The selective detection of metal ions in water, using sustainable detection systems, is of crescent importance for monitoring water environments and drinking water safety. One of the key elements of future chemical sciences is the use of sustainable approaches in the design of new materials. In this study, we design and synthesize a low-cost, water-soluble potassium salt of 3,4,9,10-perylene tetracarboxylic acid (PTAS), which shows a selective optical response on the addition of Cu2+ and Pb2+ ions in aqueous solutions. By using a water-soluble chromophore, the interactions with the metal ions are definitely more intimate and efficient, with respect to standard methods employing cosolvents. The detection limits of PTAS for both Cu2+ and Pb2+ are found to be 2 mu M by using a simple absorbance mode, and even lower (1 mu M) with NMR experiments, indicating that this analyte-probe system is sensitive enough for the detection of copper ions in drinking water and lead ions in waste water. The complexation of PTAS with both ions is supported with NMR studies, which reveal the formation of new species between PTAS and analytes. By combining a low-cost water-soluble chromophore with efficient analyte-probe interactions due to the use of aqueous solutions, the results here obtained provide a basis for designing sustainable sensing systems.

We report a computational study and analysis of the optical absorption and photodecay processes in two subnanometer metal complexes deposited on an oxide support, the regular MgO(100) surface: (i) Ag3(HCO3)(C2H4)2(O) and (ii) Ag3(CO2F)(C2H4)2(O). These aggregates are chosen as derivatives of a Ag3(CO3)(C2H4)2(O) ligand/metal-cluster/support complex, previously singled out as a key intermediate in the path of ethylene partial oxidation to ethylene epoxide catalyzed by Ag3/MgO(100), and serve as model systems to investigate photochemical phenomena in ligand/metal-cluster/support complexes by subnanometer metal catalysts, an appealing field for future research. After generating optimized initial configurations and building cluster models that take properly into account the effect of the charge-separated oxide support, we use time-dependent density-functional theory (TDDFT) to determine first the photoabsorption spectra of the two aggregates and then to follow the evolution of their excited states in the optical region. We show that complexes containing such bicarbonate and fluorocarbonate groups are sensitive to optical adsorption, often leading to ligand detachment and/or cluster disaggregation, thus pointing to an "optical frailty"of these subnanometer cluster species, possibly rationalizing previous experimental observations. Additionally, we correlate the nature of the given excitations and of the corresponding photoinduced reaction products via an analysis of overlap population-density of states (OP-DOS), geometric parameters, and spatial distribution of the molecular orbitals involved in the excitation, thus providing the set of methodological tools needed to explore this novel field.

We have studied the effects of optical-frequency light on proximitized InAs/Al Josephson junctions based on highly n-doped InAs nanowires at varying incident photon flux and at three different photon wavelengths. The experimentally obtained IV curves were modeled using a resistively shunted junction model which takes scattering at the contact interfaces into account. Despite the fact that the InAs weak link is photosensitive, the Josephson junctions were found to be surprisingly robust, interacting with the incident radiation only through heating, whereas above the critical current our devices showed non-thermal effects resulting from photon exposure. Our work indicates that Josephson junctions based on highly-doped InAs nanowires can be integrated in close proximity to photonic circuits. The results also suggest that such junctions can be used for optical-frequency photon detection through thermal processes by measuring a shift in critical current.

The question of optical bandgap anisotropy in the monoclinic semiconductor beta-Ga2O3 was revisited by combining accurate optical absorption measurements with theoretical analysis, performed using different advanced computation methods. As expected, the bandgap edge of bulk beta-Ga2O3 was found to be a function of light polarization and crystal orientation, with the lowest onset occurring at polarization in the ac crystal plane around 4.5-4.6 eV; polarization along b unambiguously shifts the onset up by 0.2 eV. The theoretical analysis clearly indicates that the shift in the b onset is due to a suppression of the transition matrix elements of the three top valence bands at Gamma point.

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The absorption of electromagnetic waves has always attracted a large interest because of its cross-the-board nature that spans from microwave to optical frequencies in both linear and nonlinear regimes. At the same time, the experimental isolation of bi-dimensional (2D) materials has recently unveiled how single layers might also be very attractive because of their unprecedented optical and absorption properties. In particular, graphene, a 2D version of graphite, exhibits a remarkably high absorption value (~2.3%) in the visible range [1] when compared to metals or dielectric materials. In this paper, we will review and illustrate the quest for the enhanced absorption in photonic nanostructures that incorporate monolayer and multilayer graphene sheets emphasizing the difference in terms of configurations and strategies proposed in literature. Then, we will detail the optical performance of graphene-based one-dimensional (1D) gratings that support guided mode resonances showing how it is possible to tune theoretically and experimentally their total absorption ranging from 2.3% to perfect absorption by means of metallic and dielectric reflectors or engineered super cells.

Dark blue aquamarine and beryl were discovered at the True Blue showing in the southern Yukon Territory in 2003. Electron-microprobe-derived compositions show up to 5.39 wt.% FeO in the darkest material, which is among the highest Fe concentration known for true beryl. The Al site totals average 2.05, with a maximum of 2.10 apfu, which implies that there is more Fe present in the sample than can be accommodated at the Al position. Charge-balance considerations and Mossbauer spectra show that the Fe is present as both Fe(2+) and Fe(3+). Optical absorption and Mossbauer spectra and the results of the X-ray and neutron single-crystal refinements suggest that there is very little Fe at the tetrahedral or channel sites. Previous investigators have proposed that the color of blue beryl is due to intervalence charge-transfer (IVCT) between Fe(2+) and Fe(3+) cations. The anisotropy of the optical absorption spectra suggest that if the mechanism responsible for the color in our samples is IVCT, the vector between the ions involved must be oriented approximately parallel to c. The only vectors that fulfill this condition and have a realistic length (2.300 angstrom) are 4d-Al and 6g-Be. Given the close proximity of the Si positions (closer than any anion sites), it is difficult to conceive of the substitution taking place at the interstitial 4d site. However, Fe could substitute at the interstitial 6g position, but likely only in very small amounts, because of the need to maintain local charge-balance. Unfortunately, there is no evidence of this in the Mossbauer spectra or in difference-Fourier maps of the X-ray-and neutron-diffraction data. For the former technique, it is likely that any doublet arising from Fe in the 6gO(6) polyhedron is too similar to the Fe in the AlO(6) octahedra to be resolved for either Fe(2+) or Fe(3+). Calculations suggest that the concentration of Fe involved in the IVCT process is 0.08 apfu Fe, of which half (0.04 apfu, 0.17 e(-)) would potentially be at the interstitial site. This amount of electrons and this nuclear density are likely too small to be seen on the difference-Fourier maps.