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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 Zn 1−x Mn x O, Zn 1−x Fe x O and Zn 1−x Co x O presented characteristic peaks at 661, 665 and 675 cm −1 , respectively. These peaks can be related to the formation of Mn 3 O 4 , Fe 3 O 4 and Co 3 O 4 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.

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