In this paper, ZnO/Zn0.9Mg0.1O single quantum well (SQW) structures were fabricated on c-plane sapphire (Al2O3) substrate by plasma-assisted molecular beam epitaxy (P-MBE). The photoluminescene (PL) peak of the SQW shifted from 3.31 to 3.37 eV as well layer thickness was decreased from 6 to 2 nm. The spectral linewidth increases with temperature due to the scattering of excitons with acoustic and optical phonons. The transition energy of the localized exciton in the ZnO/Mg0.1Zn0.9O SQW with well width of 3 nm was found to be about 3.407 eV at 80 K, consistent with theoretical calculation. The first subband energies in the conduction and valence band were calculated to be 49 and 11 meV, respectively. (V) 2008 Elsevier B.V. All rights reserved.