The results of low-temperature photoluminescence characterization of single silicon nanocrystals prepared from highly doped silicon-on-insulator wafers are presented. The effect of B, P, As, and Sb impurities on ensemble as well as individual emission spectra are determined by comparison with the line shapes of undoped nanocrystals. From the statistical analysis of the luminescence spectra, the donor ionization energies for nanocrystals emitting in the range of 1.5–2.0 eV are estimated to be 140–200 meV, while the exciton-impurity binding energy for As- and Sb-doped nanocrystals is found to be about 40–45 meV.