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Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

The development of white organic light-emitting diodes (OLEDs) holds great promise for the production of highly efficient large-area light sources. High internal quantum efficiencies for the conversion of electrical energy to light have been realized. Nevertheless, the overall device power efficiencies are still considerably below the 60-70 lumens per watt of fluorescent tubes, which is the current benchmark for novel light sources. Although some reports about highly power-efficient white OLEDs exist, details about structure and the measurement conditions of these structures have not been fully disclosed: the highest power efficiency reported in the scientific literature is 44 lm W(-1) (ref. 7). Here we report an improved OLED structure which reaches fluorescent tube efficiency. By combining a carefully chosen emitter layer with high-refractive-index substrates, and using a periodic outcoupling structure, we achieve a device power efficiency of 90 lm W(-1) at 1,000 candelas per square metre. This efficiency has the potential to be raised to 124 lm W(-1) if the light outcoupling can be further improved. Besides approaching internal quantum efficiency values of one, we have also focused on reducing energetic and ohmic losses that occur during electron-photon conversion. We anticipate that our results will be a starting point for further research, leading to white OLEDs having efficiencies beyond 100 lm W(-1). This could make white-light OLEDs, with their soft area light and high colour-rendering qualities, the light sources of choice for the future.

White organic light-emitting diodes with fluorescent tube efficiency

The ability to control the size, shape, and material of a surface has reinvigorated the field of surface-enhanced Raman spectroscopy (SERS). Because excitation of the localized surface plasmon resonance of a nanostructured surface or nanoparticle lies at the heart of SERS, the ability to reliably control the surface characteristics has taken SERS from an interesting surface phenomenon to a rapidly developing analytical tool. This article first explains many fundamental features of SERS and then describes the use of nanosphere lithography for the fabrication of highly reproducible and robust SERS substrates. In particular, we review metal film over nanosphere surfaces as excellent candidates for several experiments that were once impossible with more primitive SERS substrates (e.g., metal island films). The article also describes progress in applying SERS to the detection of chemical warfare agents and several biological molecules.

Surface-Enhanced Raman Spectroscopy

Recent startling interest for lanthanide luminescence is stimulated by the continuously expanding need for luminescent materials meeting the stringent requirements of telecommunication, lighting, electroluminescent devices, (bio-)analytical sensors and bio-imaging set-ups. This critical review describes the latest developments in (i) the sensitization of near-infrared luminescence, (ii) “soft” luminescent materials (liquid crystals, ionic liquids, ionogels), (iii) electroluminescent materials for organic light emitting diodes, with emphasis on white light generation, and (iv) applications in luminescent bio-sensing and bio-imaging based on time-resolved detection and multiphoton excitation (500 references).

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Lanthanide luminescence for functional materials and bio-sciences

Surface-enhanced Raman spectroscopy.

Highly soluble asymmetrically substituted vanadylphthalocyanines with dodecakis(2,2,2-trifluoroethoxy) groups as a donor and a mono-nitro group as an acceptor substituent, or with extended exocyclic conjugation, have been synthesized and characterized. Their linear and nonlinear optical properties were studied. Second harmonic generation of thin films of poly(methyl methacrylate) doped with these vanadylphthalocyanines was observed after electric poling at a fundamental wavelength of 1.064 μm.

Novel Asymmetrically Substituted Metallophthalocyanines for Nonlinear Optics

We report the use of substituted main-chain poly-carbazoles as hole and electron transporting polymers for electroluminescence (EL) applications. The polymers are soluble in common organic solvents and high quality thin films are obtained by spin coating method. A single layer of hole or electron transfer devices with indium tin oxide anode and aluminum cathode shows current densities up to 40–50 mA/cm2, respectively, but no visible emission from either layer. Double-layer structures combining the hole and electron transfer polymers show strong emission originated from the electron transfer layer. The peak of double-layer EL spectrum is about 30 nm redshifted to the peak of corresponding photoluminescence spectrum, which may be due to the formation of an exciplex between the two layers.

Novel main-chain poly-carbazoles as hole and electron transport materials in polymer light-emitting diodes

Mechanism of protein folding. IV. Forming and breaking of disulfide bonds in bovine pancreatic tripsin inhibitor

We demonstrate carrier injection and transport of steady-state high current density into organic thin films. The maximum current density reaches J=1053A/cm2, the highest ever reported. We employ a 25 nm-thick Copper phthalocyanine (CuPc) thin film sandwiched between an indium-tin-oxide anode and a magnesium-silver alloy cathode with an active electrode dot-size (S) of S=2.0×10-5cm2 (radius: r=25 µm). We observed that the maximum current density depends on the organic materials used, and the device size and thickness. Decreasing the organic layer thickness significantly changes the current density-voltage (J-V) characteristics, demonstrating that the rate-limiting step of the J-V characteristics changes from the carrier transport process to the carrier injection process. Our achievement of high current density exceeding 1000 A/cm2 in organic thin films is a first step towards the development of organic laser diodes that need extremely high excitation intensity.

Hiroyuki Sasabe

Papers

Novel Asymmetrically Substituted Metallophthalocyanines for Nonlinear Optics

Novel main-chain poly-carbazoles as hole and electron transport materials in polymer light-emitting diodes

Mechanism of protein folding. IV. Forming and breaking of disulfide bonds in bovine pancreatic tripsin inhibitor

Carrier Injection and Transport of Steady-State High Current Density Exceeding 1000 A/cm2 in Organic Thin Films*

A novel approach to the synthesis of conjugated carbazole trimers as multifunctional chromophores for photorefractive materials