1,721,102 research outputs found
Switching to the Brighter Lane: Pathways to Boost the Emission Intensity of Lanthanide-Doped Nanoparticles
No full textLanthanide-doped nanoparticles (LNPs) are speedily colonizing several research fields, such as biological (multimodal) imaging, photodynamic therapy, volumetric encoding displays, and photovoltaics. Yet, the electronic transitions of lanthanide ions obey the Laporte rule, which dramatically hampers their light absorption capabilities. As a result, the brightness of these species is severely restricted. This intrinsic poor absorption capability is the fundamental obstacle for untapping the full potential of LNPs in several of the aforementioned fields. Among others, three of the most promising physicochemical approaches that have arisen during last two decades to face the challenges of increasing LNP absorption are plasmonic enhancement, organic-dye sensitization, and coupling with semiconductors. The fundamental basis, remarkable highlights, and comparative achievements of each of these pathways for absorption enhancement are critically discussed in this minireview, which also includes a detailed discussion of the exciting perspectives ahead
Doping Lanthanide Ions in Colloidal Semiconductor Nanocrystals for Brighter Photoluminescence
No full textThe spectrally narrow, long-lived luminescence of lanthanide ions makes optical nanomaterials based on these elements uniquely attractive from both a fundamental and applicative standpoint. A highly coveted class of such nanomaterials is represented by colloidal lanthanide-doped semiconductor nanocrystals (LnSNCs). Therein, upon proper design, the poor light absorption intrinsically featured by lanthanides is compensated by the semiconductor moiety, which harvests the optical energy and funnel it to the luminescent metal center. Although a great deal of experimental effort has been invested to produce efficient nanomaterials of that sort, relatively modest results have been obtained thus far. As of late, halide perovskite nanocrystals have surged as materials of choice for doping lanthanides, but they have non-negligible shortcomings in terms of chemical stability, toxicity, and light absorption range. The limited gamut of currently available colloidal LnSNCs is unfortunate, given the tremendous technological impact that these nanomaterials could have in fields like biomedicine and optoelectronics. In this review, we provide an overview of the field of colloidal LnSNCs, while distilling the lessons learnt in terms of material design. The result is a compendium of key aspects to consider when devising and synthesizing this class of nanomaterials, with a keen eye on the foreseeable technological scenarios where they are poised to become front runners
Quo Vadis Nanoparticle-Enabled Fluorescence In Vivo Imaging?
No full textThe exciting advancements that we are currently witnessing in terms of novel materials and synthesis approaches are leading to the development of colloidal nanoparticles (NPs) with increasingly greater tunable properties. We have now reached a point where it is possible to synthesize colloidal NPs with functionalities tailored to specific societal demands. The impact of this new wave of colloidal NPs has been especially important in the field of biomedicine. In that vein, luminescent NPs with improved brightness and near-infrared working capabilities have turned out to be optimal optical probes that are capable of fast and high-resolution in vivo imaging. However, luminescent NPs have thus far only reached a limited portion of their potential. Although we believe that the best is yet to come, the future might not be as bright as some of us think (and have hoped!). In particular, translation of NP-based fluorescence imaging from preclinical studies to clinics is not straightforward. In this Perspective, we provide a critical assessment and highlight promising research avenues based on the latest advances in the fields of luminescent NPs and imaging technologies. The disillusioned outlook we proffer herein might sound pessimistic at first, but we consider it necessary to avoid pursuing “pipe dreams” and redirect the efforts toward achievable—yet ambitious—goals
Time resolved confocal luminescence of Nd<sup>3+</sup> doped BK7 glass microspheres
No full textInterest in dielectric microspheres is rapidly increasing because of their potential application in integrated photonics for filtering, dispersion management and all-optical switching. When doped with luminescent ions capable of laser oscillation, such as the rare-earths, these applications are extended to incorporate the potential for low threshold laser oscillation exploiting Whispering Gallery Modes (WGMs) to form cavities. This possibility has already been demonstrated in glass microspheres doped with different rare earth ions including Neodymium, of special relevance due to its high emission cross section at laser wavelengths and also because of the long lifetime of the metastable state (both facts ensuring low laser thresholds), that are presented in bulk materials. These two properties, and their possible modification during the fabrication procedure of microspheres, will dominate the final laser performance of the microspheres
Site selectively study of the Nd3+ optical centres in Ca3Sc2Ge3O12 laser garnet crystals
No full textSpatially resolved luminescence characterisation of rare earth doped chalcogenide glass microspheres
No full textThe fluorescence properties of rare earth doped chalcogenide microspheres (~ 80 µm in diameter) have been investigated by confocal luminescence experiments. The comparison of the emission spectra obtained in both microspheres and bulk material has been used to elucidate the possible influence that the fabrication procedure could have on the luminescence properties of the rare earth ions
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
Cr3+ -> Nd3+ energy transfer in the YAl3(BO3)4 nonlinear laser crystal
No full textThe energy transfer between Cr3+ and Nd3+ ions in Cr3+, Nd3+:YAl3(BO3)(4) (YAB) codoped crystals has been investigated by means of steady-state and time-resolved laser spectroscopies. The mainly nonradiative character of the energy transfer has been evidenced from the comparison between the emission spectra and the donor fluorescence decays. The analysis of the donor decay profiles has been used to determine the main dipole-dipole character of the transfer, in excellent agreement with the predictions made from the Dexter [J. Chem Phys. 21, 836 (1953)] model, as well as with the dependence of the energy-transfer rates on the acceptor concentration. The temperature behavior of the transfer rate has been analyzed considering the thermal-induced population redistribution between the E-2 and T-4(2) states of Cr3+ ions and the existence of the phonon-assisted energy transfer. We have obtained that 80% of the Cr3+-> Nd3+ energy transfer in YAB is taking place without the assistance of lattice phonons whereas almost 20% is taking place through multiphonon emission
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
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