Micro-Raman investigation of transition-metal-doped ZnO nanoparticles

We measured the Raman spectra of ZnO nanoparticles (ZnO-NPs), as well as transition-metal-doped (5% Mn(II), Fe(II) or Co(II)) ZnO nanoparticles, with an average size of 9 nm. A typical Raman peak at 436 cm(-1) is observed in the ZnO-NPs, whereas Zn1-xMnxO, Zn1-xFexO and Zn1-xCoxO presented characteristic peaks at 661, 665 and 675 cm(-1), respectively. These peaks can be related to the formation of Mn3O4, Fe3O4 and Co3O4 species in the doped ZnO-NPs. Moreover, these samples were analyzed at various laser powers. Here, we observed new vibrational modes (512, 571 and 528 cm(-1)), which are specific to Mn, Fe and Co dopants, respectively, and ZnO-NPs did not reveal any additional modes. The new peaks were interpreted either as disorder activated phonon modes or as local vibrations of Mn-, Fe- and Co-related complexes in ZnO. Copyright (C) 2007 John Wiley & Sons, Ltd.