Lifetime of excited electronic states inside the 4f configuration of rare-earth elements embedded in covalent chalcogenide glasses turns out to be sensitive to medium-range structural phase transition of the host glasses. We have measured lifetimes of 1.6 mum emission originating from Pr3+ : (F-3(3), F-3(4)) --> H-3(4) transition in amorphous Ge-Sb-Se alloys. The longest lifetime is measured at around the mean coordination number of similar to2.67, which arises coincidently from structural changes of the host glasses from two-dimensional layers to three-dimensional networks. (C) 2004 Elsevier B.V. All rights reserved.