Influence of X-ray irradiation on the optical properties of CoMTPP thin films

Thin films of 5,10,15,20-Tetrakis (4-methoxyphenyl)-21H,23H-porphine cobalt (II), CoMTPP were prepared at room temperature (300K) by the thermal evaporation technique under vacuum pressure about 2 × 10− 4Pa. The X-ray diffraction patterns showed the amorphous nature for the as-deposited and the irradiated films, whereas the powder has shown a polycrystalline with triclinic structure. Miller's indices, hkl, values for each diffraction peak in the XRD spectrum were calculated. Optical properties of CoMTPP thin films were characterized by using spectrophotometric measurements of transmittance and reflectance in the spectral range from 200 to 2500 nm. The refractive index, n, and the absorption index, k, were calculated. The obtained data were used to estimate the type of transitions and the optical and fundamental gaps before and after X-ray irradiation. In addition, the normal dispersion of the refractive index is discussed in terms of lorentz-lorentz free single oscillator model and modified lorentz Drude model of free carrier contribution.

Research Highlights
► X-ray diffraction patterns.
► Optical properties of CoMTPP thin films.
► Influence of X-ray irradiation.
► The type of electronic transition is an indirect allowed transition.