Research Group Solid State Spectroscopy and Magnetochemistry in Material Science.

Spectroscopy and Energy Transfer in Cubic Hexachloroelpasolite Crystals.

The elpasolite crystal lattice has the space-group symmetry Fm3m (O_h5) and the [LnCl₆]₃ complex ions (Ln = rare-earth ion) have site symmetry O_h. Hence the rare-earth ions are surrounded by a perfect octahedron of six chloride ions. The samples are prepared via the Bridgman method. These high symmetry crystals constitute attractive model systems for the study of cross-relaxation and energy transfer processes. The reasons for this are:

• The transition dipole moments associated with the f-f transitions of rare-earth ions located at octahedral sites are relatively small and therefore the excited states of these ions have comparatively long relaxation times. This offers interesting possibilities for optical pumping, energy storage, and energy transfer.
• The number of excited state levels is minimised due to the high site symmetry and hence the number of possible energy transfer pathways is reduced.
• The vibrational dispersion makes vibronic sidebands much broader than the electronic origins such that energy transfer is less sensitive to the exact positions of the electronic states involved.

In close collaboration with Prof. Colin D. Flint a mathematical model (the shell model) has been developed, which is particularly useful for the analysis of cross relaxation and energy transfer processes in systems with high symmetry. The model accounts for the experimental data without curve fitting to non-exponential decay curves and removes the deficiencies of the Inokuti-Hirayama equation which was developed for solutions and is not particularly well suited for crystals.

International cooperations: Prof. Colin D. Flint [Laser Laboratory, Birkbeck College, University of London, London, UK].

Publications (our own).

Current fields of research.
Research Group Solid State Spectroscopy and Magnetochemistry Group.