Magnetic resonance investigation of Mn2+ in ZnO nanocrystals

Electron paramagnetic resonance measurements were carried out to probe the structure of Mn2+ in ZnO nanocrystals with different surface conditions, modified by an annealing process. Changes in the spectra by the annealing treatment indicate the existence of three Mn2+ centers. The first is a sextet signal SI with g=2.0028 and a hyperfine coupling constant |A|=74.6×10−4 cm−1 and is present in all samples. Its hyperfine splitting is similar to Mn-doped ZnO single crystals, and therefore it is assigned to isolated substitutional Mn2+ ions. The second spectrum SII with g=2.001 and |A|=89×10−4 cm−1 decreases upon annealing. It is attributed to Mn2+ in strongly distorted environment, i.e., Mn2+ in Zn(OH)2 which is present as a surface shell of the ZnO nanoparticles. The superimposed broad background is associated with Mn–Mn clusters or dipole interactions, and it increases in intensity upon annealing.