On the luminescence of Sb³⁺ in Cs₂NaMCl₆ (with M=Sc,Y,La): a model system for the study of trivalent s² ions

The luminescence spectra and decay curves of Sb³⁺-doped Cs₂NaMCl₆ (M=Sc,Y,La) are presented. In these compounds the 5s² ion is octahedrally surrounded by six chloride ions like the s² ions in alkali halides. Therefore, they can be considered as an ideal model system. It appears that the Sb³⁺ luminescence in Cs₂NaMCl₆ is comparable with the luminescence of the isoelectronic s² ion In⁺ in potassium chloride. The emission consists of one band moving to lower energies from scandium to lanthanum, suggesting that the Stokes shift increases when the space available for the Sb³⁺ ion increases. The excitation spectra can be explained by assuming a dynamical Jahn-Teller effect to be operative in the excited state of the Sb³⁺ ion. The consequences of this interaction are discussed.