Spectroscopic studies of Ti3+ ions speciation inside MgAl2O4 spinels

An electron paramagnetic resonance (EPR) investigation on Ti-doped MgAl2O4 spinels has been made in order to study the Ti sites. The study we present here concerns the angular dependencies of the Ti 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 Mn and Ti ions. No correlation was observed between Ti 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 Mn 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.