The Nitrogen-Hole-Center Electron Transfer Imparts Reduction Ability to Eu Ion in AlN-Containing Phosphate Glasses
2019
Zheng, Wenyan | Wang, Xiyang | Mao, Wei | Qiao, Xvsheng | Xu, Shiqing | Zhang, Junjie
The europium ion possesses fascinating luminescent properties, and its oxidation state is largely governed by the interaction with doping matrixes due to the appropriate redox potential. Here, we unravel the connection between the phosphate oxynitride glass structure and stepwise valence changes from Eu³⁺ to Eu²⁺. Through tuning the introducing content of AlN in phosphate glasses, an effective reduction among Eu³⁺ ions could be readily realized. This reduction process is explained by the “Nitrogen-Hole-Center (NHC) electron transfer” model. In this model, NHC and Eu³⁺ ions play as electron donor and acceptor roles, respectively. Under continuous thermal vibration of the lattice, the electrons released from unstable NHC could be caught by their nearest neighbor Eu³⁺ ions. Moreover, nitrogen-to-oxygen substitution significantly enhances the covalency and rigidity of the glassy network by forming distorted [PO₃N] and [PO₂N₂] tetrahedrons, creating a perfect shield for Eu²⁺ and resisting the attack of oxygen.
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