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Atomic physics --- Molecular physics --- Transitions non radiatives. --- Radiationless transitions. --- Théorie moléculaire. --- Molecular theory. --- Transitions non radiatives --- Théorie moléculaire

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An ever growing demand for efficient energy conversion, for instance inluminescent lamps and solar cells, has resulted in the current significantgrowth of research on functionalized nanomaterials for these applications.Recently it has been found that reduction of size of some transition metals, like gold(Au) and silver (Ag), below 1 nm results in emergence of properties, otherwiseabsent in their bulk counterparts. These properties include, but are notlimited to, bright photoluminescence. The latter can be tuned by changing thesize of these metal particles or the chemical composition of the host matricescontaining them.Luminescent few-atom Ag nanoclusters can be synthesized in various forms, such as incolloids or stabilized within flexible polymer matrices, or solid hosts. Inthis work we have proposed a simple method, based on a widely used glassmelt-quenching technique, for preparation of Ag nanoclusters stabilized withinbulk transparent glass hosts. The glass host provides many useful benefits,e.g. relatively easy fabrication en massand long-term chemical stability (optical and structural properties of oursamples has shown no apparent degradation over the course of several years).As-prepared glass samples doped with silver demonstrate a bright (quantum yield up to 20 %at room temperature) white luminescence that can be efficiently excited using abroad range of near-ultraviolet (UV) and some visible (VIS) wavelengths.In the course of the work we have employed numerous experimental techniques suchas continuous-wave (CW), time-resolved and polarization-resolvedphotoluminescence methods, optical absorption spectroscopy, x-ray diffraction,transmission electron microscopy (TEM) and energy-filtered TEM (EFTEM), andelectron spin resonance (ESR). Using the above techniques we have been able tounambiguously assign the detected luminescence to tiny (smaller than 1 nm)silver nanoclusters. Implementation of the theoretical modelling, inparticular, density functional theory (DFT), has allowed us to identifydiamagnetic Ag-tetramers (Ag42+) as the most commonluminescent Ag species in our glass, and to calculate energy levels thataccount for the luminescence.We have deepened our understanding of the mechanism of the luminescence bystudying dependence of Ag nanoclusters emission on the glass chemicalcomposition and temperature, when both cooling a sample down to few Kelvin orheating it up to several hundredth degree Celsius. We have found out that thestrong temperature dependent interaction of Ag nanoclusters with their localatomic surrounding (glass host) limits the quantum yield of luminescence. Whilethe inter-cluster energy transfer accounts for some temperature dependentspectral features of the emission.We have demonstrated that the above energy transfer can be used to spectrallybroaden excitation windows of some rare-earth ions, particularly, Yb3+.Here the energy is transferred from Agnanoclusters excited in UV to Yb3+ions, emitting at about 1 µm, due to the spectral overlap of the Agnanoclusters emission band with the excitation band of Yb3+-ions.

academic collection --- 538.91 <043> --- Structures, including transitions--Dissertaties --- Theses --- 538.91 <043> Structures, including transitions--Dissertaties

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Phase transformations (Statistical physics) --- Amorphous substances --- Transitions de phase --- Substances amorphes --- Congresses. --- Congrès --- Congrès

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Mechanical properties of solids --- 538.91 --- Crystals --- -Electric insulators and insulation --- -Point defects --- -Semiconductors --- -Crystalline semiconductors --- Semi-conductors --- Semiconducting materials --- Semiconductor devices --- Electrical engineering --- Electronics --- Solid state electronics --- Defects, Point --- Dislocations in crystals --- Impurity centers --- Bushings --- Insulation (Electric) --- Electric resistance --- Insulating materials --- Dielectrics --- Crystallography --- Powders --- Solids --- Structures, including transitions --- Defects --- -Congresses --- Congresses --- Materials --- -Structures, including transitions --- 538.91 Structures, including transitions --- -538.91 Structures, including transitions --- Crystalline semiconductors --- Electric insulators and insulation --- Point defects --- Semiconductors --- Defects&delete&

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A cutting-edge collection of original essays from leading scholars examining the contemporary state of the ghetto in all its forms

Inner cities --- Sociology [Urban ] --- Sociology, Urban --- Urban sociology --- Cities and towns --- Central cities --- Ghettos, Inner city --- Inner city ghettos --- Inner city problems --- Zones of transitions --- Urban cores