RARE-EARTH SPECTROSCOPY IN RELATION TO MATERIALS SCIENCE

This paper deals with two aspects of rare-earth spectroscopy, viz. the charge-transfer transitions (including 4f-5d transitions) and the vibronic transitions. Efficient luminescence upon charge-transfer excitation is only possible if the luminescent centre is in stiff surroundings. This has important consequences in the development of new rare-earth phosphor materials. The vibronic lines are very weak. Their intensity varies strongly with the surroundings of the rare earth ions. Covalency plays an important role. Interaction with the second coordination sphere is demonstrated. In special cases the vibronic lines can be used as a probe of the nature of the site. An example is given for rare earth ions on a surface.