• Energy Research

Abstract In the present investigation some spectroscopic properties of several lanthanide squarate hydrates are reported. The Raman spectra show the same distinctive Jahn—Teller intensity pattern for non-totally symmetric modes, as previously observed for the free anion. In the case of the terbium salt, the Tb 3+ emission is very intense even at room temperature, revealing an efficient excitation via the ligand electronic levels. The Tb 3+ dilution in Gd 3+ or La 3+ hosts increases this excitation efficiency without any appreciable variation in the 5 D 4 excited-state lifetime. However, the Eu 3+ emission is very weak, with excited states located above the 5 D 2 level (ca. 21 550 cm −1 ) being completely quenched at room temperature. At lower temperatures higher-lying levels are not so efficiently quenched. The broad band observed in the UV excitation spectra of Eu 3+ and Tb 3+ is easily assigned to an intra-ligand transition leading to ligand-to-lanthanide ion energy transfer processes. As observed for Tb 3+ , Eu 3+ dilution in Gd 3+ or La 3+ hosts also increases the relative emission intensity mediated by the ligand, without variation in the 5 D 0 excited-state lifetime. The Eu 3+ 5 D 0 excitation spectra show vibronic structures that can be interpreted on the basis of the data available from the vibrational spectra. An increase in the vibronic intensities is observed as the lanthanide concentration is increased.

AbstractLuminescent solar concentrators (LSCs) are cost‐effective components easily integrated in photovoltaics (PV) that can enhance solar cells' performance and promote the integration of PV architectural elements into buildings, with unprecedented possibilities for energy harvesting in façade design, urban furnishings and wearable fabrics. The devices' performance is dominated by the concentration factor (F), which is higher in cylindrical LSCs compared with planar ones (with equivalent collection area and volume). The feasibility of fabricating long‐length LSCs has been essentially limited up to ten of centimetres with F < 1. We use a drawing optical fibre facility to easily scale up large‐area LSCs (length up to 2.5 m) based on bulk and hollow‐core plastic optical fibres (POFs). The active layers used to coat the bulk fibres or fill the hollow‐core ones are Rhodamine 6G‐ or Eu3+‐doped organic–inorganic hybrids. For bulk‐coated LSCs, light propagation occurs essentially at the POFs, whereas for hollow‐core device light is also guided within the hybrid. The lower POFs' attenuation (~0.1 m−1) enables light propagation in the total fibre length (2.5 m) for bulk‐coated LSCs with maximum optical conversion efficiency (ηopt) and F of 0.6% and 6.5, respectively. For hollow‐core LSCs, light propagation is confined to shorter distances (6–9 × 10−2 m) because of the hybrids' attenuation (1–15 m−1). The hollow‐core optimised device displays ηopt = 72.4% and F = 12.3. The F values are larger than the best ones reported in the literature for large‐area LSCs (F = 4.4), illustrating the potential of this approach for the development of lightweight flexible high‐performance waveguiding PV. Copyright © 2016 John Wiley & Sons, Ltd.

Polymers based on vegetable oils can be suitable candidates for the replacement of fossil polymers, for instance, polyurethanes (PU) based on castor oil. However, the synthesis PU materials are normally carried out using organic solvents, metals, and high temperatures. To overcome these problems, the sol-gel route is an alternative approach based on mild conditions to produce organic-inorganic hybrid urethanesil (Ut) environmentally friendly. Therefore, in this study, we proposed an organic-inorganic hybrid (OIH) synthesis based on castor oil (CO)-derived Ut, as well as the incorporation and interaction of europium β-diketone [Eu(tta)3(H2O)2] in organic-inorganic hybrid matrix. The Ut self-supporting hybrid was synthesized from the reaction of 3-(triethoxysilyl)propyl isocyanate (ICPTES) and CO in a 3:1 M ratio. The films were obtained using the sol-gel process, following the casting method. The CO-based OIH-Ut films showed high transmittance in the visible and infrared spectrum (90%), and urethanesil showed photoluminescence (PL) with emission at 416.0 nm when excited at 319.0 nm. The results also revealed an increase in the intrinsic quantum yield of PL (QLEu) for [Eu(tta)3(H2O)2]. It has been verified a QLEu value of 27% for the isolated complex, whereas when it is incorporated into OIH-Ut a value of 49% was observed. Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Processo FAPESP: 2020/03259–9 Processo FAPESP: 2022/03652–8 CAPES: 88887.499004/2020–00

Abstract Crystallization of binary InF3MF2 and GaF3MF2 (where M  Ba, Sr and Ca) glasses was studied. Characteristic temperatures and kinetic parameters E (activation energy) and n (Avrami exponent) were obtained. Stability against devitrification is discussed in terms of the above cited parameters and also of some others parameters proposed in literature. Optical properties (IR and upconversion emissions) are reported in different crystallized samples containing Nd3+. The main observation is that up conversion emission presents an enhanced sensibility to crystallization when compared to conventional emission.

