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La tesi si pone l'obiettivo di studiare le proprietà ottiche degli Xeni. Gli Xeni, reticoli monoelementali artificiali simili al grafene, hanno mostrato sin dalla loro scoperta grandi potenzialità per applicazioni negli ambiti dell'elettronica e della fotonica. Purtroppo, il loro utilizzo è ancora limitato dall'elevata reattività chimica e dai forti effetti di ibridazione con i substrati nativi. Conoscere la risposta ottica o termo-ottica degli Xeni, escludendo o controllando eventuali effetti del substrato, è quindi funzionale allo sviluppo di nuove tecnologie. La ricerca è stata condotta nell'ambito del progetto X-Fab (ERC COG Grant n. 772261), presso i laboratori CNR-IMM di Agrate Brianza. In questo studio vengono esaminate diverse configurazioni a base di Xene, combinando tecniche di analisi in situ (XPS e LEED) e di spettroscopia ottica (FTIR, Vis-UV e Raman), con lo scopo di determinarne la risposta ottica e valutare l'integrazione degli Xeni in un dispositivo che ne sfrutti le potenzialità. La prima configurazione analizzata prevede l'introduzione di un substrato isolante e otticamente trasparente, come lo zaffiro, a sostituzione del più diffuso argento. Lo zaffiro, nella sua orientazione (0001) presenta un reticolo a simmetria esagonale commensurato a quello di silicene e stanene. La conducibilità ottica di nano-film di stagno cresciuti tramite MBE è stata ricavata da misure di trasmittanza e riflettanza, acquisite tra 0.01 e 6.5 eV. L'analisi spettrale e il successivo confronto con dati teorici già presenti in letteratura hanno permesso di identificare delle caratteristiche non banali, in parte riconducibili allo stanene. L'analisi chimica eseguita in situ durante la crescita ha però evidenziato anche la presenza di una componente dello stagno ossidata dovuta ad effetti del substrato. Il problema emerso è stato affrontato introducendo uno strato di grafene tra i film di stagno e l'Al2O3. L'introduzione dello strato di grafene ha permesso di evitare l'ossidazione dello stagno, come confermato dall'analisi XPS. I risultati emersi dall'analisi ottica supportano invece la possibilità di stabilizzare la fase α dello stagno a temperatura ambiente proprio grazie all'introduzione dello strato di grafene. In modo concettualmente simile a quanto fatto per il film sottili di stagno con il grafene, è stata valutata la possibilità di disaccoppiare il silicene dall'argento introducendo tra i due materiali uno strato di silicene. La risposta ottica del silicene epitassiale è stata studiata attraverso la spettroscopia Raman opto-termica e con misure di riflettanza ottica. I risultati ottenuti supportano l'efficacia dello strato di stanene nel rompere l'interazione tra silicene e substrato d'argento. Inoltre, sebbene si tratti di una valutazione indiretta della risposta termica, i risultati ottenuti dall’analisi Raman aprono la strada alla determinazione delle proprietà termiche del silicene supportato. Esperimenti svolti su nano-film di silicio cresciuti epitassialmente su zaffiro hanno evidenziato un comportamento della conducibilità ottica riconducibile alla presenza di elettroni di Dirac come ci si aspetta per il silicene. Sulla base di questi risultati, la configurazione Xene-su-Al2O3 è stata sfruttata per valutare l'integrabilità degli Xeni in un dispositivo che permettesse di osservare sperimentalmente la risposta plasmonica di questi materiali. Sono stati fatti dei test di trasferimento tecnologico sulla piattaforma Xene-su-Al2O3, realizzando reticoli periodici con fotolitografia ottica e implementando un sistema di top gating a base di liquido ionico. Nonostante gli esperimenti non abbiano portato alla realizzazione di un dispositivo funzionante, i punti critici emersi dimostrano che il margine per ottenere miglioramenti è ancora ampio. The aim of this thesis is to investigate the optical properties of Xenes. Since their discovery, Xenes, artificial graphene-like single-element lattices, have shown great potential for applications in electronics and photonics. Unfortunately, their use is still limited by their high chemical reactivity and strong hybridisation effects with native substrates. Understanding the optical or thermo-optical response of Xenes, and thus excluding or controlling possible substrate effects, is therefore crucial for the development of new technologies. The research was carried out as part of the X-Fab (ERC COG Grant n. 772261) project at the CNR-IMM laboratories in Agrate Brianza. In this study, several Xenes-based configurations are investigated using a combination of in situ analysis (XPS and LEED) and optical spectroscopy (FTIR, Vis-UV and Raman) techniques to determine their optical response and evaluate the integration of Xenes into a device that exploits their potential. The first configuration analyzed involved the introduction of an insulating and optically transparent substrate, such as sapphire (Al2O3), to replace the more common silver. Sapphire, in its (0001) orientation, has a hexagonal symmetry lattice commensurate to that of silicene and stanene. The optical conductivity of tin nano-sheets grown by MBE was derived from transmittance and reflectance measurements. The measurements were carried out covering a range from 0.01 to 6.5 eV. Spectral analysis and subsequent comparison with theoretical data from the literature made it possible to identify non-trivial features, some of which can be attributed to stanene. However, in situ chemical analysis during growth also revealed the presence of an oxidised tin component due to substrate effects. This issue was solved by introducing a graphene layer between the tin films and Al2O3. The introduction of the graphene layer prevented oxidation of the tin, as confirmed by XPS analysis. The results of the optical analysis, on the other hand, support the possibility of stabilising the α phase of tin at room temperature by introducing the graphene buffer layer. The possibility of decoupling silicene from silver by introducing a layer of stanene between the two materials was evaluated. The optical response of the epitaxial silicene was studied using opto-thermal Raman spectroscopy and optical reflectance measurements. The results support the effectiveness of the stanene layer in breaking the interaction between silicene and the silver substrate. Furthermore, although this is an indirect evaluation of the thermal response, the results obtained from the Raman analysis pave the way to the determination of the thermal properties of the supported silicene. Previous experiments on silicon nano-sheets epitaxially grown on sapphire showed signature of graphene-like behavior in the low-energy optical conductivity. The Dirac-like electrodynamics is expected from the band structure of silicene. Based on these results, the Xene-on-Al2O3 configuration was used to evaluate the integrability of Xenes in a device that would allow the observation of the Dirac plasmonic response of these materials. Technology transfer tests were carried out on the Xene-on-Al2O3 platform by realizing periodic patterns using optical photolithography and implementing an ionic liquid-based top gating system. The experiments did not result in a working device. However, the critical points that emerged show that there is still plenty of room for improvement.

