Films of uranium dioxide ranging in thickness from 132 to 280 mµ were evaporated onto fused silica, annealed at a pressure of 10-6 mm Hg and 960°C, and measured for optical absorption between the wavelengths of 210 and 800 mµ. A moderately intense band observed at 240 to 500 mµ has an unsymmetrical shape with a maximum at about 318 mµ, an approximately linear part with a moderate negative slope between 318 and 380 mµ, and a large negative slope between 380 and 500 mµ. This broad band is undoubtedly at least two unresolved peaks. From 240 mµ to shorter wavelengths there is a very intense absorption band which is most probably the fundamental band for UO2. The extinction coefficient was found to vary from 0.0055±0.0007 at 650 mµ to a maximum of 0.3702±0.0010 at 360 mµ and to a value of 0.167±0.004 at 240 mµ. The index of refraction varied from 2.29±0.03 at 800 mµ to a maximum of 2.58±0.22 at 450 mµ. The effect of oxidation of the films within the UO2 phase suggests that the one unresolved band at 430 mµ is removed by oxygen and the one at 300 mµ becomes more intense.
R. J. ACKERMANN, R. J. THORN, and G. H. WINSLOW, "Visible and Ultraviolet Absorption Properties of Uranium Dioxide Films," J. Opt. Soc. Am. 49, 1107-1111 (1959)