Laser-induced colouration of V2O5

Vanadium oxide is one of the most important optoelectronic materials that are used in optical switching devices, gas and humidity sensors, and secondary Li batteries. It has been recognized that V2O5 can be coloured through electro-, photo-, and thermochromism processes. We report here that the surface of V2O5 (annealed at 580 degrees C for 4 h) pellets turned to a deep blue colour upon just one pulse ablation of the XeCl excimer laser (lambda = 308 nm, pulse duration = 36 ns, output energy = 100 ml/pulse). Also we found that when a yellow pentoxide vanadium pellet was exposed to proper excimer laser irradiation, its surface electrical conductivity changed remarkably, that is from an insulator to a semiconductor. The pentoxide vanadium sample, before and after excimer laser irradiation, was analysed with scanning electron microscopy (SEM), UV-visible diffuse reflectance spectral (W-VIS), x-ray diffraction (XRD), Raman spectrum (RS) and x-ray photoelectronic spectrum (XPS). The presence of a peak at about 830 cm(-1) in the Raman spectrum indicates that the sample after laser irradiation is sub-stoichiometric with an oxygen deficiency. XPS showed the partial reduction of V2O5 and the appearance of conduction band electrons. SEM showed that the surface of V2O5 became smooth and less porous after excimer laser irradiation. From our experimental results, it was concluded that the laser-induced colouration is attributed to thermochromism.