Influence of UV-irradiation on the structure and optical properties of polycarbonate films

Polycarbonate films were prepared by casting technique. The absorption spectral analysis showed that the unirradiated PC has no absorption bands, while the irradiated films have two shoulder bands. This suggests that PC undergoes a photo-degradation process. The absorption coefficient and the optical energy gap (Eopt) have been obtained from indirect allowed transitions in K-space. It was found that, Eg decreases with increasing the irradiation time. The width of the tail of localized states in the band gap (ΔE) was evaluated using the Urbach edge method. The refractive index (n) was determined from the analysis of the transmittance data. Analysis of the refractive index (n) yields the values of the long wavelength dielectric constant (ε∞), the average oscillator wavelength (λo), average oscillator strength (So), average oscillator energy (Eo), the refractive index dispersion parameters (Eo/So) and the dispersion energy (Ed). The dependence of refractive index on irradiation time has been discussed. It was found that the photo-induced refractive index changes are very large. These changes suggest the applicability of PC films in optical devices.