Experimental and theoretical study of the crystal-field levels and hyperfine and electron-phonon interactions in LiYF4 : Er3+

We have measured high resolution absorption spectra for the I-4(15/2)--> I- 4(13/2), I-4(11/2) infrared transitions of Er3+ ions in LiYF4. Positions of crystal-field levels and their widths were precisely determined and analyz ed. Hyperfine structure of Er-167 totaling similar to 0.2 cm(-1) was observ ed. Experimental data are described by a theory that operates with a realis tic model of the lattice dynamics and with the crystal-field parameters and electronphonon coupling constants calculated in the framework of the excha nge charge model. The hyperfine splittings of the odd mass number isotope E r-167 are calculated taking into account both magnetic dipole and electric quadrupole hyperfine interactions. The simulated hyperfine structure is in good agreement with the experimentally observed one. The one-phonon relaxat ion rates within the I-4(11/2) and I-4(13/2) crystal-field manifolds are ca lculated using the correlation functions of the Er3+ ion and ligand displac ements. The results of these calculations agree within an order of magnitud e with the measured homogeneous linewidths of the corresponding zero-phonon transitions from the ground state at low temperatures.