OPTICAL-ABSORPTION SPECTRA OF EVAPORATED V2O5 AND COEVAPORATED V2O5/B2O3 THIN-FILMS

The optical absorption spectra of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films have been studied. For higher photon energies, the absorption is found to be due to a direct forbidden electronic transition process from the oxygen 2p band to the vanadium 3d band in a similar way to that observed in crystalline V2O5. The exponential behaviour of absorption edge for lower photon energies is attributed to the electronic transitions between the tailed-off d-d states corresponding to V4+ ions. For co-evaporated V2O5/B2O3 films the optical energy gap is observed to increase with the increase in V2O5 content of the composite films.