Influence of gamma ray irradiation and annealing temperature on the optical constants and spectral dispersion parameters of metal-free and zinc tetraphenylporphyrin thin films: A comparative study
abstract
In this work, we report on the effect of c-ray irradiation and annealing temperature on the optical propertiesof metal-free tetraphenylporphyrin, HTPP, and zinc tetraphenylporphyrin, ZnTPP, thin films. Thinfilms of H2TPP and ZnTPP were successfully prepared by the thermal evaporation technique. The opticalproperties of H
TPP and ZnTPP films were investigated using spectrophotometric measurements of the
transmittance and reflectance at normal incidence of light in the wavelength range from 200 to2500 nm. The absorption spectra of H2TPP showed four absorption bands, namely the Q, B, N and Mbands. The effect of inserting Zn atom into the cavity of porphyrin macrocycle in ZnTPP molecule distortedthe Q and B bands, reduced the width of absorption region and influenced the optical constantsand dispersion parameters. In all conditions, the type of electron transition is indirect allowed transition.Anomalous dispersion is observed in the absorption region but normal dispersion occurs in the transparentregion of spectra. We adopted multi-oscillator model and the single oscillator model to interpret theanomalous and normal dispersion, respectively. We have found that the annealing temperature hasmostly the opposite effect ofc-ray irradiation on absorption and dispersion characteristics of these films.