1,720,954 research outputs found
Sol-gel synthesis of CaTiO3:Pr3+ red phosphors: tailoring the synthetic parameters for luminescent and afterglow applications
No full textPr-doped CaTiO3 (CaTiO3:Pr3+) is a promising candidate to substitute currently available red luminescent materials in applications such as LED displays [1]. Further, CaTiO3:Pr3+ is a red persistent phosphor, i.e. it exhibits a sustained red light emission for an extended duration after removal of the light source. While materials with blue or green afterglow emission are relatively common, red persistent phosphors are quite rare. As a result, CaTiO3:Pr3+ is a promising material for applications such as safety signage, sunlight storage and bio-imaging [2]. The control of the phosphor morphology is crucial for a wide range of applications, e.g. in bio-imaging and in LED and FED displays [3]. In this study, we propose new synthetic routes to tailor the morphology as well as the luminescence and afterglow properties of CaTiO3:Pr3+ for the desired application. Sol-gel syntheses were selected owing to their notable advantages with respect to the more commonly employed solid state reactions, e.g. lower reaction temperatures, higher homogeneity of the final product, and smaller particles. Two different sol-gel syntheses, followed by calcination, were investigated: one catalyzed by acetic acid and the other catalyzed by HCl in the presence of hydroxypropilcellulose (HPC) as morphology modulator. The role of the calcination temperature on the material properties was investigated in a wide temperature range (600-1200°C). The obtained samples were thoroughly characterized for their structural, morphological, optical and luminescence properties. The desired perovskite phase was obtained at a calcination temperature of 800°C or higher. The presence of HPC hindered crystallization at 600°C, while it influenced the morphological features at higher calcination temperatures. Photoluminescence measurements showed that the most crystalline samples presented the highest luminescence, irrespectively of the adopted synthetic approach. On the other hand, crystallinity had a more complex effect on persistent luminescence properties. While the samples calcined at the lowest temperature showed a negligible afterglow emission, the highest energy storage capability was exhibited by samples calcined at 800°C. The synthetic procedure played also a significant role in the afterglow emission: samples from the acetic acid synthesis are better candidates as red persistent phosphors. On the other hand, considering their high luminescent emission, low afterglow, and more porous structure, samples from HPC synthesis may be considered the most promising red phosphors for display applications
Sol-gel synthesis of CaTiO3:Pr3+ red phosphors : tailoring the synthetic parameters for luminescent and afterglow applications
Full text linkTwo sol-gel synthetic routes for the preparation of CaTiO3: Pr3+ red emitting phosphors were compared, with the aim of producing nanostructured materials with tailored luminescence/afterglow properties. The effect of the synthetic parameters, such as the addition of a stabilizer and calcination temperature, on the structural, morphological, and optical properties was investigated. The desired perovskite phase was obtained at a calcination temperature of 800 degrees C or higher. Although the use of acetic acid as the chelating agent leads to micrometric particles with heterogeneous composition, the presence of hydroxypropylcellulose (HPC) results in smaller, less aggregated particles as well as in a high phase purity. At the highest HPC content, surface Ca-rich impurities were detected, although no segregated Ca-rich phases were detectable by X-ray powder diffraction analyses. Luminescence properties were found to be positively related to the phase purity of the oxide, with the highest quantum yields at temperatures equal to or higher than 1000 degrees C. On the contrary, persistent luminescence properties were highest at intermediate calcination temperatures and for samples synthesized with acetic acid. Overall, a notable role of oxygen vacancies resulting from local Ca excess was observed, acting as trap levels promoting longer relaxation pathways. Thanks to the small-sized particles and best steady-state luminescent properties due to a substantial decrease of lattice defects, the HPC synthesis is a promising strategy for light-emitting diode applications. On the other hand, the acetic acid synthesis promoted a higher defect density, which is required for an efficient yield of light emission in the long time range and is thus more suitable for afterglow applications
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
- …
