Journal of Alloys and Compounds 374 (2004) 240–244 Analysis of f-element multiphonon vibronic spectra

Theoretical modeling of multi-phonon vibronic spectra is presented based on the Huang–Rhys theory of ion–phonon interaction in a single-mode lattice. The single-mode spectral function is modified for applications to vibronic spectra involving multiple vibrational modes. It is shown that, for lanthanide and actinide ions in crystals, f–d electronic transitions exhibit two types of vibronic couplings. One type of vibronic coupling to local and pseudo-local modes obeys Frank–Condon selection rules and has a sharp line width, whereas in the second type of vibronic coupling electronic transitions couple to lattice modes in which selectivity is absent, thus forming a broad vibronic band. The model calculation reproduces very well the experimental spectra of 5f–6d transitions of Pa4+ in Cs2ZrCl6 and 4f–5d transitions of Ce3+ in Cs2NaYCl6. © 2003 Published by Elsevier B.V