1,721,291 research outputs found
Optical spectroscopy of Dy3+ in crystalline hosts: General aspects, personal considerations and some news
No full textThis paper reports the author's point of view on the state of the art concerning the optical spectroscopy of Dy3+-containing materials, based on his personal experience and without claims of completeness, but with the intent to provide useful indications or at least elements for fruitful discussions to the people working on this subject. An overview of the absorption and emission properties of Dy3+-doped crystalline lattices is presented, based on the inspection of the available literature as well as on experimental measurements. Systematic behaviors have been related to the host composition in the frame of the Judd-Ofelt approach, and the development of criteria for predicting the luminescence characteristics of new materials is discussed. Some open problems have been pointed out, evidencing weaknesses of the theoretical model still waiting for solution. Suggestions for further experimental projects are finally proposed
Development and applications of transition metal or rare earth-based luminescent inorganic materials
No full textThis Special Issue is dedicated to luminescent inorganic materials, an extremely vast topic that often and willingly crosses over into other important fields of chemistry and physics [...
Metal-to-metal charge transfer involving Pr3+ or Tb3+ ions in transition metal oxides and its consequences on the luminescence behaviors
No full textOptical spectroscopy of Cr3+ ions in orthoenstatite MgSiO3
No full textThe absorption, luminescence and excitation electronic spectra of MgSiO3 doped with chromium were measured in the visible and near infrared regions at temperatures down to 10 K. The optical spectraare composed of both broad bands and sharp lines, showing the presence of Cr3+ substituting for both non-equivalent Mg2+ ions in distorted octahedral sites of high and low ligand field strength respectively. All the spectral features were assigned and a preferred occupation of the low field sites was evidenced. © 1993
Structural effects on the emission dynamics of oxide crystals activated with Tb3+
No full textFlux grown crystals of YPO4, GdPO4, LaPO4, CaWO4, CaMoO4, KLa(MoO4)2, GdAl3(BO3)4, and GdTa7O19 activated with Tb3+ have been comparatively characterized by Raman and luminescence spectroscopy in order to investigate the relation between structural and emission properties. Processes like host sensitization, Tb3+- Tb3+ energy transfer, formation of charge transfer states, etc., as well as their effects on the emission dynamics have been examined in the light of the spatial distribution of the involved centers. The analysis of the experimental results allows to evidence the role of the site symmetry of the active ions, of their distribution inside the lattice, of their interactions with the vibrational and electronic structure of the host, and provide useful information for understanding the luminescence properties and for the design of new Tb3+-doped materials
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
La filiera del patrimonio culturale a livello micro: il sito dei Cavalli e Carri Zhou
No full textIn questo capitolo la filiera del patrimonio culturale è applicata a un caso specifico di tutela e gestione del patrimonio in Cina: il Sito dei Cavalli e Carri Zhou a Luoyang, in Cina. Il capitolo sottolinea l’utilità del concetto di “filiera del patrimonio” nell’interpretazione di un singolo caso di gestione del patrimonio con una visione olistica ed in coerenza col capitolo precedente elabora l'analisi sulla base del modello di struttura-condotta-performance (SCP)
Spectroscopic properties of YPO4 crystals activated with Ho3+, Er3+, Tm3+
No full textThis paper presents a systematic investigation on the spectroscopic properties of YPO4 crystals activated with Ho3+, Er3+ or Tm3+, carried out in order to obtain preliminary information on the device potentialities of these materials. Relevant information about the radiative properties have been obtained by means of the Judd-Ofelt analysis of the polarized absorption spectra, measured at room temperature in the UV-vis-NIR region. The polarized emission spectra have been measured at 77 and 300 K in the visible and in the NIR upon laser excitation, and the transitions of major interest for application have been identified and characterized. The decay profiles of the main emission manifolds have been measured at room temperature in order to obtain information about the non-radiative processes active in the investigated crystals The stimulated emission cross sections have been estimated for the laser transitions in the NIR, indicating that these compounds can be considered suitable active media for laser operation
Luminescence of Fe-Doped Willemite Single Crystals
No full textThe emission and excitation spectra of Fe-doped Zn2SiO4 (willemite) crystals were measured at temperatures ranging from 10 to 298 K. The luminescence consists of two contributions, both of broadband type: an emission due to the 4T1 (4G) → 6A1 (6S) interconfigurational transition of the d5 Fe3+ ions in sites having approximate tetrahedral coordination and a second emission probably due to lattice defects induced by the requirement of charge compensation. The excitation spectrum of Fe3+ has been assigned on the basis of the ligand field theory, and the energies of the bands have been fitted with the following values of the ligand field parameters: Dq = 743 cm-1, B = 535 cm-1, and C = 3155 cm-1. From these data, it is reasonable to suppose that the Fe3+ ions responsible for the emission are located at the Si4+ distorted tetrahedral sites. © 1995 Academic Press
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