We have investigated Si-(0⩽x⩽0.13)and Ge-rich(0.90⩽x⩽1)Si1−xGexbulk crystals by photoluminescence and photoconductivity measurements. The small linewidths of the near band edge luminescence of less than 4 meV demonstrate the high quality of the crystals. Luminescence linewidth, line shape, and intensity ratios of transitions with and without phonon participation reveal a stronger influence of alloy effects on excitons on the Ge-rich side compared with the Si-rich side. Photoconductivity spectra of boron doped Si-rich and phosphorus doped Ge-richSi1−xGexcrystals show the influence of alloy composition and alloy fluctuations on the impurity levels. The shift of the photoconductivity spectra with increasing Si or Ge concentration indicates the change of the ground state energy of the impurity with changing alloy composition.