1,721,009 research outputs found
Bismuth-based advanced luminescent (nano)materials: from design to application
No full textL’attività di ricerca oggetto della tesi è focalizzata sullo studio di materiali nanostrutturati e non a base di bismuto e relativi composti aventi proprietà ottiche avanzate. Nello specifico, data la peculiare attività di luminescenza, per i materiali investigati si prevedono interessanti potenzialità per applicazioni come (nano)fosfori per la fotonica, nel bioimaging, come sensori termici, nell’anticontraffazione. La parte preponderante della ricerca ha quindi riguardato la caratterizzazione ottica dei sistemi oggetto di studio e, in particolare, la definizione e la modellizzazione dei meccanismi di luminescenza. Inoltre, al fine di incrementare l’efficienza e di aumentare il controllo della risposta in emissione, è stata sviluppata anche un’approfondita attività in relazione allo studio dell’evoluzione strutturale del materiale e all’ottimizzazione dei processi di sintesi.
Nell’ambito della macrotematica relativa ai (nano)materiali a base di bismuto, di seguito vengono specificati i sistemi oggetto della ricerca:
a) controllo della struttura in nanoparticelle di bismuta drogata con ioni lantanidi e studio dei processi di upconversion (UC) per l’attivazione delle emissioni di fluorescenza nel visibile tramite pompaggio ottico nell’IR;
b) studio del meccanismo di formazione di sistemi core-shell in nanoparticelle di silicato di bismuto drogate con ioni lantanidi;
c) studio delle fluorescenze dello ione Cr3+ in Bi2Ga4O9 e definizione delle potenzialità per l’utilizzo come sensore termico luminescente;
d) stabilizzazione dei polimorfi della bismuta tramite confinamento quantico in strutture a dimensionalità ridotta e studio delle proprietà ottiche;
e) studio della luminescenza “persistente” nel sistema Bi2+/3+ in CaSnO3;
f) sintesi di nanoparticelle di Y2O3 drogate con ioni Bi3+ e Er3+ e studio dei processi di energy transfer
Determining europium compositional fluctuations in partially stabilized zirconia nanopowders: a non-line-broadening-based method
No full textA method is reported for assessing the compositional fluctuations in a ceramic
sample, based only on the determination of the crystalline lattice parameters.
Pure tetragonal phase partially stabilized zirconia powders are synthesized
through the co-precipitation method by incorporating 4% Eu3+. The powder is
subjected to compression cycles to promote the tetragonal-to-monoclinic
transformation. The Rietveld analysis of the X-ray powder diffraction patterns,
recorded after each compression cycle, gives information about the lattice
parameters and monoclinic phase content. The determination of europium
content in the residual tetragonal phase is accomplished considering the unit cell
volume of t-ZrO2 using Vegard’s law. Using this information the compositional
fluctuations over the sample were determined by considering two possible
distributions of lanthanide ion content in the powders: a Gaussian and a Lognormal
one. It was found that the Gaussian distribution better fits the
experimental data. It was eventually demonstrated that these results are
physically meaningful
Ratiometric Optical Thermometer Based on Dual Near-Infrared Emission in Cr3+-Doped Bismuth-Based Gallate Host
No full textDetailed spectroscopic analysis of the electronic configuration of Cr3+ in Bi2Ga4O9 is reported. The material exhibits unique luminescent properties arising from the crystal field experienced by Cr3+, with simultaneous strong sharp and broadband near-infrared emissions from the 2E and 4T2 excited states, in a wide range of temperature. The system displays dual near-infrared emission characterized by a remarkable thermal sensitivity over the whole explored range of temperatures, reaching a value of 0.7 %•K-1 in the physiological range. Moreover, the possibility to absorb and emit in the first biological window, allows to consider the system as a new promising candidate for ratiometric fluorescent thermal sensing in biotechnological applications
BISMUTH SILICATE NANOPARTICLES: STRUCTURAL CONTROL AND RARE EARTH DOPING FOR UPCONVERSION
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Unexpected behavior of the 1.54 μm luminescence in Er-doped silica films
No full textMaterials such as Er:glass are still of great interest in optical communication technology for their applications in photonic devices operating at the standard telecommunication wavelengths. The 1.54 μm emission properties of the Er3+ ions embedded in glassy systems depend on several factors, as for instance the synthesis technique and the thermal history of the material. A photoluminescence investigation, made on Er:SiO2 thin films deposited by PVD for a wide range of different Er concentration and subsequently annealed in the range 50–1200 °C (with 50 °C step), was done to investigate in which way both Er concentration and thermal annealing influence the 1.54 μm emission performance of the Er:SiO2 glass system. For low Er concentration, we evidenced an unexpected 1.54 μm activity also after annealing at temperatures much lower than the usual ones. We suspect that this behavior could be related to the medium/long-range order around the Er3+ ions, as a possible consequence of local silica polymorphs formation
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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