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

The crystal-field energy-level structures of three different Er3+-dope d garnet systems are analyzed and compared in this study. The garnet h osts are Y3Al5O12 (YAG), Y3Sc2Al3O12 (YSAG) doped with TM3+ as a sensi tizer ion, and Y3Sc2Ga3O12 (YSGG) doped with Cr3+ as a sensitizer ion. The focus is on energy levels assigned to Er3+ ions substituted for Y 3+ at dodecahedral (D2 SYmmetry) sites in the cubic gamet lattices. An alyses are carried out on experimental energy-level data that span up to 29 different 2S + 1L(J) multiplet manifolds (between 0 and 44 000 c m-1) of the Er3+ 4f11 electronic configuration. These data include the locations of 117 crystal-field levels of Er3+ in YAG, 109 levels of E r3+ 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. Th e model Hamiltonian includes both atomic (''free-ion'') and crystal-fi eld interactions, parametrized to fit calculated eigenvalues to experi mentally 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, phenomenologi cal consideration of electron-correlation effects in the 4f-electron-c rystal-field interactions. The latter, correlation crystal-field (CCF) interactions, are introduced to address crystal-field splittings with in several J-multiplet manifolds that are poorly represented by one-el ectron crystal-field interaction models. Inclusion of CCF terms in the model Hamiltonian leads to dramatic improvement in the fits between c alculated and observed crystal-field splittings within the problematic multiplet manifolds. All of the energy-level analyses reported in thi s study were carried out within commensurate parametrization schemes, and the Hamiltonian parameters derived from these analyses provide a s uitable basis for comparing the 4f-electron-crystal-field interaction properties of Er3+ in YAG, YSAG, and YSGG. These analyses are based en tirely on experimental data that specify the locations of energy level s, but do not provide any explicit information about the angular momen tum (JM(J)) compositions of the crystal-field wave functions.