Europium environment and clustering in europium doped silica and sodium silicate glasses

The local environment and distribution of rare earth ions are important to the optical properties of rare earth doped oxide glasses. In this paper, we report studies of the structures of europium doped (around 1 mol% Eu2O3) silica and sodium silicate glasses using molecular dynamics simulations. By using effective partial charge potentials, systems with over 24,000 atoms were modeled in order to obtain better statistics of rare earth ion distribution. The simulated glass structures were validated by comparing the calculated neutron and X-ray structure factors with experimental data. It was found that europium ions have higher coordination number (5.9 versus 4.8) and more symmetric environments in sodium silicate glasses than in the silica glass. Rare earth ion clustering has been characterized in detail and it was found that the clustering probability of europium ions in sodium silicate glass is consistently less than that predicted from a random distribution, while the probability of clustering in pure silica glass is higher than that of random distribution at the 1 mol% doping level.