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| 2. |
- Glasbey, JC, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 3. |
- Tabiri, S, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 4. |
- Bravo, L, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 5. |
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| 6. |
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| 9. |
- Enrichi, Francesco, et al.
(författare)
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Silver doping of silica-hafnia waveguides containing Tb3+/Yb3+ rare earths for downconversion in PV solar cells
- 2016
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Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 60, s. 264-269
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to study the possibility to obtain an efficient downconverting waveguide which combines the quantum cutting properties of Tb3+/Yb3+ codoped materials with the optical sensitizing effects provided by silver doping. The preparation of 70SiO(2)-30HfO(2) glass and glass-ceramic waveguides by sol-gel route, followed by Ag doping by immersion in molten salt bath is reported. The films were subsequently annealed in air to induce the migration and/or aggregation of the metal ions. Results of compositional and optical characterization are given, providing evidence for the successful introduction of Ag in the films, while the photoluminescence emission is strongly dependent on the annealing conditions. These films could find potential applications as downshifting layers to increase the efficiency of PV solar cells
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| 11. |
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| 12. |
- Larsson, Josefin, et al.
(författare)
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A close look at the γ-ray emitting narrow-line seyfert 1 FBQS J1644+2619
- 2018
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Ingår i: Proceedings of Science. - : Sissa Medialab Srl.
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Konferensbidrag (refereegranskat)abstract
- FBQS J1644+2619 is one of the most recently discovered γ-ray emitting Narrow-Line Seyfert 1s (NLSy1s). Here we present a multiwavelength analysis of this source, focussing on a recent 80 ks X-ray observation with XMM-Newton. The spectral energy distribution of the source is similar to the other γ-ray NLSy1s, confirming its blazar-like nature. The X-ray spectrum is characterised by a hard photon index (Γ = 1.66) above 2 keV and a soft excess at lower energies. The hard photon index provides clear evidence that inverse Compton emission from the jet dominates the spectrum, while the soft excess can be explained by a contribution from the underlying Seyfert emission. This contribution can be fitted by reflection of emission from the base of the jet, as well as by Comptonisation in a warm, optically thick corona. We also compare these results with X-ray observations of other γ-ray NLSy1s. The majority of the sources have similar X-ray spectra, with properties intermediate between blazars and radio-quiet NLSy1s.
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| 13. |
- Larsson, Josefin, et al.
(författare)
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FBQS J1644+2619 : multiwavelength properties and its place in the class of gamma-ray emitting Narrow Line Seyfert 1s
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 476:1, s. 43-55
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Tidskriftsartikel (refereegranskat)abstract
- A small fraction of Narrow Line Seyfert 1s (NLSy1s) are observed to be gamma-ray emitters. Understanding the properties of these sources is of interest since the majority of NLSy1s are very different from typical blazars. Here, we present a multifrequency analysis of FBQS J1644+2619, one of the most recently discovered gamma-ray emitting NLSy1s. We analyse an similar to 80 ks XMM-Newton observation obtained in 2017, as well as quasi-simultaneous multi-wavelength observations covering the radio-gamma-ray range. The spectral energy distribution of the source is similar to the other gamma-ray NLSy1s, confirming its blazar-like nature. The X-ray spectrum is characterized by a hard photon index (Gamma = 1.66) above 2 keV and a soft excess at lower energies. The hard photon index provides clear evidence that inverse Compton emission from the jet dominates the spectrum, while the soft excess can be explained by a contribution from the underlying Seyfert emission. This contribution can be fitted by reflection of emission from the base of the jet, as well as by Comptonization in a warm, optically thick corona. We discuss our results in the context of the other gamma-ray NLSy1s and note that the majority of them have similar X-ray spectra, with properties intermediate between blazars and radio-quiet NLSy1s.
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| 14. |
- Lisi, Matteo, et al.
