Urbach’s rule of Bi4Ge3O12 doped with 3d and 4d ions

In this work, the influence of 3d (Fe, Mn) and 4d (Ru) ions on the absorption coefficient of the doped Bi4Ge3O12 (BGO) in the spectral range 3.6–4.05 eV has been determined. The validity of Urbach’s rule is verified in an illuminated and an annealed state of the samples. The dependence between the incorporation of the different dopants and the values of their Urbach’s parameters is established. The creation and the destruction of the excitons, associated with the ionized donors, are explained. The Urbach’s energy of all samples is determined.

► The values of σ0 show that the Oh and Td complexes in the doped BGO are deformed.
► The Fe3+ tetrahedrons are enlarged and the Mn2+, Ru4+ octahedrons are shrinked.
► The interaction excitons ↔ LO phonons is strongest for the illuminated BGO:Ru.
► The constant g is the biggest for BGO:Mn in the illuminated and the annealed state.