ZnO nanocrystals doped with Cd, Mg, Mn, and Fe ions were obtained by thermolysis of a family of metal cupferrates. The nanocrystals were characterized by X-ray diffraction, energy-dispersive X-ray analysis, transmission electron microscopy, UV-visible, luminescence, and excitation spectroscopy. The band gap of the nanocrystals can be tuned in the range of 2.9-3.8 eV by the use of the dopants. In most cases, the nanocrystals are sufficiently defect-free to exhibit band edge luminescence.