Railed Microfluidic Channels Enable Precise Microstructure Assembly
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dielectric anisotropic LCs, and a test NIVAGH-LC cell was manufactured using two indium-tin oxide (ITO) substrates separated by 5 μm bead spacers. The test cell exhibited a low threshold voltage of ~2.1 Vrms and a high reflectance of ~59% in the voltage-off state. The researchers reported that optimal vertical alignment depends on the magnitude differences between the POSS-LC and LC-LC interactions. The researchers said that the NIVA phenomenon is due to the adsorption of POSS nanoparticles on the inner surface of the ITO substrates, which lowers the surface tension, thereby inducing homeotropic alignment. The NIVA technique is advantageous because it can be applied at room temperature and is a relatively simple process for preparing GH-LCDs. The resulting NIVA-GH-LC cells are favorable for lowcost applications, such as price tags and timepieces, which require plastic substrates and low power consumption. The researchers demonstrated this by fabricating a flexible timepiece with 1 wt% dye and 8.5 μm spacers. The next steps are to examine the electro-optical properties and reliability of the plastic NIVAGH-LC under mechanical bending, said the researchers. SAMESHA R. BARNES
Terbium Phosphor Exhibits High Spectral Purity in the Green The color purity of the emission spectrum of terbium-doped crystals excited at wavelengths shorter than 380 nm depends on Tb3+ concentration. At low Tb3+ concentrations, the emission is dominated by the 5D3-7FJ (J = 0-6) transitions with several lines in the blue region. With increasing Tb3+ concentration, the 5D4-7FJ transitions become dominant, generating blue, green, yellow, and red lines. However, M. Gusowski and W. RybaRomanowski, from the Polish Academy of Sciences in Wroclaw, Poland, reported in the August issue of Optics Letters (DOI: 10.1364/OL.33.001786; p. 1786 ) the development of K3YF6:Tb3+—a new phosphor in which, in contrast to other terbium-doped materials reported until now, the emission is independent of the Tb3+ concentration and most of the intensity of the green emission was confined in an extremely narrow spectral bandwidth. The researchers prepared a series of
polycrystalline samples K3Y1-xTbxF6 (x = 0.03, 0.1, 0.2, and 1) by heating stoichiometric mixtures of KF3, YF3, and TbF3 at 800ºC in graphite crucibles in Ar atmosphere. They obtained monoclinic crystals with space group P21/n. Yttrium or terbium ions were sixfold-coordinated by fluorine ions and occupied strongly distorted octahedrons with centrosymmetric C i local symmetry. The emission spectra were recorded with a fluorometer system consisting of a 150 W xenon lamp coupled to an excitation monochromator and a scanning grating monochromator equipped with a photomultiplier. Excitation at a sample temperature of 8 K by 375 nm light yielded a narrow-band emission at around 545 nm, formed by three line components peaking at 540.77 nm, 541.18 nm, and 541.74 nm, related to transitions from the lowest crystal field component of the 5D4 multiplet to crystal field components of the terminal 7F5 multiplet. The rese
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