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Insight into the Partitioning and Clustering Mechanism of Rare-Earth Cations in Alkali Aluminoborosilicate Glasses
Chemistry of Materials ( IF 8.6 ) Pub Date : 2021-10-14 , DOI: 10.1021/acs.chemmater.1c01352
Hrishikesh Kamat 1 , Fu Wang 1, 2 , Kristian E. Barnsley 3 , John V. Hanna 3 , Alexei M. Tyryshkin 4 , Ashutosh Goel 1
Affiliation  

Rare-earth (RE) containing alkali aluminoborosilicate glasses find increasingly broad technological applications, with their further development only impeded by a yet-poor understanding of the coordination environment and structural role of RE cations in glasses. In this work, we combine free induction decay (FID)-detected electron paramagnetic resonance (EPR), electron spin echo envelope modulation (ESEEM), and MAS NMR spectroscopies to examine the coordination environment and the clustering tendencies of RE3+ in a series of peralkaline aluminoborosilicate glasses co-doped with Nd2O3 (0.001–0.1 mol %) and 5 mol % La2O3. Quantitative EPR spectral analysis reveals three different Nd3+ forms coexisting in the glasses: isolated Nd3+ centers, dipole-coupled Nd clusters (Nd–O–X–O–Nd, where X = Si, B, or Al), and spin-exchange-coupled Nd clusters (Nd–O–Nd and Nd–O–La–O–Nd). Extensive RE clustering is observed at high RE2O3 concentrations, with more than 90% of REs converting to dipole- and exchange-coupled Nd clusters already at [RE2O3] = 0.01 mol %. ESEEM analysis of the EPR-detectable Nd centers indicates a Na/Si-rich environment (four Na+ per Nd3+) for the isolated Nd3+ centers and a Na/Si/B-rich environment (two to three Na+ and one to two boron for each Nd3+) for the dipole-coupled Nd clusters, while the EPR-undetectable exchanged-coupled RE clusters are predicted to exist in a Na/B-rich environment. The RE clustering induces nanoscale glass phase separation, while the Na/B-rich environment of the RE clusters implies a depletion of the same elements from the remaining host glass. Based on our results, we develop a mechanistic model that explains the high tendency of RE3+ to form clusters in alkali aluminoborosilicate glasses.
更新日期:2021-10-26
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