A narrow (few meV halfwidth) dip was observed at 1.682eV in the photocurrent (PC) spectra from diamond films grown by chemical vapour deposition (CVD). The shape of the dip matched that of the absorption line from the well-known 1.682eV Si-related centre. However, optical absorption measurements show that it cannot be explained by straight absorption of light at the 1.682eV centre. A similar appearance of narrow peaks was observed in PC and absorption spectra for the interstitial-related 3 H centre in this work and for the vacancy-related GR1-8 and ND1 lines previously. The phenomenon can be explained by suggesting involvement of electron transfer process: e.g., electrons from the excited states of a given centre are captured by the defects responsible for the background PC, thus PC-(in)activating the latter. (C) 2001 Elsevier Science B.V. All rights reserved.