In situ local assessment of laser irradiation-induced phase transformations in hexagonal MoO3 microrods

Phase transformations in h-MoO3 microrods have been locally induced by laser irradiation and assessed in situ by micro-Raman and photoluminescence spectroscopy. The obtained phases and their time stability were found to depend on laser wavelength, power density and irradiation time. Red laser (633 nm) irradiation induces the stable formation of -MoO3. The corresponding oxidation dynamics appear to be triggered by diffusion processes. Considering the diverse physical properties of the different Mo oxides, red laser irradiation appears as a suitable method to tailor the functionalities of individual h-MoO3 microstructures. UV (325 nm) irradiation also transforms h-MoO3 into -MoO3, with the formation of Mo4O11 being observed in the initial stage of the irradiation process. However, this transformation seems to be unstable in time, finally giving rise to structural changes in the obtained -MoO3 phase and to the appearance of other Mo oxides. Laser irradiation also modifies the luminescence properties of the h-MoO3 microrods, giving rise to the appearance of several emission bands related to complex defects involving oxygen vacancies.