(författare)
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Right ventricular longitudinal deformation correlates closely with right ventricular myocardial fibrosis in patients with end-stage heart failure
- 2013
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Ingår i: European Heart Journal. - : Oxford University Press. - 0195-668X .- 1522-9645. ; 34, s. 780-780
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Background: Right ventricular (RV) longitudinal strain (LS) plays a key role in the evaluation of its systolic performance and clinical outcomein patients with refractory heart failure (HF). This study sought to determine the value of RVLS for prediction of RV myocardial fibrosis inpatients with severe HF undergoing heart transplantation (HTx).Methods: The cohort we studied consists of 24 patients with severe systolic HF (left ventricular ejection fraction ≤ 25%; NYHA class IV) referred between 2009 and 2013 for a simultaneous right heartcatheterization and echocardiographic evaluation before HTx.RVLS by Speckle Tracking Echocardiography (STE) was used to assess free-wall RVLS, global cavity RVLS (including all segments in the apical 4 chamber view and right atrial LS (RALS), RV fractional area change (RVFAC), RV sphericity index (RVSI) and tricuspid annular plane systolic excursion (TAPSE) were also measured. All patients underwent HTx 12±34 days afterwards. From the explanted hearts a 1 x 0,5 cmmyocardial sample of the RV lateral free wall was obtained and stainedwith hematoxylin-eosin and Masson's trichrome. The ratio of the fibrotic area to the total surface area of each section was used to estimate the extent of RV myocardial fibrosis (percentage) as (fibrotis area-total area) x 100.Results: A good correlation was found between the extent of RVmyocardial fibrosis and free-wall RVLS (r=0.72; p<0.0001), global RVLS (r=0.49; p<0.0001), RVSI (r=0.47; p<0.0001), and RALS (r= -0.46; p=0.005), with a poorer correlation with TAPSE (r= -0.32; p=0.01) and RVFAC (r= -0.25; p=ns). Of these indeces, free-wall RVLS had the strongest diagnostic accuracy for detecting severe RV myocardialfibrosis (AUC = 0.87).Conclusions: In late stage HF patients, right ventricular free wallmyocardial deformation is the best functional measure that correlateswith the extent of myocardial fibrosis. These findings should have clinical implications when interpreting other RV measurements.
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| 15. |
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| 16. |
- Enrichi, Francesco, et al.
(författare)
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Ag nanoaggregates as efficient broadband sensitizers for Tb3+ ions in silica-zirconia ion-exchanged sol-gel glasses and glass-ceramics
- 2018
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Ingår i: Optical materials (Amsterdam). - : Elsevier. - 0925-3467 .- 1873-1252. ; 84, s. 668-674
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we report the study of down-shifting silica-zirconia glass and glass-ceramic films doped by Tb3+ ions and Ag nanoaggregates, which combine the typical spectral properties of the rare-earth-ions with the broadband sensitizing effect of the metal nanostructures. Na-Tb co-doped silica-zirconia samples were obtained by a modified sol-gel route. Dip-coating deposition followed by annealing for solvent evaporation and matrix densification were repeated several times, obtaining a homogeneous crack-free film. A final treatment at 700 °C or 1000 °C was performed to control the nanoscale structural properties of the samples, resulting respectively in a glass (G) or a glass-ceramic (GC), where tetragonal zirconia nanocrystals are surrounded by an amorphous silica matrix. Ag introduction was then achieved by ion-exchange in a molten salt bath, followed by annealing in air to control the migration and aggregation of the metal ions. The comparison of the structural, compositional and optical properties are presented for G and GC samples, providing evidence of highly efficient photoluminescence enhancement in both systems, slightly better in G than in GC samples, with a remarkable increase of the green Tb3+ PL emission at 330 nm excitation: 12 times for G and 8 times for GC samples. Furthermore, after Ag-exchange, the shape of Tb3+ excitation resembles the one of Ag ions/nanoaggregates, with a broad significant absorption in the whole UV-blue spectral region. This broadband enhanced downshifting could find potential applications in lighting devices and in PV solar cells.
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| 17. |
- Enrichi, Francesco, et al.
(författare)
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Investigation of the role of Ag multimers as broadband sensitizers in Tb3+/Yb3+ doped glasses and glass ceramics
- 2018
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Ingår i: Fiber Lasers and Glass Photonics. - : SPIE - International Society for Optical Engineering.
