EPR Studies of Tb 4 + in Single Crystals of Zircon and Scheelite Structure Silicates and Germanates

Electron paramagnet ic resonance spectra of tetravalent terbium ions have been observed in host crystals of Z r S i 0 4 , H f S i 0 4 , T h S i 0 4 , T h G e 0 4 (zircon structure) and Z r G e 0 4 , H f G e 0 4 (scheelite structure) at X band and Q band and various temperatures. The spin Hamiltonian parameters have been determined from the rotat ional diagrams; the zero field splittings turned out to be extremely large, so that complex spectra far from the strong magnetic field limit had to be analyzed. In all the compounds T b 4 + substitutes for the tetragonal metal lattice sites. The incorporation of terbium, the origin of the large second-order parameters and comparisons with the spectra of trivalent gadolinium in similar systems are discussed.