~u t h o r for correspondence, facsimile: +30 314 2 1122.Abstract. Measurements of time-resolved fluorescence decay, laser-flash-induced absorption changes in the UV and at 820 nm and of the relative fluorescence quantum yield in different preparations (thylakoids, photosystem 11 (PSII) membrane fragments and PSII core complexes) from spinach led to a number of conclusions. (I) Light is transformed into Gibbs energy with trapping times of 250 ps and 130 ps in open reaction centres of PSII membrane fragments and PSII core complexes, respectively. Assuming rapid Boltzmann distribution of excitation energy and taking into account the antenna properties (size and spectral distribution), the molecular rate constant of primary charge separation is estimated to be about (3 ps)-'. (2) The electron transfer from Pheo-to Q, is characterised by a rate constant of (300 p -' . (3) The Q i reoxidation kinetics are significantly retarded in D20 suspensions. These HID isotope effects are interpreted as to reflect hydrogen-bond dependent changes in the protein dynamics that are relevant to electron transfer. (4) In PSII reaction centres closed for photochemical trapping the yield of a primary radical pair with lifetimes exceeding 1 ns is comparatively small (c 30%) at room temperature. Short illumination in the presence of Na2S204 changes the radical pair dynamics. (5) Photoinhibition under aerobic conditions impairs the primary charge separation and leads to formation of quencher(s) of excitation energy.

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We propose a new kind of optical spatial solitons in biased photovoltaicphotorefractive materials when the self-trapping beam couples coherently with a pump beam by codirectional degenerate two-wave mixing. Such solitons are a result of double balance, i.e., loss is balanced by gain provided by the pump beam via two-wave mixing, and diffraction is balanced by nonlinearity that is due to the spatially nonuniform screening of the applied field, the photovoltaic effect, and the periodic modulation of the refractive index via two-wave mixing. These solitons possess some unique properties, are stable relative to small perturbations, and can become screening-photovoltaic solitons if the pump beam is switched to a background illumination.

The energy relaxation of excitons in the organic semiconductor tetracene (film thickness 160 nm) is studied by photoluminescence from 15 to 300 K using time-correlated single-photon counting. The well-known relaxation of triplet excitons with time constant ∼7 ns is accompanied by a faster relaxation process with time constants ranging from 260 ps to 1.2 ns, depending on temperature and wavelength.

We have measured the time-resolved decay of photoexcited carriers in InGaAsP subsequent to mode-locked laser pulse excitation at 1.06 μ. Carrier decay rates were evaluated from bleaching recovery and luminescence decay measurements as a function of injected carrier density over a two-decade range (1017–1019 cm−3). At low and moderate density the decay rate follows the variation with excitation expected for radiative decay. At high carrier density (above 2×1018 cm−3), the decay rate increases more rapidly with carrier density, indicating the onset of nonradiative recombination which can be accounted for by Auger recombination with an Auger coefficient of A=2.3±1×10−29 cm6 s−1. This compares to the calculated Auger coefficient range of 0.7–1.4×10−28 cm6 s−1. We discuss the influence of our measured decay rates on the threshold temperature dependence of InGaAsP-1.3 μ lasers by calculating expected T0 values, using a range of representative values for threshold carrier density and temperature dependence of the Auger decay rate. Our results suggest that while Auger recombination does contribute to the temperture dependence of the InGaAsP-1.3 μ laser it may not alone fully account for the observed room- temperature T0 values.