ON THE LUMINESCENCE OF DIVALENT YTTERBIUM IN KMGF3 AND NAMGF3

The luminescence properties of Yb2+ in KMgF3 and NaMgF3 crystals have been investigated. The lowest levels of the excited 4f(13)5d configuration of Yb2+ in these fluorides are observed at higher energies than in any other composition. This is due to the small crystal field splitting for Yb2+ which occupies the K+ and Na+ sites. The effect of charge compensation for Yb2+ on Na+ or K+ sites is most clearly observed in NaMgF3 where two or more groups of Yb2+ ions with different luminescence properties are observed. The properties are compared with the 4f(7)-4f(6)5d luminescence of Eu2+ and the luminescence of Yb2+ in MF(2) (M = Ca, Sr, Ba). The shift of the excitation and emission bands to higher energies, and the increase in the luminescence quenching temperature for Yb2+ on the larger K+ site, is analogous to the results for the f-d luminescence of Eu2+, but is in contrast with the anomalous luminescence behavior of Yb2+ in MF(2).