Effect of Al doping on photoluminescence and laser stimulated nonlinear optical features of CdO nanostructures for optoelectronic device applications

The work presented in this article reports on the role of Al-doping in CdO thin films. Cd_1-xAl_xO thin films are prepared by employing the spray pyrolysis (SP) technique [with x = 0, 0.01, 0.05 and 0.1 at. %] to study the morphological, linear optical and nonlinear optical (NLO) properties. The study of X-ray diffraction revealed the crystalline nature of the prepared thin films, and the Al-doping improves the crystallite size. The morphology of the films is mainly influenced by the doping shown by the results of FESEM images. With an increase in the concentration of al-doping, the direct optical energy band-gap (Eg) value increased from 2.47 eV to 3.72 eV for pure to 10 at.% of Al concentrations. Room temperature photoluminescence spectra (RTPL) of the prepared samples are investigated for an in-depth understanding of the conduction band behavior of defect states. The sign and magnitude of the third-order NLO properties were determined under the Z-scan technique using a DPSS continuous wave laser as an excitation source at a wavelength of 532 nm and 200mW output power. The Z-scan data shows that the prepared material showed strong two-photon absorption (2PA) with an increase in doping concentrations from 0 to 10 (at %), thereby increasing the nonlinear absorption coefficient (β) from 0.76 × 10⁻³ to 5.61 × 10⁻³ (cmW⁻¹), nonlinear refractive index (n₂) from 1.31 × 10⁻⁸ to 1.89 × 10⁻⁸ (cm² W⁻¹) and the third-order NLO susceptibility (χ⁽³⁾) values also increased from 8.01 × 10⁻⁷ to 1.63 × 10⁻⁶ (esu). Optical Limiting characteristics of the prepared films were studied at the experimental wavelength. The inspiring results of the NLO suggest that the thin film Cd1-xAlxO is a capable and promising material for nonlinear optical devices.