Isoelectronic series of twofold coordinated Si, Ge, and Sn atoms in glassy SiO₂: a luminescence study

Luminescence centers causing optical absorption bands in the 5 eV region in oxygen-deficient pure ('Si-doped'), as well as in Ge- and Sn-doped glassy SiO₂ were studied. The spectral and particularly kinetic data show that in all cases luminescence centers with closely similar properties exist which constitute an isoelectronic series. They are attributed to defects, formed by electrically neutral twofold coordinated Si, Ge, and Sn atoms (T₂⁰ centers) in glassy SiO₂. Twofold coordinated Si causes the characteristic 'B₂' optical absorption band at 5.03 eV. Upon reaction with atomic hydrogen, T₂⁰ centers convert to the well known 'H(I)', 'H(II)' and 'H(III)' ESR-active defects. The alternative models for these defects are discussed.