Electron paramagnetic resonance study of V⁴⁺-doped KTiOPO₄ single crystals

Two chemically inequivalent V⁴⁺ ions with unequal populations were detected by electron paramagnetic resonance (EPR) in vanadium-doped KTiOPO₄ crystals grown by a flux method. The EPR spectra of these two kinds of V⁴⁺ ions exhibit axial symmetry, with the symmetry axis almost coincident with the direction of the shortest Ti-O bond, namely, the Ti to a titanyl oxygen bond. These results allow one to identify the occupation sites of the doped V⁴⁺ ions and to conclude that the doped V⁴⁺ ions form two kinds of covalent bonds with the two chemically inequivalent titanyl oxygens, resulting in two chemically inequivalent VO²⁺ ions. The EPR linewidths of these two VO²⁺ ions doped into KTiOPO₄ are narrow at room temperature. Moreover, superhyperfine structures due to phosphorus nuclei can be detected at room temperature. These characteristics make the VO²⁺ ions an excellent EPR spin probe for quality control of KTiOPO₄ single crystals.