Youichi Kurokawa

A transparent alumina film doped with laser dye and its emission properties

Abstract Laser dye (Rhodamine 6G, Rhodamine B or Oxazine 4) was doped in a matrix of alumina gel glass by the sol-gel technique using aqueous sol solution. The undesirable dye aggregation usually observed in aqueous solution is largely reduced in the film, even at a concentration as high as 10 −2 M. When this film was irradiated with a N 2 laser, the film gave laser emission with a beam divergence of about 0.1 rad. The width of the dye laser emission is 10 nm which is typical of a dye laser. The calculated conversion efficiency is 2.1%. A decrease of power is linearly proportional to the shot number, which indicates a one-photon process.

LINEAR AND NONLINEAR OPTICAL PROPERTIES OF SOL-GEL-DERIVED AU NANOMETER-PARTICLE-DOPED ALUMINA

The precursor Au-doped alumina gel film was prepared by a sol-gel method using HAuCl4⋅4H2O and alumina sol derived from AlCl3⋅6H2O. The precursor gel was heat treated in a H2 gas flow at 300–800 °C. Average particle diameters of the Au particle of doped films were in the range of 4.6–12.7 nm. In the absorption spectra of the film, plasmon resonance absorption was strongly dependent on the heat treatment temperature of the alumina matrix, showing more sharp spectra and significant red shift with decreasing particle size. It was interpreted by a modified Mie–Drude equation by taking into consideration of a spilling out of electrons from the Au particle to the alumina matrix. The measured values of χm(3) of the doped films are in the range of 9.2×10−6–4.0×10−5 esu in the neighborhood of plasmon resonance wavelength of 530–570 nm. These are larger than those reported for the other doped systems. A dominant nonlinear response on the 1–3 ps time scale was obtained, reflecting higher thermoconductivity of alumin...

Luminescence properties of Tb3+ and Eu3+-doped alumina films prepared by sol-gel method under various conditions and sensitized luminescence

Abstract Rare earth ion (Tb 3+ and Eu 3+ )-doped alumina films were prepared by the aqueous sol-gel method under various conditions. The influences of the OH groups (phonon relaxation) and rare earth ion concentration (cross-relaxation) on luminescence were examined. In regard to the former relaxation, at treatment temperature above 600°C, reciprocal lifetime decreased with OH concentration, and below 500°C, decreased markedly and nonlinearly. On the other hand, in regard to the latter relaxation, there was negligible effect on luminescence for these doped films. The quantitative treatment was tried to lifetime considering these influences. Tb 3+ and Eu 3+ co-doped alumina films showed enhanced Eu 3+ luminescence by the energy transfer from Tb 3+ to Eu 3+ . Eu 3+ luminescence intensity increased with a greater Tb 3+ concentration.

Third-order nonlinear optical properties of Disperse Red 1 and Au nanometer-size particle-doped alumina films prepared by the sol–gel method

Disperse Red 1 (DR1) and Au nanometer-size particle-doped alumina films have been prepared by the sol–gel method and then their third-order nonlinear optical (NLO) properties have been examined by the degenerated four-wave mixing method. The doped films have absorption peaks which are close to the second harmonics from KTP crystal pumped by a Nd-YAG laser. Therefore, the third-order nonlinear susceptibility χ(3) values at 532 nm were enhanced by resonance effect and gave high χ(3) values of ∼10−15 m2/v2 (∼10−7 esu).

The high dispersion of organic dye into a transparent alumina film and its applications to photochemical and non-photochemical hole burnings☆

