Refraction index and oscillator strength in MoO3 photocolored films

Amorphous MoO3 films were grown onto glass substrates by the thermal evaporation technique. Color centers in the films were generated by UV–VIS light irradiation (photochromism) in air at room temperature. As-grown films looked pale yellowish to naked eye and acquired a bluish tone after the coloration process. Refraction index and extinction coefficient were calculated on as-grown and colored samples by using macroscopic optical differential reflectance measurements fitted with the transfer matrix theoretical model. The coloration efficiency parameter and the refraction index values of MoO3 films allowed us to calculate the oscillator strength (f) value equal to 0.22±0.02 by means of the optical absorption spectra. This value was obtained by fitting the experimental results to an optional expression of Smakula's formula, derived from a semi-classical theoretical model.