We investigated the interactions between localized plasmons in gold nanorods and excitons in J-aggregates and were able to track an anticrossing behavior of the hybridized modes both in the extinction and in the photoluminescence spectra of this hybrid system. We identified the nonlinear optical behavior of this system by transient absorption spectroscopy. Finally using magnetic circular dichroism spectroscopy we showed that nonmagnetic organic molecules exhibit magnetooptical response due to binding to a plasmonic nanoparticles. In our experiments we also studied the effect of detuning as well as the effect of off- and on resonance excitation on the hybrid states
We focus on fabricating organic/inorganic halide perovskites with controlled dimensionality, size and composition and studying the optical and electrical properties of the resulting nanocrystals. By partially exchanging the most commonly used organic cation methylammonium for a cation with a larger chain we are able to fabricate two-dimensional nanoplatelets down to a single unit cell thickness.1 Through absorption and photoluminescence measurements we find that this leads to a strong-quantum size effect in the perovskites while additionally increasing the exciton bind energy to several hundreds of meV. We employ several fabrication techniques to increase the fluorescence quantum yield to be able to investigate single particles, and to study energy transport between individual nanocrystals by time-resolved spectroscopic methods. Our findings can lead to improvements in not only photovoltaic devices, but also for light-harvesting and light-emitting devices, such as LEDs and lasers.
(1) Sichert, J. A.; Tong, Y.; Mutz, N.; Vollmer, M.; Fischer, S.; Milowska, K. Z.; García Cortadella, R.; Nickel, B.; Cardenas-Daw, C.; Stolarczyk, J. K.; Urban, A. S.; Feldmann, J. Nano Letters 2015, 15, 6521.
Strong coupling of plasmons and excitons can form hybrid states, the so called “plexcitons”. Especially with molecular J-aggregated dye molecules strong interaction becomes observable even under ambient conditions. In our work we investigate the nature of plexcitonic states formed in gold nanorods coated with a cyanine dye by transient absorption spectroscopy. We demonstrate that plexcitons show tunable plasmonic and excitonic non-linear optical behaviour. Our experimental data can be explained on the basis of a simple Lorentz oscillator model. We find that both the quality factor and the coupling strength between plasmons and excitons can be optically manipulated on an ultrashort time scale.
T. Simon, D. Melnikau, A. Sánchez-Iglesias, M. Grzelczak, L. Liz-Marzán, Y. Rakovich, J. Feldmann and A. Urban, Exploring the optical non-linearities of plasmon-exciton hybrid resonances in coupled colloidal nanostructures, submitted (2016)
We present a progress report on the design and construction of the Field-Imaging Far-Infrared Line Spectrometer (FIFI LS) for the SOFIA airborne observatory. The design of the instrument is driven by the goal of maximizing observing efficiency, especially for observations of faint, extragalactic objects. Thus, FIFI LS utilizes an integral field technique that uses slicer mirrors to optically re- arrange the 2D field into a single slit for a long slit spectrometer. Effectively, a 5 X 5 pixel spatial field of view is imaged to a 25 X 1 pixel slit and dispersed to a 25 X 16 pixel, 2D detector array, providing diffraction- limited spatial and spectral multiplexing. In this manner, the instrument employs two parallel, medium resolution (R approximately 2000) grating spectrometers for simultaneous observations in two bands: a short wavelength band (42 to 110 micrometers ) and a long wavelength band (110 to 210 micrometers ). Overall, for each of the 25 spatial pixels, the instrument can cover a velocity range of approximately 1500 km/s around selected far-infrared lines with an estimated sensitivity of 2 X 10-15 W Hz1/2 per pixel. This arrangement provides good spectral coverage with high responsivity.
We are developing 2D 16 X 25 pixel detector arrays of both unstressed and stressed Ge:Ga photoconductive detectors for far-infrared astronomy from SOFIA. The arrays, based on earlier 5 X 5 detector arrays used on the KAO, will be for our new instrument, the Far Infrared Field Imaging Line Spectrometer (FIFI LS). The unstressed Ge:Ga detector array will cover the wavelength range from 40 to 120 micrometers , and the stressed Ge:Ga detector array from 120 to 210 micrometers . The detector arrays will be operated with multiplexed integrating amplifiers with cryogenic readout electronics located close to the detector arrays. The design of the stressed detector array and results of current measurements on several prototype 16 pixel linear arrays will be reported. They demonstrate the feasibility of the current concept.
We present our design for a field-imaging, far-infrared line spectrometer for the SOFIA airborne observatory. The instrument will employ two parallel, medium resolution (R approximately 1700) grating spectrometers for simultaneous observations in the wavelength bands 42 - 110 micrometer and 110 - 210 micrometer. The Littrov mounted gratings are operated in first and second order. Large stressed and unstressed 16 X 25 pixel Ge:Ga photoconductor arrays are operated in the spectrometer channel, providing good spectral coverage with high responsivity. Image slicers in each spectrometer branch redistribute the 5 X 5 pixel field of view along the 1 X 25 pixel entrance slits of the spectrographs, providing both, spatial and spectral multiplexing. Thus, for each of the 25 spatial pixels, we are able to cover a velocity range of approximately 1500 km/s around a selected far infrared line, with an estimated sensitivity of approximately 2 X 10-15 W Hz-1/2 per pixel.
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