We describe an optical approach based on Digital Holography for single-particle characterization of mineral dust and micrometric particles, focusing on the analysis of airborne particles in meltwater from Antarctic ice cores. We record the holograms formed by the superposition of the transilluminating reference beam and the waves scattered by single particles. Taking a cue from recent approaches in the field and holography methods, we process the holograms to recover both optical and morphological properties of single dust grains. As a considerable advantage over traditional light-scattering-based methods, holograms give the extinction cross section of each particle and, by numerically reconstructing the wavefront propagation, an unambiguous image of each particle whereby we derive its cross-sectional shape and size. Measurements have been carried out on samples collected from the recent EAIIST (East Antarctic International Ice Sheet Traverse) project, some of which show evidence of volcanic events. The vast majority of the detected particles show significant deviations from the isometric shape, as confirmed by both image reconstruction and extinction cross section analysis. By our analysis, we observe that experimental data have an extinction cross section up to 3 times lower than that of spherical particles with the same volume. Therefore, these deviations have an appreciable impact on the aerosol contribution to radiative forcing: retrieving particle shape may improve the modeling of the radiative properties of mineral dust and reduce the associated uncertainties.

We elucidate the crucial role of the cetyl trimethylammonium bromide (CTAB) surfactant in the anisotropic growth mechanism of gold nano-bipyramids, nano-objects with remarkable optical properties and high tunability. Atomistic molecular dynamics simulations predict different surface coverages of the CTAB (positively charged) heads and their (bromide) counterions as function of the gold exposed surfaces. High concentration of CTAB surfactant promotes formation of gold nanograins in solution that work as precursors for the smooth anisotropic growth of more elongated nano-bipyramidal objects. Nanobipyramids feature higher index facets with respect to nanorods, allowing higher CTAB coverages that stabilize their formation and leading to narrower inter-micelles channels that smooth down their anisotropic growth. Absorption spectroscopy and scanning electron microscopy confirmed the formation of nanograins and demonstrated the importance of surfactant concentration on driving the growth towards nano-bipyramids rather than nanorods. The outcome explains the formation of the monodisperse bipyramidal nano-objects, the origin of their controlled shapes and sizes along with their remarkable stability.

Eumelanin is a redox active, quinone-based biopigment, featuring a broad band absorption in the UV-Vis region. The combination of the redox and optical properties makes eumelanin an interesting candidate to explore light-assisted storage technologies. Electrodes of melanin on indium tin oxide (ITO) current collectors were investigated for their morphological and voltammetric characteristics in aqueous electrolytes. Under solar light, we observed that the capacity and the capacitance of the melanin electrodes significantly increase with respect to the dark conditions (by 63% and 73%, respectively).

We describe a robust, portable, deployable instrument for multiparametric optical characterization of single airborne particles. It is based on the Single Particle Extinction and Scattering method with additional sensors at 45° and 90° angles. Four independent optical parameters are associated to each particle. Basically, it provides a rigorous measurement of the extinction cross section and the complex amplitude of the forward scattered field. Moreover, thanks to the multiparametric single particle approach, it is possible to roughly classify the particles within a size range from a few hundreds of nanometers to some micrometers. By assigning a reasonable single scattering albedo for each population, our data are enough to fit the phase function with acceptable uncertainties. We report here the results of tests performed with water droplets, generating well controlled data without any free parameters. Data analysis is described in detail. We also report measurements performed on urban aerosol collected in the city of Milan by recovering the optical properties and feeding radiative transfer models. The findings reported here support the importance of an accurate measurement of the phase function, as already established by the Community. Copyright © 2020 American Association for Aerosol Research.

Stabilization of silicene and preservation of its structural and electronic properties are essential for its processing and future integration into devices. The stacking of silicene on stanene, creat- ing a Xene-based heterostructure, proves to be a viable new route in this respect. Here we demonstrate the effectiveness of a stanene layer in breaking the strong interaction between silicene and the Ag(111) substrate. The role of stanene as a ‘buffer’ layer is investi- gated by analyzing the optical response of epitaxial silicene through both power-dependent Raman spectroscopy and reflectivity mea- surements in the near infrared (NIR)–ultraviolet (UV) spectral range. Finally, we point out a Xene-induced shift of the silver plasma edge that paves the way for the development of a new approach to engineering the metal plasmonic response.

