Organic light emitting diodes were fabricated using a novel electrode structure. The anode structure comprised of a metallic nanowire array and was fabricated by electroplating porous aluminium oxide with copper. These devices were compared with devices with a conventional planar anode structure. The light emitting polymer Poly[(4-methylphenyl) imino-4,4'-diphenylene-(4-methylphenyl)imino-1,4-phenylene-ethenylene-2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-ethenylene-1,4-phenylene)] was used as the emissive material in single layer devices of structure Cu: TPD(4M)-MEH-PPV: Al, where the aluminium was negatively biased with respect to the copper. The DC current-voltage characteristics of both device types are presented. The electroluminescence spectra are also presented. We found that due to the reduction in active area in the nanowire device from that of the planar device the current density reached in the nanowire array anode device exceeded that in the planar anode device by a factor of eight. Similarly a relative increase in the electroluminescence intensity was also observed.
Silver nanowires with different diameters are prepared within the pores of nanoporous alumina membranes. The linear optical properties of these composites are investigated (UV-Vis spectroscopy) as well as the nonlinear optical properties (Z-Scan technique). The dependence of both linear and the nonlinear optical properties on the average diameter of the silver wires is analysed, indicating that the spectral position of the plasmon resonance is red-shifted when the wire diameter is increased. This in turn leads to a different nonlinear optical behaviour. At comparatively low incident laser pulse energies all samples show saturable absorption (enhanced transmission). For higher energies, however, a second effect occurs which finally leads to an increase in the absorption coefficient. This second effect can probably be attributed to the ionisation of the silver wires due to multiphoton absorptions and a subsequent trapping of the electrons in the dielectric membrane. The ionised species, however, shows a different optical behaviour. The occurrence of this ionisation depends on the wire diameter. The larger the diameter the lower the incident laser pulse energy needed to ionise the wires. This corresponds to an increase in the linear absorption coefficient with increasing wire diameter.
Zinc-2, 9,16,23 -tetra- tert-butyl-29H, 31H -phthalocyanines and Zinc-2, 9,16,23-tetrakis-(phenylthio)-29H, 31H-phthalocyanines were recrystallized from an acetone solution to give regular shaped spherical particles of 50nm diameter, confirmed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). A peak broadening of the Q-Band and a shift of the B-Band in the UV-Visible absorption spectrum combined with a significant fluorescence quenching was observed. The z-scan technique was used to investigate the non-linear optical properties and an increase of approximately 200% in the ratio of excited to ground state absorption cross sections in the crystal state was observed indicative of a significant increase in the optical limiting response of the crystals compared to the monomers.