Niobium dioxide films have been prepared by the radio frequency sputtering of Niobium dioxide powder targets. Polycrystalline films have been deposited onto Silicon substrates maintained at temperatures exceeding 900 K during preparation. Characterisation by X-ray diffraction and E.S.C.A. indicates that the Argon environment during sputtering must be doped with approximately 500 to 1000 ppm of Hydrogen for the growth of Niobium dioxide films. Optical measurements were carried out on single crystals and thin films of Niobium dioxide as well as Vanadium dioxide films. The optical measurements were carried out over a wavelength range of 0.5 to 15 um for Niobium dioxide and 0.5 to 6 um for Vanadium dioxide. The temperature range over which measurements were made on Niobium dioxide (in a vacuum) was from 90 to 1200 K and for Vanadium dioxide from 300 to 370 K. The optical properties (refractive index and extinction coefficient) of Niobium dioxide and Vanadium dioxide were calculated across both of their respective thermally excited transitions. It was found that there was an abrupt change in the optical properties of both Niobium dioxide and Vanadium dioxide at their respective transition temperatures.