Defect formation processes in silicon caused by electron irradiation performed at elevated temperatures are studied in detail using photoluminescence (PL) spectroscopy. The use of high temperature during electron irradiation has been found to affect considerably the defect formation process, In particular, several new unknown excitonic PL lines were discovered in carbon-rich Si wafers subjected to electron irradiation at temperatures higher than 450 degrees C, The dominant new luminescent center gives rise to a bound exciton PL emission at 0.961 eV. The center is shown to be efficiently created by electron irradiation at temperatures from 450 degrees C up to 600 degrees C. The electronic structure of the 0.961 eV PL center can be described as a pseudodonor case, where the hole is strongly bound at a level 187 meV above the valence band, while the electron is a effective-mass-like particle weakly bound by approximate to 21 meV in the BE state, (C) 1999 Elsevier Science B.V. All rights reserved.