Characterization and analysis of the 4 f-electronic states of trivalent holmium in yttrium scandium gallium garnet

Abstract

The electronic energy-level structure of Ho 3+-doped yttrium scandium gallium garnet (Ho: YSGG) is examined over the 0–41,600cm −1 spectral range. Data obtained from a combination of optical absorption, emission and emission excitation spectra measurements are used to locate and assign 232 of the 465 crystal-field (Stark) levels predicted to be split out of the 45 lowest-energy 4 f 10[SL]J multiplet manifolds of Ho 3+ in Ho: YSGG. The experimentally characterized energy-level structure is analyzed in terms of a model Hamiltonian defined to represent the major atomic-like (isotropic) interactions that contribute to the LS(term) and J(multiplet) structure of 4 f 10(Ho 3+), as well as the anisotropic crystal-field interactions that determine the splittings between Stark levels within the [SL]J multiplet manifolds of 4 f 10 (Ho 3+). A parameterized form of the model Hamiltonian is used to perform parametric fits of calculated to observed energy-level data, and the results obtained from these data fits show a root-mean-square deviation of < 9 cm −1 between the calculated and experimentally determined energies. The crystal-field interaction strengths and anisotropies determined in the present study for Ho 3+ in YSGG are compared to those determined previously for Ho 3+ in YAG (yttrium aluminum garnet, Y 3Al 5O 12) and for Er 3+ in both YSGG and YAG. These comparisons show small but clearly measurable differences between the crystal-field interactions operative in YSGG vs YAG (for both Ho 3+ and Er 3+ dopant ions). The most significant differences between the results obtained from comparative crystal-field analyses of the Ho 3+ vs Er 3+ systems are seen in the two-electron correlation-crystal-field (CCF) contributions to energy-level structure. Whereas CCF interactions appear to play a very important role in determining the energy-level structures of several 4 f 11(Er 3+) multiplet manifolds, no evidence is found for strong CCF effects on the energy-level structures of 4 f 10(Ho 3+) multiplet manifolds.