Structure analysis, linear/nonlinear optical characteristics, dielectric parameters characterization, and gamma-ray shielding of cobalt-doped TiO2 nanoparticles

Abstract

Titanium dioxide nanoparticles are widely utilized in optoelectronics, dielectric applications, and radiation shielding. However, their limited structural and functional performance in advanced applications necessitates further improvement. In this study, cobalt doping was introduced as a strategy to enhance the structural, optical, dielectric, and gamma-ray shielding properties of TiO₂ nanoparticles. Cobalt-doped titanium dioxide nanoparticles (Co-TiO₂ NPs) were synthesized using the sol–gel method to evaluate their structural properties, linear and nonlinear optical characteristics, dielectric performance, and gamma-ray shielding efficiency. X-ray diffraction (XRD) analysis confirmed a tetragonal TiO₂ phase, with the introduction of a rhombohedral CoTiO₃ phase upon increasing cobalt content. The crystallite sizes, estimated through the Williamson-Hall method, increased from 47 to 70 nm as Co content increased. UV–Vis spectroscopy showed a bandgap shift from 3.86 eV to 4.07 eV with higher cobalt concentrations. The extinction coefficient and refractive index showed decreasing trends from 1.63 × 10^–4 to 1.3 × 10^–4, and from 3.02 to 2.66, respectively, with higher Co content while the dielectric constant increased, indicating improved optical and dielectric performance. The nonlinear refractive index (n₂) decreased from 3.6 × 10^–9 to 2.78 × 10^–9 with increasing Co doping, enhancing the material's potential for nonlinear optical applications. The third-order nonlinear susceptibility (χ⁽³⁾) values indicated that Co-TiO₂ nanoparticles possess significant nonlinear optical and suitability for optoelectronic devices. Among all the Co-TiO₂ samples, the TOC-10 sample exhibited the highest linear attenuation coefficient (LAC), demonstrating its superior effectiveness in gamma-ray shielding, particularly in the energy range of 0.015–0.1 MeV.