1,721,064 research outputs found
Controlling a defect structure of the ZnGa2O4:Cr3+ spinel through synthesis parameters for persistent luminescence optimization
No full textZnGa2O4:Cr3+ (ZGO:Cr) is one of the most promising red persistent phosphors for in-vivo imaging due to its
650–750 nm emission band in the range of the so-called first biological window. In this paper, we report on how
to control the high brightness persistent luminescence of the smallest ZGO:Cr nanoparticles by optimization of
hydrothermal synthesis parameters. The influence of pH solution, the temperature of synthesis, and calcination
on the degree of inversion, lattice parameters, morphology, and crystallite size were systematically investigated.
The results have shown that different synthesis conditions modify the trap depths distribution, by mixing the
occupancy of Zn2+ and Ga3+ sites in the spinel structure, which affects the duration and intensity of persistent
luminescence. The correlation between structural changes and optical properties is established and it is possible
to control them by selecting the appropriate hydrothermal synthesis parameters
Effect of Ce3+ concentration on persistent luminescence of YAGG:Ce3+,Cr3+,Nd3+ nanophosphors obtained by the co-precipitation method
No full textSynthesis of Y3Al2Ga3O12 garnet (YAGG) nanophosphors co-doped with Ce3+, Cr3+, and Nd3+ ions by co-precipitation is reported. The effect of Ce3+ concentration on the structure of garnet and on optical properties including persistent luminescence was investigated. The X-ray diffraction measurements showed that single garnet phase was obtained. The contraction of the crystallites size was observed with increasing the cerium concentration. The combined emission of three used co-dopants together allows to extend persistent luminescence spectral range. The photoluminescence, excitation and persistent luminescence spectra were collected and the optimal Ce3+ concentration for the highest efficiency conversion of UV and blue light into the red and the near infrared emission was determined. Based on thermoluminescence data, the effect of Ce3+ concentration on the traps redistribution was also investigated
Luminescent YPO4:Eu@PVA dispersions for anti-counterfeiting ink applications
No full textA method was developed to obtain YPO4:Eu dispersions of PVA as a luminescent inks. YPO4:Eu nanoparticles were prepared by precipitation followed by hydrothermal treatment. The dispersion preparation included systematic studies to prepare a stable colloidal system and to investigate the role of parameters affecting its stability and UV-excited YPO4:Eu emission intensity. The effect of PVA concentration was studied in detail for two different PVAs to determine the optimal parameters for its use as ink with specific luminescent properties. The type of interactions responsible for the dispersion stability was also investigated
Multimodal anti-counterfeiting inks: modern use of an ancient pigment in synergy with a persistent phosphor
No full textMulti-level luminescent, transparent and non-permanent inks for anti-counterfeiting systems and security were developed. The inks emit radiation at different wavelengths based on the type of radiation used to illuminate them, providing multiple layers of safety. The red persistent phosphor Y2O2S:Eu3+,Mg2+,Ti4+ (YOS) was mixed with Egyptian Blue (EB) and dispersed in an aqueous solution of arabic gum. Imaging techniques, excitation and emission spectra, the study of luminescence over time and the duration time were used to verify that the obtained systems showed the desired optical characteristic both in the infrared and in the visible spectral ranges. The two luminescent materials act synergistically: when illuminated with UV light, YOS emits red photons over time and EB, absorbing this energy, emits infrared photons. The resulting emission characteristics are non-obvious and can be designed at the ink developing stage. The tests performed on several substrates showed that the developed luminescent inks are well suited for use in the field of security and anti-counterfeiting
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
Effect of hydrothermal time on the forming specific morphology of YPO4:Eu3+ nanoparticles for dedicated luminescent applications as optical markers
Full text linkA way to control the desired shape and microstructure of YPO4:Eu3+ nanoparticles through the precipitation
method followed by a hydrothermal treatment is reported. This method is useful for achieving very high control
over the YPO4:Eu3+ formation process with the selection of appropriate synthesis parameters. In detail, the
autoclave processing time allows control of the shape and size of nano-needle-shaped particles independently in
both directions, as confirmed by X-ray powder diffraction, FT-IR Spectroscopy and Electron Transmission Microscopy.
In order to analyse the effect of the nanoparticles’ surroundings on the excitation and relaxation
processes of luminescent ions, Eu3+ ion was used as a dopant, whose specific properties allow the study of
changes in their local surroundings by analysing emission spectra. As additionally shown, the shape and size of
the nano-needles were correlated with the luminescence properties of the particles, which are particularly
influenced by the presence of water and by its effect on emission processes from dopant ions located in the nearsurface
zone of the nanoparticles. These results proved that the shape of particles influenced the distance between
Eu3+ ions in the phosphor, such distance affected the specific emission properties, i.e. the lifetime of
excited levels of Eu3+ ions
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