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SUMMARY:Atomistic modelling of excited states and luminescence in sodium s
 ilicate glass - Dr Konstantinos Konstantinou\, Department of Chemistry\, U
 niversity of Cambridge
DTSTART:20170315T110000Z
DTEND:20170315T120000Z
UID:TALK70999@talks.cam.ac.uk
CONTACT:Joseph Nelson
DESCRIPTION:Sodium silicate glasses of various compositions are an importa
 nt class of material that form the basis of glasses for many practical app
 lications\, and theoretical understanding of their structure and optical p
 roperties is important fundamentally\, as they are among the most widely u
 sed materials in contemporary optics. An excitation of sodium silicate gla
 ss by photons whose energy lies in the fundamental absorption region leads
  to the creation of self-trapped excitons. Previous experimental studies o
 f 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 extens
 ive 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 fir
 st 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. Th
 e properties of the ground L- and excited L&#42\;-centre states\, as well 
 as the luminescence energies were calculated\, together with the propertie
 s of the electron E1&#45\; and hole H1+ centres. The results from the ab i
 nitio 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 sil
 icate glass are associated with clusters of Na ions and non-bridging oxyge
 n atoms and they demonstrate the correlation between the calculated lumine
 scence energy and the short-range order of these clusters.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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