Reduction of Eu(3+) due to a change of the topological structure of the BO3 unit in borate glass.

Adjusting and controlling an ion's chemical state has always been a focus of researchers' attention. Herein, an intense long-lasting phosphorescence of Eu(2+) is obtained without any sacrificial reductant. The remarkable self-reducing process and the unique luminescence properties stem from a variation of the topological structure of the BO3 triangle.