Spectra, energy levels, and symmetry assignments for Stark components of Eu3+(4f6) in gadolinium gallium garnet (Gd3Ga5O12)

Absorption and fluorescence spectra observed between 450 and 750 nm at 85 K and room temperature (300 K) are reported for Eu3+(4f6) in single-crystal Czochralski-grown garnet, Gd3Ga5O12 (GGG). The spectra represent transitions between the 2S+1LJ multiplets of the 4f6 electronic configuration of Eu3+ split by the crystal field of the garnet. In absorption, Eu3+ transitions are observed from the ground state, 7F0, and the first excited multiplet, 7F1, to multiplet manifolds 5D0, 5D1, and 5D2. The Stark splitting of the 7FJ multiplets (J=0–6) was determined by analyzing the fluorescence transitions from 5D0, 5D1, and 5D2 to 7FJ. The Eu3+ ions replace Gd3+ ions in sites of D2 symmetry in the lattice during crystal growth. Associated with each multiplet manifold are 2J+1 non-degenerate Stark levels characterized by one of four possible irreducible representations (irreps) assigned by an algorithm based on the selection rules for electric-dipole (ED) and magnetic-dipole (MD) transitions between Stark levels in D2 symmetry. The quasi-doublet in 5D1 was characterized by an analysis of the magneto-optical spectra obtained from the transitions observed between 5D1 and 7F1. A parameterized Hamiltonian defined to operate within the entire 4f6 electronic configuration of Eu3+ was used to model the experimental Stark levels and their irreps. The crystal-field parameters were determined through use of a Monte-Carlo method in which nine independent crystal-field parameters, image were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 57 calculated-to-experimental Stark levels is 5.9 cm−1. The choice of coordinate system, in which the nine image are real and the crystal-field z-axis is parallel to the [0 0 1] crystal axis and perpendicular to the xy plane, is identical to the choice we used previously in analyzing the spectra of Er3+ and Ho3+ garnets.