VIBRONIC RARE-EARTH SPECTROSCOPY - RESULTS AND PITFALLS

Results of our research programme on the vibronic spectroscopy of rare earth ions are summarized. They relate mainly to Pr3+ and Gd3+. In bo th cases the vibronic intensity increases with increasing degree of co valency. The higher vibronic transition rates for Pr3+ are ascribed to the larger extension of its 4f orbitals. The Delta process gives an i mportant contribution to the vibronic intensity, especially for Pr3+. Further, the vibronic intensities of isoelectronic Gd3+ and Eu2+ are c ompared. The influence of the second coordination sphere is larger tha n expected at first sight. Concentration enhancement of vibronic inten sities and line narrowing in two-photon spectra are fake effects due t o saturation.