Isotope effects on the 969 meV vibronic band in silicon

The radiation-induced vibronic band with its zero-phonon line at 969 meV is shown to have a localised mode sideband. This mode is sensitive to the isotope of carbon doping the silicon, in a way consistent with one carbon atom per optical centre. Hitherto unreported structure in the zero-phonon line is shown to be consistent with its being produced by Si isotope effects at one Si atom in the centre.