The tools of quantum chemistry are used for the description of the spectroscopic properties of materials doped by lanthanide and actinide ions. The ions of these two series have a common electronic structure of equivalent electrons, 4f and 5f, respectively. Due to this property the theoretical description of such materials is formulated in the language of operator techniques of atomic spectroscopy.
Many materials become fluorescent when doped with the lanthanides.
Using appropriate rare earth ions and particular host lattices it is possible to select the light emission with the desired wavelength from the visible and near infrared regions of spectra. This property of rare earth ions has caused an increasing interest in the application of rare earth semiconductors as active media for light emitting diodes, injection lasers and other optoelectronic devices. Lasers are used practically in almost all possible aspects of life, but their impact upon the state of the art of medicine and surgery is one of the most revolutionary ones observed since the first laser beam was generated in 1960. Virtually all applications of rare earths in crystals in the medical field are based on their unusual spectroscopic properties. In spite of the complex structure of the lattice particles of the environment of the rare earth ion in a crystal, their spectra are characterized by very sharp, atomic in nature, lines while broad bands are typically expected in the solid state.