An Analysis of the Trigonal Center Structure of Yb3+ Ion in CsCaF3

The crystal field parameters determined from interpretation of optical spectra are used to analyze distortions of a crystal lattice in the vicinity of an impurity ion and vacancy at a Cs+ site compensating the excess positive charge in the trigonal centers of Yb3+ ions in CsCaF3 crystal. Interactions of the impurity ion with the nearest neighbors (an octahedron of F- ions) and the next nearest neighbors (a cube of Cs+ ions) are considered within the superposition model. It is established that, at formation of the trigonal center, three F- ions of the nearest octahedron, placed symmetrically along the threefold axis on the side of the vacancy, move away from the impurity ion a little and significantly deviate from this axis. The second triangle of F- ions, on the contrary, comes nearer to the impurity ion and nestles on the axis of the center a little. The three Cs+ ions, the second neighbors on the side of the vacancy, slightly come nearer to Yb3+ ion and considerably nestle on the center axis. The second triangle of Cs+ ions, from the opposite side of vacancy, also comes nearer to the paramagnetic ion and also nestles on the center axis a little. The Cs+ ion, lying on the center axis, comes considerably nearer to the impurity ion.