Energy Focus: Energy harvesting in electronic displays enabled by fluorescent-dye-cascade linear polarizer
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Energy Focus Energy harvesting in electronic displays enabled by fluorescentdye-cascade linear polarizer
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s anyone with a smart phone or tablet knows, battery life is the key to a useful mobile device. Recently, luminescent solar concentrators (LSCs) have gained attention as a possible energy-harvesting technique to extend mobile battery life. When integrated into a display, LSCs steer incoming light that would otherwise be wasted (sunlight, room lights, or the internal backlight) to small photovoltaics placed inside the device perimeter. However, current LSCs reduce display quality and therefore remain impractical. Now, A.M. Velázquez and colleagues at the Massachusetts Institute of Technology have demonstrated an LSC based on cascading fluorescence that may eliminate this problem by shifting reemitted light into the infrared. They reported their findings in the October 25, 2012 online edition of Energy & Environmental Science (DOI: 10.1039/c2ee23265k). LSCs studied to date have been based on luminescent dye molecules placed
Bio Focus Bioinspired polymeric carbon nitride nanospheres dramatically improve photoredox catalysis
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any attempts have been made to create synthetic analogues of the natural photosynthesis system. However, the ability to mimic the spatial
remains largely unchanged for Ar and gas molecules with a larger kinetic diameter. In graphene membranes that have larger pores, faster leak rates were measured using a mechanical resonance method which again demonstrated sizeselective leak rates, but this time for molecules above and below the size of SF6. “Our results are consistent with theo-
retical models based on effusion through Ångstrom-sized pores,” stated group leader J. Scott Bunch, “and represent an important step toward the realization of macroscopic, size-selective porous graphene barriers.” Rich Louie
in a glass sandwich waveguide. These molecules can be aligned within a liquid crystal host, making the system into a linear polarizer, which could potentially replace the standard linear polarizers used in display technology. However, photons that result from the dye fluorescence can escape from the waveguide and be reemitted from the surface, contaminating the display image. The researchers hypothesized that they could overcome this problem by combining four different fluorescent dyes, with emission and absorption spectra that overlap to cover the optical spectrum all the way to the infrared. The final emission of this cascade could therefore be filtered out by a standard infrared filter. The researchers prepared the device by first dissolving four dyes in chloroform, mixing them with a nematic liquid-crystal host at 60°C for five minutes and desiccating the mixture for 12 hours. Next, they used capillary action to fill a 5-μm-gap liquid-crystal cell with the mixture, heating the materials to 70°C and slow-cooling them to ensure good alignment on the rubbed polyamide surfaces of the cell. The dyes chosen were (in wt% in the final device) coumarin 6
(0.3%), DCM2 (0.3%), Nile Red (0.6%),
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