This paper aims to enhance the up-conversion phenomena observed in silicon solar cells by combining a rare-earth doped phosphor with PbS quantum dots. Two different ways of adhering the up-converter and the fluorescent material to a bifacial solar cell are implemented: dissolving the powder in a spin-on oxide and by dissolving it in a silicone gel. Characterization is carried out through photocurrent and photoluminescence measurements. The improvement in photocurrent detected by the combination of the up-converter and the PbS quantum dots is 60% better than without them, demonstrating that the absorption and emission characteristics of the quantum dots embedded both in the oxide or the silicone can be tuned into [ul]the desired spectral región.

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Laser-induced fluorescence (LIF) spectra of intertidal microphytobenthos (MPB) communities were obtained in the laboratory with a 532 nm pulsed Nd:YAG laser. The laser-induced chlorophyll (chl) fluorescence emission spectra of MPB in mud and sand sediments were characterized by a band in the red region with a maximum at ca. 685 nm. Biomass accumulation on the surface of the mud due to cell migration caused a shift to longer wavelengths (up to 5 nm) of the red emission maximum and the development and increase of an emission shoulder at the far-red region (maximum at ca. 732 nm), probably owing to increased re-absorption of chl fluorescence within the denser microalgae biofilm. Direct relations were observed between MPB biomass proxies (normalized difference vegetation index [NDVI] and phytobenthos index [PI]) and fluorescence intensity. LIF was used to track migratory rhythms of epipelic benthic microalgae in muddy sediments, which are absent in epipsammic communities in sand: progressive accumulation of biomass occurred at the sediment surface during diurnal low tide periods and was followed by a rapid downward migration before tides began to cover the sampling site. When exposed to high light, surface biomass decreased in migratory biofilms, indicating that diatom cells avoid photoinhibitory light levels. This phenomenon is known as behavioral photoprotection. For the first time, LIF was applied to study intertidal MPB communities to adequately describe surface biomass, which included changes due to migration. KEY WORDS: Chlorophyll · Behavioural photoprotection · Benthic diatom · Microalgae biofilmResale or republication not permitted without written consent of the publisher

The aim of the present work was to develop a method for the remote assessment of the impact of fire and drought stress on Mediterranean forest species such as the cork oak (Quercus suber) and maritime pine (Pinus pinaster). The proposed method is based on laser induced fluorescence (LIF): chlorophyll fluo rescence is remotely excited by frequency doubled YAG:Nd laser radiation pulses and collected and analyzed using a telescope and a gated high sensitivity spectrometer. The plant health criterion used is based on the I 685 /I 740 ratio value, calculated from the fluorescence spectra. The method was benchmarked by comparing the results achieved with those obtained by conventional, continuous excitation fluorometric method and water loss gravimetric measurements. The results obtained with both methods show a strong correlation between them and with the weight loss measurements, showing that the proposed method is suitable for fire and drought impact assessment on these two species.

In this work, a systematic study of the influence of growth conditions on the anomalous formation of ternary In x Ga 1-x As nanowires is presented. Free-standing nanowires, of nominal InAs composition, were grown by molecular beam epitaxy on GaAs (111)B substrates at different temperatures and As 4 beam equivalent pressures. The morphology, chemical composition, and crystal structure of the nanowires were investigated by scanning electron microscopy, X-ray energy dispersive spectroscopy, and X-ray diffraction techniques. It was found that a strong incorporation of Ga occurs during the growth creating a homogeneous ternary In x Ga 1-x As alloy in the nanowires with very low residual strain. The GaAs molar fraction was found to increase with the growth temperature and to decrease with the As 4 beam equivalent pressure. A nanowire growth model, taking into account the creation and diffusion of Ga adatoms from the substrate surface toward the nanowires, was used to explain the incorporation of Ga atoms and the formation of the ternary alloy. This model predicts that the GaAs/InAs composition ratio in the nanowires follows an Arrhenius law as a function of the growth temperature with an inverse square root dependency of the As 4 beam equivalent pressure as a pre-exponential factor. The theory was found to fit well the experimental data with an activation energy of 1 eV. It is also shown that the activation energy corresponds to the energy necessary to create Ga adatoms on the surface of the GaAs (111)B substrate. Both experimental and theoretical results show that in this range of growth conditions the limiting factor for the formation of the In x Ga 1-x As alloy in the nanowires is not the diffusion length of the Ga and In adatoms on the substrate surface and nanowires side walls but the density of available Ga adatoms on the substrate surface.