I-6 EMISSION AND VIBRONIC TRANSITIONS OF EU2+ IN KMGF3

The vibronic transition probability of the P-6(7/2) --> S-8(7/2) transition of Eu2+ in KMgF3 crystals is reported and compared with those of Eu2+ in LiBaF3 and of Gd3+ in some fluoride compounds. The differences in A(vib) can be attributed to the differences in admixture of the opposite parity 4f(6)5d states. For the first time the 6I emission of Eu2+ is reported. 6I emission can be observed because the lowest energetic 4f(6)5d level is situated above the I-6(7/2) level of Eu2+. The high energetic position of the lowest 4f(6)5d level is explained by the small crystal-field splitting and the energetically high position of the centre of gravity of the 4f(6)5d states. The decay time of the 6I emission at 4.2 K is 96 mus. Above 25 K the 6I emission is completely quenched via the lowest 4f(6)5d level, which is at some 50 cm-1 above the I-6(7/2) level and some 3350 cm-1 above the P-6(7/2) level.