ENERGY-LEVELS AND CORRELATION CRYSTAL-FIELD EFFECTS IN ER3+-DOPED GARNETS

The crystal-field energy-level structures of three different Er3+-doped garnet systems are analyzed and compared in this study. The garnet hosts are Y3Al5O12 (YAG), Y3Sc2Al3O12 (YSAG) doped with TM3+ as a sensitizer ion, and Y3Sc2Ga3O12 (YSGG) doped with Cr3+ as a sensitizer ion. The focus is on energy levels assigned to Er3+ ions substituted for Y3+ at dodecahedral (D2 SYmmetry) sites in the cubic gamet lattices. Analyses are carried out on experimental energy-level data that span up to 29 different 2S + 1L(J) multiplet manifolds (between 0 and 44 000 cm-1) of the Er3+ 4f11 electronic configuration. These data include the locations of 117 crystal-field levels of Er3+ in YAG, 109 levels of Er3+ in YSAG, and 92 levels of Er3+ in YSGG. The energy-level analyses are based on the use of a parametrized model Hamiltonian for the 4f11 electronic configuration of Er3+ in a crystal field of D2 symmetry. The model Hamiltonian includes both atomic (''free-ion'') and crystal-field interactions, parametrized to fit calculated eigenvalues to experimentally observed energies. The crystal-field part of the Hamiltonian is defined to include the standard one-electron interaction operators, as well as additional operators that provide a partial, phenomenological consideration of electron-correlation effects in the 4f-electron-crystal-field interactions. The latter, correlation crystal-field (CCF) interactions, are introduced to address crystal-field splittings within several J-multiplet manifolds that are poorly represented by one-electron crystal-field interaction models. Inclusion of CCF terms in the model Hamiltonian leads to dramatic improvement in the fits between calculated and observed crystal-field splittings within the problematic multiplet manifolds. All of the energy-level analyses reported in this study were carried out within commensurate parametrization schemes, and the Hamiltonian parameters derived from these analyses provide a suitable basis for comparing the 4f-electron-crystal-field interaction properties of Er3+ in YAG, YSAG, and YSGG. These analyses are based entirely on experimental data that specify the locations of energy levels, but do not provide any explicit information about the angular momentum (JM(J)) compositions of the crystal-field wave functions.