Optical characterization and thermal aging tests are performed on a sputter-deposited coating, consisting of SiO2/Cr2O3/Cr/Cr2O3 layers, designed and developed as a selective solar absorber to be used for unconcentrated solar thermal applications. Both measurements are performed by using a home-made apparatus, which mimics a flat plate collector under high vacuum. A Performance Criterion ( P C η ( T ) ), based on absorber efficiency is proposed, and a forecast of service lifetime is obtained. As a result of the thermal aging tests, the selective solar absorber under study appears to be highly efficient at mid temperatures (up to 573 K) and thermally stable at temperatures (up to 690 K).

We present the results obtained using Cr2O3 as selective absorbing layer on aluminium film substrate. The thin films were deposited by electron beam evaporation using a multiple crucible e-gun able to deposit 4 materials in sequence without breaking the vacuum. Optical characterization of the multilayer films is based on ellipsometry and hemispherical reflectivity. The complex refractive index has been determinate and it has been used to design a selective solar absorber with high absorptance.

Submitted by JOSÉ DIEGO FERNANDES (jd.fernandes@unesp.br) on 2021-02-04T13:22:56Z No. of bitstreams: 1 Tese_JDFernandes_POSMAT_04jan21.pdf: 6053514 bytes, checksum: 29d477b808eb175d178bac8099416244 (MD5) Approved for entry into archive by Lucilene Cordeiro da Silva Messias null (lubiblio@bauru.unesp.br) on 2021-02-05T13:38:15Z (GMT) No. of bitstreams: 1 fernandes_jd_dr_bauru.pdf: 6053514 bytes, checksum: 29d477b808eb175d178bac8099416244 (MD5) Made available in DSpace on 2021-02-05T13:38:15Z (GMT). No. of bitstreams: 1 fernandes_jd_dr_bauru.pdf: 6053514 bytes, checksum: 29d477b808eb175d178bac8099416244 (MD5) Previous issue date: 2021-10-13 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Filmes finos de materiais orgânicos vêm sendo utilizados em diversas aplicações e seu arranjo supramolecular (espessura, organização molecular, morfologia, cristalinidade e agregados) é um fator determinante para suas propriedades ópticas e elétricas, implicando na escolha da aplicação tecnológica. Nesta tese de doutorado, filmes finos de dois derivados de perileno (bis butilimido perileno - acrônimo BuPTCD - e bis fenetilimido perileno - acrônimo PhPTCD) foram fabricados pelas técnicas de deposição física a vapor (PVD, do inglês Physical Vapor Deposition) e Langmuir-Shaefer (LS). Os objetivos foram investigar a influência da estrutura química das moléculas de BuPTCD e PhPTCD sobre o arranjo supramolecular nos filmes PVD e LS, e determinar como este arranjo influencia as propriedades ópticas (absorção e emissão) dos filmes finos. Os resultados obtidos neste trabalho indicam que diferenças na estrutura química molecular produz arranjos supramoleculares distintos e, consequentemente, influencia as propriedades ópticas dos filmes finos. Os filmes PVD e LS de BuPTCD apresentaram maior quantidade de agregados H, são mais cristalinos e têm menores valores de rugosidade quando comparados aos filmes PVD e LS, respectivamente, de PhPTCD. Ao comparar os filmes fabricados pela mesma técnica, foi verificado que a eficiência radiativa (ER) dos filmes fabricados com o BuPTCD é maior que do PhPTCD. Os resultados indicaram que a ER não depende apenas dos agregados J (agregados emissores), mas também de outros tipos de agregados moleculares e da cristalinidade. Complementarmente, verificou-se que a conversão interna (CI) entre os estados eletrônicos S2→S1 diminui nos filmes quando agregados moleculares e cristalinidade são favorecidos. Portanto, este trabalho demostrou que conhecer o arranjo supramolecular e sua influência sobre as propriedades ópticas é fundamental para a otimização de dispositivos optico-eletrônicos. Thin films of organic materials have been used in several applications and their supramolecular arrangement (thickness, molecular organization, morphology, crystallinity and aggregates) is a determining factor for their optical and electrical properties, implying the choice of technological application. In this PhD thesis, thin films of two perylene derivatives ((bis(butylimido)perylene - BuPTCD - and bis(phenetylimido)perylene - PhPTCD)) were produced by physical vapor deposition (PVD) and Langmuir-Shaefer (LS) techniques. The objectives were to investigate the influence of the chemical structure of the BuPTCD and PhPTCD molecules on the supramolecular arrangement of the PVD and LS films, and to determine how this supramolecular arrangement influences the optical properties (absorption and emission) of thin films. The PVD and LS films of BuPTCD showed a higher amount of H aggregates, greater crystallinity and lower values of roughness when compared with PVD and LS films, respectively, of PhPTCD. When comparing films made using the same technique, it was found that the radiative efficiency (ER) of films made with BuPTCD is greater than that of PhPTCD. The results indicated that the RE depends not only on J aggregates (emitting aggregates), but also on other types of molecular aggregates and crystallinity. In addition, it was found that the internal conversion (CI) between S2 → S1 decreases in films when molecular aggregates and crystallinity are favored. Therefore, this work demonstrated that knowing the supramolecular arrangement and its influence on optical properties is fundamental for the optimization of optical-electronic devices. 88882.330117/2019-01

