Energy levels and symmetry assignments for Stark components of Ho3+(4f10) in yttrium gallium garnet (Y3Ga5O12)

Absorption and fluorescence spectra observed between 1950 and 320 nm at sample temperatures of 8, 78, and 293 K, representing more than 900 transitions between 24 multiplets L2S+1J of Ho3+(4f10) split by the crystal field, have been analyzed in Czochralski-grown single crystals of Ho3+ doped-yttrium gallium garnet (Y3Ga5O12 or YGG). The Ho3+ ions replace Y3+ ions in sites of D2 symmetry during crystal growth. Associated with each multiplet manifold are 2J+1 nondegenerate crystal-field split sublevels (Stark levels) characterized by one of four different irreducible representations (irreps) associated with D2 symmetry. The energy and irrep assignments for individual experimental Stark levels were established by an algorithm that makes use of the selection rules for electric-dipole (ED) and magnetic-dipole (MD) transitions between Stark levels. Nearly degenerate Stark levels (quasidoublets) in several manifolds have been observed and investigated by magneto-optical methods reported in a separate study. Of the 252 predicted Stark levels associated with the 24 multiplet manifolds, 241 were experimentally determined of which 161 had symmetry irreps unambiguously identified by the algorithm method and confirmed by crystal-field modeling studies. A final least-squares fitting between 241 calculated-to-experimental Stark levels was obtained with a standard deviation of 4.86 cm−1 (rms error of 4.60 cm−1). The algorithm works best for identifying irreps when neighboring excited Stark levels are sufficiently separated so that a pattern of temperature-dependent (“hot band”) transitions can be unambiguously associated with each excited Stark level.

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