Exciton Antennae and Concentrators From Core-Shell and Corrugated Carbon Nanotube Filaments of Homogeneous Composition

There has been renewed interest in solar concentrators and optical antennae for improvements in photovoltaic energy harvesting and new opto-electronic devices. In this work, we dielectrophoretically assemble single-walled carbon nanotubes (SWNTs) of homogeneous composition into aligned filaments that can exchange excitation energy, concentrating it to the center of core-shell structures with radial gradients in the optical band gap. We find an unusually sharp, reversible decay in photoemission that occurs as such filaments are cycled from ambient to only 353 K, attributed to the strongly temperature dependent second order Auger process. Core-shell structures consisting of annular shells of mostly (6,5) SWNT (Eg = 1.20 eV ) and cores with bandgaps smaller than those of the shell (Eg = 1.02 eV (11,3) to 0.98 eV (8,7)) demonstrate the concentration concept: broad band absorption in the ultraviolet (UV) - near-infrared (nIR) wavelength regime provides singular photoemission at the (8,7) SWNT. This approach demonstrates the potential of specifically designed collections of nanotubes to manipulate and concentrate excitons in unique ways.