Improved electrical and optical properties of MEH-PPV light emitting diodes using Ba buffer layer and porphyrin

It has been found that insertion of a thin Ba buffer layer between the Al electrode and the MEH-PPV layer results in a significantly higher current density in ITO/MEH-PPV/Al polymer light-emitting diodes due to a reduction of the potential barrier at the cathode-polymer interface. The photoluminescence is found to increase with the addition of porphyrin-containing platinum as the central atom, showing that some of the triplet excitons decay radiatively as a result of mixing porphyrin.     

Modified five-layer asymmetric coupled quantum well (M-FACQW) for giant negative refractive index change

We have analyzed the electrorefractive properties of a GaAs/AlGaAs modified five-layer asymmetric coupled quantum well (M-FACQW). The theoretical analyses show that the M-FACQW is expected to exhibit a giant negative electrorefractive index change Δn in the transparent-wavelength region away from the absorption edge. The influence of fluctuations in layer thickness on the electrorefractive properties of the M-FACQW was also investigated. Although the fluctuation in layer thickness deteriorates the characteristics of Δn in the M-FACQW, the M-FACQW still maintains a very giant Δn compared with that of a conventional rectangular quantum well without thickness fluctuation. In addition, we have fabricated the M-FACQW with monolayer accuracy by solid-source molecular beam epitaxy, and measured its photoabsorption current. The experimental results are in good agreement with the calculated properties. This indicates that the M-FACQW has great potential for use in ultra-wideband and low-voltage optical modulators and switches.     

Temperature compensated coupled cavity diode lasers

It has been shown theoretically that the temperature coefficient of the oscillation wavelength in semiconductor lasers can be reduced to zero by coupling an external cavity whose optical length decreases with temperature. Here are described two types of temperature compensated coupled cavity (TC³) diode lasers and their properties calculated in the steady state. In such devices an interference effect due to multi-cavities is expected to cause unstable mode hopping behaviour, but it was found to be settled by choosing an adequate external cavity length.     

Long lifetime operation of an ArF-excimer laser

An experimental investigation to improve the lifetime of a discharge-excited ArF-excimer laser is presented. The three dominant factors restricting its lifetime are CF₄ generation in the laser gas, color-center formation in the optics and input power density reduction due to electrode ablation. Copper electrodes were superior to nickel electrodes in regard to electrode ablation. A gas lifetime of more than 10⁹ shots (about one month at 400 Hz) is shown for an ArF-excimer laser with a liquid-nitrogen trap and high-temperature zirconium alloy trap.     

πNN Dynamics in pp → pp,pp →πd and πd →πd Processes Below 1 GeV

pp and πd scattering and pp →πd reaction processes at incident proton laboratory energies T _L ≤ 1 GeV are studied in the framework of πNN dynamics. For this purpose three-body calculations are performed with the πN interaction in the P ₁₁, P ₃₃, S ₁₁ and S ₃₁ states and NN forces in the ³ S ₁ -³ D ₁, ¹ S ₀, and ³ P ₂ states. In addition, the backward-going pion contribution at the πNΔ vertex, the πN-ρN coupling, the heavy-meson exchanges in the NN → NN driving term, and the effect of the off-shell structure in the πN-ρN P ₃₃ interaction are taken into account. Received March 28, 1994; revised July 29, 1994; accepted for publication August 31, 1994     

Structure of water incorporated in amphoteric polymer thin films as revealed by FT-IR spectroscopy

The structure and hydrogen bonding of water incorporated in a thin film of amphoteric terpolymers composed of various ratios of MA, DMAPMA, and BMA were analyzed using the band shapes of the O--H stretching in the IR spectra. At an early stage of sorption of water, the IR spectrum for the water incorporated in the film with comparative contents of MA and DMAPMA residues was similar to that for free water. This is consistent with the tendency for zwitterionic polymers, but is in contrast with the drastic change in the IR spectrum of water incorporated in non-ionic polymer films such as polyBMA. These results suggest a correlation between the mildness of the charge-balanced polymers to the structure of incorporated water and their blood compatibilities.     

Near Infrared Light-to-Heat Conversion for Liquid-Phase Oxidation Reactions by Antimony-Doped Tin Oxide Nanocrystals

Effective utilization of the sunlight for chemical reactions is pivotal for dealing with the growing energy and environmental issues. So far, much effort has been focused on the development of semiconductor photocatalysts responsive to UV and visible light. However, the near infrared and infrared (NIR-IR) light occupying ∼50 % of the solar energy has usually been wasted because of the low photon energy insufficient for the band gap excitation. Antimony doping into SnO₂ (ATO) induces strong absorption due to the conduction band electrons in the NIR region. The absorbed light energy is eventually converted to heat via the interaction between hot electrons and phonons. This Concept highlights the photothermal effect of ATO nanocrystals (NCs) on liquid-phase oxidation reactions through the NIR light-to-heat conversion. Under NIR illumination even at an intensity of ∼0.5 sun, the reaction field temperature on the catalyst surface is raised 20–30 K above the bulk solution temperature, while the latter is maintained near the ambient temperature. In some reactions, this photothermal local heating engenders the enhancement of not only the catalytic activity and selectivity but also the regeneration of catalytically active sites. Further, the photocatalytic activity of semiconductors can be promoted. Finally, the conclusions and possible subjects in the future are summarized.     

Synthesis of totarane diterpenes: totarol, maytenoquinone, 6-deoxymaytenoquinone and 8,11,13-totaratriene-12,13-diol

The syntheses of four totarane diterpenes-totarol, 8,11,13-totaratriene-12,13-diol, 6-deoxymaytenoquinone and maytenoquinone-are described. Totarol was synthesized via cyclization of a modified polyene. 8,11,13-Totaratriene-12,13-diol was prepared from natural totarol by ortho-oxidation with mCBPO (m-chlorobenzoyl peroxide). Maytenoquinone and 6-deoxymaytenoquinone were synthesized from 8,11,13-totaratriene-12,13-diol. 1H-NMR analysis showed that tautomeric isomerization between 6-deoxymaytenoquinone (2-hydroxy-4-quinone methide) and the ortho-quinone was very slow.     

Methylene blue-containing silica-coated magnetic particles: a potential magnetic carrier for photodynamic therapy

We present the preparation and characterization of methylene blue-containing silica-coated magnetic particles. The entrapment of methylene blue (MB), a photodynamic therapy drug under study in our group, in the silica matrix took place during the growth of a silica layer over a magnetic core composed of magnetite nanoparticles. The resulting material was characterized by transmission electron microscopy (TEM), light scattering, and X-ray diffraction. It is composed of approximately 30 nm silica spheres containing magnetic particles of 11 +/- 2 nm and methylene blue entrapped in the silica matrix. The immobilized drug can generate singlet oxygen, which was detected by its characteristic phosphorescence decay curve in the near-infrared and by a chemical method using 1,3-diphenylisobenzofuran to trap singlet oxygen. The lifetime of singlet oxygen was determined to be 52 micros (in acetonitrile) and 3 micros (in water), with both values being in good agreement with those in the literature. The release of singlet oxygen (etaDelta) was affected by the encapsulation of MB in the silica matrix, which caused a reduction to 6% of the quantum yield of MB free in solution. The magnetization curve confirmed the superparamagnetic behavior with a reduced saturation magnetization in respect to uncoated magnetic nanoparticles, which is consistent with the presence of a diamagnetic component over the magnetite surface. The result is a single particle platform that combines therapy (photosensitizer) and diagnostic (MRI contrast agent) possibilities at the same time, as well as drug targeting.