Direct sunlight facility for testing and research in HCPV

A facility for testing different components for HCPV application has been developed in the framework of “Fotovoltaico ad Alta Efficienza” (FAE) project funded by the Sicilian Regional Authority (PO FESR Sicilia 2007/2013 4.1.1.1). The testing facility is equipped with an heliostat providing a wide solar beam inside the lab, an optical bench for mounting and aligning the HCPV components, electronic equipments to characterize the I-V curves of multijunction cells operated up to 2000 suns, a system to circulate a fluid in the heat sink at controlled temperature and flow-rate, a data logging system with sensors to measure temperatures in several locations and fluid pressures at the inlet and outlet of the heat sink, and a climatic chamber with large test volume to test assembled HCPV modules

Ultra high vacuum beam pipe of the Einstein Telescope project: Challenges and perspectives

The Einstein Telescope (ET) is a project aiming to realize a facility to host a gravitational wave (GW) detector of the third generation. The new instrument will change our vision of the Universe by observing millions of GW signals emitted during the coalescence of stellar and intermediate-mass black hole binary systems. It will permit to shed light on the first phase of the Universe formation and it will contribute to solving the dark matter enigma. The new GW detector is conceived as a series of six nested Michelson interferometers forming a triangle of 10 km side. The laser light biasing the interferometers must propagate in large ultra-high vacuum (UHV) tubes in order to reduce the noise induced by the residual gas pressure fluctuations, setting a requirement on the residual pressure in the 10 - 10 mbar range. The vacuum system will be made of a pipe with a 1 m diameter and an overall length of 120 km, making ET one of the largest UHV systems ever made. The giant UHV project asks for attentive optimization of material choice, manufacturing processes, post-processing treatments of the tubes, and pumping systems in order to find a cost-effective solution. In this article, we shortly review the vacuum solution adopted in the case of the second generation of GW detectors. After a general description of the main elements that constitute the ET vacuum system, the detailed design being the subject of the next 3 years of work, we will present a refined calculation of the noise due to residual-gas pressure fluctuations in the ET beam pipe

Effects induced by UV laser radiation on the blue luminescence of silica nanoparticles

The effects induced on the blue luminescence centered around 2.8 eV, characteristic of silica nanoparticles, were investigated by monitoring its intensity during and after exposure to the third and the fourth harmonic of a Nd:YAG pulsed laser. The luminescence trend is found to be dependent on the UV photon energy: 3.50 eV photons induce a partial bleaching followed by a recovery in the post-irradiation stage; 4.66 eV photons cause a total bleaching permanent after the irradiation. These results are interpreted as the conversion of luminescent defects towards stable and metastable configurations

Luminescence from nearly isolated surface defects in silica nanoparticles

A structured emission/excitation pattern, proper of isolated defects, arises in a vacuum from silica nanoparticles. The luminescence, centered around 3.0–3.5 eV, is characterised by a vibronic progression due to the phonon coupling with two localised modes of frequency ∼1370 cm−1 and ∼360 cm−1, and decays in about 300 ns at 10 K. On increasing the temperature, the intensity and the lifetime decrease due to the activation of a non-radiative rate from the excited state. Concurrently, the temperature dependence of the lineshape evidencesth e low coupling with non-localised modes of the matrix (Huang–Rhys factor S ~ 0.2) and the poor influence of the inhomogeneous broadening. These findings outline an uncommon behaviour in the field of the optical properties of defects in amorphous solids, evidencing that the silica surface can allocate luminescent defects almost disentangled from the basal network

Defect-related visible luminescence of silica nanoparticles

We have investigated the visible emission of silica nanoparticles by time-resolved luminescence spectra. We have characterized the spectroscopic properties of the blue band, centered around 2.8 eV, peculiar of as received samples and we have evidenced the effects induced by high power UV laser irradiation on the emitting defects. Moreover, the comparison with the luminescence of samples thermochemically treated in controlled atmosphere allows us to critically discuss the structural model proposed in the current literature

Visible-ultraviolet vibronic emission of silica nanoparticles

We report the study of the visible-ultraviolet emission properties and the structural features of silica nanoparticles prepared through a laboratory sol–gel technique. Atomic force microscopy, Raman and Infrared investigations highlighted the 10 nm size, purity and porosity of the obtained nanoparticles. By using time resolved photoluminescence techniques in air and in a vacuum we were able to single out two contributions in the visible emission: the first, stable in both atmospheres, is a typical fast blue band centered around 2.8 eV; the second, only observed in a vacuum around the 3.0–3.5 eV range, is a vibrational progression with two phonon modes at 1370 cm-1 and 360 cm-1. By fully characterizing the spectroscopic features of this structured emission, we determine its vibronic properties and clarify the different origins with respect to the blue luminescent defect

Vibronic structures in the visible luminescence of silica nanoparticles

We report the spectroscopic characterization in air and in vacuum atmosphere of the visible luminescence related to silica surface defects. Time resolved photoluminescence technique allows to discern two contribution: the first one, observed both in air and in vacuum, is the well known blue band, peaked around 2.8 eV decaying in τ~5 ns; the second, only observed in vacuum, is a structured emission in the violet range characterized by two vibronic progressions spaced 1370 cm-1 and 360 cm-1 decaying in τ~90 ns. On the basis of these spectroscopic properties, we revise the structural models of luminescent defects