1,720,999 research outputs found
POSTER-Summer school "NANO–OPTICS: PRINCIPLES ENABLING BASIC RESEARCH AND APPLICATIONS" -Erice, Sicily, Italy; July 4-19, 2015
No full textPOSTER- Summer School- INTERNATIONAL SCHOOL OF ATOMIC AND MOLECULAR SPECTROSCOPY/NANO–OPTICS: PRINCIPLES ENABLING BASIC RESEARCH AND APPLICATIONS- presso ETTORE MAJORANA FOUNDATION AND CENTRE FOR SCIENTIFIC CULTURE ( Erice, Sicily, Italy; July 4-19, 2015) che illustra Topics and Lecturers della Scuola Internazionale e le informazioni per la Applicatio
Surface energy and nucleation modes
No full textDeposition is a manufacturing process in which a precursor material is delivered to a surface on which it reorganizes by interplay between thermodynamics and kinetics. The evolution of the microstructure of the deposit (layers with thicknesses between a few atomic layers and several micrometers [films] or nanostructure distributions or nanostructured films) is highly dependent on the physical conditions (i.e., the deposition technique and parameters) under which deposition takes place, apart from the choice of materials. Understanding the mechanisms underlying the structural and morphological evolution of a growing deposit is essential to being able to tailor the properties and performances of functional materials at the atomic scale depending on the deposition approach. In this chapter a comprehensive overview to the classical theory of growth will be given, with a focus on the importance of kinetic factors and processes as well as the growth manipulations enabled by a prototypal far-from-equilibrium deposition technique, such as
pulsed laser depositio
Luminescence spectroscopy of nanophosphors
No full textThe properties of phosphor materials in nanoscale form, usually termed “nanophosphors”, present particular aspects that are worthy of extensive investigations at both fundamental and applicative level. Nanophosphors are mainly represented by compounds doped with rare earths, whose 4f optically active electrons are protected from static and dynamic perturbations by the 5s and 5p subshells. In this paper we first review the spectroscopy of rare earth ions and the properties of bulk phosphors (physical mechanisms underlying luminescence processes, thermal line broadening and line shift) and then consider the corresponding scenario at the nanoscale and discuss the role that spectroscopy may play in the investigation of nanophosphors. The paper aims at giving a background to a reader new to the spectroscopy of nanophosphors and useful points of discussion as well as guidelines for further studies
Nanophosphors: From rare earth activated multicolor-tuning to new efficient white light sources
No full textThe huge and impossible to list number of publications dealing with luminescent materials demonstrates widespread interest at both fundamental and technological level in their spectroscopic properties and applications. Moreover consequences, opportunities and challenges of spatial confinement have prompted worldwide interest in nanoscale-sized luminescent materials, termed nanophosphors (n-PSPs) as a valid alternative to fluorophores and semiconductor quantum dots. In this contribution the main classes of luminescent materials as well as spectroscopy of rare earth (RE)-activated phosphors (PSP) are first overviewed with focus on REs’ transitions, luminescence mechanisms, electron-lattice dynamics, thermal line broadening and line shift. Then, the corresponding scenario for n-PSPs is presented and discussed, by providing many examples, with focus on the effects of spatial confinement and surface-to-volume ratio on luminescence efficiency, lifetime of the excited states, electron-phonon dynamics, luminescence quenching, confinement of dopants and tuning of multicolor emission. In particular, RE-activated multicolor emission is intensively investigated to produce white light for indoor and outdoor lighting. In this respect, recent reports are mentioned about a new class of efficient broadband white light emitting n-PSPs consisting of nominally un-doped RE-free oxide nanopowders and TM-doped hosts with temperature-independent emission. The novelty of this approach lies in presenting a route alternative to the presently investigated strategies to obtain WL sources that mainly include RE dopants and single-phase compounds containing REs as stoichiometric components
Nanomaterials: Basic concepts and quantum models
No full textThe term “nanosystem” refers to a system with at least one spatial dimension scaled down to the nanometer-scale (<100 nm) and includes zerodimensional systems (such as metallic, semiconducting and ceramic nanoparticles), one-dimensional systems (such as nanowires, nanotubes and nanorods) and twodimensional structures (thin films or plates). The fascinating properties of materials at the nanoscale are continuing to attract the scientific interest in many research fields at both applicative and fundamental levels. The impossible to comprehensively review large number of reports and results available in the literature demonstrates the complexity in describing all the functionalities offered by the nanosystems as well as their properties as related to their fabrication approaches apart from departure from bulk form. To be able to gain insight into the potentialities and new future perspectives offered by the nanoworld and nanotechnology, knowledge and understanding of the physical fundamentals is a necessary starting point. In this review paper, we consider and discuss the spectroscopy of nanomaterials by pointing out differences and breaking points as compared to the bulk counterparts, the importance of the surfaces, the characteristic length-scales (De Broglie wavelength, Fermi wavelength and exciton Bohr radius) that define various confinement regimes, the physics underlying the formalism to calculate the electronic dispersion of the low-dimensionality systems and the technological benefits on the excitonic binding energy implied by low-dimensionality (zero-, one- and twodimensionaity). The presented discussion aims at laying a foundation to further studies for a reader new to the field of nanomaterials
Impurity-vacancy complexes and ferromagnetism in doped sesquioxides
