In side-by-side EPR and Xe-129 NMR studies, the occupancy sites of Cu2+ ions in copper-exchanged NaY zeolites are found to depend on the state of reduction/oxidation cycle, the concentration of Cu2+ ions, the sample temperature, and the adsorbate present in the zeolites. The structural features of Y zeolites in the presence of Xe, He, H-2, and O-2 under various reduction and oxidation conditions are examined carefully by these two spectroscopic techniques. The EPR spectral features of Cu2+ in the presence of O-2 adsorbate vary as a function of temperature. The temperature dependence study allows us to calculate the activation energy of migration of Cu2+ from small cages to supercages, which is found to be 9.7 +/- 0.8 kJ/mol. A model is proposed to explain the spectral changes.