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The preparation of powder samples of aluminum nitride activated by dysprosium, AlN/Dy 3+ , was achieved for the first time using a low-temperature, solution-based approach. Aqueous solutions of aluminum and dysprosium nitrates was first converted to hydroxides and then to ammonium-metal hexafluorides ͑Al 1−x Dy x ͑NH 4 ͒ 3 F 6 . Finally, this complex ammonium salt was converted to finely divided powders of Al 1−x Dy x N via a pyrolysis reaction in a high-purity ammonia flow inside a tubular quartz furnace at 900°C. The phase purity and crystallinity of the material were determined using X-ray diffraction and energy dispersive spectroscopy. The intraconfigurational f-f transitions of Dy 3+ were investigated using photoluminescence ͑PL͒ and photoluminescence excitation ͑PLE͒ measurements. The excited states of Dy 3+ in this large-gap nitride were identified from a careful analysis of PL and PLE results. It was also observed from the PLE measurements that the Dy 3+ ions in this host are excited through energy transfer from both the excited state of the host lattice and defects. Measurements using site-selective spectroscopy suggest multiple sites for Dy 3+ ions in AlN. A theoretical model describing the excitation process and saturation of excited states of Dy 3+ at higher intensity of the exciting radiation is also proposed.The narrow band emissions due to the forbidden f-f intraconfigurational transitions of rare earth ͑RE͒ ions in semiconductors are of considerable interest in different optoelectronic applications including light emitting diodes ͑LEDs͒ 1-5 and optical communication amplifiers. 6,7 In particular, nitride semiconductors, such as AlN, GaN, InN, and their alloys, doped with RE ions are receiving increasing attention due to their potential application in LED sources for generating white light. 3-5 From the perspective of engineering solid-state light sources, these materials have two unique advantages. First, the nitride semiconductors and their alloys offer a large range of energy gaps from 0.7 eV 8 to 6.2 eV compared to other semiconductors. Second, the multiplet structure of RE ions and transitions involving the corresponding energy levels do not depend strongly on the host lattice due to shielding of the 4f orbitals by 5s and 5p orbitals. 9 These two unique features enable engineering light sources with desired color coordinates and color temperatures. 10 Additionally, if these materials could also be optimized to have high efficacy, their use both as phosphors and active layers in a doubleheterostructure design of LED lighting sources could lead to breakthroughs in general lighting.However, fluorescence from RE ions in nitride hosts is a relatively unexplored area of research in RE ion spectroscopy. This is partly due to the difficulties involved in synthesizing high-purity nitride powders and partly because of the lack of any need for such materials in the past. Recent developments of III-V nitride-based LEDs have generated interest in these materials. There have been some recent studies involvi...

Nine carbon blacks with iodine surface areas ranging between 60 and 1222 m~/gm and with dibutyl phthalate absorption numbers ranging between 125 and 420 cm3/100 gm have been evaluated as lithium/oxyhalide cell cathode materials. Two criteria have been considered: their ability to serve as heterogeneous catalysts for the cathodic half-cell reaction (a function of both internal surface area and specific activity), and their ability to accommodate the continuous deposition of solid discharge products with minimal internal resistance losses (a function of both the porosity and pore size distribution of the agglomerated carbon particle aggregates). For carbons with surface areas of at least 250 m2/gm, overvoltages for SOCI.2 reduction are practically independent of carbon black surface area. Furthermore, cathode porosities and Li/SOCI2 cell discharge capacities both correlate with the DBP absorptometer numbers characteristic of the high surface area carbon blacks themselves. If the activity of a low surface area carbon is augmented via a catalytic additive (e.g., supported platinum), overvoltages similar to those obtained with high surface area carbons and complete utilization of the cathode's internal pore volume are achieved. The use of cathode "pore formers" may also lead to improved performance characteristics, particularly at very high current densities where pore former particle diameters averaging about 200 ~m yield optimal performance results. Of the commercially available carbon blacks examined, Ketjenblack EC and Black Pearls 2000 function best as Li/SOC]2 cell cathode materials, greatly outperforming the standard carbon, Shawinigan acetylene black.