ESR OF V4+ IN ALPHA-RBTIOPO4 SINGLE-CRYSTALS

We have recorded and investigated the ESR spectrum of vanadium-doped a lpha-RbTiOPO4 single crystals in the temperature interval 77-300 K, Tw o 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 correspo nding to axial symmetry with the parameters g(parallel to 1) = 1.9305, g(perpendicular to 1) = 1.9565, A(parallel to 1) = -168.2 X 10(-4) cm (-1), and A(perpendicular to 1) = -54.3 X 10(-4) cm(-1) for V1 centers and g(parallel to 2) = 1.9340, g(perpendicular to 2) = 1.9523, A(para llel to 2) = 169.0 X 10(-4) cm(-1), and A(perpendicular to)2 = -55.2 X 10(-4) cm(-1) for V2 centers. A model of a paramagnetic center is pro posed: The vanadium ions replace titanium ions in two structurally dis tinct positions Ti1 and Ti2 (V1 and V2 centers, respectively). The pos sibility that a VO2+ ion forms when alpha-RbTiOPO4 crystals and crysta ls of the KTP group (KTiOPO4, NaTiOPO4, alpha- and beta-LiTiOPO4), stu died earlier, are doped with vanadium is discussed. (C) 1998 American Institute of Physics. [S1063-7834(98)03003-2].