1,720,957 research outputs found
Sol-gel synthesis of and luminescent properties of Pr³⁺ in different host matrices
No full textLuminescent ZrO2:Pr3+ , SiO2:Pr3+, ZnO:Pr3+ and ZnS:Pr3+ nanophosphors were synthesized by a sol-gel method, dried, ground and annealed in air at 600oC (SiO2:Pr3+, ZrO2:Pr3+, ZnO:Pr3+ and ZnS:Pr3+) or 280oC (ZrO2:Pr3+). The chemical composition of the powder phosphors was analyzed by energy dispersive x-ray spectrometer (EDS). The structure and particle sizes were determined with x-ray diffraction (XRD) and particle morphology was analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SiO2:Pr3+ was amorphous even after annealing at 600oC. ZrO2:Pr3+ annealed at 280oC showed an amorphous structure but the material crystallized when the annealing temperature was increased to 600oC. The particle sizes estimated from the XRD peaks were ∼2±0.2 nm (dried ZnS and ZnO) and ∼8±0.1 nm (ZrO2:Pr3+ annealed at 600oC). Particle sizes increased to ∼17-20±0.2 nm in diameter for annealed ZnS:Pr3+ and ZnO:Pr3+. The UV-Vis spectrophotometer was used to determine the absorption properties of the nanophosphors and their band absorption showed a blue shift compared to their bulk counterparts. Powder phosphors were also irradiated with 325 nm (He-Cd) laser to study photoluminescence (PL) properties. PL spectra were obtained for both undoped and Pr3+ -doped nanophosphors. A broad emission band was observed at 498 nm with a shoulder at 416 nm from SiO2:Pr3+ annealed at 600oC. ZrO2:Pr3+ annealed at 280oC showed two emission bands in the visible range at 459 nm and 554 nm. A broad green emission band at 567 nm and a shoulder at 607 nm were observed for dried ZnO:Pr3+ nanophosphor and the shoulder at 607 nm was enhanced significantly when the Pr3+ concentration was increased. Annealed ZnO:Pr3+ (280oC) nanophosphor showed a green emission band centered around 533 nm and a shoulder at 624 nm. Dried ZnS:Pr3+ nanophosphor showed a blue emission centered at 445 nm and the PL intensity increased with an increase of Pr3+ ions concentration. All these emissions were coming from the host matrices and not from the Pr3+ ion when the powders were excited by 325 nm (3 eV) photons. SiO2 and SiO2:Pr3+ powder phosphors were subjected to prolonged 2 keV electron beam irradiation in an ultra high vacuum (UHV) chamber at a base pressure of 1x10-9 torr. The surface reactions and degradation of cathodoluminescence intensity were monitored using Auger electron spectroscopy (AES) and cathodoluminescence (CL) spectroscopy respectively. CL emission of SiO2 showed a maximum emission peak at 451 nm and a shoulder at 478 nm and SiO2:Pr3+ showed a multiple peak emissions located at 510 nm, 614 nm, 730 nm, 780 nm and 970 nm which are attributed to the transitions in the Pr3+ ions. The SiO2:Pr3+ CL intensity decreased with time as a result of continuous exposure to 2 keV electrons. The Auger peak-to-peak height as a function of energy spectrum showed that there were changes on the surface chemistry of the powders as a result of prolonged irradiation by 2 keV electrons. It is most likely that non-luminescent layers were formed on the surface and they contributed to the CL intensity degradation. A high concentration of volatile gas species, which might have contributed to the CL degradation, was detected with a residual gas analyzer (RGA). Cathodoluminescence was not measured for ZnO:Pr3+,ZnS:Pr3+ and ZrO2:Pr3+ due to charging of the powder phosphors and ZrO2:Pr3+ did not emit light under high energy electron exposure (2 keV).National Research Foundation (NRF)University of the Free State (UFS
The effects of the ZnO nanoparticles buffer layer on organic solar cells
No full textOrganic photovoltaics devices have drawn a lot of attention as means for the renewable energy conversion due to the remarkable combination prospective low cost of manufacturing and rapid improvement of performance approaching the traditional silicon solar cells. By introducing metal oxides in organic photovoltaics, the organic solar cells show great potential in terms of device performance with high exciton dissociation, the favorable charge transport ability and the air stability. In this study, ZnO nanostructures are investigated as a buffer layer in organic solar cells (OSCs), focusing on their impact on the device performance.
ZnO nanoparticles, nanoflakes and nanoflowers were successfully synthesized using a wet chemistry route. Based on X-ray diffraction (XRD), the ZnO nanopaticles, nanoflakes and nanoflowers exhibited a hexagonal wurtzite structure matching the standard JCPDS data, card number 80-0075. The particle morphology of ZnO nanostructures was analyzed using field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). SEM revealed spherical nanoparticles, randomly oriented nanoflakes and nanoflowers clusters. TEM revealed nanorods clustered into nanoflowers. UV-visible absorption spectra of ZnO nanostructures exhibited peaks at ~251 nm and ~348 nm, attributed to structural defects and intrinsic excitons, respectively.
Conventional and inverted organic solar cells were successfully fabricated. The fabrication process of conventional solar cells was optimized by varying several important parameters in the photo-active blend (P3HT:PCBM). The performance of OSCs improved when the active layer was cast from the chlorobenzene solution rather than 1,2-dichlorobenzene solution. Varying the blend ratio also revealed improved device performance with the 1:0.6 weight ratio. All these parameter processes can significantly influence the device performance.
The effects of ZnO particle morphology on the performance of OSC devices were investigated. The best photovoltaic properties were obtained from devices with the ZnO nanoflakes and nanoparticles as electron extraction layers both spin coated from solutions of 0.5 mg/mL ZnO concentration. The ZnO nanoflakes morphology gave relatively higher power conversion efficiency (PCE) of 3.08 % versus 2.37 % from the ZnO nanoparticles.
The effects of thermal treatment before (pre annealing) and after (post-annealing) the deposition of Al electrode on the conventional devices were also investigated. Improved photovoltaic properties were observed from the post-fabrication annealed device. The inverted device with ZnO nanoparticles electron extraction layer revealed a relatively improved performance versus that with ZnO nanoflowers. Finally the compositional depth profiling and surface imaging were carried out for both conventional and inverted devices and the results indicated that the bulk heterojunction (BHJ) layer was P3HT enriched and there was diffusion of some other elements into the BHJ layer. The surface imaging showed homogeneous as well as inhomogeneous distribution of ions on the surface.University of the Free State (UFS)National Research Foundation (NRF)Photonic Initiative of South Africa (PISA)Korea Research Council of Fundamental Science and Technology (KRCF)The KIST for NAP (National Agenda Project
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
