Optimization of band structure and quantum-size-effect tuning for two-photon absorption enhancement in quantum dots

The two-photon absorption, 2PA, cross sections of PbS quantum dots, QDs, are theoretically and experimentally investigated and are shown to be enhanced with increasing quantum confinement. This is in contrast to our previous results for CdSe and CdTe QDs where the reduced density of states dominated and resulted in a decrease in 2PA with a decrease in QD size. Qualitatively this trend can be understood by the highly symmetric distribution of conduction and valence band states in PbS that results in an accumulation of allowed 2PA transitions in certain spectral regions. We also measure the frequency nondegenerate 2PA cross sections that are up to five times larger than for the degenerate case. We use a k·p four-band envelope function formalism to model the increasing trend of the two-photon cross sections due to quantum confinement and also due to resonance enhancement in the nondegenerate case.     

Development of yarn-guiding equipment for man-made fibre machines

Conclusions Technology has been developed for making yarn-guide equipment from the high-alumina ceramic VK 94-1. Lots of 11 types of yarn-guiding equipment have been made and tested under manufacturing conditions.Technology has been developed for obtaining a definite microgeometry of the yarn-guide equipment surface.Ceramic disks have been made for texturizing-stretching machines.Translated from Khimicheskie Volokna, No. 4, pp. 16–18, July–August, 1989.     

Interactions of 16alpha,17alpha-cyclohexane derivatives of progesterone with the progesterone receptor from rat uterus

Pregna-D'-pentaranes, 16alpha,17alpha-cyclohexanoprogesterone and 6alpha-methyl-16alpha,17alpha-cyclohexanoprogestero ne, were found to specifically interact with the progesterone receptor of soluble fraction from rat uterus. The formation of complexes between 3H-labeled derivatives of these steroids and the protein was complete within 1 to 3 h at 0-4 degreesC. The dissociation of these complexes was a two-phase process, the contribution of the fast dissociating complexes decreasing with increasing preincubation time. The dissociation constant (k-1) values for progesterone, 16alpha, 17alpha-cyclohexanoprogesterone, and 6alpha-methyl-16alpha, 17alpha-cyclohexanoprogesterone complexes with the protein after 1 h preincubation were 6.5 +/- 0.8, 8.8 +/- 5.5, and (16.6 +/- 5.6).10(-4) sec(-1) for the fast phase and 5.1 +/- 0.5, 3.5 +/- 0.8, and (2.8 +/- 0.6).10(-5) sec(-1) for slow phase, respectively. The equilibrium Kd values were 11.7 +/- 2.1, 19.0 +/- 2.0, and 66.1 +/- 14.6 nM for progesterone, 16alpha,17alpha-cyclohexanoprogesterone, and 6alpha-methyl-16alpha,17alpha-cyclohexanoprogestero ne, respectively. The steroids mutually inhibited the binding of their 3H-labeled derivatives to the protein, the inhibition being of competitive type. In the case of [3H]6alpha-methyl-16alpha, 17alpha-cyclohexanoprogesterone, the inhibitory efficacy of progesterone declined with an increase of its concentration; this points to possible heterogeneity of binding sites for the 3H-labeled ligand. The comparison of the results with those obtained by us earlier (Biochemistry (Moscow), 1996, 61, 1034-1041) suggests the existence of significant species differences in progesterone receptor structure within or near the region that interacts with the D-ring of a hormone molecule.     

Engineering the temporal response of photoconductive photodetectors via selective introduction of surface trap states

Photoconductive photodetectors fabricated using simple solution-processing have recently been shown to exhibit high gains (>1000) and outstanding sensitivities ( D* > 10(13) Jones). One ostensible disadvantage of exploiting photoconductive gain is that the temporal response is limited by the release of carriers from trap states. Here we show that it is possible to introduce specific chemical species onto the surfaces of colloidal quantum dots to produce only a single, desired trap state having a carefully selected lifetime. In this way we demonstrate a device that exhibits an attractive photoconductive gain (>10) combined with a response time ( approximately 25 ms) useful in imaging. We achieve this by preserving a single surface species, lead sulfite, while eliminating lead sulfate and lead carboxylate. In doing so we preserve the outstanding sensitivity of these devices, achieving a specific detectivity of 10(12) Jones in the visible, while generating a temporal response suited to imaging applications.     

Sensitive solution-processed Bi2S3 nanocrystalline photodetectors

Solution-processed nanocrystal optoelectronic devices offer large-area coverage, low cost, and compatibility with a wide range of substrates. Recently, photodetectors and photovoltaics based on spin-coated nanoparticle films have shown tremendous progress in performance. However, high-performance devices reported to date have employed either Pb or Cd, raising concerns regarding environmental impact and regulatory acceptance. Herein we report a high-performance solution-processed photodetector based instead on Bi2S3 nanocrystals. The devices exhibit photoconductive gain on the order of 10 combined with temporal response on the 10 ms time scale. The resultant solution-processed Bi2S3 nanorod photoconductive photodetectors are of interest in visible and near-infrared (NIR) wavelength applications requiring video-frame-rate temporal response.