Positron annihilation studies of vacancy-type defects and room temperature ferromagnetism in chemically synthesized Li-doped ZnO nanocrystals

•Evidence of zinc vacancy-induced intrinsic ferromagnetism in Li-doped ZnO.•Modification of defects and properties through alkali metal substitution.•Study of defect-modification using positron annihilation spectroscopy.•New way to prepare ZnO-based magnetic semiconductor for spintronic applications. In this article, we have investigated the effects of Li incorporation on the lattice defects and room-temperature d0 ferromagnetic behaviour in ZnO nanocrystals by correlating X-ray photoelectron, photoluminescence and positron annihilation spectroscopic study in details. It is found that at low doping level (