75 research outputs found
Relation structure-luminescence dans les verres dopés terre rare
Les matĂ©riaux inorganiques dopĂ©s terre rare sont Ă lâorigine de nombreuses applications dans le domaine de la photonique (lasers, guides dâonde actifs, amplificateurs Ă fibreâŠ). Les propriĂ©tĂ©s de luminescence des ions terre rare Ă©tant essentiellement liĂ©es Ă la structure locale qui les entoure, il sâavĂšre nĂ©cessaire de caractĂ©riser et de comprendre ce lien pour pouvoir optimiser les matĂ©riaux synthĂ©tisĂ©s aujourdâhui et envisager les matĂ©riaux de demain. Câest tout lâobjet des travaux prĂ©sentĂ©s Ă lâoccasion de cette HDR qui rĂ©sume lâensemble de mes activitĂ©s de recherche menĂ©es dans le cadre du laboratoire LPhiA. Au sein de lâĂ©quipe « couches minces et verres dopĂ©s », jâai ainsi pu dĂ©velopper des techniques dâinvestigation originales, sâappuyant sur la modĂ©lisation de structures vitreuses par dynamique molĂ©culaire et le calcul de leurs propriĂ©tĂ©s de luminescence. En Ă©troite collaboration avec des Ă©quipes rĂ©alisant la synthĂšse et la caractĂ©risation expĂ©rimentales, ces activitĂ©s de modĂ©lisation ont ainsi permis de comprendre les spĂ©cificitĂ©s de ce lien entre structure et luminescence, essentiellement dans des verres silicatĂ©s, mais aussi dans des matrices fluorĂ©es et plus rĂ©cemment dans des vitrocĂ©ramiques
Simulation of ultrashort heat pulses on vitreous thin plates-application to the determination of dynamic constants
Date du colloque : 09/2010International audienc
Cutoff effect in molecular dynamics simulations of interaction induced light scattering spectra
International audienceA strong dependence of the interaction induced light scattering integrated intensity with the cutoff radius was previously reported in noble liquids molecular dynamics simulations (A.J.C. Ladd, T.A. Litovitz, J.H.R. Clarke, L.V. Woodcock, J. Chem. Phys. 72 (1980) 1759; and J.H.R. Clarke, L.V. Woodcock, Chem. Phys. Lett. 78 (1981) 121). It was concluded that the uncertainties arising from this effect were much larger than can be tolerated in any evaluation of the light scattering mechanism. No real explanation or solution ever appeared in the literature on this problem. Here we report a very strong dependence of the interaction induced spectra calculated by molecular dynamics simulations on the number of atoms used in a liquid argon simulation. We show that this effect is proportional to the square of the density involved in the simulation-4 and that it obeys to a Rcutoff power law with the cutoff radius Rcutoff. To obtain accurate spectra up to high frequency shifts, large cutoff radii have then to be used corresponding to thousands of atoms in the simulation. The time of the simulation is then prohibited. An explanation for both effects is proposed and two different methods to solve this problem are tested. @ 1997 Elsevier Science B.V
Molecular dynamics simulation of Eu3+ in aqueous solution comparison with experimental luminescence spectra
Using molecular dynamics simulations, we have studied the environment of Eu3+ salts in aqueous solution. In the case of hydration number of 8, the symmetry of the first hydration shell is found to be very close to the D4d. We have therefrom calculated the ligand field parameters according to the point charge model. The luminescence spectra were reconstructed from this set of computed Bkq, and finally compared with experimental spectra
Molecular dynamics simulations of rare-earth-doped glasses
In the recent years the use of the molecular dynamics technique has become very common in the study of glass. The purpose of the present paper is to focus on recent advancements on the use of this method to investigate rare-earth-doped glasses. We report an overview of the use of simulations to study their specific structural features and luminescence properties
Numerical Simulations of the Structure and Spectroscopic Properties of Rare-Earth Doped Glasses
A review of the research that has been devoted to the simulation of the structure and spectroscopic properties of rare-earth doped glasses is presented. Since the seminal papers of Brawer and Weber who have applied Monte-Carlo or molecular dynamics techniques, some other very important results have been reported concerning the local structure of the dopants. As a result, crystal field models have been applied and several pecularities of the optical spectra of rare earth ions in glasses have been understood
Molecular dynamics simulation of phase transitions in crystalline lead (II) fluoride
Using classical molecular dynamics applied to crystalline PbF2, we have simulated transitions between cubic and orthorhombic phases and reciprocally. These transitions were induced by pressure and temperature treatments. The orthorhombic phase was evidenced by analysis of different distribution functions and XRD spectra drawn from the ions positions in the simulated samples. (C) 2014 Elsevier B.V. All rights reserved
Molecular dynamics simulation of trivalent europium in aqueous solution: A study on the hydration shell structure
As a prelude to a spectroscopic investigation of doped wet gels, we have made molecular dynamics simulations of a very dilute EuCl3 solution. The symmetry properties of the first hydration shell of Eu3+ have been determined. The 8 water molecules of this shell are roughly arranged according to the square antiprism D 4d pseudoâsymmetry. Though the arrangement of oxygens is little distorted from regular positions, the orientation of the water molecules themselves is found to be not so well organized at room temperature
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