Structure Prediction of Rare Earth Doped BaO and MgO Containing Aluminosilicate Glasses–the Model Case of Gd2O3

Abstract

The medium-range atomic structure of magnesium and barium aluminosilicate glasses doped with Gd2O3 as a model rare earth oxide is elucidated using molecular dynamics simulations. Our structure models rationalize the strong dependence of the luminescence properties of the glasses on their chemical composition. The simulation procedure used samples’ atomic configurations, the so-called inherent structures, characterizing configurations of the liquid state slightly above the glass transition temperature. This yields medium-range atomic structures of network former and modifier ions in good agreement with structure predictions using standard simulated annealing procedures. However, the generation of a large set of inherent structures allows a statistical sampling of the medium-range order of Gd3+ ions with less computational effort compared to the simulated annealing approach. It is found that the number of Si-bound non-bridging oxygen in the vicinity of Gd3+ considerably increases with growing ionic radius and concentration of network-modifier ions. In addition, structure predictions indicate a low driving force for clustering of Gd3+, yet no precise correlation between the atomic structure and luminescence lifetimes can be conclusively established. However, the structure models provided in this study can serve as a starting point for future quantum mechanical simulations to shed a light on the relation between the atomic structure and optical properties of rare earth doped aluminosilicate glasses.

The Structure of Gd3+-Doped Li2O and K2O Containing Aluminosilicate Glasses from Molecular Dynamics Simulations

“…In the case of glasses with low dopant concentration, large unit cells (>10 4 atoms) are required when using standard simulated annealing approaches [37]. In our previous work [26], an alternative approach has been applied for the structural characterization of rare-earth-doped glasses, the so-called inherent structure (IS) sampling. This simulation procedure allows the use of smaller unit cells for the statistically robust sampling of the atomic medium-range order around rare-earth ions.…”

“…This also results in a large difference in the luminescence properties of the doped rare-earth ions, as explained earlier. Additionally, the results are compared to simulation results of magnesium and barium aluminosilicate glasses of equimolar compositions reported by our group [26]. This work aims to gain further insight into the structure of the aluminosilicate glass network and to analyze in detail the compositional effect of the network-modifying ions on the local environment of the Gd 3+ ions in these glasses.…”

“…In the latter case, an additional network modifier cation is required for charge compensation [18,22]. Oxygen triclusters have so far only been detected in calcium aluminosilicate glasses [23], but they are often reported by computational methods [18,[24][25][26][27][28][29]. In glasses with an NMO/Al 2 O 3 ratio < 1, non-bridging oxygen should not occur, however, NBO are still reported in combination with comparably high concentrations of five-or six-fold aluminum [18,19,21].…”

“…This structural model implies a micro-segregation in-network modifier-rich regions, the so called depolymerized zones or percolation channels and regions of high network former concentration [18,30]. For binary alkali silicate glasses, this structural model is supported by diffusion and conductivity measurements [33], however, for aluminosilicate glasses, it is so far only supported by numerous computational investigations [18,26,28]. The size and permeation of these zones are most probably decreased with decreasing NMO/Al 2 O 3 ratio.…”

Tb3+as probe ion—Clustering and phase separation in borate and borosilicate glasses

“…The decreasing lifetime for NBS1 from approximately 4 to 3 ms could be caused by a change in the local surrounding of the Tb 3+ ions with increasing doping concentration. Investigations with different methods show that network modifier ions of high field strength, such as, for example, rare earth ions, prefer the coordination with non‐bridging oxygen sites . Therefore, at low doping concentrations the Tb 3+ ions should be coordinated mainly with SiØ 3 O ‐ groups.…”