Linear and nonlinear optical properties of alizarin red S thin films

Abstract

In this work, alizarin red S (ARS) powder is deposited into thin films using thermal evaporation technique. Subsequently, the as-deposited films are annealed. The structural properties of ARS powder and films in the as-deposited as well as annealed conditions are investigated by the Fourier transform infrared spectroscopy and X-ray diffraction. The ARS powder shows a polycrystalline nature with monoclinic structure, while the films have revealed nanocrystallites distributed in an amorphous matrix. The thermal stability of ARS films up to 398 K is confirmed via employing differential scanning calorimeter. Further, the annealing process results in an increment of both the average crystallite size and the dislocation density and reduced the microstrain. Regarding optical studies, the direct transitions in ARS films are existed with an onset and optical energy band gaps equal to 1.84 and 2.93 eV, respectively, and upon annealing, these values have increased to 1.79 and 2.98 eV, respectively. Finally, the nonlinear refractive index and the third-order nonlinear optical susceptibility are decreased upon annealing process.

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