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Justin M. Hodgkiss - One of the best experts on this subject based on the ideXlab platform.

  • Capturing ultrafast spectral evolution with transient grating Photoluminescence Spectroscopy
    Proceedings of SPIE, 2016
    Co-Authors: Kai Chen, Joseph K. Gallaher, Shyamal K. K. Prasad, James E. A. Webb, Pall Thordarson, Justin M. Hodgkiss
    Abstract:

    We have developed a new method, transient grating Photoluminescence Spectroscopy (TGPLS), allowing the collection of broadband ultrafast Photoluminescence Spectroscopy with low Photoluminescence background. In TGPLS, two ultrafast laser pulses generate a multiplexed transient grating (TG) by the optical Kerr effect. The gated signal is diffracted by the TG and spatially separated from background fluorescence. This high performance nonlinear optical gate delivers time resolution less than 200 fs, spectral bandwidth covering the entire visible region with extremely low fluorescence background. Here we present two applications of TGPLS that provide deeper insight into ultrafast energy transfer in multi-chromophore perylene arrays and ultrafast structural relaxation in oligothiophenes.

  • Transient Grating Photoluminescence Spectroscopy: An Ultrafast Method of Gating Broadband Spectra
    Journal of Physical Chemistry Letters, 2014
    Co-Authors: Kai Chen, Joseph K. Gallaher, Alex J. Barker, Justin M. Hodgkiss
    Abstract:

    Ultrafast Photoluminescence (PL) Spectroscopy can cleanly resolve excited-state dynamics and coupling to the environment, however, there is a demand for new methods that combine broadband detection and low backgrounds. We present a new method, transient grating Photoluminescence Spectroscopy (TGPLS), that addresses this challenge by exploiting a focusing geometry where ultrafast broadband spectra are transiently diffracted away from the background PL. We show that TGPLS can resolve the complex spectral relaxation observed in conjugated polymer and oligomer solutions, with an essentially flat spectral response throughout the visible region and potentially beyond. The benefits we demonstrate using TGPLS could expand access to spectral information, particularly for other multichromophoric and heterogeneous materials where complex spectral relaxation is expected.

  • broadband ultrafast Photoluminescence Spectroscopy resolves charge photogeneration via delocalized hot excitons in polymer fullerene photovoltaic blends
    Journal of the American Chemical Society, 2013
    Co-Authors: Kai Chen, Alex J. Barker, Matthew E Reish, Keith C Gordon, Justin M. Hodgkiss
    Abstract:

    Conventional descriptions of excitons in semiconducting polymers do not account for several important observations in polymer:fullerene photovoltaic blends, including the ultrafast time scale of charge photogeneration in phase separated blends and the intermediate role of delocalized charge transfer states. We investigate the nature of excitons in thin films of polymers and polymer:fullerene blends by using broadband ultrafast Photoluminescence Spectroscopy. Our technique enables us to resolve energetic relaxation, as well as the volume of excitons and population dynamics on ultrafast time scales. We resolve substantial high-energy emission from hot excitons prior to energetic relaxation, which occurs predominantly on a subpicosecond time scale. Consistent with quantum chemical calculations, ultrafast annihilation measurements show that excitons initially extend along a substantial chain length prior to localization induced by structural relaxation. Moreover, we see that hot excitons are initially highly ...

Kai Chen - One of the best experts on this subject based on the ideXlab platform.

  • Capturing ultrafast spectral evolution with transient grating Photoluminescence Spectroscopy
    Proceedings of SPIE, 2016
    Co-Authors: Kai Chen, Joseph K. Gallaher, Shyamal K. K. Prasad, James E. A. Webb, Pall Thordarson, Justin M. Hodgkiss
    Abstract:

    We have developed a new method, transient grating Photoluminescence Spectroscopy (TGPLS), allowing the collection of broadband ultrafast Photoluminescence Spectroscopy with low Photoluminescence background. In TGPLS, two ultrafast laser pulses generate a multiplexed transient grating (TG) by the optical Kerr effect. The gated signal is diffracted by the TG and spatially separated from background fluorescence. This high performance nonlinear optical gate delivers time resolution less than 200 fs, spectral bandwidth covering the entire visible region with extremely low fluorescence background. Here we present two applications of TGPLS that provide deeper insight into ultrafast energy transfer in multi-chromophore perylene arrays and ultrafast structural relaxation in oligothiophenes.

