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 aspect s of the vibronic coupling strength in lanthanide ion compounds. The theore tical 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 det ailed comparison with calculations bused on previous existing models is mad e. 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+, Gd3and 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 al so the experimentally observed host-lattice dependence. Furthermore, the mo del also predicts a stronger vibronic coupling for the Eu2+ and Sm2+ ions t han for the isoelectronic Gd3+ and Eu3+ ions, as experimentally observed in fluoride host lattices. (C) 2000 Elsevier Science Ltd, All rights reserved .