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 O^2- 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.