Hiromasa Nishikiori

Absorption spectra of rhodamine B dimers in dip-coated thin films prepared by the sol-gel method

Abstract Thin films including rhodamine B (RB) which were dip-coated using the sol-gel reaction of tetraethyl orthosilicate (TEOS) have been prepared as a function of time and their absorption spectra observed 72 h after preparation of the thin films. One monomer and two dimers (H- and J-types) are clearly and simultaneously resolved both for RB in the thin films and the water-ethanol mixed solvent. Just after mixing the reaction system, the proportion of the dimers for RB was significant, and the H and J dimer amounts were nearly equal. As the sol-gel reaction proceeded, the relative contribution from the monomer species increased. The relative contribution of the monomer to that of the dimers reached a constant value long before the gelation time. This behavior indicates that the dye molecules are encapsulated in a certain structural region (pores) long before the gelation point of the sol-gel reaction of TEOS.

Photocatalytic degradation of chlorinated ethenes

Degradation of three chlorinated ethenes, trichloroethylene, trans-1,2-dichloroethylene and cis- 1,2-dichloroethylene, by UV-light irradiated TiO2 catalyst prepared by the sol-gel method in dry air at ambient temperature have been examined by using FTIR measurement. The chlorinated ethenes rapidly decomposed to produce dichloroacethyl chloride, CO, HCl, and COCl2. For trans- and cis-1,2-DCE systems isomerization to each other is found to be the first step of the degradation. The C = C bond of the chlorinated ethenes interacts directly with TiO2 site and, consequently, the degradation results in several products on the catalyst surface in these systems.

Novel fabrication of NIR-vis upconversion NaYF4:Ln (Ln = Yb, Er, Tm) crystal layers by a flux coating method

High quality upconverting NaYF4:Ln (Ln = Yb, Er, Tm) crystal layers were successfully fabricated directly onto glass substrates at a relatively low temperature of 350 °C by a novel two-step flux coating method. First, mixed pastes of solute (NaF and YF3) and dopants (LnF3) were coated on glass substrates by simple bar-coating, and then flux pastes (NaNO3 or NaNO3–NaF) were coated onto the dopant-containing solute layer. After the two-step coating, raw material-coated substrates were heated at 350 or 400 °C in an electric furnace. To remove the remaining flux, the crystal layers were washed with warm water. Finally, high quality, nanotextured NaYF4:Ln crystal layers with good adhesion were directly grown onto the glass substrates. These crystal layers consisted of densely packed idiomorphic NaYF4:Ln crystals. In particular, individual NaYF4:Ln crystals were typically shaped as hexagonal prisms. The NaYF4:Ln crystal phases depended strongly on the heating conditions, i.e., temperature and time. The NaNO3 and NaNO3–NaF fluxes were effective for the growth of high-quality idiomorphic NaYF4:Ln crystals. Additionally, the upconversion fluorescence properties of NaYF4:Ln crystal layers were controlled by changing dopant types and ratios. The NaYF4:10%Yb,1%Er, NaYF4:50%Yb,1%Er, NaYF4:20%Yb,1%Tm and NaYbF4:1%Er crystal layers emitted green, orange, blue and red fluorescences, respectively, under 980 nm laser irradiation.

An ab initio study on the phosgene–water complex

Abstract The potential energy surface of the phosgene–water (Cl2CO–H2O) complex has been investigated by quantum chemical calculations at the MP2 level with the 6-31++G(d,p), 6-311++G(d,p), aug-cc-pVDZ, and aug-cc-pVTZ basis sets. Two minima have been found on the PES. The structures of Cl2CO–H2O complexes are calculated to be (I) perpendicular with C⋯O and O⋯H contacts and (II) coplanar with a Cl⋯O contact. In complex I a contacting CO bond is lengthened while two C–Cl bonds are shortened. In complex II a contacting C–Cl bond is shortened, while an uncontacting C–Cl bond is lengthened. Natural bond orbital analysis revealed intermolecular charge transfers occur followed by intramolecular charge rearrangement.

Preparation of Cu-doped TiO2 via refluxing of alkoxide solution and its photocatalytic properties

Cu-doped TiO2 was prepared by the refluxing of a mixture of copper and titanium alkoxides. The refluxing improved the Cu2+ dispersion in the TiO2 and formed effective Ti–O–Cu bonds. The impurity states due to the highly dispersed Cu2+ were presumed to trap the electrons in the conduction band of the TiO2 and prevent charge recombination of the electrons and holes. Consequently, the prolonged charge separation duration was suggested to enhance the photocatalytic activity of the Cu-doped TiO2. This enhancement was confirmed by the hydroxyl radical generation and organic compound degradation. The Ti–O–Cu bonds and electronic interaction between Cu and Ti should effectively promote the electron trapping. The Cu-doped TiO2 exhibited a visible light-induced activity due to the transition from the TiO2 valence band to the Cu2+ impurity states.

