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The combined time-resolved photoluminescence (PL) and theoretical study performed on luminescent [Mo6Bri8Bra6]2−-based systems unambiguously shows that their NIR-luminescence is due to at least two emissive states. By quantum chemical studies, we show for the first time that important geometrical relaxations occur at the triplet states either by the outstretching of an apex away from the square plane of the Mo6 octahedron or by the elongation of one Mo–Mo bond. Experimental PL measurements demonstrate that the external environment (counter-ions, crystal packing) of the cluster has a noticeable impact on its relaxation processes. Temperature and excitation wavelength dependence of the two components of the luminescence spectra is representative of multiple competitive de-excitation processes in contradiction with Kasha's rule. Our results also demonstrate that the relaxation processes before and after emission can be tracked via fast time-resolved spectroscopy. They also show that the surroundings of the luminescent cluster unit and the excitation wavelength could be modulated for target applications. [ABSTRACT FROM AUTHOR]

Recently, Nanoarchitectonics has been introduced as a new concept that refers to a technology system for arranging nanoscale structural units in a required architecture. Multifunctional properties are achieved by a combination of several materials in a well-defined architecture. In the frame of this concept, composite nanoarchitectures represent a new class of nanostructured entities that integrate various dissimilar nanoscale building blocks including clusters, particles, wires and films. The heterogeneous composite nanostructured materials are composed by definition of multi-(nano)components, each tailored to address different requirements. As one of the nanocomponents, nanometer sized metal clusters (<2 nm), which consist of less than a few dozens of metal atoms, could be defined as a link between atom and nanoparticle. In this paper, we will focus on our results on new nano-composites involving Mo atom nanosized cluster units for optical, nanobiotechnology, energy and environmental applications. [ABSTRACT FROM AUTHOR]

Abstract: Europium-doped lead germanate and lead fluorogermanate glasses are studied by using differential thermal analysis, X-ray diffraction, photoluminescence and fluorescence lifetimes measurements of the 5D j , j =0, 1, 2 levels. PbF2 addition increases the thermal stability of the lead germanate glass, while Eu3+ ions promote the crystallization of β-PbF2:Eu3+ nano-crystals embedded in a glassy matrix. In the lead fluorogermanate glasses, Eu3+ ions exhibit a strong affinity for F− ions although oxygen ions are much more numerous. It appears that luminescence concentration quenching is not important, while cross relaxation is very efficient in the glasses. The results allow to propose for these glasses a molecular model in which small fluorine rich island, incorporating the Eu3+ ions in low symmetry sites, are separated from each other by chains of germanate (GeO4)4− ions linked together. [Copyright &y& Elsevier]

Oxyfluoride glasses (GeO2-PbO-PbF2) doped with erbium and/or ytterbium fluorides were prepared. Highly transparent glass-ceramics, containing β-PbF2 nanocrystallites, were successfully obtained by controlled glass devitrification and were studied as they could lead to promising optical applications. To characterize the samples, differential thermal analysis, x-ray diffraction, and transmission electron microscopy were performed, revealing a variation of the crystallites size, the crystallites number and β-PbF2 crystallization temperature according to the doping ion. Indeed, the analyses indicated differences between erbium and ytterbium fluorides in promoting the crystallization of the fluoride phase. Although both fluorides act as seeds for β-PbF2 heterogeneous nucleation, erbium fluoride has higher nucleation efficiency than ytterbium fluoride and runs the nucleation process in co-doped samples. Energy dispersive x-ray microanalysis insured high rare-earth segregation into the crystallites, proving the formation of a solid solution Pb1-x-yErxYbyF2 + x+y, also confirmed by the unit cell parameter study. [ABSTRACT FROM AUTHOR]