1,721,010 research outputs found
Tailoring functionality through synthetic strategy in heterolanthanide assemblies
No full textAn overview of the different strategies proposed for the preparation of heterolanthanide assemblies suitable
to work as (multi-) functional materials, highlighting their structure/property relationship, is provided.
Three classes of compounds are selected: multi-dimensional coordination frameworks, polynuclear discrete molecules and flexible large molecules formed by two or more coordinating units connected by a linker. Synthetic approaches and potential functionalities are discussed on the basis of lanthanide ion discrimination and the structural arrangement of the heterometallic assembly
Enhanced photoluminescence of organic dyes embedded in sol-gel organosilane thin films
Full text linkWe investigated photoluminescence properties of Dyomics dyes DY650 and DY831 when incorporated into solid thin films fabricated using two distinct sol–gel precursors, namely, tetraethoxysilane (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS). Surprisingly, a significant enhancement in both photoluminescence lifetime and quantum yield was observed in the films derived from GPTMS, contrasting conventional behavior documented in literature for dyes dispersed within solid matrices. This phenomenon is attributed to the unique molecular environment surrounding the dyes in the GPTMS matrix, which was inferred to suppress nonradiative decay channels for the photoexcited dyes. Our findings provide valuable insights into the intricate interplay between dye molecules and their host matrices, shedding light on the potential applications of GPTMS-based systems in enhancing photoluminescence properties for various technological advancements
The role of excitons in 3D and 2D lead halide perovskites
No full textThe success of lead halide perovskites as active materials in solar cells and light-emitting diodes (LEDs) is often traced back to the unique properties of their optical excitations. At room temperature and under all device operating conditions, photoexcitation of perovskites creates free carriers and not bound excitons, even in compounds with exciton binding energy several times larger than room temperature thermal energy. As a consequence, absorbed photons can be readily converted in an electric current of electrons and holes to be collected at perovskite edges, leading to efficient solar cells. A thorough review of the large body of experimental evidence on perovskite photophysics however leads to quite a different picture, where excitons are anything but negligible. First of all, they are responsible for the very large absorption coefficients close to the band gap, which can reach as much as 105 cm-1. The magnitude of such an effect depends on the exciton binding energy, whose value proved to be elusive and tricky to assess. Second and more surprising, excitons are responsible for most light emission in perovskites, in spite of being greatly outnumbered by free carriers. The resulting dynamics of optical emission is governed by the ratio between exciton formation through pairing of free carriers and exciton radiative recombination. When the importance of excitons is taken into account, new avenues in lead halide perovskites appear more clearly, particularly the rise of layered, bidimensional (2D) perovskites, where excitonic effects are further enhanced, without compromising the fact that free carriers are the majority of photexcitations
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
Hydrophilicity and Water Contact Angle on Methylammonium Lead Iodide
No full textSurface properties are often assessed with measurements of the contact angle of a water drop. The process is however flawed for the very important class of hybrid perovskite materials, extensively employed in solar cells and optoelectronics research, because they are water soluble and their surface degrades during contact angle measurements. While hybrid perovskites are considered to be highly hydrophilic, a contact angle with water of 83° can be measured, as if they were almost hydrophobic. By combining experiments and simulations, the actual value is explained as the result of the interaction of water with degraded superficial layers that form over sub-millisecond time scale at the water/perovskite interface. The models are validated against contact angle measurements for water on a variety of substrates, and are referenced to with the Young–Dupré relation between liquid–solid adhesion and contact angle. Present work reconciles the hydrophilic nature of methylammonium lead iodide with the apparent hydrophobic behavior in contact angle measurements, proposing a methodology for the study of contact angle on evolving substrates
Extending the Lasing Wavelength Coverage of Organic Semiconductor Nanofibers by Periodic Organic-Organic Heteroepitaxy
No full textAppropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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