We have studied the characteristics of InxGa1-xN epilayers grown on sapphire substrates by using photoluminescence (PL), optical absorption (OA), photocurrent (PC) and persistent photoconductivity (PPC) measurements. For the undoped InxGa1-xN epilayers containing high In composition, we observed the Stokes shift, S-shaped temperature-dependent PL emission, and PPC effect. These results show a strong dependence on In contents in the properties of InxGa1-xN epilayers. The decay kinetics of the PPC effect has been investigated, from that, the depth of the localization caused by alloy potential fluctuations (APFs) in InxGa1-xN epilayers is determined. However, for Si-doped InxGa1-xN epilayers, the Stokes shift, S-shaped temperature-dependent PL peak shift and PPC effect have not been observed. (c) 2005 Elsevier B.V. All rights reserved.