We report an analysis of the operation of a new type of laser resonator with two-dimensional distributed feedback from a photonic crystal. The gain medium consists of a 2-(4-biphenylyl)-5(4-tert-butylphenyl)-1,3,4-oxadiazole host doped with Coumarin 490 and DCM and is deposited on lithographically patterned Si/SiO2 structures. Bragg reflections caused by the grating diminish the group velocity of photons along some directions of crystallographic symmetry to zero, and the resulting feedback gives rise to laser oscillations. Dispersion relations for photons were calculated analytically and are used to interpret the laser emission spectra.

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Electrical impedance measurements on poly-p-phenylene-vinylene (PPV) light-emitting diodes in the frequency range between 100 Hz and 10 MHz are reported. A significant difference can be revealed between the device characteristics of light-emitting diodes eliminated on indium-tin-oxide (ITO) and those of other high-work-function metals (e.g., Au). Thermal conversion of the precursor polymer on ITO substrates results in a p-type doping of the conjugated polymer PPV. Hence, devices in the configuration ITO/PPV/Al display Schottky behavior, which can be modeled by a simple equivalent circuit of two RC elements in series, representing a bulk and a junction region. The low-frequency device capacitance displays a pronounced voltage dependence and, from a detailed analysis, the ionized acceptor concentration NA, the diffusion potential VD, and the width of the space charge region w can be obtained. Typical values for NA are 1016–1017 cm−3, and for VD within the range 1–1.5 V, resulting in a width w of the space charge region at zero bias of about 50–150 nm. Via temperature-dependent investigations a transition from a p-type semiconductor Schottky diode at room temperature to a metal/insulator(polymer)/metal structure at lower temperatures is revealed.

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The beginning of the plastics age: Just over one hundred years ago, on July 13 1907, Leo H. Baekeland applied for a patent for the processing of a product that had an enormous influence on the development of our technology, and which changed our habits forever. The patent described Bakelite, the first synthetic plastic, which heralded our entrance into the plastics age.