In 2013, the international Commission on Atmospheric Chemistry and Global Pollution (iCACGP) and the International Global Atmospheric Chemistry (IGAC) Project Americas Working Group (iCACGP/IGAC AWG) was formed to build a cohesive network and foster the next generation of atmospheric scientists with the goal of contributing to a scientific community focused on building collective knowledge for the Americas. The Latin America–Caribbean (LAC) region shares common history, culture, and socioeconomic issues but, at the same time, it is highly diverse in its physical and human geography. The LAC region is unique because approximately 80% of its population lives in urban areas, resulting in high-density hotspots of urbanization and vast unpopulated rural areas. In recent years, most countries of the region have experienced rapid growth in population and industrialization as their economies emerge. The rapid urbanization, the associated increases in mobile and industrial sources, and the growth of the agricultural activities related to biomass burning have degraded air quality in certain areas of the LAC region. Air pollution has negative implications for human health, ecosystems, and climate. In addition, air pollution and the warming caused by greenhouse gases could impact the melting of Andean glaciers, an important source of freshwater. To better understand the links between air pollution and climate, it is necessary to increase the number of atmospheric scientists and improve our observational, analytical, and modeling capacities. This requires sustained and prioritized funding as well as stronger collaboration within the LAC region.
Continuous wave and time-resolved photoluminescence studies as a function of temperature have been performed on disordered In x Ga 1Àx P/GaAs quantum wells. Simulations of stationary and transient spectra, by using a two-exciton kinetic model, allow the observation of a red shift of the effective mobility edge when temperature increases. From the temperature dependence of the radiative lifetime it can be also deduced that independent localization of electrons and holes seems to be the most likely mechanism for exciton localization in our samples. On the other hand, values ranging from 0.8 to 5.6 ps have been obtained for the radiative lifetime at k k = 0. . The co-existence of localized and free excitons reflected in the two-class exciton kinetic model presented in a previous work [3] seems to describe the experimental results obtained by continuous-wave-(PL) and time-resolved-photoluminescence (TRPL) measurements as a function of temperature in In x Ga 1Àx P/GaAs quantum wells. An effective mobility edge (E ME ) defined by a Fermi function was introduced in that model. In this paper, we present an study of the variation of E ME when temperature increases and, by considering two limiting cases, we try to make a deeper view inside of the exciton in-plane localization nature.
In x Ga 1± ±x P/GaAs (x 0.541 and 0.427) heterostructures, grown by Atomic Layer Molecular Beam Epitaxy (ALMBE) on low temperature substrates, have been characterised by pressure-dependent and time-resolved photoluminescence experiments. The excitonic optical transitions and recombination dynamics are both influenced by the particular band alignments of these systems. The valence band offset has been found to have approximately the same absolute value (DE VB % 380 meV), independent of the In content of the alloy in the barrier, whereas the conduction band offset varies appreciably depending on the alloy band gap. The huge valence band offset implies a strong asymmetry in the confinement of carriers, affecting the exciton recombination dynamics in the quantum wells.
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