Masayoshi Yoshida

Three‐layered multicolor organic electroluminescent device

We have realized a three‐layered multicolor organic electroluminescent device utilizing poly (9,9‐dihexylfluorene) and perylene derivatives as emission layers, with diamine derivatives as an electron blocking layer. Emission colors could be selected either blue or red by changing the polarity of the applied voltage. By driving with an ac biased electric field, both emission colors were observed and the intensity ratio of each emission color was modulated by the frequency of the applied ac field.

Ultraviolet Electroluminescent Diode Utilizing Poly(methylphenylsilane)

Electroluminescent (EL) diode utilizing poly(methylphenylsilane) (PMPS) has been fabricated and its optical and electroluminescent characteristics have been investigated. We have succeeded in demonstrating ultraviolet emission at 353 nm from the PMPS EL diode for the first time.

Electroluminescent Diodes Utilizing Polysilanes

Electroluminescent (EL) diodes utilizing polysilanes have been fabricated, and their optical and electroluminescent characteristics have been investigated. We have succeeded in demonstrating electroluminescence from the ultraviolet region to the visible region using the EL diodes with thin polysilane films. The diode characteristics are discussed taking the polymer structure into consideration.

Two-Band Electroluminescent Emission in Organic Electroluminescent Diode with Phthalocyanine Film

An electroluminescent (EL) diode utilizing metal-free phthalocyanine ( H2Pc) has been fabricated by the vacuum evaporation method. The optical characteristics of the EL diode, such as the spectra of absorption, photocurrent and electroluminescence, have been investigated, and their temperature dependence has been discussed. We have found, for the first time, that the EL spectrum has two discrete peaks at around 480 nm and above 800 nm.

Unique electrical and optical characteristics in poly(p-phenylene)-C/sub 60/ system

Abstract Electrical and optical properties of both poly( p -phenylene) (PPP) and PPP-C 60 films prepared by evaporation methods have been studied in detail. Fluorescence and electroluminescence of PPP have been found to be influenced by incorporated C 60 . Photoconductivity and junction characteristics of PPP and PPP-C 60 have also been clarified.

Color-Variable Electroluminescent Diode with Single Quantum Well Structure Utilizing 8-Hydroxyquinoline Aluminum and Aromatic Diamine

A color-variable electroluminescent diode has been realized utilizing a 1-nm-thick dye molecule layer with single-quantum-well (SQW) structure. The electroluminescent (EL) spectrum changes with increasing applied voltage from 8 V to 20 V. The result is discussed in terms of the shift of the recombination region toward the ITO electrode, depending on applied voltage.

Electrical and optical properties of molecularly doped conducting polymers

Abstract Novel electrical and optical characteristics have been observed in conducting polymers doped with molecular dopants such as fullerenes (C60, C70 etc.), photochromic dyes and another (guest) conducting polymer. Highly effective photo-induced charge transfer results in various effects such as photoluminescence quenching, photoconductivity enhancement, electroluminescence quenching and persistent photoconductivity which have been observed in fullerene-doped conducting polymers. Unique photo-sensitive characteristics have also been found in conducting polymer/ fullerene systems. Photoluminescence and photoconductivity in conducting polymers doped with photochromic dyes have been changed dramatically by photo-induced isomerization of photochromic dyes and memory effects in both dark conductivity and photoconductivity have been observed. We also present here some results on conducting polymer-conducting polymer mixtures and discuss general features of such composites. These characteristics can be explained by the asymmetry of the relative electronic energy states of conducting polymer and molecular dopants on account of self-trapping effects. Superconductivity evolved upon alkali metal doping of C60-conducting polymer composites, and has been confirmed by low-field microwave absorption (LFMA) and SQUID magnetometry measurements. The origin of superconducting phases in this doubly doped conducting polymer is discussed.

Novel Optical Properties of Fullerene Doped Conducting Polymers: Scenario of Photo Process, Persistent Photoconductivity and Enhanced Electroluminescence Quenching

Abstract Earlier we found that photoluminescence (PL) in conducting polymer with non-degenerated ground state (NDGS CP) is quenched remarkably upon doping by small amount of fullerenes such as C60 and C70. Here we show that electroluminescence is quenched even much more stronger indicating that each C60 molecule acts as a multiple trapping and/or recombination center for carriers. On the other hand photoconductivity (PC) in NDGS CP and also in conducting polymer with degenerated ground state (DGS CP) such as polyacetylene derivatives is enhanced significantly upon fullerene doping at the excitation of (a) the wavelengths of the inter-band transition in conducting polymer and (b) allowed and (c) forbidden optical transitions in fullerene. Remarkable polarity effect is observed in the spectral response of enhanced photoconductivity, proving that positively charged mobile carriers in polymeric chains contribute to PC. The effect of persistent photoconductivity at room temperature is found in C60/CP (conducti...

Unique Electroluminescent Characteristics of Light-Emitting Diode Utilizing Poly(3-alkylthiophene) Containing Fluorescent Dye

Electroluminescent (EL) diodes utilizing poly(3-alkylthiophene) containing fluorescent dyes have been fabricated and their unique characteristics have been studied. The EL efficiency has been enhanced by a factor of 100 in poly(3-alkylthiophene) diodes doped with cyclopentadiene derivative compared with that in undoped poly(3-alkylthiophene) diodes. Color-variable light emission with increasing applied voltage, as well as improvement of the EL efficiency, has been observed in diodes with poly(3-alkylthiophene) containing oxadiazole derivative.

Novel properties of molecularly doped conducting polymers and junction devices

Abstract Properties of conducting polymers, especially optical properties, have been found to be strongly influenced by doping of molecular dopants such as C 60 , aromatic molecules, photo chromic dyes and different structures of conducting polymers, which are interpreted in terms of dynamics of photo-excited electrons, holes and excitons by taking electronic energy states of both conducting polymer and molecular dopants into consideration. Novel characteristics have also been observed upon double doping, superconductivity and ferromagnetism upon doping of Alkali metal and TDAE into C 60 doped conducting polymer, respectively. Molecular doped conducting polymers also have exhibited novel junction characteristics such as high efficiency of photovoltaic effects, light sensitive FET characteristics and voltage and its polarity dependent electroluminescence