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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.

A cobalt alkoxide, Co(OCH 2 CH 2 O), has been prepared from the reaction of cobalt acetate with ethanediol. This compound crystallizes as disk-shaped particles with diameter and thickness in the 0.4-1 mm and 100-250 nm ranges, respectively. Structural characterization (X-ray and electron diffraction) shows a layered arrangement with a brucite-like structure presenting a turbostratic disorder. The interlayer spacing and the CoÁ Á ÁCo distance within the layer are c = 8.27 A ˚and a = 3.09 A ˚, respectively. UV-visible spectroscopy studies established that the Co(II) ions are located on octahedral sites. IR spectroscopy showed that the ethylene glycolate anions (OCH 2 CH 2 O) 2À chelate the Co(II) cations. The magnetic properties of the compound were measured in the range of 2-300 K. Below 20 K, the compound exhibits 3D ferromagnetic order and the hysteresis loop shows a very high remanence-to-saturation ratio typical of a uniaxial magnetocrystalline anisotropy.

accessory. Samples were prepared by evaporating a drop of solution on a carbon (Agar) grid.Nonlinear Optical Measurements: Harmonic light scattering measurements were conducted with a Q-switched Nd:YAG (yttrium aluminum garnet) laser emitting pulses of about 40 ns at 1.91 lm. Metal nanoparticles with various shapes and organizations are desired in order to understand nanometer-scale properties, and they are attractive for several applications in the fields of optics, electronics, and magnetism. As far as magnetic storage is concerned, very high storage density requires high magnetic anisotropy to overcome thermal effects and to prevent superparamagnetic behavior, which appears as the size of the magnetic single-domain particles is reduced. Several kinds of magnetic anisotropy can be considered for this application, including: i) magnetocrystalline anisotropy (for example, of CoPt and FePt alloys with tetragonal structures); [1±3] ii) exchange anisotropy of ferromagnetic/antiferromagnetic core±shell particles; [4] and iii) shape anisotropy of elongated magnetic particles such as rods and wires.[5]The chemical synthesis of nanoparticles presents the advantage of simplicity and low cost compared with physical approaches. Moreover, it is now well-established that the structure of fine cobalt particles prepared by physical means under high vacuum is size-dependent: the face-centered cubic (fcc) phase is stabilized for mean diameters below 20 nm. [6,7] In contrast, several examples of hexagonal close-packed (hcp) cobalt nanoparticles prepared by wet-chemical processes have been reported. [8,9] The synthesis of metal nanoparticles with anisotropic shapes by liquid-phase processes is an interesting challenge, because in most cases the isotropic shapes minimize their surface energy in solution.In this context, several solid hosts have been used as templates for the anisotropic growth of metal particles, for example, mesoporous silica [10] and carbon nanotubes.[11] The most COMMUNICATIONS 338

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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Yb(3+)-Er(3+) co-doped fluoride nanoparticles have been prepared. When pumped by 975 nm laser diode into absorption band of Yb(3+), the laser-induced temperature rise up to 800 degrees C has been detected in the nanoparticles by measuring the ratio of the intensities of the thermalised up-conversion luminescence bands (2)H(11/2)-->(4)I(15/2) and (4)S(3/2)-->(4)I(15/2) of Er(3+). These results show that a controlled optical heating of the nanoparticles and their surrounding nano-volumes can be realised, while the location and temperature rise of the nanoparticles and heated nano-volumes can be detected distantly by means of luminescence.