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

Ni2+ ions in CsCaF3 and CsCdF3 have been studied by optical and magnetic resonance techniques. The EPR spectrum of Ni2+ in an octahedral environment with small distortions due to random strains in the crystal has been measured. g and superhyperfine (SHF) tensors have been obtained and discussed. From the analysis of the SHF constants the Ni2+-F distances are estimated and compared with those in other fluoroperovskites. The optical absorption and photoluminescence spectra have been measured 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. Luminescence decay measurements show that there is a strong change in the lifetime of the 1T2g(D) level going from Ca to Cd crystals as previously observed in similar fluoroperovskites having Rb instead of Cs. Finally, a new excitation for the Ni2+ luminescence has been observed in 300 K X-irradiated crystals and the possible mechanisms involved in this process are discussed.