In this work, we demonstrate a novel way of fabricating oriented composite nanowires consisting of arranged nanoparticles. The structures are produced by an advanced pulsed laser deposition technology involving the simultaneous ablation of two metal targets, Fe and Ag. The depositions are carried out in air at atmospheric pressure in the presence of a magnetic field by using nanosecond laser pulses delivered by a Nd:YAG laser system operating at its fundamental wavelength. Samples are thus produced composed by iron oxide and silver at different percentage ratios. Their morphology represents nanowires with few tens of microns in length and an orientation predominantly following the direction of the magnetic force lines. The study on the optical properties of the structures thus produced revealed plasmon resonance behavior in their transmission spectra with its position depending on the ratio between the two building materials. UV–vis spectra were also obtained with polarized light. Higher transmission was measured for light polarized perpendicular to the length of the nanowires, compared to the case of polarization parallel to the nanowires. The structures can find applications in the design of novel polarization and magneto-optics devices, as well as in nanoelectronics and spintronics.

Bimetallic nanoparticles have a myriad of technological applications, but investigations of their chemical and physical properties are precluded due to their structural complexity. Here, the chemical ordering and optical properties of AgPd, AuPd, and AuPt nanoparticles have been studied computationally. One of the main aims was to clarify whether layered ordered phases similar to L11 one observed in the core of AgPt nanoparticles [ Pirart, J.; et al. Nat. Commun. 2019, 10, 1982 ] are also stabilized in other nanoalloys of coinage metals with platinum-group metals, or the remarkable ordering is a peculiarity only of AgPt nanoparticles. Furthermore, the effects of different chemical orderings and compositions of the nanoalloys on their optical properties have been explored. Particles with a truncated octahedral geometry containing 201 and 405 atoms have been modeled. For each particle, the studied stoichiometries of the Ag- or Au-rich compositions, ca. 4:1 for 201-atomic particles and ca. 3:1 for 405-atomic particles, corresponded to the layered structures L11 and L10 inside the monatomic coinage-metal skins. Density functional theory (DFT) calculations combined with a recently developed topological (TOP) approach [ Kozlov, S. M.; et al. Chem. Sci. 2015, 6, 3868-3880 ] have been performed to study the chemical ordering of the particles, whose optical properties have been investigated using the time-dependent DFT method. The obtained results revealed that the remarkable ordering L11 of inner atoms can be noticeably favored only in small AgPt particles and much less in AgPd ones, whereas this L11 ordering in analogous Au-containing nanoalloys is significantly less stable compared to other calculated lowest-energy orderings. Optical properties were found to be more dependent on the composition (concentration of two metals) than on the chemical ordering. Both Pt and Pd elements promote the quenching of the plasmon.

Different scattering processes take place when photons propagate inside turbid media. Many powerful experimental techniques exploiting these processes have been developed and applied over the years in a large variety of situations from fundamental and applied research to industrial applications. In the present paper, we intend to take advantage of Static Light Scattering (SLS), Dynamic Light Scattering (DLS), and Time-Resolved Transmittance (TRT) for investigating all the different scattering regimes by using scattering suspensions in a very large range of scatterer concentrations. The suspensions were prepared using Intralipid 20%, a material largely employed in studies of the optical properties of turbid media, with concentrations from 10&minus, 5% to 50%. By the analysis of the angular and temporal dependence of the scattered light, a more reliable description of the scattering process occurring in these samples can be obtained. TRT measurements allowed us to obtain information on the reduced scattering coefficient, an important parameter largely used in the description of the optical properties of turbid media. TRT was also employed for the detection of inclusions embedded in Intralipid suspensions, by using a properly designed data analysis. The present study allowed us to better elucidate the dependence of scattering properties of Intralipid suspensions in a very large concentration range and the occurrence of the different scattering processes involved in the propagation of light in turbid media for the first time to our knowledge. In so doing, the complementary contribution of SLS, DLS, and TRT in the characterization of turbid media from an optical and structural point of view is strongly evidenced.

A novel crystal scintillator of RbBa2I5:Eu2+ was grown by the Bridgman–Stockbarger method. Its luminescence and scintillation properties were investigated. Under X-ray excitation, the crystal demonstrates blue luminescence peaking at 436 nm associated with 4f65d1→ 4f7 radiative transitions of Eu2+ ions. The main X-ray luminescence decay constant is 800 ns. The light output of RbBa2I5:3%Eu2+ sample under 662 keV excitation is 58,200 ph/MeV.