Photoinduced electron transport in dye-containing titania gel films

Amorphous dye-containing titania gel films were prepared on ITO electrodes coated with a crystalline titania foundation from titanium alkoxide sols containing a dye at room temperature. Photoinduced electron transport in the amorphous titania gel film was investigated by spectroscopic and photovoltaic measurements. Influences of the structure and morphology of the multilayered film on the photoelectron transport and electrically conductive properties were discussed. The photocurrent was observed from only the layer contacting the crystalline titania foundation. The electron transport from the amorphous upper layers was limited. Steam treatment of the electrodes improved the electron transport due to crystallization of the amorphous titania to anatase accompanied by enhancement of its electrical conductivity. The efficiency of the dye-sensitized electron transport in the steam-treated titania film was close to that of the anatase film prepared by heating at 773 K. The dye-containing titania layers functioned as efficient sensitizers.

Solvent effect on fluorescence spectra of a spirooxazine

Fluorescence and excitation spectra of spironaphthoxazine (SNO) in various solvents have been investigated systematically. The fluorescence in low-polar solvents normally originated from SNO in the excited state. In protic high-polar solvents, fluorescence from an excited intermediate species (X*h) relaxed from a part of the excited SNO by breaking a C-O bond in the oxazine ring was also observed. It has been found that a ground-state intermediate species (Xs), transformed from a part of ground-state SNO, is directly excited to its excited state (Xs*), which displays fluorescence in aprotic high-polar solvents.

Monomer-Dimer Equilibrium of Rhodamine B Encapsulated in Si Al and Si Ti Binary-Oxide Thin Films

Si—Al and Si—Ti binary-oxide thin films including Rhodamine B (RB) have been prepared. They were dip-coated as a function of time after mixing of each sol-gel reaction system. The absorption and fluorescence spectra of the individual films have been observed. These spectra were analyzed in order to clarify the behavior of RB along with the change in the environment around the RB molecules, caused by the progress of the sol-gel reaction, in the fluid sol and the prepared thin films. Some amount of the RB dimers (H- and J-types) were formed in the Si—Al and Si—Ti binary-oxide films (Si : M = 75 : 25) prepared at the initial stage of the sol-gel reaction and aged under relative humidity of 60%. In the case of Si—Al binary-oxide films, the amount of the J-dimer decreased along with the reaction time at which the films were prepared, indicating that growing polymer networks of metal alkoxides around the RB molecules prevent the formation of the J-dimer. On the other hand, larger amounts of the H- and J-dimers were formed in the Si—Ti binary-oxide films prepared at longer reaction time of the solution. RB interacts more strongly with —TiOH compared with —AlOH. In the case of the Si—Ti binary-oxide films, with the progress of the sol-gel reaction, RB molecules in the prepared films easily cohere around the —TiOH and form the dimers because of increase in the amount of the —TiOH and contraction in the volume of the spaces where RB molecules exist.

Preparation of dye-adsorbing ZnO thin films by electroless deposition and their photoelectrochemical properties.

Dye-adsorbing ZnO thin films were prepared on ITO films by electroless deposition. The films were formed in an aqueous solution containing zinc nitrate, dimethylamine-borane, and eosin Y at 328 K. The film thickness was 1.2-2.0 μm. Thinner and larger-plane hexagonal columns were produced from the solution containing a higher concentration of eosin Y. A photocurrent was observed in the electrodes containing such ZnO films during light irradiation. The photoelectrochemical performance of the film was improved by increasing the concentration of eosin Y because of increases in the amount of absorbed photons and the electronic conductivity of ZnO.

Influence of Water On Molecular Forms of Rhodamine b in dIp-Coated Thin Films

Dip-coated thin films including rhodamine B have been prepared using the sol-gel reaction of tetraethyl orthosilicate under relative humidity of 30% and 60%. They have been aged under relative humidity of 20%, 60%, and 95% for 5 days. According to the absorption spectra, just after the preparation of the films and under higher humidity, a larger amount of the dimers (H-and J-types) were formed in the films. Five days after the preparation of the films and aged under higher humidity, the H-dimer increased. On the other hand, the J-dimer increased, regardless of humidity under which the films were aged.