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Notes: Fluorescence spectra and rise as well as decay curves of 1-ethylpyrene (EPy) in poly(methyl methacrylate) films changed using a XeCl (308-nm) excimer laser as an ablation source. This phenomenon was observed not only for the ablated area but also for the masked region of about 20 μm around the ablated area and was attributed to the change of the dispersion condition of EPy. Effects of laser ablation upon properties of polymer films were elucidated by analyzing fluorescence dynamics using a microscope and under a total internal reflection condition.

Notes: We investigated the electroluminescence (EL) performance of organic light emitting diodes having a thick doped hole transport layer [(DHTL):650 nm–1.5 μm]. The basic cell structure is an anode/DHTL/hole transport layer [(HTL):50–60 nm]/emitter layer [(EML):50–60 nm]/cathode. We examined various combinations of host polymers and guest molecules as a component of DHTL in this device structure. During the course of the materials' search, we found that the best combination of a hole transport polycarbonate polymer (PC–TPD–DEG) and a tris (4-bromophenyl) aminium hexachroloantimonate (TBAHA) as a dopant enabled us to form a uniform thick DHTL (typically 650 nm–1.5 μm thick), which resulted in excellent EL performance. The thick DHTL not only showed considerable reduction in cell resistance compared with a conventional anode/DHTL (without doping)/HTL/EML/cathode device with the same thicknesses of the organic layers, but also greatly contributed to the enhancement of the device stability, particularly to pinhole problems that can occur with conventional 100-nm-thick thin devices. Furthermore, the interposed HTL between DHTL and EML was confirmed to function not only as a HTL but also as electron and exciton blocking layers. Without the HTL, the EL quantum efficiency (ΦEL) was low, because of the serious exciton energy transfer and/or electron migration from EML to DHTL where the PC–TPD–DEG:TBAHA complex layer had absorption at around 485 nm based on a charge transfer complex between them. We could increase it by interposing a thin transparent N,N′-diphenyl-N,N′bis(3-methyl phenyl)-1,1′-biphenyl-4,4′-diamine or 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino] biphenyl (α-NPD) layer between DHTL and EML, while keeping the driving voltage low. With the DHTL (650 nm, 10 wt % of TBAHA) showed a luminance of 4004 cd/m2 at 10.0 V and 220 mA/cm2, of which the performance was comparable with that of typical thin film devices. Furthermore, we could expand the DHTL thickness up to 1.5 μm. An indium tin oxide (ITO)/DHTL (10 wt %)(1.5 μm)/α-NPD (60 nm)/Alq (60 nm)/MgAg device showed a luminance of 2600 cd/m2 at 18.0 V and 210 mA/cm2 with enhanced duration stability. In addition, the duration properties of the devices were also examined in the device structure of an ITO/DHTL (650 nm)/α-NPD (60 nm)/Alq(doped with rubrene 4.2 wt %) (60 nm)/MgAg. The half decay of the initial luminance successively exceeded over 1000 h under a constant current density of 10 mA/cm2. © 1999 American Institute of Physics.

Notes: We investigated electroluminescent (EL) characteristics of single-layer organic light emitting diodes (SOLEDs). Our SOLED devices are composed of an inert polymer as a binder, in which hole transport molecules, emissive electron transport molecules (ETMs), and highly fluorescent dopants as luminescent centers are dispersed. We examined two typical dopants: rubrene and coumarin 6. These exhibited different charge carrier recombination and emission mechanisms. The dopant concentration dependence of the current density–voltage–luminance relationships clearly showed the importance of carrier trapping by dopant molecules for obtaining high luminance. When the dopant was rubrene, we observed that charge carriers were well trapped by the dopant molecule. This means that direct recombination of holes and electrons occurred on the dopant molecules and trapping significantly enhanced the external EL quantum efficiency ΦEL. For coumarin 6, on the other hand, we observed that charge carriers primarily recombined at the emissive ETMs and that the energy transfer from the host to the guest coumarin 6 molecule dominated the EL process. A comparison of these distinct processes revealed that carrier trapping by dopant molecules was necessary to enhance ΦEL in SOLED devices. In our best SOLED device with rubrene as a dopant, we measured luminance of 2800 cd/m2 at J=100 mA/cm2, which corresponds to ΦEL=0.85%. © 1999 American Institute of Physics.

