1,720,998 research outputs found
Luminescence study of the f-f transition of Pr(3+) (1)D(2) and (3)P(0) states in KYF(4) crystals and powders
No full textKYF(4):Pr(3+) was prepared in the two forms of single crystal and polycrystalline powder. The visible photoluminescence properties of KYF(4):Pr(3+) single crystal and powder have been comparatively investigated, and the special attentions were paid to the luminescence in the red region from the f-f transition of Pr(3+) (3)P(0) and (1)D(2) states. We used two different pump sources of an Argon-ion laser tuned to a wavelength of 457.9 nm, 445 nm and a blue GaN laser diode emitting at 445 nm, exciting the (3)P(1) and (3)P(2) states of Pr(3+) ion, respectively. The observed strong and sharp emission line at 594.6 nm for the KYF(4):Pr(3+) powder and crystal should be ascribed to (3)P(0)-(3)H(6) transition of Pr(3+), and an increase in the 3P0 emission upon 457.9 nm excitation was also observed and was attributed to the [(3)P(0),(3)H(4)] -> [(3)H(6), (1)D(2)] cross-relaxation mechanism. Further study on room temperature lifetime and temperature-dependent fluorescence emission of (1)D(2)-(3)H(4) and (3)P(0)-(3)H(6) transitions indicated that there was obvious lifetime difference for the (1)D(2) and (3)P(0) states of Pr(3+) in the present KYF(4) host
Investigation of Pr-doped fluoride crystals as possible white-light emitters
No full textWhite-light emission from BaY(2)F(8), KYF(4), KY(3)F(10) and LiLuF(4) samples with different Pr(3+) doping levels from 0.3% to 3% is described. We report here their CIE chromatic coordinates and the intrinsic emission efficiency as the ratio of the absorbed and the emitted signal. Optical absorption spectra and luminescence spectra were acquired at room temperature after visible pumping. The calculation of Commission Internationale de l'Eclairage (CIE) coordinates shows that white emission is obtained from all the samples independent of both the doping level and incident power. The CIE coordinates closest to the white point are (0.35, 0.32) from the 0.3% Pr(3+):BaY(2)F(8) sample. We also measured the intrinsic emission efficiency of all the crystals. The best obtained is 60%. (C) 2009 Elsevier B.V. All rights reserved
Optical spectroscopy of the Dy3+ ion in YPO4 crystals
No full textThe excited state dynamics Y1-xDyxPO4 (x= 0.005 - 0.1) single crystals have been investigated as a function of the temperature and of the concentration. When x=0.005 the 4F 9/2 emission decays exponentially with time constant of the order of 480-500 μs. For higher doping levels the curves are non exponential, indicating that energy transfer processes take place. The Inokuti-Hirayama model applied to the analysis of the decay profiles of the 3% doped crystal has allowed to obtain information about the transfer mechanism
Energy Levels and Emission Parameter of the Dy3+ Ion Doped Into the YPO4 Host Lattice
No full textSingle crystals of Dy3+-doped YPO4 have been grown from Pb2P2O7 flux and investigated by optical spectroscopy techniques. The energy level scheme of the active ion has been deduced from the low temperature spectra and reproduced by means of a crystal-field calculation. The room temperature absorption spectra have been analysed in the framework of the Judd�Ofelt approach, and the results of this analysis have been applied in a discussion concerning the spectral composition of the visible luminescence.JRC.DG.E.6 - Actinides researc
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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