Transient absorption spectra of nanocrystalline TiO2 films at high excitation density

We found that transient absorption spectra of nanocrystalline TiO2 films changed under high excitation density conditions. The spectra could be reproduced by accounting for three spectral components: holes, trapped electrons, and conducting electrons. On the basis of the observed spectral features, we concluded that the absorption coefficient due to trapped electrons was affected by generated holes at high excitation density.