Optical properties of pristine and UV irradiated Rose Bengal (RB) films have been investigated
using transmittance and reflectance methods. The refractive index (n) and extinction coefficient (k)
of RB films were directly calculated from absolute values of transmission and reflection spectra.
Single oscillator parameters and the Drude model of free carrier absorption have been used for the
analysis of refractive index dispersion. The fundamental absorption edge data were analyzed
within the frame work of the band- to-band electron transitions theory. The thickness of RB films
has no influence on absorption and refractive indices in the investigated thickness range and
within the experimental error. UV irradiation caused a structural transformation of amorphous
pristine film to polycrystalline RB film, which resulted in the decrease of absorption coefficient,
energy gap and refractive index. The optical functions and their dependence on UV exposure time
were directly calculated from the spectral distribution of dielectric constant.