1,721,047 research outputs found
Assessment of Crystalline Materials for Solid State Lighting Applications: Beyond the Rare Earth Elements
Full text linkIn everyday life, we are continually exposed to different lighting systems, from the home interior to car lights and from public lighting to displays. The basic emission principles on which they are based range from the old incandescent lamps to the well-established compact fluorescent lamps (CFL) and to the more modern Light Emitting Diode (LEDs) that are dominating the actual market and also promise greater development in the coming years. In the LED technology, the key point is the electroluminescence material, but the fundamental role of proper phosphors is sometimes underestimated even when it is essential for an ideal color rendering. In this review, we analyze the main solid-state techniques for lighting applications, paying attention to the fundamental properties of phosphors to be successfully applied. Currently, the most widely used materials are based on rare-earth elements (REEs) whereas Ce:YAG represents the benchmark for white LEDs. However, there are several drawbacks to the REEs’ supply chain and several concerns from an environmental point of view. We analyze these critical issues and review alternative materials that can overcome their use. New compounds with reduced or totally REE free, quantum dots, metal–organic framework, and organic phosphors will be examined with reference to the current state-of-the-art
Electronic components authentication via physical analysis
Full text linkCounterfeit electronics is a reliability problem. Undetected counterfeits can lead to increased scrap rates, early field failures, and rework rates, causing a dramatic reduction in the reliability of systems. Identifying counterfeit devices can be challenging because not everything that seems suspect is necessarily fake. On the other hand, counterfeiters keep growing and adapting
4‐nitrophenol efficient photoreduction from exfoliated and protonated phenyl‐doped graphitic carbon nitride nanosheets
Full text linkThe photoreduction of 4‐nitrophenol to 4‐aminophenol by means of protonated and exfo-liated phenyl‐doped carbon nitride is reported. Although carbon nitride‐based materials have been recognized as efficient photocatalysts, the photoreduction of 4‐nitrophenol to 4‐aminophenol is not allowed because of the high recombination rate of the photogenerated electron–hole pairs. In this paper, we show the morphology effects on the photoactivity in phenyl‐doped carbon nitride. Structural (TEM, XRD, Raman) and optical characterization (absorption, photoluminescence) of the pro-tonated and exfoliated phenyl‐doped carbon nitride (hereafter pePhCN) is reported. The increased photocatalytic efficiency, with respect to the bulk material, is underlined by the calculation of the kinetic constant of the photoreduction process (2.78 × 10−1 min−1 and 3.54 × 10−3 min−1 ) for pePhCN and bulk PhCN, respectively. Finally, the detailed mechanism of the photoreduction process of 4‐ nitrophenol to 4‐aminophenol by modified phenyl carbon nitride is proposed
Evaluation of flexible organic transistor stability in harsh conditions
No full textCharacterizing the degradation of organic electronics is fundamental for the exploitation of this technology in different scenarios, including aerospace and biomedical applications. In this paper, flexible printed organic transistors were exposed to controlled environmental conditions that may resemble those for the above-mentioned applications, including thermal and radiation stresses. The effect of encapsulation layers in enhancing the device reliability is discussed
New phosphors with strongly reduced content of critical raw materials for lighting applications
No full textAluminium silicate crystal is proposed as new promising inert matrix as host of luminescent ions. In particular, we studied the luminescence properties of single doped and multi-doped Al2SiO5 samples (doping elements: Ce, Tb, Cr, Fe, Zr) to explore their suitability as phosphors in modern lighting systems. The Al2SiO5 host matrix, obtained in nano-sized crystals belonging to the high temperature phase known as sillimanite, allows to narrow down the presence of rare earth elements exclusively to the dopants, thus providing a promising solution to the critical raw material concern. The crystals doped with Fe, Ce and Zr are mainly excited in the UV range, and they are good candidate as phosphors in compact fluorescent lamp systems. Terbium single doped samples are efficient phosphors in the green region with direct excitation in the deep UV region, but their excitation spectrum can be down-shifted to near UV range in in co-doped Ce:Tb samples. Indeed, thanks to the efficient energy transfer from cerium ions, the green emission from Tb ions can be excited by commercial AlGaN light emitting diode, suggesting Ce:Tb doped Al2SiO5 crystals as promising phosphors for green LED system. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Strength and weakness of rare earths based phosphors: Strategies to replace critical raw materials
No full textRare earth based phosphors are largely the most applied luminescent materials in the present lightening devices. Their ubiquity in lighting system, like light emitting diodes or compact fluorescent lamps, is related to the optical high efficiency of the rare earth as luminescent ions but also to the relative easiness of growth technique as well high structural stability of rare earth based host matrices, like garnets, perovskites and oxyorthosilicatas. On the other hand, the need of new devices virtually free of any elements with high supply disruption, the ones classified by EU community and US government as critical raw materials, boosts the research for alternatives materials. In this paper, we focalize on the optical properties of the REE based phosphors with the intent to underline the performances the new materials should grant, thus addressing the possible direction for new material development. In particular the features related to the possibility of tuning the luminescence, the interaction among doping ions and with surface defects were analysed. Finally, a general model to predict the role of the REE in a host matrix is analysed. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
A reduced ABC model for the carrier imbalance problem in GaN/InGaN quantum wells
No full textA reduction of the ABC model that deals with the carrier imbalance problem in GaN/InGaN quantum wells is proposed. It is shown that, after the definition of a proper effective carrier density, the band-to-band recombination rate can be expressed using only one probability coefficient, thus reducing the free parameters of the model with no loss of efficiency. On the contrary, the reduced model allows a more efficient description of the carrier density in the high current regime and expressing the carrier lifetime in a large range of current densities as τ∝1/J. In addition, by checking experimental data available in the literature, we show that the reduced model allows a better match of the internal quantum efficiency droop curve vs current density as compared to the ABC model and equivalent to more sophisticated package-based models
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
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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