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 S-I with g = 2.0028 and a hyperfine coupling constant \A\ = 74.6 x 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 S-II with g = 2.001 and \A\ = 89 x 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. (C) 2003 American Institute of Physics.