Electron paramagnetic resonance spectra of Er3+ in the monoclinic KY(WO4)2 crystal

Electron paramagnetic resonance (EPR) studies of Er3+ of single-crystal KY(WO4)2 have been carried out at X-band frequencies over a temperature range from 4.2 to 300 K. The main x- and z-axes of the g-tensor in the ac plane do not coincide with the crystallographic a-and c-axes, while the y- and b-axes are parallel. The EPR spectrum is characterized by a strong anisotropy of the g-factors (gz = 13.25 ± 0.05, gx = 0 ± 0.1, gy 3.378 ± 0.005) and of the hyperfine interaction parameters (Az = -469 ± 3, Ax = 0 ± 3.5, Ay = -120.75 ± 0.8 in 10-4 cm-1). The temperature dependence of the g-factors is caused by an anharmonic part of the spin-phonon Hamiltonian as well as by a rotational contribution to this Hamiltonian. A spin-lattice relaxation is shown to result from two Orbach processes through the first and second excited levels of an electronic spectrum