Specific features of Eu^(3+) and Tb^(3+) magnetooptics in gadolinium-gallium garnet (Gd_3Ga_5O_(12))

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 D2 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 D2 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 5D1 （Eu3＋） and 5D4 （Tb3＋） multiplets. Ultraviolet （UV） excitation （300 nm） of the 6PJ and 6IJ states of Gd3＋ in the doped GGG crystals led to emission from 5D4 （Tb3＋） and 5D1 and 5D0 （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.