A model based on Rayleigh–Gans–Debye light‐scattering theory has been developed to describe the light transmission properties of fine‐grained, fully dense, polycrystalline ceramics consisting of birefringent crystals. This model extends light transmission models based on geometrical optics, which are valid only for coarse‐grained microstructures, to smaller crystal sizes. We verify our model by measuring the light transmission properties of fully dense (>99.99%), polycrystalline α‐Al2O3 (PCA) with mean crystal sizes ranging from 60 to 0.3 μm. The remarkable transparency exhibited by PCA samples with small crystal sizes (<2 μm) is well explained by this model.

Commercial corundum powder and a liquid‐shaping approach are used for manufacturing complex hollow components and large flat windows of sintered and hot isostatically pressed Al2O3 ceramics having grain sizes of 0.4–0.6 μm at relative densities of >99.9%. High macrohardness (HV10 = 20–21 GPa) and four‐point bending strength (600–700 MPa; 750–900 MPa in three‐point bending) are associated with a real in‐line transmission of 55%–65% through polished plates. The submicrometer microstructure and the optical properties can be retained for use at >1100°C using dopants that shift the sintering temperature to high values without additional grain growth.

We present a study of photo- and electroluminescence of SiGe dots buried in Si and compare them with structures containing smooth SiGe layers. The SiGe dot structures were fabricated by low-pressure chemical vapor deposition using the Stranski–Krastanov growth mode (island growth). We show that the localization of excitons in the dots leads to an increase of the luminescence efficiency at low excitation compared to smooth SiGe layers (e.g., quantum wells). At higher excitation the efficiency decreases which is attributed to nonradiative Auger recombination processes in the dots.