  • Transient Grating Photoluminescence Spectroscopy: An Ultrafast Method of Gating Broadband Spectra
    Journal of Physical Chemistry Letters, 2014
    Co-Authors: Kai Chen, Joseph K. Gallaher, Alex J. Barker, Justin M. Hodgkiss
    Abstract:

    Ultrafast Photoluminescence (PL) Spectroscopy can cleanly resolve excited-state dynamics and coupling to the environment, however, there is a demand for new methods that combine broadband detection and low backgrounds. We present a new method, transient grating Photoluminescence Spectroscopy (TGPLS), that addresses this challenge by exploiting a focusing geometry where ultrafast broadband spectra are transiently diffracted away from the background PL. We show that TGPLS can resolve the complex spectral relaxation observed in conjugated polymer and oligomer solutions, with an essentially flat spectral response throughout the visible region and potentially beyond. The benefits we demonstrate using TGPLS could expand access to spectral information, particularly for other multichromophoric and heterogeneous materials where complex spectral relaxation is expected.

  • broadband ultrafast Photoluminescence Spectroscopy resolves charge photogeneration via delocalized hot excitons in polymer fullerene photovoltaic blends
    Journal of the American Chemical Society, 2013
    Co-Authors: Kai Chen, Alex J. Barker, Matthew E Reish, Keith C Gordon, Justin M. Hodgkiss
    Abstract:

    Conventional descriptions of excitons in semiconducting polymers do not account for several important observations in polymer:fullerene photovoltaic blends, including the ultrafast time scale of charge photogeneration in phase separated blends and the intermediate role of delocalized charge transfer states. We investigate the nature of excitons in thin films of polymers and polymer:fullerene blends by using broadband ultrafast Photoluminescence Spectroscopy. Our technique enables us to resolve energetic relaxation, as well as the volume of excitons and population dynamics on ultrafast time scales. We resolve substantial high-energy emission from hot excitons prior to energetic relaxation, which occurs predominantly on a subpicosecond time scale. Consistent with quantum chemical calculations, ultrafast annihilation measurements show that excitons initially extend along a substantial chain length prior to localization induced by structural relaxation. Moreover, we see that hot excitons are initially highly ...

Alex J. Barker - One of the best experts on this subject based on the ideXlab platform.

  • Transient Grating Photoluminescence Spectroscopy: An Ultrafast Method of Gating Broadband Spectra
    Journal of Physical Chemistry Letters, 2014
    Co-Authors: Kai Chen, Joseph K. Gallaher, Alex J. Barker, Justin M. Hodgkiss
    Abstract:

    Ultrafast Photoluminescence (PL) Spectroscopy can cleanly resolve excited-state dynamics and coupling to the environment, however, there is a demand for new methods that combine broadband detection and low backgrounds. We present a new method, transient grating Photoluminescence Spectroscopy (TGPLS), that addresses this challenge by exploiting a focusing geometry where ultrafast broadband spectra are transiently diffracted away from the background PL. We show that TGPLS can resolve the complex spectral relaxation observed in conjugated polymer and oligomer solutions, with an essentially flat spectral response throughout the visible region and potentially beyond. The benefits we demonstrate using TGPLS could expand access to spectral information, particularly for other multichromophoric and heterogeneous materials where complex spectral relaxation is expected.

  • broadband ultrafast Photoluminescence Spectroscopy resolves charge photogeneration via delocalized hot excitons in polymer fullerene photovoltaic blends
    Journal of the American Chemical Society, 2013
    Co-Authors: Kai Chen, Alex J. Barker, Matthew E Reish, Keith C Gordon, Justin M. Hodgkiss
    Abstract:

    Conventional descriptions of excitons in semiconducting polymers do not account for several important observations in polymer:fullerene photovoltaic blends, including the ultrafast time scale of charge photogeneration in phase separated blends and the intermediate role of delocalized charge transfer states. We investigate the nature of excitons in thin films of polymers and polymer:fullerene blends by using broadband ultrafast Photoluminescence Spectroscopy. Our technique enables us to resolve energetic relaxation, as well as the volume of excitons and population dynamics on ultrafast time scales. We resolve substantial high-energy emission from hot excitons prior to energetic relaxation, which occurs predominantly on a subpicosecond time scale. Consistent with quantum chemical calculations, ultrafast annihilation measurements show that excitons initially extend along a substantial chain length prior to localization induced by structural relaxation. Moreover, we see that hot excitons are initially highly ...

