Spectroscopic studies of Ti3+ ions speciation inside MgAl2O4 spinels

Abstract : An electron paramagnetic resonance (EPR) investigation on Ti-doped MgAl2O4 spinels has been made in order to study the Ti3+ sites. The study we present here concerns the angular dependencies of the Ti3+ EPR lines and the variations of the EPR spectra due to a modification of the TiO2 content or of the chemical composition from MgAl2O4 to MgAl4O7 and MgAl6O10. In all the studied samples except one, we observe the presence of both Mn2+ and Ti3+ ions. No correlation was observed between Ti3+ amount and TiO2 content; the titanium ions are located in three different sites: the octahedral B site of the spinel structure; the tetrahedral A site and a last site which remains unclear. On the contrary, the major part of the Mn2+ ions is assumed to be in the tetrahedral A site of the spinel structure and a minor part in the octahedral B site. Our work demonstrates the overall interest of EPR spectroscopy in the study of the paramagnetic optically active ions inside optical materials.