Rare Earth Ion-Host Crystal Interactions. 3. Three-Parameter Theory of Crystal Fields.

摘要

A systematic approach in selecting solid-state materials that offer promise as new lasers with predetermined characteristics is of fundamental importance. Reliable predictions of the energy levels and transition probabilities of a laser active ion in a given host would greatly facilitate this goal. The three-parameter theory of crystal fields is used to derived crystal-field parameters for the first rare-earth series, lanthanides, in CaWO4. The parameters q and eta of the theory describe covalent effects in the host lattice; q represents the effective oxygen charge, and eta represents the effective oxygen-tungsten distance. The third parameter tau represents the expansion of the radial 4f wavefunction from its Hartree-Fock value. Values of tau are found for the ions Nd(3+), Tb(3+), Dy(3+), Ho(3+), Er(3+), and Tm(3+), and are determined for the other rare earths by a linear fit. Energy levels and ground state g-values are calculated using the derived crystal-field parameters.