1,720,958 research outputs found
Engineering the Aggregation of Dyes on Ligand-Shell Protected Gold Nanoparticles to Promote Plexcitons Formation
Full text linkThe ability to control the light–matter interaction in nanosystems is a major challenge in the field of innovative photonics applications. In this framework, plexcitons are promising hybrid light–matter states arising from the strong coupling between plasmonic and excitonic materials. However, strategies to precisely control the formation of plexcitons and to modulate the coupling between the plasmonic and molecular moieties are still poorly explored. In this work, the attention is focused on suspensions of hybrid nanosystems prepared by coupling cationic gold nanoparticles to tetraphenyl porphyrins in different aggregation states. The role of crucial parameters such as the dimension of nanoparticles, the pH of the solution, and the ratio between the nanoparticles and dye concentration was systematically investigated. A variety of structures and coupling regimes were obtained. The rationalization of the results allowed for the suggestion of important guidelines towards the control of plexcitonic systems
Er3+-to-dye energy transfer in DNA-coated core and core/shell/shell upconverting nanoparticles with 980 nm and 808 nm excitation of Yb3+ and Nd3+
Full text linkThe capability of upconverting nanoparticles (UCNPs) to convert near infrared (NIR) into visible light has become an important feature for biosensing, imaging, therapy, and their combination. While significant achievements have been accomplished during the last decade developing nanohybrids based on UCNPs as energy donors in Förster resonance energy transfer (FRET) systems, it is still challenging to understand and control FRET from UCNPs to dyes and to adapt the NIR excitation wavelength. Here, we describe the synthesis, characterization, and steady-state and time-resolved FRET analysis of UCNP-DNA nanohybrids, in which dye labelled single stranded (ss)DNA was attached to Yb-Er-co-doped core UCNPs (c-UCNPs) and c-UCNPs with a thin Nd-doped shell and a second thin undoped shell (css-UCNPs). Despite differences in sizes, compositions, donor-acceptor distances, brightness, and excitation wavelength (980 nm for Yb3+ and 808 nm for Nd3+), all UCNP-DNA nanohybrids showed very similar concentration dependent FRET-quenching of UCNP luminescence with efficiencies between 0 and ∼20%. We analyzed luminescence intensities, decay times, and rise times and could show the entanglement of excitation and emission kinetics by simply changing the excitation wavelength from 980 nm to 808 nm for the same css-UCNPs. Time-gated FRET-sensitized dye luminescence showed dye-ssDNA concentration dependence over four orders of magnitude (1 nM to 10 μM), which suggested a possible application to nucleic acid biosensing for both 808 and 980 nm excitation
Selective switching of multiple plexcitons in colloidal materials: Directing the energy flow at the nanoscale
Full text linkCoupling of molecular emitters to plasmon resonances in metal nanostructures has long been investigated to control the light-matter interaction at the nanoscale. The emergence of different coupling behaviors can be governed by the various combinations of emitters and plasmonic substrates, as well as the spatial arrangement of the individual components. Here colloidal assembly methods are exploited to prepare a responsive nanosystem where two sets of plexcitonic resonances in different coupling regimes can be selectively switched on and off, acting on external conditions such as concentration and presence of anions. The two sets of plexciton resonances are built exploiting the strong coupling between cationic gold nanoparticles and the same molecular moiety, an anionic porphyrin, in different aggregation states. When both plexciton resonances are simultaneously activated in the system, evidence for a plexciton relaxation cascade has been found in photoluminescence experiments. These findings have fundamental implications for achieving control over energy flow at the nanoscale
Coherent Dynamics in Solutions of Colloidal Plexcitonic Nanohybrids at Room Temperature
Full text linkThe increasing ability to prepare systems with nanoscale resolution and address their optical properties with ultrashort time precision is revealing quantum phenomena with tremendous potential in quantum nanotechnologies. Colloidal plexcitonic materials promise to play a pivotal role in this scenario. Plexcitons are hybrid states originating from the mixing of the plasmon resonances of metal nanostructures with molecular excitons. They allow nanoscale confinement of electromagnetic fields and the establishment of strong couplings between light and matter, potentially giving rise to controllable and tunable coherent phenomena. However, the characterization of the ultrafast coherent and incoherent dynamics of colloidal plexciton nanohybrids remains highly unexplored. Here, two dimensional electronic spectroscopy (2DES) is employed to study the quantum coherent interactions active after the photoexcitation of these systems. By comparing the response of the nanohybrids with the one of the uncoupled systems, the nonlinear photophysical processes at the base of the coherent dynamics are identified, allowing a step forward toward the effective understanding and exploitation of these nanomaterials
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
Appropriate 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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