Nanostructured ␤-SiC, with crystallite size in the range of 5-20 nm in agglomerates of 50 -150 nm, was formed by reactive high-energy ball milling and consolidated to a relative density of 98% by sintering at 1700°C without the use of additives. X-ray line broadening analysis gave a crystallite size of 25 nm, while transmission electron microscopy observations showed the crystallite size to be in the range of 30 -50 nm. Evidence demonstrating the role of a disorder-order transformation in the densification process is provided by changes in the diffraction peak patterns and in the integral width with temperature. R. Riedel-contributing editorManuscript No. 10245.

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is one of the most versatile ceramics, utilized in an amazing range of structural and optical applications. In fact, chromium-doped single crystal Al 2 O 3 was the basis for the fi rst laser. Today, most photoluminescent (PL) materials rely on rare earth (RE) rather than transition-metal dopants because RE doping produces greater effi ciencies and lower lasing thresholds. RE-doped alumina could provide an extremely versatile PL ceramic, opening the door for a host of new applications and devices. However, producing a transparent RE:Al 2 O 3 suitable for PL applications is a major challenge due to the very low equilibrium solubility of RE ( ∼ 10 −3 %) in Al 2 O 3 in addition to alumina's optical anisotropy. A method is presented here to successfully incorporate Tb 3+ ions up to a concentration of 0.5 at% into a dense alumina matrix, achieving a transparent light-emitting ceramic. Sub-micrometer alumina and nanometric RE oxide powders are simultaneously densifi ed and reacted using current-activated, pressure-assisted densifi cation (CAPAD), often called spark plasma sintering (SPS). These doped ceramics have a high transmission ( ∼ 75% at 800 nm) and display PL peaks centered at 485 nm and 543 nm, characteristic of Tb 3+ emission. Additionally, the luminescent lifetimes are long and compare favorably with lifetimes of other laser ceramics. The high transparencies and PL properties of these ceramics have exciting prospects for high energy laser technology.