2 research outputs found
Excitation Energy Dependent Ultrafast Luminescence Behavior of CdS Nanostructures
Selected
semiconductor nanostructures provide extremely localized
coherent light sources. Here an ensemble of CdS nanostructures was
excited by UV/vis femtosecond laser pulses and their ultrafast luminescence
characteristics were investigated as functions of the pulse energy
fluence and the photon quantum energy. All optical Kerr gating enabled
studies of the emission dynamics with a time resolution of 150 fs
avoiding any influence on the CdS emission. The initially observed
emission built up after a delay of 0.1–3 ps and decayed rapidly
in a biexponential way, strongly dependent on both the laser energy
fluence and the quantum energy. The central wavelength of the emission
spectrum revealed a significant blue-shift within the first few ps
followed by a transient red-shift relative to spontaneous excitonic
emission of CdS. All findings are mainly attributed to stimulated
radiative carrier recombination in the laser excited electron–hole
plasma after its thermalization with the CdS lattice
Plasmonic Coupling and Long-Range Transfer of an Excitation along a DNA Nanowire
We demonstrate an excitation transfer along a fluorescently labeled dsDNA nanowire over a length of several micrometers. Launching of the excitation is done by exciting a localized surface plasmon mode of a 40 nm silver nanoparticle by 800 nm femtosecond laser pulses <i>via</i> two-photon absorption. The plasmonic mode is subsequently coupled or transformed to excitation in the nanowire in contact with the particle and propagated along it, inducing bleaching of the dyes on its way. <i>In situ</i> as well as <i>ex situ</i> fluorescence microscopy is utilized to observe the phenomenon. In addition, transfer of the excitation along the nanowire to another nanoparticle over a separation of 5.7 μm was clearly observed. The nature of the excitation coupling and transfer could not be fully resolved here, but injection of an electron into the DNA from the excited nanoparticle and subsequent coupled transfer of charge (Dexter) and delocalized exciton (Frenkel) is the most probable mechanism. However, a direct plasmonic or optical coupling and energy transfer along the nanowire cannot be totally ruled out either. By further studies the observed phenomenon could be utilized in novel molecular systems, providing a long-needed communication method between molecular devices