Tailoring the nonlinear optical susceptibility χ(3), photoluminescence and optical band gap of nanostructured SnO₂ thin films by Zn doping for photonic device applications

We report the influence of Zinc (Zn) doping on the structural, optical, and nonlinear optical properties of tin oxide (SnO₂) thin films prepared by chemical spray pyrolysis technique. The photoluminescence studies shows the formation of oxygen vacancy defect states upon Zn incorporation. Nonlinear behavior observed in NBE emission were attributed to variations in the crystallinity of the samples upon Zn incorporation. X-Ray diffraction patterns reveals that all the films are polycrystalline in nature having tetragonal rutile structure. The band gap energy values decreased from 3.71 eV to 3.30 eV with increase in the Zn concentration due to formation of defect states and atomic structural disordering. The surface morphology and average surface roughness of the samples were investigated using Atomic force microscopy which endorses the shift from the crystalline state to the amorphous state. The sign and magnitude of nonlinear refractive index and nonlinear absorption coefficient was found out by Z-scan technique with a continuous wave laser as the excitation source. The third order optical Susceptibility χ⁽³⁾ has found to be increased from 1.08 × 10⁻³ esu to 2.20 × 10⁻³ esu upon Zn incorporation. The Z-scan results reveal that the films exhibit self-defocusing nonlinearity. Enhancement in the optical nonlinearity upon doping enables the applicability of the material in various optoelectronic device applications.