Electron paramagnetic resonance study of V 4+-doped KTiOPO 4 single crystals

Abstract

Two chemically inequivalent V 4+ ions with unequal populations were detected by electron paramagnetic resonance (EPR) in vanadium-doped KTiOPO 4 crystals grown by a flux method. The EPR spectra of these two kinds of V 4+ 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 V 4+ ions and to conclude that the doped V 4+ ions form two kinds of covalent bonds with the two chemically inequivalent titanyl oxygens, resulting in two chemically inequivalent VO 2+ ions. The EPR linewidths of these two VO 2+ ions doped into KTiOPO 4 are narrow at room temperature. Moreover, superhyperfine structures due to phosphorus nuclei can be detected at room temperature. These characteristics make the VO 2+ ions an excellent EPR spin probe for quality control of KTiOPO 4 single crystals.