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We report an investigation on the effect of - and - interactions in the electronic structure, and especially in the band-gap value, of wurtzite wide-gap diluted magnetic semiconductors ZnO (, Mn, Fe, Co, Ni, Cu). Thin films prepared by pulsed laser deposition are investigated by means of optical absorption at low-temperature and photoelectron spectroscopy. Pure wurzite phase is shown to be maintained for Co and Mn concentrations up to 25 and for Cr up to 10, while in the case of Fe, Ni, and Cu, other phases are present for concentrations higher than 5, 2, and 1, respectively. The band gap of the ZnO alloy increases at a rate of 9, 22, 4, and 23 meV/ for , Mn, Fe, and Co, respectively, and decreases at a rate of about 14 and 10 meV/ for and Cu. Photoelectron spectroscopy of the ZnO valence band for and Co shows that the emergence of the transition metal-related photoemission peak is clearly correlated to a larger binding energy of the O 2 …