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Konferensbidrag (refereegranskat)abstract
- Rare earth ions (RE3+) have typical photoluminescence emissions due to internal 4f orbital transitions. These emissions are narrow, with long excited state lifetimes and have the capability of spectral manipulation like wavelength shifting, down-conversion or up-conversion processes. Therefore, RE-doped materials are widely used for optical applications. However, the narrow absorption bandwidths and the small excitation cross sections for their optical transitions are major limiting factors for the full exploitation of their potentials. In this work, we show that the addition of metal nanoaggregates as broadband and efficient sensitizers can be a viable strategy to overcome these limits. Silica-zirconia (70% SiO2 – 30% ZrO2) glass-ceramic films doped by Tb3+/Yb3+ ions and an additional 5 mol.% of Na2O were prepared by sol-gel synthesis followed by a thermal annealing at 1000°C. Ag introduction was then obtained by ion-exchange in a molten salt bath and the samples were subsequently annealed in air at 380°C or 430°C to induce the migration and aggregation of the metal. The structural, compositional and optical properties of the materials were investigated, providing evidence for efficient broadband sensitization of the rare earth ions by energy transfer from Ag-dimers or multimers, which could have applications for increasing the efficiency of silicon solar cells.
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| 18. |
- Hermann, DS, et al.
(författare)
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Electro-optic modulation of light by a planar waveguide based on ferroelectric liquid crystals
- 2000
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Ingår i: Molecular Crystals and Liquid Crystals Science and Technology. - 1058-725X. ; 352, s. 813-
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Tidskriftsartikel (refereegranskat)abstract
- We present electro-optic switching from a planar waveguide with a ferroelectric liquid crystal overlayer and discuss the operating principle and the parameters significant for the operation of the device. We have found electro-optic response times of about 20 mus at best as well as a high (5.7%) transmittance in the ON-state of the device. The contrast ratio was 4:1 ON to OFF state.
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| 19. |
- Righini, Giancarlo C., et al.
(författare)
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Light management in solar cells : Recent advances
- 2017
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Konferensbidrag (refereegranskat)abstract
- Efficient light management is critical for the enhancement of the efficiency of solar cells. The performance of a solar cell is determined by the efficiency of the absorption process of light via excitation of electron-hole pairs and extraction of these generated charge carriers. The absorption, in turn, has a few limiting factors: one is related to the small size and acceptance angle of the active region, another to the reduced spectral sensitivity of the active material, which does not use a part of the solar radiation. Correspondingly, the energy harvesting may be improved in two ways: a) light trapping schemes may be adopted to make the cell 'thicker' by exploiting scattering and/or reflection effects. Plasmonic structures, constituted by patterned metal films or nanoparticles, demonstrated to be very effective for directing and enhancing the incident light beam. b) up- and down-conversion processes may be exploited to convert the frequencies of the solar spectrum from near-mid-IR and from blue-UV regions, respectively, to the region of maximum absorption of the cell. Thin glassy or glass-ceramic films doped with rare earth ions proved to be very suitable for this purpose. Here, an overview of recent results achieved in the use of plasmonic structures by different research groups will be reported, and different approaches will be compared.
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| 20. |
- Zur, Lidia Z., et al.
(författare)
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Comparison between glass and glass-ceramic silica-hafnia matrices on the down-conversion efficiency of Tb3+/Yb3+ rare earth ions
- 2019
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Ingår i: Optical materials (Amsterdam). - : Elsevier. - 0925-3467 .- 1873-1252. ; 87, s. 102-106
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the investigation of energy transfer efficiency in Tb3+-Yb3+ co-doped SiO2-HfO2 glass and glass-ceramic waveguides is presented. Cooperative energy transfer between these two ions allows to cut one UV or 488 nm photon in two 980 nm photons and could have important applications in improving the performance of photovoltaic solar cells. Thin films with different molar concentrations of rare earths, up to a total concentration of 21%, were prepared by a sol-gel route, using dip-coating deposition technique on SiO2 substrates. The ratio between Yb3+ and Tb3+ ions in all the prepared thin films is constant and equal to 4. The energy transfer between Tb3+ and Yb3+ ions in glass and glass-ceramic waveguides shows the higher efficiency for glass-ceramic with a maximum quantum transfer efficiency of about 190% for the sample containing 19% of rare earths.
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