Impurities and defects in group IV elements (Diamond: impurities, defects, paramagnetic centers; Silicon: solubility, segregation and distribution coeff., impurity levels, excited bound states of acceptors and donors, photoluminescence properties, paramagnetic centers, vibrational modes, oxygen-related defects; Germanium: solubility, segregation, impurity levels, capture and photoionization cross-sections, luminescence of bound excitons, EPR, local vibration modes).