Excitonic absorption and Urbach's tail in bismuth sulfide single crystals

The absorption coefficient of bismuth sulfide single crystals has been measured through more than four orders of magnitude and in the range of energies from 1.25 to 1.70 eV. A detailed study as a function of temperature has been carried out from 29 to 300 K. An Urbach tail for low values of absorption has been found. This tail and its temperature evolution fit the expression for ionic materials. An excitonic region appears at low temperature and the shape of the exciton peak is Gaussian, which corresponds to a strong exciton-phonon coupling. The exciton binding energy is estimated (28±3 meV) and then the energy gap at 29 K is obtained (E _g =1.523±0.003 eV). The fundamental electronic transition has been found to be a strongly anisotropic allowed direct transition. From reflectivity measurements a localized level at 1.361 eV at 29 K has been found. The change of the gap with temperature is interpreted through an electron-phonon mechanism.     

Tin-related shallow donor in indium selenide

Hall-effect measurements in indium selenide samples doped with different amounts of tin are reported. The temperature dependance of free-electron concentration is interpreted through a single-donor single-acceptor model from which the ionisation energy of the tin related shallow donor (22 meV) and the compensation ratio are obtained. At low temperature the electron concentration departs from activated behaviour and tends to be constant. This can be interpreted through the existance of two-dimensional subbands related to interlayer planar aggregates of donor impurities that are located in energy below the tin-related donor level.     

Tetrahedral versus octahedral Mn site coordination in wurtzite and rocksalt Zn1−xMnxO investigated by means of XAS experiments under high pressure

We present the results of x-ray absorption measurements carried out in Zn_1−xMn_xO thin films under high pressure. The Mn environment remains essentially the same for nominal Mn concentrations given by x=0.05, 0.1, 0.15 and 0.25. Both the XANES (X-ray Absorption Near Edge Structure) and EXAFS (Extended X-ray Absorption Fine Structure) indicate that Mn occupies the Zn site, being surrounded by four oxygen atoms at 2.02±0.01 Å. The substitutional hypothesis is reinforced by comparing the differences between the ambient (wurtzite) and high pressure (rocksalt) spectra, which correspond to tetrahedral and octahedral Mn environments.     

Effect of Enzymatic Digestion of Protein Derivatives Obtained from <Emphasis Type="Italic">Mucuna pruriens</Emphasis> L. on Production of Proinflammatory Mediators by BALB/c Mouse Macrophages

Inflammation is considered to be a major risk factor for the pathogenesis of chronic non-communicable diseases. Macrophages are important immune cells, which regulate inflammation and host defense by secretion of proinflammatory mediators. Obtaining biopeptides by enzymatic hydrolysis adds value to proteins of vegetative origin, such as Mucuna pruriens L. The present study evaluated the effect of enzymatic digestion of protein derivatives obtained from M. pruriens L. on the production of proinflammatory mediators by BALB/c mouse macrophages. Five different molecular weight peptide fractions were obtained (F?>?10, 5–10, 3–5, 1–3, and <?1 kDa, respectively). At 300 μg/mL, F5–10 kDa inhibited 50.26 and 61.00% NO and H₂O₂ production, respectively. Moreover, F5–10 kDa reduced the IL-6 and TNFα levels to 60.25 and 69.54%, respectively. After enzymatic digestive simulation, F5–10 kDa decreased the inflammatory mediators.     

Molecular and Electronic‐Structure Basis of the Ambipolar Behavior of Naphthalimide–Terthiophene Derivatives: Implementation in Organic Field‐Effect Transistors

A new family of naphthalimide‐fused thienopyrazine derivatives for ambipolar charge transport in organic field‐effect transistors is presented. Their electronic and molecular structures were elucidated through optical and vibrational spectroscopy aided by DFT calculations. The results indicate that these compounds have completely planar molecular skeletons which promote good film crystallinity and low reorganization energies for both electron and hole transport. Their performance in organic field‐effect transistors is compared with twisted and planar naphthaleneamidine monoimide‐fused terthiophenes in order to understand the origin of ambipolarity in this new series of molecular semiconductors.