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Atomistic modelling of excited states and luminescence in sodium silicate glass

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Sodium silicate glasses of various compositions are an important class of material that form the basis of glasses for many practical applications, and theoretical understanding of their structure and optical properties is important fundamentally, as they are among the most widely used materials in contemporary optics. An excitation of sodium silicate glass by photons whose energy lies in the fundamental absorption region leads to the creation of self-trapped excitons. Previous experimental studies of the ground and electronically excited states of sodium silicate glasses have been interpreted in terms of the so-called L-centre model describing the short-range order in the glass structure. However, in spite of extensive experimental studies, no atomistic calculations of the L-centres have been performed so far to investigate the proposed qualitative models and shed light on their atomistic structures. In this talk, I present the first atomistic calculations of localised states in sodium silicate glasses. The geometric and electronic structures of localised states in Na2O-3SiO2 glass are investigated by means of classical and ab initio simulations. The properties of the ground L- and excited L*-centre states, as well as the luminescence energies were calculated, together with the properties of the electron E1- and hole H1+ centres. The results from the ab initio calculations are compared to the experimental data and the predicted excitation and luminescence energies are in good agreement with them. The calculations confirm that the lowest triplet excited states in sodium silicate glass are associated with clusters of Na ions and non-bridging oxygen atoms and they demonstrate the correlation between the calculated luminescence energy and the short-range order of these clusters.

This talk is part of the Electronic Structure Discussion Group series.

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