A theoretical calculation of vibronic coupling strength:: the trend in the lanthanide ion series and the host-lattice dependence

This paper reports a comparison between theoretical and experimental aspects of the vibronic coupling strength in lanthanide ion compounds. The theoretical calculations also have the objective of applying and testing a model developed by one of us. Due to the amount of information and results no detailed comparison with calculations bused on previous existing models is made. The emphasis is given to the P-3(0) --> H-3(4), D-5(0) --> F-7(2), P-6(7/2) --> S-8(7/2) and D-1(2) --> H-3(6) transitions of the Pr3+, Eu3+, Gd3+ and Tm3+ ions, respectively. The divalent lanthanide ions Eu2+ and Sm2+ in LiBaF3 are also included in the analysis as model systems. In these systems the agreement between the theoretical and the experimental vibronic rates is quite satisfactory, The calculations reproduce the observation that the vibronic coupling is stronger in the beginning (Pr3+) and at the end (Tm3+) of the lanthanide ion series and weaker at the center (Eu3+, Gd3+), and also the experimentally observed host-lattice dependence. Furthermore, the model also predicts a stronger vibronic coupling for the Eu2+ and Sm2+ ions than for the isoelectronic Gd3+ and Eu3+ ions, as experimentally observed in fluoride host lattices. (C) 2000 Elsevier Science Ltd, All rights reserved.