We have modeled the optical properties of the ZnMgO/ZnO/ZnMgO system and correlated them to its transport properties by employing an effective mass equation method. By its construction our method was sensitive to the barrier thickness of the system. From our results we deduce that there are more states in the well than resonant tunneling peaks in the transport data. The "missing" states in the electrical characteristics are not seen because of their much lower localization in the well. However these states are responsible for the UV activity of the system. Reducing the barrier thickness changes dramatically the localization of the states in the well without affecting significantly the energy levels. Hence the electrical properties can be changed without changing significantly the optical properties. (C) 2004 Published by Elsevier Ltd.