Evaluation of the energetics of electron trap states at the nanocrystalline titanium dioxide/aqueous solution interface via time-resolved photoacoustic spectroscopy

Time-resolved photoacoustic spectroscopy (TRPAS) has been employed to probe directly the trap state energetics of photogenerated electrons in nanocrys talline colloidal titanium dioxide dispersed in aqueous solution. Deconvolu tion of the photoacoustic signals obtained following bandgap excitation all owed for separation of components associated with conduction band electron trapping, trapped electron-hole recombination, and a slower recombination s tep. The results indicate that the lifetime of the electron-hole pair is on the order of 25 ns with about 60% of the trapped electrons recombining on this time scale. The electron trapping sites were determined to lie, on ave rage, 0.8 eV below the conduction band edge. (C) 2000 Elsevier Science B.V. All rights reserved.