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Electronic properties of silver chloride : influence of excitons on the charge dynamics

Abstract : In 1848, Edmond Becquerel proposed one of the first techniques of color photography. This technique raised a long-standing debate in the scientific community concerning the origin of the observed colors. In 2019, Victor de Seauve, during his thesis at the Muséum National d'Histoire Naturelle in Paris, could clarify some important issues, proposing a new explanation. The aim of the present thesis was to participate in this effort of comprehension, by adding theoretical insight. The first question is which level of theory one may adopt in order to correctly describe the electronic and optical properties of AgCl. Our calculations show that only the solution of the Bethe-Salpeter equation is able to describe the optical spectrum of AgCl, since the spectrum is dominated by a strong peak at the absorption onset, due to a bound exciton. Moreover, the calculation has to be based on a band structure that results from a self-consistent GW calculation. In order to make the Bethe-Salpeter calculations possible, a previously proposed model dielectric function was used in an improved way. Our results well describe the measured absorption spectra, and enable us to analyse and interpret the observations. In the hypothesis brought forward by the team at the Museum, the light excites a silver nanoparticle, followed by a transfer of charge at the interface between the nanoparticle and AgCl. In order to be able to study this phenomenon, we have developed a numerical approach describing the charge dynamics due to an external perturbation. In particular, this approach has allowed us to show that a bound exciton influences the charge dynamics significantly. Finally, we have set up a first model meant to simulate the charge transfer between a silver nanoparticle and AgCl, based on a simplified heterostructure. We have shown how the absorption spectrum of AgCl changes due to its neighbourhood to the silver metal, and how these changes can be described by the effective medium theory. Calculations of the density induced by a periodic perturbation have been carried out. These calculations remain cumbersome, and the study will continue with the idea to combine ab initio calculations with effective medium theory.
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  • HAL Id : tel-03220942, version 1

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Arnaud Lorin. Electronic properties of silver chloride : influence of excitons on the charge dynamics. Materials Science [cond-mat.mtrl-sci]. Institut Polytechnique de Paris, 2020. English. ⟨NNT : 2020IPPAX087⟩. ⟨tel-03220942⟩

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