The changes observed in the valence state and local structure of the Cu species present in the Cu ion-exchanged Y zeolite during thermovacuum treatment have been investigated by ESR and photoluminescence techniques. Especially, the reduction behavior of the Cu(II) monomers and Cu(II) dimers which exist in the Y zeolite has been studied according to the changes seen in their ESR spectra during such thermovacuum treatment. Moreover, the mechanism for the formation of the Cu(I) monomers and dimers after thermovacuum treatment has been proposed based on investigations of the deconvoluted photo luminescence spectra. (C) 2004 Elsevier Inc. All rights reserved.