No full textBased on hybrid density-functional calculations, we propose that ferromagnetism in the prototypical bixbyite sesquioxide In2O3 doped with Cr is due to Cr-oxygen vacancy complexes, while isolated Cr cannot support carrier-mediated magnetic coupling. Our proposal is consistent with experimental facts such as the onset of ferromagnetism in O-lean conditions only, the low or vanishing net moment in unintentionally doped material, and its increase upon intentional doping. © 2014 American Physical Society
On the efficient warm white-light emission from nano-sized Y2O3
No full textWe consider the reported emission of white light (WL) in the spectral range from 400 to beyond 900 nm induced by monochromatic infrared light (803.5 and 975 nm) continuous wave excitation of nominally un-doped yttrium oxide (Y2O3) nano-powders. Based on the experimental evidence, such an emission feature is a nano-scale phenomenon, resembles very closely the emission from an incandescent lamp (mimicking the sunlight, i.e., the most comfortable light to human eyes) and exhibits very high efficiency (864 lum/W) and nearly theoretical (i.e., 99) color rendering index. At the fundamental level, the origin of this phenomenon is still unexplained. In this paper we address the fundamental questions raised by the reported occurrence of WL emission from Y2O3 nanopowders and attempt an interpretation at a more fundamental level. In particular we focus on the multiphoton-absorption and nonexponential decay patterns of the reported WL emission as starting points to formulate models and interpretations of the experimental occurrences still lacking in the literature. Our discussion invokes the electronic dispersion of Y2O3 and nanoscale effects, which is supported by the experimental evidence according to which the observed warm WL emission is a nanoscale phenomenon with properties that only can be explained by nanoscale physics
Nanophosphors-Based White Light Sources
Full text linkMiniaturization requests and progress in nanofabrication are prompting worldwide interest in nanophosphors as white-emission mercury-free lighting sources. By comparison with their bulk counterparts, nanophosphors exhibit reduced concentration quenching effects and a great potential to enhance luminescence efficiency and tunability. In this paper, the physics of the nanophoshors is overviewed with a focus on the impact of spatial confinement and surface-to-volume ratio on the luminescence issue, as well as rare earth-activated multicolor emission for white light (WL) output. In this respect, the prominently practiced strategies to achieve WL emission are single nanophosphors directly yielding WL by means of co-doping and superposition of the individual red, green, and blue emissions from different nanophosphors. Recently, a new class of efficient broadband WL emitting nanophosphors has been proposed, i.e., nominally un-doped rare earth free oxide (yttrium oxide, Y2O3) nanopowders and Cr transition metal-doped garnet nanocrystals. In regard to this unconventional WL emission, the main points are: it is strictly a nanoscale phenomenon, the presence of an emitting center may favor WL emission without being necessary for observing it, and, its inherent origin is still unknown. A comparison between such an unconventional WL emission and the existing literature is presented to point out its novelty and superior lighting performances
Practical strategy to realistically measure the swelling ratio of poly(dimethylsiloxane) without underestimation due to the solvent volatility
No full textWe present an experimental method for measuring “realistically” the swelling ratio in terms of weight (SRW) of PDMS, where “realistically” means without the underestimation involved by the standard protocol (weight-measurements in open environment with time-delay incompatible with fast solvent evaporation rate). Comparison with the literature demonstrates that misleading conclusions can result under application of the standard protocol to very volatile solvents. To discuss this point, we develop a mathematical expression of SRW including solvent properties and the effective amount of sorbed solvent determining a weight gain, consider two solvents with different volatility that severely swell PDMS (i.e., toluene and dichloromethane), check that the results of our measurements are consistent with theoretical predictions, demonstrate that our protocol rules out any dependence of SRW on the solvent volatility and its reliability to measure and compare SRW values of PDMS (or any swelling polymer/soft material) in the case of solvents with very different volatility
Silver nanoparticles in complex biological media: assessment of colloidal stability and protein corona formation
No full textEngineered silver nanoparticles (AgNPs) are among the most used nanomaterials in consumer products, therefore concerns are raised about their potential for adverse effects in humans and environment. Although an increasing number of studies in vitro and in vivo are being reported on the toxicity of AgNPs, most of them suffer from incomplete characterization of AgNPs in the tested biological media. As a consequence, the comparison of toxicological data is troublesome and the toxicity evaluation still remains an open critical issue. The development of a reliable protocol to evaluate interactions of AgNPs with surrounding proteins as well as to assess their colloidal stability is therefore required. In this regard, it is of importance not only to use multiple, easy-to-access and simple techniques but also to understand limitations of each characterization methods. In this work, the morphological and structural behaviour of AgNPs has been studied in two relevant biological media, namely 10 % FBS and MP. Three different techniques (Dynamic Light Scattering, Transmission Electron Microscopy, UV–Vis spectroscopy) were tested for their suitability in detecting AgNPs of three different sizes (10, 40 and 100 nm) coated with either citrate or polyvinylpyrrolidone. Results showed that UV–Vis spectroscopy is the most versatile and informative technique to gain information about interaction between AgNPs and surrounding proteins and to determine their colloidal stability in the tested biological media. These findings are expected to provide useful insights in characterizing AgNPs before performing any further in vitro/in vivo experiment
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