Structure and formation mechanism of Ge E (') center from divalent defects in Ge-doped SiO2 glass

We have performed ab initio quantum-chemical calculations on clusters of atoms modeling a divalent Ge defect in Ge-doped SiO (2) glasses. It has been found that the divalent Ge defect interacts with a nearby GeO (4) tetrahedron, forming complex structural units that are responsible for the observed photoabsorption band at approximately 5 eV. We have shown that these structural units can be transformed into two equivalent Ge E' centers by way of the positively charged defect center.