Yoichi Kawakami - One of the best experts on this subject based on the ideXlab platform.

  • surface plasmon enhanced spontaneous emission rate of ingan gan quantum wells probed by time resolved Photoluminescence Spectroscopy
    Applied Physics Letters, 2005
    Co-Authors: Koichi Okamoto, Axel Scherer, Yukio Narukawa, Isamu Niki, Takashi Mukai, Yoichi Kawakami
    Abstract:

    We observed a 32-fold increase in the spontaneous emission rate of InGaN/GaN quantum well (QW) at 440 nm by employing surface plasmons (SPs) probed by time-resolved Photoluminescence Spectroscopy. We explore this remarkable enhancement of the emission rates and intensities resulting from the efficient energy transfer from electron-hole pair recombination in the QW to electron vibrations of SPs at the metal-coated surface of the semiconductor heterostructure. This QW-SP coupling is expected to lead to a new class of super bright and high-speed light-emitting diodes (LEDs) that offer realistic alternatives to conventional fluorescent tubes.

  • Time-resolved Photoluminescence Spectroscopy in GaN-based semiconductors with micron spatial resolution
    Journal of Luminescence, 2000
    Co-Authors: Tomoaki Izumi, Yukio Narukawa, Koichi Okamoto, Yoichi Kawakami, Sg. Fujita, Shuji Nakamura
    Abstract:

    Abstract Recombination dynamics in GaN-based layers have been studied by means of Photoluminescence Spectroscopy having spectral and spatial resolution. It was found that PL lifetime ( τ PL ) of the epitaxially laterally overgrown GaN (ELO-GaN), which consists of the regions with high (window) and low (wing) threading dislocation density (DD), was dominated by the nonradiative recombination process at room temperature (RT), and that the τ PL measured at wing region (DD=10 6  cm −2 ) was 86 ps which is slightly larger than the value (70 ps) at window region (DD=10 8  cm −2 ). These indicate that threading dislocations limit hardly the emission efficiency even with these DD-levels, and that the device performance is mainly limited by other types of nonradiative recombination centers.

Koichi Okamoto - One of the best experts on this subject based on the ideXlab platform.

  • surface plasmon enhanced spontaneous emission rate of ingan gan quantum wells probed by time resolved Photoluminescence Spectroscopy
    Applied Physics Letters, 2005
    Co-Authors: Koichi Okamoto, Axel Scherer, Yukio Narukawa, Isamu Niki, Takashi Mukai, Yoichi Kawakami
    Abstract:

    We observed a 32-fold increase in the spontaneous emission rate of InGaN/GaN quantum well (QW) at 440 nm by employing surface plasmons (SPs) probed by time-resolved Photoluminescence Spectroscopy. We explore this remarkable enhancement of the emission rates and intensities resulting from the efficient energy transfer from electron-hole pair recombination in the QW to electron vibrations of SPs at the metal-coated surface of the semiconductor heterostructure. This QW-SP coupling is expected to lead to a new class of super bright and high-speed light-emitting diodes (LEDs) that offer realistic alternatives to conventional fluorescent tubes.

  • Time-resolved Photoluminescence Spectroscopy in GaN-based semiconductors with micron spatial resolution
    Journal of Luminescence, 2000
    Co-Authors: Tomoaki Izumi, Yukio Narukawa, Koichi Okamoto, Yoichi Kawakami, Sg. Fujita, Shuji Nakamura
    Abstract:

    Abstract Recombination dynamics in GaN-based layers have been studied by means of Photoluminescence Spectroscopy having spectral and spatial resolution. It was found that PL lifetime ( τ PL ) of the epitaxially laterally overgrown GaN (ELO-GaN), which consists of the regions with high (window) and low (wing) threading dislocation density (DD), was dominated by the nonradiative recombination process at room temperature (RT), and that the τ PL measured at wing region (DD=10 6  cm −2 ) was 86 ps which is slightly larger than the value (70 ps) at window region (DD=10 8  cm −2 ). These indicate that threading dislocations limit hardly the emission efficiency even with these DD-levels, and that the device performance is mainly limited by other types of nonradiative recombination centers.