FLUORESCENCE LINE NARROWING IN MN4+ DOPED GADOLINIUM GALLIUM GARNET

The laser excitation and luminescence spectra of the R-lines of the Mn 4+ in gadolinium gallium garnet show that the large broadening which t hey exhibit is partially related to presence of charge-compensating Ca 2+ ions, even for the case of manganese center without close compensat ion. Remaining part of the broadening is due to antiferromagnetic exch ange interaction between Mn4+ and surrounding them six Gd3+ ions. The spectra remain broadened in magnetic fields below 6 T and the higher m agnetic fields up to 20 T removes the broadening related to the spin-s pin interaction. Luminescence and excitation spectra at 2.2 K show tha t the transitions occur between levels which magnetic numbers differ b y 0 or +/- 1. The estimated value of the spin-spin exchange constant f or the ground state of Mn4+ is approximately equal to J approximate to 1.9 cm(-1).