• Energy Research

We measure and model the complex dielectric response of indium tin oxide films fabricated by nanocrystal deposition and sintering.

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.

The present work introduces the conceptual design of the optics for a spectral-splitting and light-guiding photovoltaic (PV) four-terminal (4T) module with appealing features for bifacial operation. The geometry here described performs low-gain 2D concentration in the visible (VIS) spectrum and can couple a Si solar cell to a wide-bandgap (WG) one. We analyze and discuss the conditions of applicability of the solution from the optical viewpoint. The performance analysis has been performed using commercial ray-tracing software (ZEMAX OpticStudio), by admitting direct and isotropically diffused solar irradiation at standard AM1.5G spectrum.

In this paper, we numerically investigate the fluorescence decay of Tm-doped tellurite glasses with different dopant concentrations. The aim is to find a set of data that allows the prediction of material performance over a wide range of doping concentrations. Among the available data, a deep investigation of the reverse cross-relaxation process (3F4, 3F4, →3H6, 3H4) was not yet available. The numerical simulation indicates that the reverse cross-relaxation process parameter can be calculated by fitting the slow decaying 3H4 fluorescence tails emitted when the pump level is almost depopulated. We also show that the floor of the 3H4 decay curve is indeed related to a second exponential constant, half the 3F4 lifetime, kicking in once the 3H4 level depopulates. By properly fitting the whole set of decay curves for all samples, the proposed value for the reverse cross-relaxation process is 0.03 times the cross-relaxation parameter. We also comment on the measurement accuracy and best set-up. Excellent agreement was found between the simulated and experimental data, indicating the validity of the approach. This paper therefore proposes a set of parameters validated by fitting experimental fluorescence decay curves of both the 3H4 and 3F4 levels. To the best of our knowledge, this is the first time a numerical simulation has been able to predict the fluorescence behavior of glasses with doping levels ranging from 0.36 mol% to 10 mol%. We also show that appropriate calculations of the reverse cross-relaxation parameter may have a significant effect on the simulation of laser and amplifier devices.

Doped glasses and glass ceramics may support effective down conversion of high-energy photons and provide better exploitation of the solar spectrum.

The solar cells efficiency may be improved by better exploitation of the solar spectrum, making use of the downconversion mechanism, where one high energy photon is cut into two low energy photons [1]. The choice of the matrix is a crucial point to obtain an efficient down-conversion process with rare-earth ions. When energy transfer between rare earth ions is used to activate this process, high emission and absorption cross sections as well as low cutoff phonon energy are mandatory. A low phonon energy host lattice reduces non-radiative transition rates leading to the increase of the luminescent quantum yield and of the energy transfer efficiency. Recently, some studies have demonstrated that fluoride and oxyfluoride glasses may be valid systems to support an effective quantum cutting process [2-4]. As a fluoride material, the relatively low phonon energy, around 600cm-1, of the ZLAG (70ZrF4 23.5LaF3 0.5AlF3 6GaF3 in mol%) glass makes it highly suitable for applications involving energy transfers. In this study, attention is focused on the assessment of the energy transfer efficiency between the Pr3+ and Yb3+ ions in bulk fluoride glasses ZLAG.

Photonic crystals can integrate plasmonic materials such as indium tin oxide (ITO) in their structure. Exploiting ITO plasmonic properties it is possible to tune the photonic band gap of the photonic crystal upon the application of an external stimuli. In this work, we have fabricated a one-dimensional multilayer photonic crystal via radiofrequency sputtering and we have triggered its optical response with ultrafast pump-probe spectroscopy. Upon photoexcitation we observe a change in the refractive index of indium tin oxide. Such effect has been used to create a photonic crystal that change its photonic bandgap in an ultrafast time scale. All optical modulation in the visible region, that can be tuned by designing the photonic crystal, has been demonstrated. 7 pages, 3 figures