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Finite size line broadening and superradiance of optical transitions in two dimensional long-range ordered molecular aggregates
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10.1063/1.4813521
/content/aip/journal/jcp/139/4/10.1063/1.4813521
http://aip.metastore.ingenta.com/content/aip/journal/jcp/139/4/10.1063/1.4813521
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

Schematic presentation of a domain of finite size (4 × 4) of the brickwall () phase of PTCDA with indicated unit cell. The S/S transition dipole is indicated on one molecule. In addition interaction energies of this molecule with next neighbor and next-next neighbor molecules are given.

Image of FIG. 2.
FIG. 2.

Fluorescence (FL) and fluorescence excitation (FLE) spectra of PTCDA in the (top) and the diluted () phase (bottom), both measured at a cryostat temperature of 20 K. The excitation wavelengths were 471 nm and 465 nm, respectively, whereas the detection wavelength (λ) for the FLE spectra was 555 nm and 534 nm, respectively.

Image of FIG. 3.
FIG. 3.

Exciton band structure of the phase, calculated for a very large (400 × 400 molecules) domain and representation of the Brillouin zone.

Image of FIG. 4.
FIG. 4.

Comparison of the 0-0 line shape in the fluorescence excitation (FLE) spectra of the and the phase at 20 K (λ = 625 nm and 534 nm, respectively). The spectrum of the phase was shifted by −405 cm for alignment of the peak maxima. The absence of the vibronic modes in the spectrum of the phase, that are seen for the phase, e.g., at 19 660, and 19 700 cm, and 19 840 cm is due to the superradiance of the phase. In addition, a spectrum of a very diluted phase, where the molecules are solely adsorbed at steps sites, is displayed for comparison to illustrate the site broadening of the spectrum of the phase. The peak position of this spectrum was shifted by about −535 cm. For further details see text.

Image of FIG. 5.
FIG. 5.

(a) Comparison of the experimental FLE spectrum (black) of the phase at 20 K and λ = 658 m (black) and calculated spectra for three domains of different sizes ( ) (red) with 4, 7, and 15. The experimental and calculated spectra were aligned at the positions of the peak maxima. For further details see text. (b) Comparison of the experimental FLE spectrum (black) of the phase as above with calculated spectra. The red stick spectrum is the spectrum for a single domain of 7 × 7 molecules. The green spectrum includes additional site disorder. The blue spectrum is the spectrum for a Poissonian distribution of domain sizes with the mean of 7 in the and directions. The purple spectrum is obtained from the blue by convolution with a Lorentzian with a FWHM of 5 cm.

Image of FIG. 6.
FIG. 6.

Fluorescence spectra of the phase as a function of temperature demonstrating the superradiance. The excitation wavelength was 476 nm. The inset shows the number of coherently emitting molecules determined from the enhancement of the 0-0 transition with decreasing temperature. For further details see text.

Image of FIG. 7.
FIG. 7.

Experimental (black) and calculated (red) fluorescence excitation spectra of the 0-0 line of the phase for a domain size ( ) (red) with 7 at three different temperatures (λ = 625 nm (100 K, 160 K) and 548 nm (260 K)). The inset shows the temperature dependence of the parameter Δɛ. Note the compressed scale of the wavenumber axis with respect to Fig. 5(a) .

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/content/aip/journal/jcp/139/4/10.1063/1.4813521
2013-07-22
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Finite size line broadening and superradiance of optical transitions in two dimensional long-range ordered molecular aggregates
http://aip.metastore.ingenta.com/content/aip/journal/jcp/139/4/10.1063/1.4813521
10.1063/1.4813521
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