Specific features of Eu3+ and Tb3+ magnetooptics in gadolinium-gallium garnet (Gd3Ga5O12)

We reported magnetooptical properties of Eu3+(4f((6))) and Tb3+(4f((8))) in single crystals of Gd3Ga5O12 (GGG), Y3Ga5O12 (YGG), and Eu3+(4f((6))) in Eu3Ga5O12 (EuGG) for both ions occupying sites of D-2 symmetry in the garnet structure. Absorption, luminescence, and magnetic circular polarization of luminescence (MCPL) spectra of Tb3+ in GGG and YGG and absorption and magnetic circular dichroism (MCD) of Eu3+ in EuGG were studied. The data were obtained at 85 K and room temperature (RT). Magnetic susceptibility of Eu3+ in EuGG was also measured between 85 K and RT. The magnetooptical and magnetic susceptibility data were modeled using the wavefunctions of the crystal-field split energy (Stark) levels of Eu3+ and Tb3+ occupying D-2 sites in the same garnets. The results reported gave a precise determination of these Stark level assignments and confirmed the symmetry labels (irreducible representations) of the closely-spaced Stark levels (quasi-doublets) found in the D-5(1) (Eu3+) and D-5(4) (Tb3+) multiplets. Ultraviolet (UV) excitation (<300 nm) of the P-6(J) and I-6(J) states of Gd3+ in the doped GGG crystals led to emission from D-5(4) (Tb3+) and D-5(1) and D-5(0) (Eu3+) through radiationless energy transfer to the 4f((n-1))5d band of Tb3+ and to UV quintet states of Eu3+. The temperature-dependent emission line shapes and line shifts of the magnetooptical transitions excited by UV radiation suggested a novel way to explore energy transfer mechanisms in this rare-earth doped garnet system.