The photo-absorption and photoluminescence properties of 2-coordinated Si, Ge and Sn defect centers, and magnetic interactions of the corresponding [=Si-H]•, [=Ge-H]• and [=Sn-H]• structures, the H(I), H(II) and H(III) centers, respectively, were studied by means of ab initio quantum-chemical methods. By using cluster models and configuration interaction wave functions, the transition energies to the lowest singlet and triplet states and the corresponding emissions and lifetimes were determined. The computed optical properties were in close agreement with those proposed for the 2-coordinated centers in pure and doped silica. The hyperfine interactions of the paramagnetic H(I), H(II) and H(III) centers were studied by using unrestricted Hartree-Fock and density-functional theory. The proposed attributions were consistent with the calculations. The results provided strong support for the suggestion that 2-coordinated Si was the origin of one component of the 5eV B2 absorption band in amorphous silica.

Optical Transitions and EPR Properties of Two-Coordinated Si, Ge, Sn and Related H(I), H(II) and H(III) Centers in Pure and Doped Silica from ab initio Calculations. G.Pacchioni, R.Ferrario: Physical Review B, 1998, 58[10], 6090-6