Electron Magnetic Resonance (EMR) and related studies of transition metal (3dN) dopants in titanium dioxide (TiO2) systems: guide in tailoring the material's properties for specific technological applications

Abstract

Doping the transition metal (TM) ions into TiO₂, both anatase and rutile forms, has garnered significant interest due to their impact on the structural, spectroscopic and magnetic properties of these materials. By different doping concentrations of specific TM ions, these key physical properties can be customized for specific applications in diverse areas such as catalysis, optoelectronics, spintronics, and metamaterials. Electron Magnetic Resonance (EMR) spectroscopy techniques are particularly powerful tools for investigating TM ions in coordination complexes. To lay the groundwork, we overview crystallography, synthesis, and spectroscopic techniques. The basics of spin Hamiltonian (SH) theory are recapped. This enables interpretation of EMR spectra and physical properties of TM ions in TiO₂ systems in terms of SH parameters. Experimental EMR-related studies of TM (3d^N) ions in doped and undoped TiO₂ systems are comprehensively surveyed to identify key aspects and highlight important issues. Computational studies utilizing various approaches to model SH parameters and thus verify experimentally measured parameter values are also surveyed. This review signifies that integrating experimental techniques with modeling approaches enables a more profound understanding of the key physical properties. The systematic analysis of literature data and categorization of various aspects and issues may facilitate creation of innovative materials with customized properties for particular applications. This may encourage additional research to discover new capabilities of the TiO₂-based adaptable semiconductors.