Optical transient bleaching of photochromic polytungstic acid

Abstract The nonlinear optical properties of UV-coloured colloidal polytungstic acid imbedded in polyvinylalcohol film have been studied using a picosecond pump–probe technique. The intervalence charge transfer bands in the red-near IR region were found to exhibit transient bleaching that decays monoexponentially with the characteristic time of ∼300 ps. The results obtained are discussed in terms of the splitting of energy levels of metal ion in the ligand field and the delocalization of valence states.