Change in the distribution state of Mn2+before and after annealing was examined by electron spin resonance (ESR) in order to elucidate the electroluminescence properties of Mn‐doped ZnS modified by Cu. Formation of Mn2+ion pairs and clusters, as determined from the hyperfine structure of ESR profiles, was revealed to be dominant for concentration quenching. ©1995 American Institute of Physics.