A series of V–O alloy films were sputter deposited on glass substrates using a vanadium target and rf-excited Ar/O2discharges containing 2%–8% O2. On the basis of x-ray results, the films were nominally identified as vanadium pentoxide. Optical transmission and reflection characteristics were measured by double-beam spectrophotometry in the 390- to 700-nm-wavelength region. From these measurements, the absorption coefficient &agr; was determined as a function of the incident photon energyh&ngr;. The absorption edge of all films showed two distinct regions of behavior: a high photon energy region in which &agr; varied linearly with (h&ngr;)2and a low-energy tail. The behavior of &agr; is discussed in terms of the structural and electronic changes in the films due to nonstoichiometry and compared to results obtained for single crystal V2O5.