Abstract:

Optical properties of cobalt ferrite (CoFe₂O₄) nanoparticles are modeled and simulated employing finite element analysis (FEA) and density functional theory (DFT) for different particle sizes. The simulated absorption maxima of electronic excitations is red-shifted from 330 nm to 410 nm using finite element analysis and from 331.27 nm to 409.07 nm using quantum mechanical method, with increasing particle sizes from 40 nm to 50 nm. The measured absorption maxima matched the simulated results reasonably well and red-shifted to longer wavelengths from 315.59 nm to 426.73 nm with the increase in particle sizes from 30 nm to 50 nm. The DFT simulated, FEA simulated and experimentally derived optical band gap energies, E_g, were also acquired and compared. The simulated E_g values decreased from 3.228 to 2.478 eV and from 3.266 to 2.456 eV, while the experimental E_g value decreased from 3.473 to 2.697 eV, with increasing the particle sizes. The research demonstrated that the optical absorption of CoFe₂O₄ nanoparticles can be described with high accuracy using the quantum mechanical interpretation based on DFT. FEA based simulations have shown limitations for smaller (< 40 nm) nanoparticles likely due to the increased surface scattering that prevented a stable solution for simulations beyond the quasistatic limit. The DFT computational tool developed by this study can enable both the low cost computation and highly reliable prediction of optical absorption properties and optical band edges, and thus contribute to understanding and design of CoFe₂O₄ nanoparticle properties prior to fabrication and functionalization of them, for a wide range of applications especially for sensing and photonic wave modulations.

Key words: Cobalt ferrite (CoFe₂O₄) nanoparticles, Optical properties, Band gap energy, DFT simulation of nanoparticles, COMSOL simulation of nanoparticles