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Flexible glass photonics is a cutting-edge technological and scientific research field that, thanks to a very broad spectrum of applications, has tremendously grown during the last decade and is now a strategic topic. Here, we present the results of the spectral transmittance and reflectance of a 10-layer SiO2/TiO2 1D photonic crystal deposited on a flexible polymeric substrate under different bending conditions, obtained with a home-made adjustable sample holder.

Flexible SiO2/HfO2 1D photonic crystals and active SiO2–HfO2:Er3+ all-glass flexible planar waveguides fabricated by radio frequency sputtering, are presented. The 1D photonic crystals show a strong dependence of the optical features on the light incident angle: i) blue-shift of the stopband and ii) narrowing of the reflectance window. Nevertheless, the most interesting result is the experimental evidence that, even after the 1D photonic crystals breakage, where the flexible glass shows naked-eye visible cracks, the multilayer structures generally maintain their integrity, resulting to be promising systems for flexible photonic applications thanks to their optical, thermal and mechanical stability. The flexible planar waveguides, fabricated on ultrathin flexible glass substrate, showed an attenuation coefficient lower than 0.2 dB/cm at 1.54 μm, and exibits emission in the NIR region, resulting particularly suitable as waveguide amplifier in the C band of telecommunications.

We introduce the conceptual design of the optical core for a spectral‐splitting and light‐guiding four‐terminal (4T) photovoltaic (PV) module, with appealing features for bifacial operation. We analyze the applicability of the solution and its performance using a commercial ray‐tracing software for direct and diffused solar irradiance at standard AM1.5G spectrum. The core is a right‐angle transparent wedged (RAW) prism. Complementary, two dichroic mirrors are optically coupled to the rear and bottom faces of the wedge to perform the spectral‐splitting (SS) function. Low‐gain concentration in the visible (VIS) band is provided by combining dichroic reflections with achromatic total internal reflection (TIR) at the topmost air‐dielectric interface for light guiding. The module can support 4T heterojunction connection, implemented with wide‐bandgap (WG) solar cells for the VIS and silicon‐based solar cells for the near infrared (NIR). At a geometrical concentration gain CG‐VIS ≈ 4 and wide optical acceptance angle θA ≈ 48°, also VIS diffused light is effectively collected and a spectrally integrated optical efficiency ηo,diff = 62%, (ηo(diff,NIR) =45%, ηo(diff,VIS) = 17%) is estimated. Under direct illumination ηo,dir > 80% is obtained over the whole angular acceptance with a maximum optical efficiency ηo,dir‐MAX ≈ 88.7% at θi = 37°. Low‐concentrating RAW‐SS can work stationary and trackless. The tilt angle for the orientation β is set according to the latitude at the installation site, and in the northern hemisphere, it is more north‐oriented with respect to standard panels. The collection of albedo irradiance from the ground is favored, since the scaling coefficient for self‐shading of the module at sun elevation ϕ is lower than for standard flat panels of equivalent input area and normally oriented. The decrease in self‐shading is therefore an asset for bifacial operation and specifically effective at lower latitudes where solar irradiance is stronger. The possible applications range from sub‐watt indoor PV and Internet‐of‐Things power suppliers to utility‐scale plants and building‐integrated solutions. [ABSTRACT FROM AUTHOR]

Abstract: Reaction between EuCl3 and the ligand 1,3-di(thien-2-yl)propane-1,3-dione (L) leads to luminescent coordination compounds [Eu[L.sub.3][(EtOH).sub.2]](1), [Eu[L.sub.2][(i-PrOH).sub.4]]Cl (2) and [Eu[L.sub.3]([(i-PrOH).sub.2]](3), isolated as single crystals in high yield (70%-95%). The Eu/[beta]-diketonate ratio [...]

Density functional theory-based methods have been exploited to look into the structural, vibrational and electronic properties of antenna ligands, all of them being crucial factors for the reliable design of customized luminescent lanthanide (Ln3+) complexes. The X-ray structures, UV-Vis absorption spectra and triplet (T1) energies of three novel β-diketone ligands with a thienyl group and naphthyl (L1), phenanthryl (L2), and pyrenyl (L3) polycyclic aromatic hydrocarbons as substituents have been modelled. Vibronic progressions provide a strong contribution to the L1 and L2 absorption spectra, while the L3 absorption spectrum needs the assumption of different conformational isomers in solution. T1 energies have been estimated either through the vertical- or the adiabatic-transition approach. The comparison with the phosphorescence spectra of Gd3+ complexes allowed us to infer that the latter approach is the most suitable one, in particular when sizable ligands are involved. Results obtained for the isolated antennas can be directly compared with those of the corresponding Ln3+ complexes, due to the unanimously accepted assumption that the excitation is ligand-centred. [ABSTRACT FROM AUTHOR]

A series of Gd 3+ complexes ( Gd1 - Gd3 ) with the general formula GdL 3 (EtOH) 2 , where L is a β-diketone ligand with polycyclic aromatic hydrocarbon substituents of increasing size ( 1 - 3 ), was studied by combining time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy and DFT calculations to rationalize the anomalous spectroscopic behavior of the bulkiest complex ( Gd3 ) through the series. Its faint phosphorescence band is observed only at 80 K and it is strongly red-shifted (∼200 nm) from the intense fluorescence band. Moreover, the TR-EPR spectral analysis found that triplet levels of 3 / Gd3 are effectively populated and have smaller | D | values than those of the other compounds. The combined use of zero-field splitting and spin density delocalization calculations, together with spin population analysis, allows us to explain both the large red shift and the low intensity of the phosphorescence band observed for Gd3 . The large red shift is determined by the higher delocalization degree of the wavefunction, which implies a larger energy gap between the excited S 1 and T 1 states. The low intensity of the phosphorescence is due to the presence of C-H groups which favor non-radiative decay. These groups are present in all complexes; nevertheless, they have a relevant spin density only in Gd3 . The spin population analysis on NaL models, in which Na + is coordinated to a deprotonated ligand, mimicking the coordinative environment of the complex, confirms the outcomes on the free ligands.

A theoretical protocol combining density functional theory (DFT) and multireference (CAS) calculations is proposed for a Eu 3+ complex. In the complex, electronic levels of the central Eu 3+ ion are correctly calculated at the CASPT2 level of theory, and the effect of introducing different numbers of states in the configuration interaction matrices is highlighted as well as the shortcomings of DFT methods in the treatment of systems with high spin multiplicity and strong spin-orbit coupling effects. For the 5 D 0 state energy calculation, the inclusion of states with different multiplicity and the number of states considered for each multiplicity are crucial parameters, even if their relative weight is different. Indeed, the addition of triplet and singlets is important, while the number of states is relevant only for the quintets. The herein proposed protocol enables a rigorous, full ab initio treatment of Eu 3+ complex, which can be easily extended to other Ln 3+ ions.