Singulet | EPFL Graph Search

La notion de « singulet » prend un sens différent selon qu'on l'utilise dans le domaine de la physique ou de la chimie. Dans le domaine de la physique En physique théorique, un singulet peut faire référence à

une représentation uni-dimensionnelle (par exemple une particule dont le spin disparaît).
deux ou plusieurs particules corrélées de telle façon que le moment angulaire total de l'état soit égal à zéro.

En physique atomique, les singulets sont fréquemment présentés comme l'une des deux façons de combiner le spin de deux électrons, l'autre étant le triplet. Le produit de deux représentations de doublets peut être décomposé comme étant la somme de la représentation d'un triplet et de la représentation triviale, un singulet. De façon plus prosaïque, une paire d'électrons de spin ½ peut être combinée de façon à aboutir à un état total de spin 1 ou de spin 0. La forme singulet d'une paire d'électrons lui donne beaucoup de particularités. Elle joue un rôle f

Complexes luminescents de lanthanides avec des dérivés du cyclène comme briques pour l'ingénierie de sondes analytiques biomédicales

This work deals with the engineering of a new luminescent complex of lanthanide, able to be specifically grafted onto biological materials and to emit a characteristic light useful in quantifying the concentration of the target molecules. We have based our molecular design on TbL1, wich possesses a significant quantum yield in water pointing to an efficient intramolecular energy transfer. We have elaborated the synthesis of a ligand derived from L1 and named L3, by functionalizing one of the chromophoric groups into a moiety able to couple the luminescent sensor to biological materials. The synthesis of the complexes was then realized. The thermodynamic study of the ligands L1 and L3, and their terbium complexes in water was made to establish the distribution diagrams and to compare their behaviour, especially at neutral pH. In addition, EuL1 was also investigated and the complexation constants of TbL1, EuL1 and TbL3 in water showed that these molecules are thermodynamically stable in aqueous media. Characterization of EuL3 in the solid state by high resolution luminescence allowed us to determine the geometry of the coordination sphere of the Eu(III) ion, which possesses a distorded C4 symmetry. The detailed study of the Eu(III) ion transitions evidenced two different sites, possibly arising from an equilibrium induced by the competition between a water molecule and the carboxylate function. This interpretation is in line with the measured lifetimes of the Tb(III) and Eu(III) excited states and the calculation of the hydration number of the complexes in aqueous solution. The determination of the energy of the singlet state and triplet states of the ligand, as well as of the emitting levels of the Ln(III) ions in solution showed that their relative values are favorable for a good intramolecular energy transfer. The quantum yields of TbL3 and EuL3, which amount to 2.6 % and 1.4 %, respectively, are lower than those of the complexes with L1, denoting that the presence of the acid function increases losses in the energy transfer. However, these values remain sizeable enough for potential biomedical applications. The study of the intermolecular energy transfer from EuL1, EuL3 and TbL3 to the acceptor Cy5 has proved promising, and the resulting yields were 90 % for EuL1 and 80 % for the complexes with L3.

EPFL2004

Control of spin configuration in half-metallic La0.7Sr0.3MnO3 nano-structures

André Bisig

We investigate the interplay between the governing magnetic energy terms in patterned La0.7Sr0.3MnO3 (LSMO) elements by direct high-resolution x-ray magnetic microscopy as a function of temperature and geometrical parameters. We show that the magnetic configurations evolve from multidomain to flux-closure states (favored by the shape anisotropy) with decreasing element size, with a thickness-dependent crossover at the micrometer scale. The flux-closure states are stable against thermal excitations up to near the Curie temperature. Our results demonstrate control of the spin state in LSMO elements by judicious choice of the geometry, which is key for spintronics applications requiring high spin-polarizations and robust magnetic states. (C) 2011 American Institute of Physics. [doi:10.1063/1.3623480]

2011

Complexes luminescents de lanthanides avec des dérivés du cyclène comme briques pour l'ingénierie de sondes analytiques biomédicales

EPFL2004