Coexistence mechanism of Eu2+/Eu3+ ions in YAl3(BO3)4: Crystal structure, luminescence property, and substitution defects.

The coexistence mechanism of Eu2+ and Eu3+ ions in YAl3(BO3)4 host under different reducing conditions is investigated and confirmed in great detail, which can be described by three aspects as following. First, Eu3+ is protected by the layered structure of YAl3(BO3)4. Second, the number of the interstitial defects ((Al)i...,(Y)i...) increases with increasing Eu2+ to maintain the charge balance of the system. And these defects can capture free electrons which are used for the reduction of Eu3+. Finally, free holes become more and more with the number of nonequivalent substitution defects (EuY') increasing, which make the 5d electrons of Eu2+easily escape to the conduction band and Eu2+ convert to Eu3+. This work will be of great significance to research coexistence of multiple valence ions in the structure of borate and defect motion with nonequivalent substitution. [ABSTRACT FROM AUTHOR]