Laser-induced photocoloration in molybdenum oxide thin films

Photocoloration refers to the induced change in the color of a transparent material exposed to a light source whose excitation wavelength is in the ultraviolet (UV) spectral range. Compared to conventional light sources, UV lasers can enhance this effect. The color change is significantly related to the structural and chemical properties of the irradiated material. This change leads to the appearance of an absorption band in the near-infrared range, with corresponding variations in the optical properties of the material. Molybdenum oxide has been demonstrated to exhibit a superior coloration response to UV radiation. In this work, MoO₃ thin films were irradiated with a 325-nm UV laser. The dependence of the resulting absorption bands on the amorphous and substoichiometric nature of the films was investigated. Moreover, the valence states of molybdenum were analyzed, and the absorption bands were statistically resolved to elaborate on the coloration mechanisms.