VIBRONIC TRANSITIONS OF TM3+ IN VARIOUS LATTICES

Vibronic transition probabilities have been derived for Tm3+ in LiYF4, YOGI and Na5La(WO4)(4). Determination of the vibronic transition prob abilities for Tm3+ is not easy, but, as far as they can be determined, it is shown that they have the same order of magnitude as those for P r3+ and are significantly larger than those of Gd3+. These results giv e an indication that the electron-phonon coupling strength is large in the beginning and at the end of the trivalent lanthanide ion series a nd small in the centre. To explain the variation in vibronic transitio n probabilities for Pr3+, Gd3+ and Tm3+, the position of the opposite parity states, the lanthanide contraction and the shielding of the 4 f electrons are considered.