NONLINEAR SPECTROSCOPY OF PHOTOCOLOURED POLYTUNGSTIC ACID NANOCOMPOSITES

Picosecond absorption spectroscopy was used in an investigation of non linear optical processes in nanostructured composites based on polytun gstic acid, which were photocoloured by preliminary UV irradiation, Th e absorption bands responsible for the photocoloration and associated with intervalent charge transfer were bleached by the action of powerf ul laser pulses. The characteristic monoexponential relaxation time of the process was similar to 300 ps, The results obtained were analysed taking account of the special features of the splitting of the energy levels of tungsten ions with different degrees of oxidation and of de localisation of the valence states within separate elements of the pol ytungstic acid structure.