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 (g(z) = 13.25 +/- 0.05, g(x) = 0 +/- 0.1, g(y) = 3.378 +/- 0.005) and of the hyperfine interaction parameters (A(z) = -469 +/- 3, A(x) = 0 +/- 3.5, A(y) = -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.