In this source apportionment study, an original approach based on receptor modelling was tested to relate primary and secondary organic aerosol (OA) contributions - estimated from ACSM (Aerosol Chemical Speciation Monitor) measurements - to their emission sources. Moreover, thanks to the coupling of optical and chemical variables as input to the receptor model, information such as the impact of mineral dust to the aerosol absorption in the atmosphere and estimates for the absorption Ångström exponent (α) of the sources were retrieved. An advanced source apportionment study using the Multilinear Engine (ME-2) was performed on data collected during February 2017 in Rome (Italy), in the frame of the CARE (Carbonaceous Aerosol in Rome and Environs) experiment. A complete chemical characterisation (elements, non-refractory components, and carbonaceous components) was carried out, and the aerosol absorption coefficients b(λ) at 7 wavelengths (370, 470, 520, 590, 660, 880, and 950 nm) were retrieved by an Aethalometer AE33; all these variables (chemical + optical) were used as input to the receptor model. The final constrained solution consisted of nine factors which were assigned to major sources impacting on the investigated site (hereafter sources are referred to as: biomass burning, nitrate and aged aerosol, traffic exhaust, sulphate, mineral dust, marine aerosol, traffic non-exhaust, local source, and polluted marine aerosol), comprising both local urban sources and contributions from long-range transport. The bootstrap analysis supported the goodness of the solution. Total OA concentration from ACSM was apportioned by our receptor model and afterwards compared with HOA (hydrocarbon-like organic aerosol), BBOA (biomass burning-like organic aerosol), and OOA (oxygenated organic aerosol) concentrations obtained as results from an independent source apportionment study previously performed. As an original result of this work, insights on OA contributions were thus retrieved: (1) the contribution of organic aerosol assigned by ME-2 to the traffic exhaust source was fully comparable to HOA assessed by ACSM data analysis; (2) our source apportionment results gave the relevant indication that the OOA apportionment made on ACSM data likely includes a secondary OA contribution due to biomass burning. Other relevant results came from b apportionment obtained by our multi-variable source apportionment approach: traffic exhaust was the main contributor to aerosol absorption in the atmosphere, but mineral dust contribution was also notable when a not negligible mineral dust transport episode was registered at the measurement site. In addition, source dependent optical absorption parameters (i.e. the absorption Ångström exponent - α - and the mass absorption cross section at different wavelengths) were retrieved without any a-priori assumption. In perspective, our modelling approach paves the way to more powerful source apportionment approaches which have the potential of providing much more insights on aerosol properties and sources., The CARE experiment was realised under the patronage of the Councilor for environmental sustainability of Roma Capitale. The authors are grateful to all members of the research groups who participated to the CARE experiment.

The handling of inorganic scintillators (e.g., alkali metal halides) can benefit from the availability of polymeric materials able to adhere to their surface. Polymeric materials, such as epoxy resins, can act as protective coatings, as adhesives for photodiodes to be connected with the scintillator surface, and as a matrix for functional fillers to improve the optical properties of scintillators. Here, the optical properties of two epoxy resins (E-30 by Prochima, and Technovit Epox by Heraeus Kulzer) deposited on the surface of a scintillator crystal made of CsI(Tl) were investigated, in order to improve the detection of high-energy radiation. It is found that these resins are capable of adhering to the surface of alkali metal halides. Adhesion, active at the epoxy–CsI(Tl) interface, can be explained on the basis of Coulomb forces acting between the ionic solid surface and an ionic intermediate of synthesis generated during the epoxy setting reaction. Technovit Epox showed higher transparency, and it was also functionalized by embedding white powdered pigments (PTFE or BaSO4) to achieve an optically reflective coating on the scintillator surface.

The knowledge of how the different types of nitrogen centers affect the electrochemical and optical properties of Nitrogen-doped carbon quantum dots (N-CDs) is of paramount importance in the design and synthesis of these nanostructures. In fact, from the knowledge of the redox centers of N-CDs it is possible tune their energetic levels in order to realize the suitable matches for the design of opto-electronic, photovoltaic or catalytic devices. Herein we present a study of the electrochemical and the optical responses of N-CDs, obtained by hydrothermal method from citric acid and urea. The main issue is to investigate the role played by the specific nitrogen centers in their redox processes. From the voltammetric responses we showed that the observed oxidation processes of N-CDs involve their graphitic and pyrrolic N-atoms, respectively, while the reduction process regards their protonated pyridinic N-atoms. Then, from spectro-electrochemical determinations, we explained that the oxidation of the graphitic N-atoms is a two electron process that gives an N-oxide form through the reaction with a molecule of water and the loss of two protons. Finally we discussed the observed pH-dependence of both the optical and the electrochemical responses of our N-CDs to explain the role played by their pyridinic N-atoms.

International audience; Silica-based optical fibers, fiber-based devices and optical fiber sensors are today integrated in a variety of harsh environments associated with radiation constraints. Under irradiation, the macroscopic properties of the optical fibers are modified through three main basic mechanisms: the radiation induced attenuation, the radiation induced emission and the radiation induced refractive index change. Depending on the fiber profile of use, these phenomena differently contribute to the degradation of the fiber performances and then have to be either mitigated for radiation tolerant systems or exploited to design radiation detectors and dosimeters. Considering the strong impact of radiation on key applications such as data transfer or sensing in space, fusion and fission-related facilities or high energy physics facilities, since 1970′s numerous experimental and theoretical studies have been conducted to identify the microscopic origins of these changes. The observed degradation can be explained through the generation by ionization or displacement damages of point defects in the differently doped amorphous glass (SiO2) of the fiber's core and cladding layers. Indeed, the fiber chemical composition (dopants/concentrations) and elaboration processes play an important role. Consequently, identifying the nature, the properties and the generation and bleaching mechanisms of these point defects is mandatory in order to imagine ways to control the fiber radiation behaviors. In this review paper, the responses of the main classes of silica-based optical fibers are presented: radiation tolerant pure-silica core or fluorine doped optical fibers, germanosilicate optical fibers and radiation sensitive phosphosilicate and aluminosilicate optical fibers. Our current knowledge about the nature and optical properties of the point defects related to silica and these main dopants is presented. The efficiency of the known defects to reproduce the transient and steady state radiation induced attenuation between 300 nm and 2 µm wavelength range is discussed. The main parameters, related to the fibers themselves or extrinsic - harsh environments, profile of use - affecting the concentration, growth and decay kinetics of those defects are also reviewed. Finally, the main remaining challenges are discussed, including the increasing needs for accurate and multi-physics modeling tools.

