Luminescence concentration quenching in Gd2O3:Eu(3+) nanocrystals results from strong interactions among O(2-) ions and Eu(3+) ions. Because all synthesized Gd2O3:Eu(3+) nanocrystals present the same cubic crystalline phase regardless of Eu(3+) concentration, it is possible to study the optical properties as a function of the dopant concentration. The emission intensities and lifetime curves for Gd2O3:Eu(3+) were analyzed by a simple rate equation model to study the interaction between the O(2-) ions and Eu(3+) ions. The rate equation model considers that such interaction is driven by the following energy transfer processes: the direct energy transfer (O(2-) → Eu(3+)), back-transfer (Eu(3+) → O(2-)), and direct energy migration (Eu(3+) → Eu(3+)). The exact solution of this model agrees with the experimental results, luminescence concentration quenching is reproduced and the corresponding energy transfer rates are reported. Quantitative results suggest that the direct energy transfer and direct energy migration processes are the main responsible for the luminescence concentration quenching, whereas the back-transfer process promotes the Eu(3+) emission.

Ag/TiO 2 nanocomposites are usually regarded as an effective synergy for high antimicrobial performance under ultraviolet-visible light conditions. This study confirmed that the surface plasmon resonance of Ag NPs plays an important role in relation to the NPs size and consequently with the antibacterial effect of the nanocomposite. We observed that under visible light the reactivity of TiO 2 cannot be amplified when it is supporting Ag NPs that have an inactive photocatalytically surface. The results confirmed that the antimicrobial effectiveness of nanocomposite based on Ag NPs supported-TiO 2 is closely associated to the contact surface area and to the electronic performance of the noble metal.

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Summary In the present work, porous supports from carbonized agave flower stalk (CAFS) were prepared and tested in solar water evaporation. These supports were characterized by FTIR and UV/Vis spectroscopies, and their morphology and structure were determined by SEM microscopy. The results of these studies showed a wide absorption range in the UV/Vis‐NIR (200‐1100 nm), consisting of structures with micropores and well oriented microchannels whose morphology resembles micro‐packed bed distillation columns. Pure water evaporation efficiency of CAFS was studied as a function of the thickness of the support and its diameter under visible light irradiation at different power density. It was observed that optimal thickness of the support is 4.05 mm with 1.99 kg h−1 m−2 of evaporation rate and 97.5% of efficiency under 1300 W m−2 of illumination, therefore, this support was tested in the simulated seawater evaporation (3.5% NaCl) with multiple evaporation cycles under 1300 W m−2 of light irradiation, achieving 1.91 kg h−1 m−2 of evaporation rate and 93% of efficiency, which demonstrates that this material is comparable to its synthetic counterparts and opens a possible new line of commercial use of agave sub product.