Structure and Formation Mechanism of Ge $\mathit{E}{}^{\prime }$ Center from Divalent Defects in Ge-doped ${\mathrm{SiO}}_2$ Glass

We have performed ab initio quantum-chemical calculations on clusters of atoms modeling a divalent Ge defect in Ge-doped $\mathrm{SiO}{}_2$ glasses. It has been found that the divalent Ge defect interacts with a nearby $\mathrm{GeO}{}_4$ tetrahedron, forming complex structural units that are responsible for the observed photoabsorption band at $\sim 5\mathrm{eV}$. We have shown that these structural units can be transformed into two equivalent Ge $E^{\prime }$ centers by way of the positively charged defect center.