A closure experiment was conducted over Svalbard by comparing Lidar measurements and optical aerosol properties calculated from aerosol vertical profiles measured using a tethered balloon. Arctic Haze was present together with Icelandic dust. Chemical analysis of filter samples, aerosol size distribution and a full set of meteorological parameters were determined at ground. Moreover, scanning electron microscopy coupled with energy-dispersive X-ray (SEM-EDS) data were at disposal showing the presence of several mineralogical phases (i.e., sheet silicates, gypsum, quartz, rutile, hematite). The closure experiment was set up by calculating the backscattering coefficients from tethered balloon data and comparing them with the corresponding lidar profiles. This was preformed in three subsequent steps aimed at determining the importance of a complete aerosol speciation: (i) a simple, columnar refractive index was obtained by the closest Aerosol Robotic Network (AERONET) station, (ii) the role of water-soluble components, elemental carbon and organic matter (EC/OM) was addressed, (iii) the dust composition was included. When considering the AERONET data, or only the ionic water-soluble components and the EC/OM fraction, results showed an underestimation of the backscattering lidar signal up to 76, 53 and 45% (355, 532 and 1064 nm). Instead, when the dust contribution was included, the underestimation disappeared and the vertically-averaged, backscattering coefficients (1.45±0.30, 0.69±0.15 and 0.34±0.08 Mm-1 sr-1, at 355, 532 and 1064 nm) were found in keeping with the lidar ones (1.60±0.22, 0.75±0.16 and 0.31±0.08 Mm-1 sr-1). Final results were characterized by low RMSE (0.36, 0.08 and 0.04 Mm-1 sr-1) and a high linear correlation (R2 of 0.992, 0.992 and 0.994) with slopes close to one (1.368, 0.931 and 0.977, respectively). This work highlighted the importance of all the aerosol components and of the synergy between single particle and bulk chemical analysis for the optical property characterization in the Arctic .

Inversion-symmetric crystals are optically isotropic and thus naively not expected to show dichroism effects in optical absorption and photoemission processes. Here, we find a strong linear dichroism effect (up to 42.4%) in the conduction band of inversion-symmetric bilayer MoS$_2$, when measuring energy- and momentum-resolved snapshots of excited electrons by time- and angle-resolved photoemission spectroscopy. We model the polarization-dependent photoemission intensity in the transiently-populated conduction band using the semiconductor Bloch equations and show that the observed dichroism emerges from intralayer single-particle effects within the isotropic part of the dispersion. This leads to optical excitations with an anisotropic momentum-dependence in an otherwise inversion symmetric material., Comment: 10 pages including supporting information, 3 figures in the main paper and 4 figures in the supporting information

In spite of the advances in laser diagnostics in combustion, the effect of rapid laser irradiation on the physical/chemical properties of soot particles is far from being comprehensively understood. Optical properties, particle nanostructure and aggregate size of laser-irradiated soot particles are analyzed in this paper. Carbonaceous particles sampled from nitrogen-quenched diffusion flames of ethylene and methane are irradiated on-line by a 1064-nm short laser pulse. Wavelength-resolved extinction measurements in the visible range are used to follow their transformation by varying the laser energy density. A variation of the extinction coefficient of the irradiated particles compared to the extinction coefficient of the pristine ones is observed, especially for ethylene soot. The particle nanostructures are analyzed by Raman spectroscopy and the effect of laser irradiation on aggregate structure is evaluated by measuring particle size distributions. The results indicate that both soot nanostructure and optical properties are strongly dependent on the laser energy density when irradiated by a laser source. This is significant for ethylene soot, while for methane soot the degree of variation of such properties is less pronounced, at least in the investigated heating conditions. © 2020 Elsevier Inc.

Large transparent surfaces in building façades can be a cause of high energy demand and discomfort conditions in buildings. Since standard static solutions for glazing and shading devices are not sufficient to overcome these drawbacks, a new dynamic shading device based on the integration of phase change materials (PCM) in an alveolar polycarbonate panel was proposed. The concept of the innovative translucent shading is to act as a self-controlling device able to reduce and modulate both light and solar heat gain in the indoor environment and to improve the thermal inertia of the envelope. To provide input data for energy and daylighting computational tools on a building scale, a complete thermal and optical characterisation of the PCMs and of the dynamic shading systems was carried out. Different typologies of PCM (paraffin waxes, salt hydrates and bio-based PCMs) with different melting temperature (in the range of 26–44 °C) and different colour of the polycarbonate panel (blue, green, opal and crystal) were investigated. Specific experimental protocols were implemented to compare the properties of various configurations of the new technology. Results show that the preferable PCMs are the paraffin waxes, due to their stable thermal properties, high latent heat of fusion and narrow melting temperature range. With regard to the thermal resistance of the system, a slightly better performance was measured with the bio-based PCM. According to the optical characterisation, it can be stated that the preferable colours of polycarbonate are green and crystal. The outcomes are promising, but several limits still need to be overcome at the technological and architectural level. © 2017 Elsevier B.V.

