Interconversion mechanisms of Ge-related oxygen deficient defects in germanium dioxide optical fiber

The interconversion mechanisms of Ge-related oxygen deficient defects including Ge-related oxygen deficient center (GeODC), Ge-related E' center (Ge-E') and germanium lone pair center (GLPC) have been investigated in germanium dioxide optical fiber. Our results revealed that the conversion paths from GeODC through Ge-E' centers, GLPC and then back to GeODC were similar in four- to six-membered rings. Furthermore, the transformation from Ge-E' to GLPC is spontaneous, indicating that it is the most likely to take place. We employed first-principles calculations to calculate optical properties and electronic properties of Ge-related oxygen deficient defects as well. All these models have a series of absorption peaks at 4-6 eV in the optical absorption spectrum, which may be related to the defect levels generated in the band gap. Our work provides a better understanding of the interaction among the three defects in germanium dioxide optical fiber.