EPR AND OPTICAL STUDY OF NI-2+ IONS IN CSCAF3 AND CSCDF3

Ni2+ ions in CsCaF3 and CsCdF3 have been studied by optical and magnet ic resonance techniques. The EPR spectrum of Ni2+ in an octahedral env ironment with small distortions due to random strains in the crystal h as been measured. g and superhyperfine (SHF) tensors have been obtaine d and discussed. From the analysis of the SHF constants the Ni2+-F dis tances are estimated and compared with those in other fluoroperovskite s. The optical absorption and photoluminescence spectra have been meas ured at different temperatures. A dynamical Jahn-Teller (J-T) coupling of the excited electronic levels of Ni2+ to the lattice vibrations is tentatively proposed in order to account for some of the results. Lum inescence decay measurements show that there is a strong change in the lifetime of the 1T2g(D) level going from Ca to Cd crystals as previou sly observed in similar fluoroperovskites having Rb instead of Cs. Fin ally, a new excitation for the Ni2+ luminescence has been observed in 300 K X-irradiated crystals and the possible mechanisms involved in th is process are discussed.