Vanadium-doped sample
The optical spectrum of this vanadium sample before irradiation retains the same UV absorption as the undoped sample and exhibits extra visible peaks.
These extra peaks show some indication of the presence of V3+ and V4+ ions. The presence of V5+ ions is not clearly confirmed because
The stability of the optical spectra within the UV-near visible absorption upon irradiation can be interpreted on the same basis as indicated by the presence of high percent of heavy Bi3+ ions.
The resolution of induced band at 650 nm can be related to the generation of more V3+ ions by photochemical reduction of V5+ and V4+ ions by accepting
generated electrons during the irradiation process.