Abstract The dyes active in PHB (photochemical hole burning) and NPHB (non-PHB) were embedded in matrices of transparent alumina film by the sol-gel process using hydrous alumina sol derived from aluminum chloride. The dyes doped were sodium resorufin, 5,8-dihydroxy-1,4-naphthoquinone (DNQ) and α,β,γ,δ-tetrakis(4-sulphophenyl) porphine (TPPS). The undesirable dye aggregation usually observed in aqueous solution is largely reduced in the film even at a concentration as high as 10 −2 M. Spectral shifts were observed in the absorption spectra of the films similarly to those in polar matrices. The spectrum of TPPS doped into the film corresponds to that in aqueous solution at pH 2.5. It seems thus that the protonation occurs for resorufin and TPPS in the films. Reflecting this fact, the spectrum of the DNQ film contains the band active in PHB while the spectra of the resorufin and TPPS films do not. The latter dyes reveal active bands on exposure to NH 3 gas because of deprotonation. The thermal durability of the hole profile was investigated by the temperature cycling method. Some discussion is given on the thermal durability in the alumina film compared to those in polystyrene (PS) and poly(methyl methacrylate) (PMMA).

Photo-properties of rare earth ion (Er3+, Eu3+ and Sm3+)-doped alumina films prepared by the sol–gel method

Abstract Rare earth ion (Er 3+ , Eu 3+ and Sm 3+ )-doped alumina films have been prepared by the sol–gel method, using AlCl 3 -derived alumina sol. The effects of dopant concentration and treatment temperatures on the photo-properties of absorption and emission have been examined for the doped films. These sol–gel-derived alumina matrices gave a high-dopant concentration (∼15 mol% per alumina).

Enantioselective esterification of racemic ibuprofen in isooctane by immobilized lipase on cellulose acetate-titanium iso-propoxide gel fiber.

Lipase (Candida rugosa) was entrap-immobilized on cellulose acetate-titanium iso-propoxide gel fiber by the sol-gel method. The immobilized lipase was used for the direct synthesis of (S)-ibuprofen ester from racemic ibuprofen using propyl alcohol as an acyl acceptor in isooctane. The activity of the immobilized lipase was decreased to about 10-20% that of native lipase. However, the reaction was more enantioselective compared to that with native lipase. The stability for repeated use was improved by immobilization.

Nonlinear optical and XPS properties of Au and Ag nanometer-size particle-doped alumina films prepared by the sol–gel method

Abstract Au and Ag nanometer-size particle-doped alumina films were prepared by the aqueous sol–gel method. Their XPS and third-order nonlinear optical properties were examined. The XPS results gave evidence of an interaction between Au and alumina. Third-order susceptibilities, χ(3) and χ(3)/α obtained by degenerate four-wave mixing method were in the order of 10−8 esu and 10−10 esu.cm for doped films, respectively.

Preparation conditions and optical properties of rare earth ion (Er3+ and Eu3+)-doped alumina films by the aqueous sol–gel method

Transparent alumina and rare earth ion (Er3+ and Eu3+) highly doped alumina films (15 mol %) were prepared by the aqueous sol–gel method, in order to examine the effects of various preparation conditions on the structure and optical properties of doped films. The results showed that when the gel was heat treated, it lost free and bound water and was converted into the oxide by way of a series of intermediate phases although the oxide as a whole remained structureless. The thermogravimetric analysis curve showed a marked weight loss in the temperature range of 100–500 °C and the slow loss continuing at higher temperature of 800 °C. High doping may reflect noncrystalline structure of alumina. The fluorescence of Eu3+ sensitive of microstructure increased especially corresponding to this weight loss with treatment. The Ω2 indicative of the asymmetric environment of Er3+ showed a similar increase. Concentration quenching for doped films treated at 800 °C was not significant in this concentration range. Lifeti...

Creation of long lasting luminescence in transparent aluminas

We have examined long lasting luminescence of transparent alumna and Tb3+–Zn2+(Ca2+)-codoped alumina films prepared by the aqueous sol-gel method. A strong luminescence of 300–500 nm was observed for nondoped alumina, and was shown to depend on the treat temperature of gel. The luminescence was not observed for alumina treated at temperatures higher than 600 °C. The luminescence band was composed of plural components due to oxygen defect sites in alumina. The lasting luminescence of Tb3+–Zn2+(Ca2+)-codoped alumina were observed after irradiation for several seconds using a UV lamp (15 W). The results indicated that the oxygen defect sites of alumina serve as a photoelectron trap center and that the AlV site serves as a hole trap center, which can be thermally released at room temperature.