Exciton antennas and concentrators from core–shell and corrugated carbon nanotube filaments of homogeneous composition

Journal name:
Nature Materials
Year published:
Published online


There has been renewed interest in solar concentrators and optical antennas for improvements in photovoltaic energy harvesting and new optoelectronic 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 centre of core–shell structures with radial gradients in the optical bandgap. We find an unusually sharp, reversible decay in photoemission that occurs as such filaments are cycled from ambient temperature to only 357 K, attributed to the strongly temperature-dependent second-order Auger process. Core–shell structures consisting of annular shells of mostly (6,5) SWNTs (Eg=1.21 eV) and cores with bandgaps smaller than those of the shell (Eg=1.17 eV (7,5)–0.98 eV (8,7)) demonstrate the concentration concept: broadband absorption in the ultraviolet–near-infrared wavelength regime provides quasi-singular photoemission at the (8,7) SWNTs. This approach demonstrates the potential of specifically designed collections of nanotubes to manipulate and concentrate excitons in unique ways.

At a glance


  1. Optical properties of a (6,5)-enriched SWNT fibre: photoluminescence and strong EET.
    Figure 1: Optical properties of a (6,5)-enriched SWNT fibre: photoluminescence and strong EET.

    a, Upper panel: an optical image of a SWNT fibre supported on a tungsten tip; lower panel: a corresponding two-dimensional near-infrared InGaAs photoluminescence image (with 658-nm-wavelength laser excitation, 1 mW), showing bright photoluminescence from the very end of the fibre in a solid state, confirming a high degree of semiconductor purity. Note that the light emission at the upper-right corner is due to a halogen lamp source. b, A corresponding PLE map demonstrating the majority of (6,5) chirality. c, The photoluminescence spectra of both an As-separated solution and a solid-state fibre taken at 570-nm-wavelength monochromatic light excitation, corresponding to the E22 transition of individual (6,5) SWNTs in an aqueous solution10. Note that the peak of the fibre (solid red line, ∼1,008 nm) is redshifted (by about 30 meV) from that of individual SWNTs in an aqueous solution (solid blue line, ∼984 nm).

  2. PLE map and reversible photoluminescence change as a function of temperature.
    Figure 2: PLE map and reversible photoluminescence change as a function of temperature.

    a,b, Typical near-infrared (970–1,280 nm) PLE maps of a fibre (inset of a) taken at temperatures of 298 (a) and 357 K (b). c, Quantum yield of both types of SWNT present in the fibre versus temperature (the quantum yield is defined as the ratio of photons emitted to photons absorbed). Inset: The quantum yield of the (6,5) tube on a different scale. d, Photoluminescence intensities of both (6,5) and (7,6) emissions versus temperature (both experimental data and model fit). e, Quantum yield of the fibre (both experimental data and its fit) versus the temperature, demonstrating a monotonic decrease with increasing temperature. The Auger rate constant ka is largely responsible for the strong decrease in the quantum yield with temperature. f, Temperature dependence of all of the first- and second-order rate constants in the system, calculated from theory (kr,(6,5),kr,(7,6)) or from numerical simulations based on the model developed (kEET,kd,ka). Inset: The dependence of the activation barrier of both kd and ka on temperature.

  3. Spatially resolved, temperature-dependent photoluminescence behaviour under an in-house-built dual-channel microscope.
    Figure 3: Spatially resolved, temperature-dependent photoluminescence behaviour under an in-house-built dual-channel microscope.

    a, Temperature-evolutional, high-resolution near-infrared photoluminescence intensity maps of the total relative density around a fibre suspended on a thermal-isolation microscope stage blanketed with continuous, ultrahigh-purity N2 (>99.999%) with a flow rate of 3 l min−1. b, Normalized differential intensity contour plots of the same fibre, mapping spatial variations with temperature in the local emission energy (see main text and Supplementary S6 for details). c, A detailed close-up of the photoluminescence intensity along the fibre axis showing a reversible recovery of the energy with temperature.

  4. Development of an exciton antenna from a core–shell carbon nanotube structure.
    Figure 4: Development of an exciton antenna from a core–shell carbon nanotube structure.

    a, An optical image of the exciton antenna (scale bar, 2 μm) with a schematic. b, A top view of the antenna structure, where the curved black arrows indicate the inward EET on photoexcitation. c, The resulting excitation profile, demonstrating the dominant emission produced from the smallest-bandgap element (8,7) on photoexcitation over a broad range extending from ultraviolet to near-infrared wavelengths. d, Experimental data showing the photoluminescence intensity for each type of SWNT in the exciton antenna for excitation at 570 nm and at room temperature.


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Author information

  1. These authors contributed equally to this work

    • Jae-Hee Han &
    • Geraldine L. C. Paulus


  1. Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Jae-Hee Han,
    • Geraldine L. C. Paulus,
    • Daniel A. Heller,
    • Paul W. Barone,
    • Chang Young Lee,
    • Moon-Ho Ham,
    • Changsik Song &
    • Michael S. Strano
  2. Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Jae-Hee Han,
    • Chang Young Lee &
    • Michael S. Strano
  3. Advanced Material Laboratories, Sony Corporation, Kanagawa, 243-0021, Japan

    • Ryuichiro Maruyama
  4. Department of Energy and Biological Engineering, Kyungwon University, Seongnam, Gyeonggi-do 461-701, South Korea

    • Woo-Jae Kim
  5. School of Mechanical Engineering, Birck Nanotechnology Center, Bindley Bioscience Center, Purdue University, West Lafayette, Indiana 47907, USA

    • Jong Hyun Choi
  6. Departamento de Fı´sica, Universidade Federal de Minas Gerais, Belo Horizonte, MG 30123-970, Brazil

    • C. Fantini


M.S.S. and J-H.H. conceived and designed the experiments. J-H.H. and G.L.C.P. carried out the experiments and theoretical calculation, and J-H.H., G.L.C.P. and M.S.S. analysed the data. D.A.H. designed and built the in-house dual-channel microscope. R.M., D.A.H., W-J.K., P.W.B., C.Y.L., J.H.C., M-H.H., C.S. and C.F. partly assisted in doing experiments and commented on the results. J-H.H., G.L.C.P. and M.S.S. wrote the paper.

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