TIME-DEPENDENT ELECTROCHROMISM OF NANOCRYSTALLINE TIO2 FILMS IN PROPYLENE CARBONATE SOLUTION OF LICLO4

Electrochromism of nanocrystalline TiO2 films under cathodic bias in p ropylene carbonate containing LiClO4 was studied by time-dependent abs orption and fluorescence spectroscopies. The absorption spectra reveal ed two absorption bands near 700 and 420 nm. The absorption band near 700 nm showed a blue shift and an increase in absorbance with time. Th e blue shift seemed to be due to the progressive involvement of the tr apped electrons in the lower energy levels within the shallow surface states. The newly observed band near 420 nm appeared to have originate d from the deep surface states which, lying 1.3-1.8 eV below the condu ction band, were gradually filled with electrons in the shallow surfac e states.