied. Series of Mg3V2O8, , and Sr3V2O8 phosphors were also synthesized and compared to the phosphor in terms of PL emission and internal quantum yield, and it was found that is the most efficient phosphor among the other phosphors studied with quantum yield of 60%. The visible light irradiated photocatalytic activity of these phosphors was investigated and it was found that the hydrothermal exhibited enhanced activity.

Giant Improvement on the Afterglow of Sr4Al14O25:Eu2+,Dy3+Phosphor by Systematic Investigation on Various Parameters

Highly intense, long persistent Sr4Al14O25:Eu2+,Dy3+ blue-green phosphor with different B3+, Eu2+, Dy3+, and Ag+ contents was prepared by solid-phase reaction at various temperatures in reductive atmosphere of 10% H2 in N2. The effects of synthesis parameters like calcination temperature and time, calcination environment, effect of stoichiometry of the host composition, and additives like addition of boron and rare earth ions (Eu, Dy) were studied in detail. Results revealed that the phosphor containing ~40 mol% H3BO3 showed dense and pure Sr4Al14O25 phase with higher emission intensity, but in the samples containing less than 20 mol% H3BO3 mixed phases consisting of Al2O3, SrAl12O19 and SrAl2O4 were observed, while in higher H3BO3 content, SrAl2B2O7 phases predominated. When the stoichiometry of Al/Sr was 3.7, the best phosphorescence and afterglow were noted. The phosphor containing 4 at.% of Eu and 8 at.% of Dy, and 3 at.% Ag exhibited the maximum initial intensity of 5170 mcd·m−2 and the longest persistency of greater than 30 hours over the value of 5 mcd·m−2, higher than the commercial products and applicable for various display applications involving indoor as well as outdoor uses.

Preparation and Characteristics of Eu and Dy Doped Sr4Al14O25 Phosphor

Sr4Al14O25:Eu2+, Dy3+ long persistent phosphors with different B, Eu and Dy contents were prepared by solid phase reaction at various temperatures in H2/N2=1/9 atmosphere. X- ray diffraction and scanning electron microscopy observations showed that, when the phosphor was doped with 40 at% B, single dense Sr4Al14O25 phase was formed but for the samples with less than 40 at% B, mixed phases containing SrAl12O19 and SrAl2O4 were observed while for higher B content (100 at%) SrAl2B2O7 phases appeared. The phosphor showed emission peak centered at 500 nm with blue green color. When 40 at% of H3BO3 was added and doped with 4 at% of Eu and 8 at% of Dy, it showed the maximum initial intensity of 3170 mcd.m-2 and the longest persistency which is greater than 20 h over value of 5 mcd.m-2.

Antibacterial properties of titanate nanofiber thin films formed on a titanium plate

A sodium titanate nanofiber thin film and a silver nanoparticle/silver titanate nanofiber thin film formed on the surface of a titanium plate exhibited strong antibacterial activities against methicillin-resistant Staphylococcus aureus, which is one of the major bacteria causing in-hospital infections. Exposure of the sodium titanate nanofiber thin film to ultraviolet rays generated a high antibacterial activity due to photocatalysis and the sodium titanate nanofiber thin film immediately after its synthesis possessed a high antibacterial activity even without exposure to ultraviolet rays. Elution of silver from the silver nanoparticle/silver titanate nanofiber thin film caused by the silver ion exchange reaction was considered to contribute substantially to the strong antibacterial activity. The titanate nanofiber thin films adhered firmly to titanium. Therefore, these titanate nanofiber thin film/titanium composites will be extremely useful as implant materials that have excellent antibacterial activities.

Synthesis and magnetic property of cobalt hydroxide carbonate and cobalt oxide nanowires

The present study is the first to report the successful synthesis of layered cobalt hydroxide carbonate nanowires templated by dodecyl sulfate assemblies by a homogeneous precipitation method using urea. The layered structure was composed of a cobalt hydroxide carbonate phase 1.9 nm thick and a dodecyl sulfate phase 2.3 nm thick. The width and length of the nanowires were tens of nm and greater than several micrometers, respectively. The layered cobalt hydroxide carbonate nanowires were transformed into Co3O4 and CoO nanowires by calcination in air and in vacuum, respectively, and were exfoliated to form ultrathin cobalt hydroxide carbonate nanowires approximately 3 nm wide. The present study also showed a dependence of the size and morphology on the magnetism of cobalt hydroxide carbonate. Although cobalt hydroxide carbonate nanorods synthesized in the presence of Na2SO4·10H2O and lamellar-shaped cobalt compound templated by a mixture of C16H33OSO3− and C18H37OSO3− were antiferromagnetic materials, the layered cobalt hydroxide carbonate nanowires exhibited ferrimagnetism. This expression of ferrimagnetism was considered to be due to the formation of ultrathin cobalt hydroxide carbonate phases in the nanowires. Moreover, the Neel temperature of the obtained Co3O4 nanowires, which exhibited antiferromagnetism, was lower than that of commercially available Co3O4 particles.

Mechanical properties of strontium ferrites with duplex structure

Abstract The microstructures and the mechanical properties of the strontium ferrites (Sr-ferrites) with duplex structure were examined. As-received Sr-ferrites had a homogeneous microstructure and their average grain size was 1.58 μm. Some grains increased up to 106 μm and 228 μm in size after annealing at 1250 °C for 1 h and 6 h, respectively. The volume fractions of the large grains were 4% after 1 h-annealing and 45% after 6 h-annealing. According to the microstructural evolution, the bending strength decreased from 148 MPa (as-received) to 140 MPa (3 h-annealing) and 93 MPa (6 h-annealing), but the fracture toughness increased from 2.14 MPa · m 1/2 (as-received) to 2.20 MPa · m 1/2 (3 h-annealing) and 2.36 MPa · m 1/2 (6 h-annealing). These results indicated that the large grains in the duplex structure acted as both fracture origins and reinforcements. The Weibull modulus of materials was improved from 7 (as-received materials) to 17 (material after 3 h-annealing) and 9.5 (material after 6 h-annealing).