Analytic Modeling of the of J–V Characteristics of Quantum Dot-Based Photovoltaic Cells

An analytic model of [Formula: see text]–[Formula: see text] characteristics of photovoltaic devices based on quantum dot (QD) solids is developed. The model yields the upper estimation of the power conversion efficiency and predicts its extremal dependence on the diffusion length of excitons. The predictive power of our model is approved by the comparison with the experimental data for PbS QD-based solar cells.

Sol–Gel Fabrication and Luminescence Properties of Multilayer Eu-Doped BaTiO3–SiO2 Xerogel Nanostructures

With the use of sol–gel method BaTiO3–SiO2 multilayer structures were fabricated on glass or fused silica substrates employing dipping or spinning procedure. The photonic stop band was observed in the reflection and transmission spectra of the multilayer structure annealed at [Formula: see text]C. It is redshifted with an increase of the thicknesses of BaTiO3 and SiO2 layers. For structures comprising Eu-doped BaTiO3 layers of different thicknesses photoluminescence with the main band at 614[Formula: see text]nm was detected. It is characterized with the double-exponential decay with the lifetimes of about 0.5[Formula: see text]ms and 1.1[Formula: see text]ms which do not depend significantly on the photonic stop band position.

High-performance aerosol sampler with liquid phase recirculation and pre-concentration of particles

Testing the surrounding environment for the presence of biogenic aerosols is crucial in ensuring its safety for the population. It is often necessary to collect aerosol samples from large areas in short time, which demands excellent particle collection efficiency, a sufficient incoming air flow rate and a capacity to maintain the viability of the collected samples. Below we present the aerosol sampler with a high volumetric flow rate based on a two-stage particle concentration algorithm and consisting of a virtual impactor and a cyclone concentrator with a recirculating liquid phase. We provide all necessary calculations and an algorithm for modeling impactor parameters. The sampler was tested using dry and liquid formulations dispersed into the particles of 0.5 to 5 μm in diameter. We demonstrate that at volumetric flow rates over 4,000 l/min efficiency of particle collection into the liquid phase at a volume of 10 ml makes over 20% of the total aerosol mass and at volumetric flow rates over 300 l/min this value is over 60%. The proposed device maintains viability of the collected microorganisms. The sampler is portable, with flexible settings for sampling and cleaning, and can be controlled remotely over the network.

Comparison of fluorescence excitation modes for cdse semi-conductor quantum dots used in medical research

Fluorescence spectroscopy is a powerful tool used in applied biological and medical research. Colloid semi-conductor quantum dots are promising fluorescent tags for simultaneous detection of different biopathogens. The techniques employing these tags can be improved by selecting the optimal modes for signal excitation and detection. The aim of the present work was to derive a mathematical expression to describe the signal-to-noise ratios in the pulsed and modulated excitation modes. Below, we compare these two modes of fluorescence excitation in ultralow quantities of quantum dots. We demonstrate that modulated excitation should be preferred for CdSe/ZnS quantum dots given that signal accumulation time is over 100 mc and the photosensor is exposed to background light of > 1 μW.

Modeling and Optimization of the Porous Silicon Photonic Structures

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Optoelectronic Properties of Semiconductor Quantum Dot Solids for Photovoltaic Applications

Quantum dot (QD) solids represent a new type of condensed matter drawing high fundamental and applied interest. Quantum confinement in individual QDs, combined with macroscopic scale whole materials, leads to novel exciton and charge transfer features that are particularly relevant to optoelectronic applications. This Perspective discusses the structure of semiconductor QD solids, optical and spectral properties, charge carrier transport, and photovoltaic applications. The distance between adjacent nanoparticles and surface ligands influences greatly electrostatic interactions between QDs and, hence, charge and energy transfer. It is almost inevitable that QD solids exhibit energetic disorder that bears many similarities to disordered organic semiconductors, with charge and exciton transport described by the multiple trapping model. QD solids are synthesized at low cost from colloidal solutions by casting, spraying, and printing. A judicious selection of a layer sequence involving QDs with different size, composition, and ligands can be used to harvest sunlight over a wide spectral range, leading to inexpensive and efficient photovoltaic devices.

Laser ion mobility spectrometry in the detection of ultra-low quantities of explosives

The paper presents the results of research and development of ion mobility spectrometer with laser ion sources for detecting ultra-low quantities of explosives in air. Particular attention is paid to the mechanisms of the formation of negative ions. It is shown that laser ionization with respect to ion mobility spectrometry provides an increase of sensitivity and selectivity of detection. The ion mobility spectra of the most common nitro explosives are investigated. The detection threshold for laser ion mobility spectrometer was reached at the level of 10^-14g/cm³ (for trinitrotoluene).