A Review on Linear and Nonlinear Optical Properties of Transition Metal Oxide Nanoparticle Thin Films: Fundamentals, Mechanisms, and Applications

The rapid advancement of nanoscience and nanotechnology has opened new avenues for designing materials with tailored properties at the nanoscale. Among these materials, Transition Metal Oxide (TMO) nanoparticle thin films have garnered significant attention due to their unique structural, electronic, and optical properties. These films, composed of nanoparticles, combine the benefits of nanoscale confinement with the versatility of film-based architectures, enabling their integration into photonic devices, sensors, optoelectronics, and energy systems. Study of linear and non-linear optical properties is essential to understanding the interactions between light and matter in materials. Linear optical properties such as absorption, transmission, and refractive index provide valuable insights into the band structure, defect states, and electronic transitions. For advanced photonic applications including optical limiting, optical switching, laser protection, and frequency conversion second- and third-order nonlinear effects are crucial. These nonlinear effects include Second-Harmonic Generation (SHG), Two-Photon Absorption (TPA), and variations in the nonlinear refractive index.