The crystallographic and magnetic properties of CaRu 1−x Mn x O 3 ͑0 Յ x Յ 1.0͒ were investigated in detail by x-ray powder diffraction, magnetization, and magnetic Compton scattering measurements. The lattice parameters show considerable deviation from Vegard's law. Ferromagnetism appears at a relatively large Mn concentration ͑x Ն 0.2͒, and the magnetization and the Curie temperature have a maximum at a Mn content near x = 0.7. The magnetic Compton scattering measurement revealed that Mn makes a dominant contribution to the magnetization and the Mn moment is antiparallel to the Ru moment, which is induced by Mn doping. The anomalous change in the unit cell volume and the occurrence of ferromagnetism were discussed on the basis of the mixed-valence model of Mn 3+ , Mn 4+ , Ru 4+ , and Ru 5+ ions. The Mn-composition dependence of the spontaneous magnetization was explained semiquantitatively assuming ͑1͒ ferromagnetic coupling between Mn 3+ and Mn 4+ ions, ͑2͒ antiferromagnetic coupling between Ru 5+ and Mn ions, and ͑3͒ the theoretical spin moments of Mn 3+ , Mn 4+ , and Ru 5+ . The ferromagnetic interaction between Mn 3+ and Mn 4+ ions seems to make a dominant contribution to the Curie temperature. The CaRu 1−x Mn x O 3 system is considered to be a ferrimagnet induced through competition between the ferromagnetic interaction between Mn ions and the antiferromagnetic interaction between Ru 5+ and Mn ions.
Extrinsic atoms were doped into multiwalled carbon nanotubes (MWCNTs) using microwave plasma-enhanced chemical vapor deposition. Doped nitrogen atoms alter the original parallel graphenes into highly curved ones including some fullerene-like structures. Doped nitrogen atoms could replace carbon atoms in MWCNTs and therefore increase the electronic density that enhances the electron field emission properties. On the other hand, the incorporation of boron into the carbon network apparently increases the concentration of electron holes that become electron traps and eventually impedes the electron field emission properties. Fowler-Nordheim plots show two different slopes in the curve, indicating that the mechanism of field emission is changed from low to high bias voltages. beta values could be increased by an amount of 42% under low bias voltages and 60% under high bias voltages in the N-doped MWCNTs, but decreased by an amount of 8% under low bias region and 68% under high bias voltage in the B-doped MWCNTs. (C) 2003 American Institute of Physics
High efficiency green emission is crucial to the designs of energy‐saving display and lighting. Efficient electroluminescent green emitters with both wet‐ and dry‐process feasibility is highly desirable in order to realize, respectively, cost‐effective large roll‐to‐roll manufacturing and high performance products. In this study, high‐efficiency, phosphorescent, green organic light emitting diodes with a novel iridium complex, bis[5‐methyl‐8‐trifluoromethyl‐5H‐benzo(c)(1,5)naphthyridin‐6‐one] iridium (acetylacetonate), are demonstrated. They possess both wet‐ and dry‐processing possibilities. The emitter exhibits a short excited‐state lifetime, 1.25 μs, and a high quantum yield, 69%, due to the efficient intersystem crossing of the ground state to the excited state. Using 4,4′‐bis(carbazol‐9‐yl)biphenyl as a host, the device shows at 1000 cd m−2 an external quantum efficiency (EQE) of 21% and power efficiency of 64 lm W−1 via vapor deposition, while 26% EQE and 69 lm W−1 by spin‐coating, the highest among all reported wet‐processed green organic light emitting diodes. Besides electroluminescence, the high device efficiency may also be attributed to the employed device architecture enabling therein an electron trap to facilitate the injection of this minor carrier against that of a hole, leading to a balanced carrier‐injection, and hence a high carrier recombination and in turn a high device efficiency.
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