We have studied the transport properties of electron-and hole-dominated MEH-PPV, poly͑2-methoxy,5-͑2Ј-ethyl-hexoxy͒-p-phenylene vinylene͒, devices in the trap-free limit and have derived the temperature-dependent electron and hole mobilities (ϭ 0 e ␥ͱE) from the space-charge-limited behavior at high electric fields. Both the zero-field mobility 0 and electric-field coefficient ␥ are temperature dependent with an activation energy of the hole and electron mobility of 0.38Ϯ0.02 and 0.34Ϯ0.02 eV, respectively. At 300 K, we find a zero-field mobility 0 on the order of 1Ϯ0.5ϫ10 Ϫ7 cm 2 /V s and an electric-field coefficient ␥ of 4.8Ϯ0.3 ϫ10 Ϫ4 (m/V) 1/2 for holes. For electrons, we find a 0 an order of magnitude below that for holes but a larger ␥ of 7.8Ϯ0.5ϫ10 Ϫ4 (m/V) 1/2. Due to the stronger field dependence of the electron mobility, the electron and hole mobilities are comparable at working voltages in the trap-free limit, applicable to thin films of MEH-PPV.

An electroluminescent device comprising a transparent or translucent Support, a transparent or translucent first electrode, a Second conductive electrode and an electrolu minescent phosphor layer Sandwiched between the transpar ent or translucent first electrode and the Second conductive electrode, wherein the first and Second electrodes each comprises a polymer or copolymer of a 3,4dialkoxythiophene, which may be the Same or different, in which the two alkoxy groups may be the same or different or together represent an optionally Substituted oxy-alkylene oxy bridge; a display comprising the above-mentioned elec troluminescent device; a lamp comprising the above mentioned electroluminescent device; manufacturing processes for the above-mentioned electroluminescent devices, and the use of Such devices for the integrated backlighting of Static and dynamic posters and Signage.

We study the effect of blended and layered titanium dioxide (TiO 2) nanoparticles on charge transfer processes in conjugated polymer photovoltaics. A two order of magnitude increase in photoconductivity and sharp saturation is observed for layered versus blended structures, independent of the cathode work function. Using electrodes with similar work functions, we observe low dark currents and open circuit voltages of 0.7 V when a TiO 2 nanoparticle layer is self-assembled onto the indium-tin-oxide electrode. Our results for the layered morphologies are consistent with charge collection by exciton diffusion and dissociation at the TiO 2 interface.

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We demonstrate that mixing insulating oxide nanoparticles into electroluminescent polymer materials results in increased current densities, radiances, and power efficiencies in polymer light emitting diode devices. For low driving voltages, an order of magnitude increase in current density and light output is achieved with minimal loss in device lifetime. At 5 V, we achieve radiances of 10 000 cd/m 2 with external quantum efficiencies ϳ1% for nanoparticle/MEH-PPV composite films.

Magnetic correlations in all four phases of pure and doped vanadium sesquioxide (V 2 O 3 ) have been examined by magnetic thermal-neutron scattering. Specifically, we have studied the antiferromagnetic and paramagnetic phases of metallic V 2Ϫy O 3 , the antiferromagnetic insulating and paramagnetic metallic phases of stoichiometric V 2 O 3 , and the antiferromagnetic and paramagnetic phases of insulating V 1.944 Cr 0.056 O 3 . While the antiferromagnetic insulator can be accounted for by a localized Heisenberg spin model, the long-range order in the antiferromagnetic metal is an incommensurate spin-density wave, resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations with a ''single lobe'' spectrum in the Stoner electron-hole continuum. Furthermore, our results in metallic V 2 O 3 represent an unprecedentedly complete characterization of the spin fluctuations near a metallic quantum critical point, and provide quantitative support for the self-consistent renormalization theory for itinerant antiferromagnets in the small moment limit. Dynamic magnetic correlations for បϽk B T in the paramagnetic insulator carry substantial magnetic spectral weight. However, they are extremely short-ranged, extending only to the nearest neighbors. The phase transition to the antiferromagnetic insulator, from the paramagnetic metal and the paramagnetic insulator, introduces a sudden switching of magnetic correlations to a different spatial periodicity which indicates a sudden change in the underlying spin Hamiltonian. To describe this phase transition and also the unusual short-range order in the paramagnetic state, it seems necessary to take into account the orbital degrees of freedom associated with the degenerate d orbitals at the Fermi level in V 2 O 3 . ͓S0163-1829͑98͒06443-1͔

The electron and hole charge distributions and the luminance profile in organic light-emitting diodes (OLEDs) depend upon the bulk properties of the emissive layer, as well as on the injection characteristics at the anode and cathode interfaces. We address the problem of separating the relative contributions of hole injection, electron injection, and recombination to the overall performance of single layer OLED devices. Using the approach of Parmenter and Ruppel [J. Appl. Phys. 30, 1548 (1959)], and including Langevin recombination, expressions are derived for the current–voltage and radiance–current dependencies in terms of electron and hole mobility, luminescence yield, and a “current balance” factor. When one carrier dominates the current flow, as in many practical cases, it is possible to obtain a simple asymptotic relationship which permits a test of the assumptions required to obtain the analytic solution. Experimental data from poly(2-methoxy-5(2′-ethyl)hexoxy-phenylenevinylene) diodes fabricated with various anode and cathode materials are evaluated in the context of this analytical approach.

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