Can contamination of the environment by dioxins cause craniofacial defects?

Cleft lip and cleft palate also known as orofacial cleft is a congenital malformation involving the partial or total lack of anatomical continuity of craniofacial tissue. The most common environmental factors that may cause orofacial clefts include pharmaceuticals, alcohol, addictive drugs, and tobacco smoke. Living in the area of industrial factories, garbage, ironworks, crematoria, wastewater treatment plants, and plastic waste landfills also has a significant impact on the development of the craniofacial defects. Some of the main factors causing the formation of congenital craniofacial defects are dioxins, of which emission to the environment is an important environmental and health problem. Dioxins are a diverse group of organic chemical compounds, derivatives of oxanthrene and fumarates, which are organoleptically imperceptible. Acting mainly through induction of inflammation, they influence a number of metabolic processes, including the process of bone mineralization and embryonic development. In this work, we highlight the problem of orofacial cleft including the impact of dioxin on development of this defect and the recommended prevention.

Enhancement of photoluminescence from GaInNAsSb quantum wells upon annealing: improvement of material quality and carrier collection by the quantum well.

In this study we apply time resolved photoluminescence and contactless electroreflectance to study the carrier collection efficiency of a GaInNAsSb/GaAs quantum well (QW). We show that the enhancement of photoluminescence from GaInNAsSb quantum wells annealed at different temperatures originates not only from (i) the improvement of the optical quality of the GaInNAsSb material (i.e., removal of point defects, which are the source of nonradiative recombination) but it is also affected by (ii) the improvement of carrier collection by the QW region. The total PL efficiency is the product of these two factors, for which the optimal annealing temperatures are found to be ~700 °C and ~760 °C, respectively, whereas the optimal annealing temperature for the integrated PL intensity is found to be between the two temperatures and equals ~720 °C. We connect the variation of the carrier collection efficiency with the modification of the band bending conditions in the investigated structure due to the Fermi level shift in the GaInNAsSb layer after annealing.

Model of hopping excitons in GaInNAs: simulations of sharp lines in micro-photoluminescence spectra and their dependence on the excitation power and temperature.

The model of hopping excitons in semiconductors proposed by Baranovskii et al (1998 Phys. Rev. B 58 13081) has been modified and applied to explain sharp lines observed in micro-photoluminescence (µ-PL) spectra of GaInNAs alloys and their changes with excitation power and temperature. Instead of two types of recombination centres (radiative and nonradiative centres) introduced by Baranovskii et alwe have proposed one kind of localization centre with radiative and nonradiative rates. Such a modification is justifiable due to our recent experimental observations for GaInNAs alloys and allows us to explain the fast thermal quenching of localized emission from this alloy. Our simulations clearly show that the individual sharp PL lines observed at low temperatures appear for this material due to exciton hopping between localization centres. Taking into account saturation effects and the exciton dissociation phenomenon, it has been shown that the observed changes in power- and temperature dependent µ-PL spectra can be excellently reproduced by the modified model.