Isomer shifts have been determined for the 37 keV gamma -radiation of substitutional ¹²¹Sb impurities acting as donors in elemental group IV and as acceptors in group VI sites in II-VI compound semiconductors. Site-selective ion implantation techniques of radioactive precursors to the ¹²¹Sb isotope combined with suitable annealing techniques have been applied to achieve the impurity lattice locations. The isomer shifts, and thus the contact electron densities, for the Sb donors and acceptors are remarkably similar to those for (iso-electronic) Sb on V sites in III-V semiconductors. This leads to the general qualitative conclusion that the nominal electronic charges of +or-e giving rise to either the donor electron or the acceptor hole potential are not highly localised on the donor or acceptor impurity. The small but systematic differences observed for donor and acceptor ground-state contact densities indicate, however, a stronger bonding of the additional electronic charge accumulated on the acceptor impurity than for the donor electron on the donor impurity. A predominant s character is further indicated for the Sb donor ground state from very small differences in electron density for neutral and ionised donors, whereas a prevailing p character is evident for the acceptor state. Results for impurity-defect complexes are discussed briefly.