Insight into the Partitioning and Clustering Mechanism of Rare-Earth Cations in Alkali Aluminoborosilicate Glasses

Rare-earth (RE) containing alkali aluminoborosilicate glasses find increasingly broad technological applications, with their further development only impeded by yet-poor understanding of coordination environment and structural role RE ions in glasses. In this work we combine free induction decay (FID)-detected electron paramagnetic resonance (EPR), spin echo envelope modulation (ESEEM), MAS NMR spectroscopies, to examine the clustering tendencies RE3+ a series peralkaline co-doped Nd2O3 (0.001-0.1 mol%) 5 mol% La2O3. Quantitative EPR spectral analysis reveals three different Nd3+ forms coexisting glasses: isolated centers, dipole-coupled Nd clusters (Nd-O-X-O-Nd, where X = Si/B/Al), spin-exchange-coupled clusters, (Nd-O-Nd) (Nd-O-La-O-Nd). Extensive is observed at high RE2O3 concentrations, more than 90% REs converting dipole- exchange-coupled already [RE2O3] 0.01 mol%. ESEEM EPR-detectable centers indicates Na/Si-rich (four Na+ per Nd3+) for Na/Si/B-rich (2-3 1-2 boron each while EPR-undetectable exchanged-coupled are predicted exist Na/B-rich environment. The induces nano-scale glass phase separation, implies depletion same elements from remaining host glass. Based on our results, develop mechanistic model that explains tendency form