Notes: This paper reports on the effect of low energy He+ ion-beam bombardment upon the structure of pyrene thin films formed on quartz substrates. Films are prepared by vacuum evaporation during ion bombardment at room temperature. The structure of the film is controlled by the kinetic energy and current density of the ions. The colorless and transparent crystalline films preferentially oriented with their {001} plane parallel to the substrates are obtained by bombardment of 350 to 500 eV, 60 nA/cm2 He+ ions. Ion-beam irradiation of the higher ion current density enhances intermolecular chemical reactions and, as a result, a crystalline polymer with its {001} plane parallel to the substrate is produced.

Notes: We have evaluated a synthetic red fluorescent dye, 6-methyl-3-[3-(1,1,6,6-tetramethyl-10-oxo2,3,5,6-tetrahydro-1H,4H,10H-11 -oxa-3a-aza-benzo[de]anthracen-9-yl)-acryloyl]-pyran-2,4-dione (AAAP), as a dopant for an organic light-emitting diode (LED). Bright emission of a good red (maximum luminance: 5600 cd/m2, chromaticity coordinates: x=0.63, y=0.36) was obtained. The device consisted of ITO/TPD(50 nm)/Alq3 doped with AAAP(1.5 mol %,15 nm)/bOXDF(20 nm)/Alq3(25 nm)/Mg:Ag (ITO: indium tin oxide, TPD: N, N′-diphenyl- N,N′-di(3-methylphenyl)-1, 1′biphenyl-4,4′-diamine, Alq3: tris (8-hydroxyquinolinato)-aluminum (III), bOXDF:2,2-bis[5-(4-biphenyl)-1,3,4-oxadiazole-2-yl-4,1 -phenylene]-hexafluoropropane). The bands of fluorescence of the Alq3 host and of absorption of the AAAP dopant overlap in an advantageous way, and insertion of the bOXDF layer between the emission layer, doped with AAAP, and Alq3 layer, made for a device with good properties. © 2000 American Institute of Physics.

Notes: We demonstrated the fabrication of a 200 nm×2 mm array of organic light-emitting diodes (OLEDs) on a glass substrate. The photolithographic technique using an optical phase shift mask allowed us to construct a super-fine resolution patterning of OLEDs. A single organic electroluminescent (EL) layer composed of an inert poly(methylmethacrylate) polymer binder and tetraphenylbendidine and tris(8-quinolinol) aluminum molecules was fabricated on a fine-resolution photoresist patterning by a spin coating method. The lines and spaces of the photoresist patterning were 200 nm. The emitting area was well confined by the regular array of residual photoresist resin walls. Finally, a MgAg cathode layer was uniformly deposited on the organic layer. We observed anisotropic EL spectra between the directions perpendicular and parallel to the patterning of OLED arrays. Furthermore, we observed a large difference of EL intensities between them. We assume that the anisotropic EL characteristics are caused by the confinement effect of photons inside the submicrometer-sized OLED array. © 1999 American Institute of Physics.

Notes: We report an organic solid-state distributed feedback laser consisting of an organic active layer and a Bragg grating without morphological change. The active layer consists of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostryl)-4H-pyran as a laser dye, tris(8hydroxyquinoline) aluminum as a host, and poly(methyl methacrylate) as a binder. The threshold and linewidth of the laser are 400 μJ/cm2 and 1.5 nm, respectively. With this laser, the Bragg grating exists out of the active layer and the grating surface is flat, which are very important for device fabrication and electric driving of the laser. © 2000 American Institute of Physics.