The performance of chemically synthesized lead sulfide ͑PbS͒ quantum dots ͑QDs͒ in planar, nontracking luminescent solar concentrators ͑LSCs͒ is evaluated using spectroscopic and photovoltaic techniques. Spatially resolved measurements are used to investigate and analyze the role of reduced self-absorption on the LSC efficiency. From comparative measurements of samples with Rhodamine B and CdSe/ZnS QDs it is established that PbS LSCs generate nearly twice the photocurrent in silicon cells than the other materials, achieving an integrated optical efficiency of 12.6%. This is attributed primarily to the broadband absorption of PbS which allows optimum harvesting of the solar spectrum.

Membrane protein lateral diffusion can be constrained in several ways: Diffusion can be slower than that predicted for a simple, fluid lipid bilayer; diffusion can be confined to certain regions within the total membrane; and diffusion may not be equally probable in all directions, i.e. it may be anisotropic. We know that protein diffusion is reduced by increasing concentrations of membrane proteins and by interactions of the diffusant with structure(s) peripheral to the membrane. The molecular nature of such peripheral constraints has been difficult to pinpoint, but attention is now being directed to the extracellular matrix in addition to the membrane-associated cytoskeleton. There are many proteins that are confined to lateral domains in differentiated, isolated cells and in cells organized into tissue. The mechanisms that maintain such inhomogeneous distributions should be elucidated in the next few years. Whether lateral diffusion of membrane proteins over distances of a few micrometers is usually isotropic or anisotropic will be ascertained in the near future using imaging methods combined with photobleaching.

We investigate the performance of cylindrical luminescent solar concentrators (CLSCs) with near-infrared lead sulfide quantum dots (QDs) in the active region. We fabricate solid and hollow cylinders from a composite of QDs in polymethylmethacrylate, prepared by radical polymerization, and characterize sample homogeneity and optical properties using spectroscopic techniques. We additionally measure photo-stability and photocurrent outputs under both laboratory and external ambient conditions. The experimental results are in good agreement with theoretical calculations which demonstrate that the hollow CLSCs have higher absorption of incident radiation and lower self-absorption compared to solid cylindrical and planar geometries with similar geometric factors, resulting in a higher optical efficiency.

We study photo-induced static and dynamic spectral changes in self-assembled CdSe=ZnS quantum dot (QD) thin films with varying QD concentrations under ambient conditions. Using spatially resolved scanning photoluminescence microscopy in conjunction with spectrally resolved time-correlated photon counting, we measure the variations in spectral intensity, emission wavelength, and recombination lifetimes as functions of photo-exposure time. We find that at low concentrations photo-darkening and photo-oxidation rates slow down with increasing QD density, but in the high concentration limit these rates are strongly enhanced. Our measurements lead us to conclude that the interplay of photo-induced surface trap discharging with preferential photo-oxidation of smaller QDs is further modulated by resonant energy transfer driven by strong inter-dot interactions in highly concentrated samples. Our results would imply that the efficiency and longevity of semiconducting nanoparticle based opto-electronic devices will be limited by the concentration of the active material V C 2011 American Institute of Physics.

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SUMMARY The use of low‐light‐level video cameras and solid‐state image detectors in conjunction with image digitizers for optical microscopy is increasing dramatically as more people learn about such systems, and as they become more powerful, less expensive, and easier to use. However, there is currently little information available allowing comparison between cameras, or for determining camera suitability for a given experiment. In this paper, we describe a series of tests designed to characterize the performance of low‐light‐level cameras. The results of these tests should assist in the selection of appropriate cameras for given video microscopy applications.

We demonstrate the formation and spatial modulation of strongly coupled gallium selenide quantum dot ͑QD͒ nanoassemblies suspended in a nematic liquid-crystal ͑NLC͒ matrix at room temperature. Using static and dynamic optical techniques we show that the coupled QDs aggregate with a well-defined directionality commensurate with the NLC director axis. This results in highly anisotropic spectral properties of the QD assembly. The spatial orientation of the aggregates is selectively controlled in situ by the application of in-plane electric fields. The strong interdot coupling further increases the excitonic recombination rate which is both direction and electric field dependent. This electrical modulation, a noninvasive process, could potentially be an important functionality for the design and creation of building blocks for novel optoelectronic devices.

We demonstrate increased intra-ensemble energy transfer (ET) in monodispersed semiconducting quantum dots (QDs), mediated by localized plasmons on metallic thin films with nano-scale wrinkles. The increased ET results in a net spectral red-shift, up to threefold increase in emission intensity, and a faster radiative recombination rate of the ensemble. The extent of the red-shift is dependent on QD size, and is largest for the QDs where the absorption spectrum overlaps the plasmonic resonance of the film. This effect has a uniform, macroscopic manifestation and may provide an inexpensive option of improving performance of QD based photovoltaic devices.