Room temperature ferromagnetism and photoluminescence in Cu-doped ZnO nanocrystals.

The Zn(1-x)Cu(x)O (x = 0.0-3.5%) nanocrystals have been synthesized by a simple sol-gel method. X-ray diffraction, optical absorption and photoluminescence measurements were employed to validate consistently the incorporation of Cu ions into the ZnO wurtzite lattice without formation of secondary phases for Zn(1-x)Cu(x)O (x < 2.0%). Meanwhile, it was found that the substituted Cu-doping leads to the reduction of the band gap and the appearance of the structured green emission. Magnetization measurement showed that the low Cu-doping (x < 1.0%) develops the ferromagnetism, but the high Cu-doping destroys sharply the ferromagnetism due to the formation of the antiferromagnetic coupling among the neighboring Cu ions. It is indicated that the rational Cu-doping can tune optical and magnetic properties in ZnO.