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Interactions de nano-objets luminescents (agrégats ou nano-films) avec leurs environnements: effets structuraux et diélectriques.

Abstract : Since the end of latest century, interest has shifted towards nano-crystals because of the observed modifications of their properties as compared to those of bulk materials, called size effects. Some changes are still quite controversial and depend strongly on the preparation method and the influence on the surface states and the structural disorder. My thesis is focused on the influence of surroundings of the Eu3+:Gd2O3 nanomaterial (nano clusters or nanofilms) on their physical properties from the structural and dielectric point of view.

In the first part of my thesis, we study the interactions of Eu3+:Gd2O3 clusters deposited by low energy clusters beam deposition embed in sol-gel Gd2O3 or TiO2 matrix film. After heat treatments, we observe clusters diffusion in surroundings and crystallisation of Eu3+:Gd2Ti2O7 pyrochlore structure for TiO2 matrix. So we studied the fabrication of this compound through two ways based on segregation and inter-diffusion of oxide nanometric thin films: Eu3+:Gd2O3 clusters between two TiO2 sol-gel layers and a TiO2/ Eu3+:Gd2O3/TiO2 multilayer. Eu3+:Gd2Ti2O7 crystallises at lowest temperature in first way but the second way gives best crystallised samples. Then nanomaterial properties are strongly linked to elaboration process.

In the second part of my work, we investigate the relationship between the radiative lifetime of a luminescent center and the surrounding refractive index. For the first time, we evaluate experimentally this critical distance by using a fluorescence sol gel nano-layer of Eu3+:Gd2O3 as a local probe. After each record, an additional high index passive thin layer of TiO2 recovers the film. As the number of passive layers increases, the lifetime decreases until we reach stabilization. Then the influence sphere diameter of the refractive index is estimated to be 150 nm or a quarter of emission wavelength. These values correspond to the critical dimension where the macroscopic definition of the refractive index should be applied at the nanometric scale.
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Contributor : Vincent Le Bihan <>
Submitted on : Monday, October 20, 2008 - 11:44:45 AM
Last modification on : Wednesday, November 20, 2019 - 2:38:31 AM
Long-term archiving on: : Monday, June 7, 2010 - 8:50:56 PM


  • HAL Id : tel-00332025, version 1



Vincent Le Bihan. Interactions de nano-objets luminescents (agrégats ou nano-films) avec leurs environnements: effets structuraux et diélectriques.. Physique [physics]. Université Claude Bernard - Lyon I, 2008. Français. ⟨tel-00332025⟩



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