Structural and Optical Properties of Nanocrystalline 3-(2-Benzothiazolyl)-7-(diethylamino) Coumarin (C6) Thin Films for Optoelectronic Application

In the current work, the structural and optical properties of thermally evaporated 3-(2-Benzothiazolyl)-7-(diethylamino) coumarin [Coumarin 6 (C6)] thin films on a pre-cleaned quartz substrate were studied as a function of the annealing temperature. The influence of annealing on the structural, morphological, and molecular structures was investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectroscopy, respectively. The XRD and AFM results confirmed that the as-deposited and annealed films have nanostructural features (30.96–45.34 nm). Also, the increase in roughness of the C6 thin film surface resulted from particle agglomeration and coalescence. Optical constants of C6 thin films were derived from the transmittance T ( λ ) and reflectance, R ( λ ) measurements in the spectral range of 200–2500 nm. Analysis of the optical absorption coefficient data indicates that the type of electronic transition in these films is an indirect allowed transition. The estimated optical band gap was decreased from 2.12 eV to 2.01 eV as the annealing temperature was increased. Dispersion and dielectric parameters were determined as functions of the annealing temperature. Lastly, nonlinear optical parameters such as the third-order nonlinear susceptibility, χ (3) and nonlinear refractive index, n (2) were estimated and influenced by annealing temperature. The optical properties of C6 thin films were showed that C6 thin films would be used in a wide range of photonic applications Graphical Abstract