Influence of d-d transition electrons and thickness variations on the excited-state optical properties: Nonlinear optical characterization of Cr2O3 thin film

The structural, morphological, linear, and nonlinear optical properties of Cr₂O₃ thin films with different thicknesses deposited by the thermal deposition, were measured. The structural and morphological parameters of films, determined by XRD, FESEM, and AFM images, are compared to the linear and nonlinear optical characteristics of these media. The bandgap of prepared thin films was obtained from DRS spectra. The electron effective mass ($m_e^{\ast }/m_0$), linear refractive index ($n_0$), optical static, and high frequency dielectric constant (${\epsilon }_0$ , ${\epsilon }_{\infty }$) values were calculated by using the band gap energy values. Increasing the thicknesses of thin films causes to decrease the band gap, an increase RMS, increase the size of nanoparticles and the nonlinear responses of thin films. The high magnitude of n₂, and β belonged to the Cr₂O₃ (300 nm-thickness) in the order of 10⁻⁵ cm²/W, and 10⁻¹ cm/W respectively. The fluctuations in nonlinear responses observed at different thicknesses are attributed to d-d transitions and intraband scattering of equilibrium electrons influenced by laser radiation, as indicated by the nonlinearity data. The considerably elevated refractive non-linearity values in the analyzed film materials suggest their potential for practical applications in optoelectronic devices.