We show that the main mechanism for the dc voltage or dc current induced insulator-metal transition in vanadium dioxide VO(2) is due to local Joule heating and not a purely electronic effect. This "tour de force" experiment was accomplished by using the fluorescence spectra of rare-earth doped micron sized particles as local temperature sensors. As the insulator-metal transition is induced by a dc voltage or dc current, the local temperature reaches the transition temperature indicating that Joule heating plays a predominant role. This has critical implications for the understanding of the dc voltage or dc current induced insulator-metal transition and has a direct impact on applications which use dc voltage or dc current to externally drive the transition.

High temperature imaging using a thermally compensated cantilever resistive probe for scanning thermal microscopy J.

With the aim of analyzing the properties of the waves that are scattered by nanoslits on metallic surfaces, we provide a direct observation of the near-field in a slit-doublet experiment at optical wavelengths. We show that two distinct waves are involved: a surface plasmon polariton and another wave with a free-space character. From the recorded data, we have extracted the amplitudes and phases of these waves, their damping characteristic lengths and their relative weights as a function of the separation distance from the slit. The analysis is fully supported by a quantitative agreement with vector-theory computational results.

We report on an experimental technique to quantify the relative importance of electric and magnetic dipole luminescence from a single nanosource in structured environments. By attaching a Eu^{3+}-doped nanocrystal to a near-field scanning optical microscope tip, we map the branching ratios associated with two electric dipole and one magnetic dipole transitions in three dimensions on a gold stripe. The relative weights of the electric and magnetic radiative local density of states can be recovered quantitatively, based on a multilevel model. This paves the way towards the full electric and magnetic characterization of nanostructures for the control of single emitter luminescence.

Much research has been devoted to molybdenum octahedral clusters Mo 6 since the discovery of the A x Mo 6 Y 8 solidstate series (Y = S, Se, Te) in the early 1970s.[1] Indeed, their interesting physical properties and potential applicationse.g., superconductivity at high critical field, thermoelectric, catalysis, or redox intercalation processes -have stimulated the research of many groups. [2] (Fig. 1). The physical properties of Mo 6 solid-state compounds are related to the number of electrons available for metal-metal bonding within the cluster (valence electron count, VEC) and to the strength of interaction between the units. Mo-centered electrons are located on twelve metal-metal bonding molecular orbitals of the molecular orbital diagram. Their full occupation leads to a closed-shell configuration with a VEC of 24.[ [8,9] that can be used for the formation and organization of supramolecular assemblies as well as hybrid materials. Hybrids can be synthesized either by the grafting of functional donor ligands in apical position or through the association of anionic cluster units with organic or organometallic cations by cation metathesis or electrochemical techniques.[10]The large emission region of the [Mo 6 X 14 ] 2-anion in the red and near infrared (580-900 nm) is particularly interesting for biotechnology applications as it is selectively transmitted through tissues owing to the relatively low absorption at these wavelengths.[11] Anionic Mo 6 cluster units are usually associated with alkali counter cations within inorganic solids. Indeed, the use of inorganic cluster compounds as luminescent dyes, for instance in bio-imaging strategies, presupposes that both clusters and counter cations are embedded in an inert matrix in order to avoid ionic diffusion, oxidization of the cluster, or apical ligand exchanges in aqueous media, which will precipitate the cluster as a hydroxo species.

A bright persistent photoluminescence has been observed in Er(3+)-doped nanoparticles prepared by selective dissolution of bulk oxyfluoride nano-glass-ceramics. A 2 orders of magnitude decrease of intensity of the (4)S(3/2)-->(4)I(15/2) green emission band of Er(3+) in these nanoparticles is observed in magnetic fields up to 50 T. This strong luminescence sensitivity to magnetic field can be used for localization and distant optical detection of magnetic field in nanovolumes with a field-resolution of 0.01 T.

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The combined time-resolved photoluminescence (PL) and theoretical study performed on luminescent [Mo6Br(i)8Br(a)6](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.