Influence of annealing temperature on structural and optical properties of nanocrystalline Platinum octaethylporphyrin (PtOEP) thin films

• XRD, FESEM and FT-IR have been used to identify the structure properties.
• The effects of annealing on the optical properties of PtOEP films have been reported.
• The values of the optical band gap were red shifted by thermal annealing.
• The normal dispersion behavior of refractive index was analyzed by WDD model.
• The non-linear optical properties were estimated using empirical relation.

Thermal evaporation technique was used to prepare the Platinum octaethylporphyrin (PtOEP) thin films at room temperature. The deposited films were studied before and after thermal annealing at 373 and 473 K for 3 h under vacuum (10−3 Pa). The film structure, surface morphologies and molecular structure were investigated as a function of annealing temperature by X-ray Diffraction (XRD), Field-Emission Scanning Electron Microscopy (FESEM) and Fourier-transform infrared techniques (FT-IR) respectively. The results confirmed that the as-deposited and annealed films have nanostructural features. Optical constants of the as-deposited and annealed films have been obtained in the wavelength range 200–1100 nm by using spectrophotometric measurements. Analysis of the spectra of absorption coefficient showed indirect allowed transition and optical energy gap found to decrease with increase in annealing temperature. The dispersion of refractive index at the normal dispersion (λ > 600 nm) was discussed in terms of single oscillator model of Wemple–Didomenico. Based on generalized Miller’s rule the third order non-linear susceptibility, χ(3) and nonlinear refractive index, n2 were estimated and studied at lower photon energy and showing lower value for the annealed film.