ESR of V4+ in α-RbTiOPO4 single crystals

We have recorded and investigated the ESR spectrum of vanadium-doped α-RbTiOPO4 single crystals in the temperature interval 77–300 K. Two types of structurally distinct centers, V1 and V2, with a 4:1 ratio of the peak intensities were observed. The angular dependences of the resonance magnetic fields are described by a spin Hamiltonian corresponding to axial symmetry with the parameters g∥1=1.9305, g⊥1=1.9565, A∥1=−168.2×10−4cm−1, and A⊥1=−54.3×10−4cm−1 for V1 centers and g∥2=1.9340, g⊥2=1.9523, A∥2=−169.0×10−4cm−1, and A⊥2=−55.2×10−4cm−1 for V2 centers. A model of a paramagnetic center is proposed: The vanadium ions replace titanium ions in two structurally distinct positions Ti1 and Ti2 (V1 and V2 centers, respectively). The possibility that a VO2+ ion forms when α-RbTiOPO4 crystals and crystals of the KTP group (KTiOPO4, NaTiOPO4, α-and β-LiTiOPO4), studied earlier, are doped with vanadium is discussed.