Photoluminescence characteristics of nanocrystalline TiO2 films grown by at
omic layer deposition were studied. In dependence of growth conditions the
films consisted of anatase, rutile and TiO2-II phases. A broad band and two
sharp peaks were observed in the photoluminescence spectra measured under
continuous-wave Ar+ laser excitation at temperatures 5-165 K. At 5 K the ma
ximum of the broad band was at 2.24 eV in the anatase films, and at 2.37-2.
40 eV in the rutile and TiO2-II films. The intensity of sharp Lines peaking
at 3.31 and 3.37 eV depended on the crystal structure of the films and inc
reased significantly after X-ray irradiation. The temperature dependence an
d decay times of different emission bands were also investigated. The data
obtained allowed a defect-trapped-exciton interpretation of the sharp peaks
although the free-exciton origin of the 3.31 eV peak could still be argued
. The broad-band emission at 2.24-2.40 eV was obviously due to self-trapped
exciton recombination. (C) 1998 Elsevier Science S.A. All rights reserved.