During the last decades many studies have been carried out to investigate how point defects and aggregates respond and evolve in natural Type Ia diamonds as a result of treatments, and a number of underlying mechanisms have been identified and interpreted. However, the analysis of radiation-induced creation/ionization of defects, as well as their migration and aggregation in secondary defect structures, often requires experimental approaches which can hardly constitute a simple-to-use diagnostic tool for the identification of artificially treated diamonds. Here we disclose a novel simple indicator of artificial exposure of Type Ia diamonds to ionizing radiations and subsequent annealing. This indicator consists in narrow photoluminescence lines in the red region, between 681 and 725 nm, we recently found to result from vacancies trapped by interstitial carbon aggregates and platelets. Our results demonstrate that interstitial structures become sites of vacancy trapping – by thermal migration of radiation-induced vacancies – only when diamond undergoes treatments. We give the rigorous validation of the new spectroscopic probe of artificial treatments analysing photoluminescence and infrared absorption spectra of well-known H1b and H1c centres in a hundred samples. Importantly, the method is based on emission lines which do not require neither high photon-energy excitation nor cryogenic temperatures.

Polycarbonate panels could be considered as a suitable and cheap solution for walls, roofs, and sheds in non-residential buildings and, at the same time, granular silica aerogel is one of the most promising nano-materials for energy saving in buildings. In the paper, three types of advanced multiwall PC panels (thickness 16, 25, and 40 mm) with translucent granular aerogel were investigated by experimental (thermal and optical) and numerical characterization. By comparing thermal performance of air and aerogel-filled PC systems, it can be noticed that the impact of the aerogel is remarkable: the reduction in U-value is 46%-68%, depending on the aerogel layer thickness. U-value is 1.4 W/m2K for the 16 mm thickness sample and it is 0.6 W/m2K when the thickness increases up to 40 mm. The systems keep their performance in horizontal position, when they are used as roofs. Light transmittance is 0.61 and 0.42 for 16 mm and 40 mm respectively and the reduction with respect to air-filled panels is acceptable (15%) for 16 mm and significant (40%) for 40 mm thickness. The aerogel has also a remarkable impact on the reflectance spectrum, especially between 400 and 1400 nm. The solar factor is 0.58 for 25 mm thickness, quite similar to the low-e glazing one. Finally, energy simulations for a case study showed that aerogel-filled PC systems outperform conventional double glazing systems both for heating and cooling energy demands. However, when compared to low-e glazings, the benefits of the translucent material (also considering the highest thickness) in the interspace are lower for heating and negligible for cooling energy demands. The aerogel-filled polycarbonate systems could be a valid solution for non-residential buildings, enhancing the thermal performance and the light control of the building envelope, especially when they are used as roofs. © 2018 Elsevier B.V.

An analytical overview of experimental results about the heat transfer capabilities of nanofluids is presented, using widely scattered available information from diverse literature sources. It is shown that, despite the large number of publications available about this issue, only few studies provide quantitative estimates on a complete set of experimental conditions so far and many studies are not coherent. Bearing in mind this problem, in this study a selection of the most valuable papers has been done, taking into account different points of view and hypotheses. Even if this work cannot be considered exhaustive of the complete literature in the field of nanofluids, it can be taken into account as a quick reference guide to have an overview of the different heat transfer phenomena in nanofluids and how the most important parameters (size, shape, concentration, materials etc.) influence the expected thermal performance of nanofluids. (C) 2014 Elsevier Ltd. All rights reserved.

In grape berries, extreme oxidative stress results in skin tissue bleaching and brownish areas appearance. Thus, these damages could negatively affect the fruit quality and the commercial value. The paper focuses on the chlorophyll roles in sunburn symptoms appearance in white skinned grape berries. In the present work, 20 cultivars were studied in three phenological stages. Berries were kept under temperature and light controlled conditions. Chlorophyll content and symptom appearance were quantified by reflectance spectroscopy indexes. The central role of radiation (and, thus, photo-oxidative damages) in berry sunburn injuries was underlined. Cultivars were classified, based on their susceptible or tolerant responses to radiation excess.

The radiative properties of Dy-doped glasses and glass-ceramic phosphors with varying lead and cadmium fluoride content are investigated in the present study for white light emitting applications. The precipitation of cubic lead fluoride phase of 10-18 nm crystallites was determined with the help of x-ray diffraction studies and the nanocrystalline nature was confirmed with scanning electron microscopy studies. The small size of the nanocrystallites enables the fabrication of transparent glass-ceramics which is verified by UV-vis spectroscopic study. The photoluminescence and lifetime measurements indicate towards progressive changes in the Dy3+ ion surroundings and propose enhanced energy transfers taking place post-heat treatments. Finally, CIE chromaticity coordinates are found to lie in the white region proposing the suitability of the present studied materials for color display devices. ©2014 Elsevier B.V. All rights reserved.

