Linear and nonlinear optical properties of irradiated Toluidine Blue thin films

Abstract

Homogeneous thin films of Toluidine Blue (TB) are successfully prepared by thermal evaporation technique. Fourier Transform Infrared (FTIR) confirms the high chemical stability of TB films after UV and γ-irradiation. X-ray diffraction (XRD) patterns confirm the polycrystalline phase of the powder form, and as amorphous phase of the thin films. Both of UV and γ-irradiation processes, show a limited effects on the morphology of TB thin films. Dispersion parameters such as dispersion energy, the oscillator energy, the value of the dielectric constant at high frequency, and the ratio of free carriers to the effective mass of charge carrier have been calculated for both pristine and irradiated thin films. The optical absorption spectra of TB thin films reveal three main peaks, in the UV and visible region of spectra, corresponding to n−π∗ and π−π∗ orbital molecular transitions. The onset and optical energy gaps are found to be 1.38 and 2.95 eV for the pristine thin films, respectively. Our results indicate that the irradiation by UV and gamma rays have not affected either the type of transition or the energy gap values. The third order susceptibility (non-linear optical susceptibility χ3, The nonlinear refractive index n2 and the non-linear absorption coefficient βc are calculated.