Spectra, energy levels, and symmetry assignments for Stark components of Eu 3+(4f 6) in gadolinium gallium garnet (Gd 3Ga 5O 12)

Abstract

Absorption and fluorescence spectra observed between 450 and 750 nm at 85 K and room temperature (300 K) are reported for Eu 3+(4f 6) in single-crystal Czochralski-grown garnet, Gd 3Ga 5O 12 (GGG). The spectra represent transitions between the 2 S+1 L J multiplets of the 4f 6 electronic configuration of Eu 3+ split by the crystal field of the garnet. In absorption, Eu 3+ transitions are observed from the ground state, 7F 0, and the first excited multiplet, 7F 1, to multiplet manifolds 5D 0, 5D 1, and 5D 2. The Stark splitting of the 7F J multiplets ( J=0–6) was determined by analyzing the fluorescence transitions from 5D 0, 5D 1, and 5D 2 to 7F J . The Eu 3+ ions replace Gd 3+ ions in sites of D 2 symmetry in the lattice during crystal growth. Associated with each multiplet manifold are 2 J+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 D 2 symmetry. The quasi-doublet in 5D 1 was characterized by an analysis of the magneto-optical spectra obtained from the transitions observed between 5D 1 and 7F 1. A parameterized Hamiltonian defined to operate within the entire 4f 6 electronic configuration of Eu 3+ 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, B q k , 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 B q k 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 Er 3+ and Ho 3+ garnets.