This study presents a new bionanocomposite coating on poly(ethylene terephthalate) (PET) made of pullulan and synthetic mica. Mica nanolayers have a very high aspect ratio (α), at levels much greater than that of conventional exfoliated clay layers (e.g., montmorillonite). A very small amount of mica (0.02 wt %, which is φ ≈ 0.00008) in pullulan coatings dramatically improved the oxygen barrier performance of the nanocomposite films under dry conditions, however, this performance was partly lost as the environmental relative humidity (RH) increased. This outcome was explained in terms of the perturbation of the spatial ordering of mica sheets within the main pullulan phase, because of RH fluctuations. This was confirmed by modelling of the experimental oxygen transmission rate (OTR) data according to Cussler’s model. The presence of the synthetic nanobuilding block (NBB) led to a decrease in both static and kinetic coefficients of friction, compared with neat PET (≈12% and 23%, respectively) and PET coated with unloaded pullulan (≈26% reduction in both coefficients). In spite of the presence of the filler, all of the coating formulations did not significantly impair the overall optical properties of the final material, which exhibited haze values below 3% and transmittance above 85%. The only exception to this was represented by the formulation with the highest loading of mica (1.5 wt %, which is φ ≈ 0.01). These findings revealed, for the first time, the potential of the NBB mica to produce nanocomposite coatings in combination with biopolymers for the generation of new functional features, such as transparent high oxygen barrier materials., University of Milan-Action "Research Support Plan" (15-6-3024000-402)

Zinc oxide (ZnO) nanoparticles were synthesized on diatomite (DE) surface by a low temperature sol gel technique, starting from zinc acetate dihydrate (Zn(CH3COO)2 • 2H2O) solution in water/ethyl alcohol, in presence of triethanolamine (TEA) with functions of Zn2+ chelating agent, catalyst and mediator of nanoparticle growth on DE surface. Microstructural features were investigated by field emission scanning electron microscopy and x-ray diffraction. ZnO crystalline nanoparticles, well distributed both on the surface and into the porous architecture of diatomite, were obtained just after the synthesis carried out at 80 °C without the need of calcination treatments. The optical properties of ZnO/DE hybrid powders were measured for the first time by means of photoacoustic spectroscopy (PAS). A new method to retrieve both the optical absorption and scattering coefficients from PAS is here discussed for powder aggregates. The fingerprint of the zinc oxide nanoparticles has been highlighted in the Mie scattering resonance in the UV-Vis range, and in the enhancement of the optical absorption with respect to diatomite. © 2017 IOP Publishing Ltd.

The market penetration of polycarbonate (PC) multi-sheets panels for building applications is increasing due to intrinsic properties of the material: high transparency, reduced weight if compared to glass and competitive costs. The presence of air gaps within the panel assures good thermal insulation; however, to further improve the thermal properties of the component, the air gaps can be filled by granular silica aerogel. These materials are also characterized by high scattering optical properties, so that the incident radiation can be diffused in the built environment, preventing from glare. This paper deals with the characterization of several configurations of PC systems, differing in thickness and geometry. Thermal transmittance measurements were carried out using a guarded hot plate apparatus, according to EN 674:2011. Spectral transmittance and reflectance measurements were carried out by means of a large integrating sphere apparatus, broad-band light and solar quantities were then calculated. A valid data set of product specification is thus provided. The investigated polycarbonate systems could be a valid solution in place of classic windows for non-residential buildings, enhance the thermal insulation and the light control of the building envelope, thus providing improved comfort conditions for occupants. © 2017 The Authors. Published by Elsevier Ltd.

Cu2ZnSnS4 (CZTS) thin films and solar cells were successfully prepared using a new process based on spray pyrolysis technique. The main advantage of the proposed process is the avoiding of sulphurisation process at high temperature and in toxic gases like H2S. X-ray diffraction studies and Raman spectroscopy confirmed the formation of good-quality microcrystalline CZTS films in a tetragonal structure. Optical measurements showed that CZTS films have a direct band gap and high absorption coefficient (4 × 104 cm−1) as requested for solar cell application. CZTS solar cell prototypes deposited on low-cost flexible plastic substrates were prepared and tested.

Optical techniques are increasingly employed for monitoring cell–matrix interactions in suitably prepared 3D scaffolds. The ability of designing and realizing synthetic extracellular matrix with well-controlled optical properties is a crucial need in this field. For this purpose a crosslinked hyaluronic acid (HA) scaffold is prepared. Fourier transform infrared and UV–vis spectroscopies enable to monitor the scaffold preparation process and to evidence scaffold high transparency and low fluorescence in the visible range. 3D optical characteristics of the HA scaffold are tested by two-photon microscopy (TPM) imaging of embedded fluorescent microbeads and alive keratinocytes labeled with vital PKH67 dye at different depths from the scaffold surface. Some useful indications about the potentiality of TPM measurements for the determination of attenuation coefficient of turbid media are also reported. Moreover, the use of the presented HA scaffold for preparing tissue phantoms for fluorescence imaging or diffuse imaging is proposed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45243.

The considerable spread of Cu2ZnSnS4 (CZTS) optical properties reported in the literature is discussed in terms of material stoichiometry. To this purpose, kesterite thin films were prepared by sulfurization of multilayered precursors of ZnS, Cu and Sn, changing the relative amounts to obtain CZTS layers with different compositions. X-Ray Diffraction (XRD), Energy Dispersive X-Ray (EDX) spectroscopy, X-Ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy were used for structural and compositional analysis. XRD quantitative phase analysis provides the amount of spurious phases and information on Sn-site occupancy. The optical properties were investigated by spectrophotometric and Photothermal Deflection Spectroscopy (PDS) measurements to assess the absorption coefficient of samples with different compositions. The PDS data show an increase of the sub-band absorption as the Sn content decreases. The results are interpreted assuming the formation of additional defects as the tin content is reduced. Those defects can also be responsible for the decrease of the band gap energy value as the Sn/Cu ratio is decreased. © 2013 Elsevier B.V. All rights reserved.