Electron paramagnetic resonance and optical spectroscopy of Ti-doped CaYAlO4

Abstract
Ti-doped CaYAlO4 crystals were grown in a reducing atmosphere. The absorption spectrum with peaks at 408 nm and 540 nm observed at room temperature was strongly polarized along the a and b axes. EPR measurements in the temperature range of 4.2-300 K have found that Ti3+ ions in CaYAlO4 show orthorhombic symmetry. In order to explain the optical and EPR results, we have proposed that the Ti3+ ions are perturbed by an O2- ligand ion vacancy on the c axis and additionally by either an Al3+ ion vacancy or a substituted Ti4+ ion at neighbouring Al3+ ion sites in the c plane containing the Ti3+ ions. This model can explain the polarization of the absorption spectrum and, also, enable us to deduce that the absorption bands with peaks at 408 nm and 540 nm are due to the perturbed Ti4+ and Ti3+ octahedra, respectively.