AbstractRelative to the Er3+:gold-nanoparticle (Er3+:Au–NP) axis, the polarization of the gold nanoparticle can be longitudinal (electric dipole parallel to the Er3+:Au–NP axis) or transverse (electric dipole perpendicular to the Er3+:Au–NP axis). For longitudinal polarization, the plasmon resonance modes of gold nanoparticles embedded in Er3+-doped germanium–tellurite glass are activated using laser lines at 808 and 488nm in resonance with radiative transitions of Er3+ ions. The gold nanoparticles were grown within the host glass by thermal annealing over various lengths of time, achieving diameters lower than 1.6nm. The resonance wavelengths, determined theoretically and experimentally, are 770 and 800nm. The absorption wavelength of nanoparticles was determined by using the Frohlich condition. Gold nanoparticles provide tunable emission resulting in a large enhancement for the 2H11/2→4I13/2 (emission at 805nm) and 4S3/2→4I13/2 (emission at 840nm) electronic transitions of Er3+ ions; this is associated with the quantum yield of the energy transfer process. The excitation pathways, up-conversion and luminescence spectra of Er3+ ions are described through simplified energy level diagrams. We observed that up-conversion is favored by the excited-state absorption due to the presence of the gold nanoparticles coupled with the Er3+ ions within the glass matrix.

Abstract BiVO4 nanoparticles deposited onto TiO2 nanotube arrays (TNT) are used as heterostructured photoanodes in a compact-design photo-electrocatalytic (PEC) cell for solar-driven water splitting. No dopants, photosensitizers or other cocatalysts are added to enhance the catalytic activity but attention is focused on the relationship between TNT nanostructure (necessary for the novel compact-design PEC cell) and method of BiVO4 deposition. Three indicators are used to evaluate the catalytic performances: i) photocurrent density, ii) H2 production rate, and iii) solar-to-hydrogen efficiency (STH). Their dependence on photoanode characteristics (i.e. grade of TNT crystallinity) and operational parameters, such as anolyte concentration (NaOH in the range 0.1–1.0 M) and type of solar illumination (open spectrum or AM 1.5G filtered light), is analysed. While a linear relationship is observed between H2 production rate and photocurrent density, the behaviour of STH efficiency is more complex. An ordered and crystalline TNT film is necessary to maximize photocurrent density and H2 production rate, which can be further enhanced by depositing BiVO4. However, the methodology of BiVO4 deposition and the specific TNT nanoarchitecture have a marked influence in terms of light absorption, electronic conductivity and rate of reaction between photogenerated holes and OH−. This leads to an improvement or a depression of the photocatalytic behaviour as BiVO4 may in some cases favour charge recombination. Thus, understanding the role of the photoelectrodes in relation to the operational conditions may favour the preparation of scalable electrodes for improving performances of PEC cells in the generation of solar fuels.

Energy conversion, involving UV and Vis absorption to generate near infrared (NIR) emission at 1000 nm from nanostructured Pr3+/Yb3+ co-doped SiO2-Nb2O5 for solar cell application was the main focus of this work. The synthesis, structural and optical characterization of Pr3+/Yb3+ co-doped 70SiO2-30Nb2O5 nanocomposites and planar waveguides prepared by the sol gel method are reported. The influence of the rare earth content and thermal annealing on the crystallization process and the luminescence properties was studied. The excitation spectra revealed the energy transfer between the Pr3+ and Yb3+, involving mainly the 3P2 level of Pr3+ ions. Multiphonon decay and cross relaxation processes take place at higher rare earth concentration and annealing temperature, which increases the 1D2 level population and consequently the NIR emission from the Pr3+ ions. The nanostructured Pr3+/Yb3+ co-doped SiO2-Nb2O5 nanocomposites and waveguides show interesting NIR emission and optical properties for photonic applications.