Plasmonic surface enhancement of dual fluorescence and phosphorescence emission from organic semiconductors: effect of exchange gap and spin-orbit coupling

Dual singlet-triplet fluorescence-phosphorescence emitting compounds demonstrate that plasmonic surface enhancement is controlled solely by the underlying oscillator strength of a transition: metal-free compounds with weak spin-orbit coupling show no enhancement in phosphorescence efficiency even though fluorescence is amplified.     

Coherent Generation and Detection of Continuous Terahertz Waves Using Two Photomixers Driven by Laser Diodes

We report on a completely coherent, tunable, continuous-wave THz system where, for the first-time, both the transmitter and receiver are log-periodic-antenna coupled LTG-GaAs based finger-photomixers. This compact room-temperature system exhibits signal-to-noise ratios (> 10³) comparable to or better than what is reported in the literature, and has potential applications in high-resolution spectroscopy and imaging. For the purpose of demonstration, we also present results of spectroscopy measurements carried out on fused silica, which are in agreement with previously published THz-TDS measurements.     

Ueber gasanalytische Methoden und Apparate

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Halochrome Molekeln. 7. Mitteilung. Synthese und acidobasisches Verhalten substituierter Heteroarenochinazoline

Halochromic Molecules. Synthesis and Acidobasic Properties of Substituted Heteroarenoquinazolines We have synthetized a series of substituted heteroarenoquinazolines. The 90-MHz FT ¹H-NMR spectra of starting and final products supported the postulated structures. Fragmentation in the mass spectra also were consistant with the assumed structures. With acid, the compounds partly from ring-opened, intensely coloured triphenylcarbenium salts of the Rhoduline-R type (C. I. 42565). UV/VIS spectra of the salts are discussed on the basis of VEPPP-CI calculations. The ?_pH* curves in buffered MeOH/H₂O solutions and the pK* values are determined. The title compounds undergo very complex protonation equilibria.     

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Book reviews

     

Time averages for unpredictable orbits of deterministic systems

In many cases, the orbits of deterministic systems displaying highly irregular oscillations yield smoothly converging time averages. It may happen, however, that these time averages do not converge and themselves display wild oscillations. This is analyzed for heteroclinic attractors and hyperbolic strange attractors.     

Solution of the generalized master equation for an externally driven and environmentally damped two-level system

Using the Generalized Master Equation (GME) we investigate the dynamics of a two-level system which is subjected both to the influence of a thermal reservoir and to an external driving field. The coupling with the phonon reservoir is represented by the usual (energy-conserving) linear-displacements interaction, which makes the model exactly solvable in the absence of the external field. The coupling with the external field is treated within the Rotating Wave Approximation (RWA). We obtain an exact formal solution of the GME and we construct a hierarchical class of weak-driving approximations avoiding usual assumption of a weak coupling to the bath. The populational difference is damped in a nontrivial manner: the relaxation is nonexponential with long-time tail behaviour in the asymptotic region. The evolution is analysed as a function of temperature, the strength of the coupling, the strength of the external field and the detuning. Our model is formally identical to the spin-boson model and our approach gives a systematic improvement of the noninteracting-blip approximation.