Electronic Structures

The mission of the LM section is to develop new luminescence materials by knowledge based design instead of trial-and-error. To do so we need fundamental knowledge on the level energies of luminescent activator ions and how that all depends on structural and chemical properties of the host compound. In  2012 the chemical shift model was developed by prof. P. Dorenbos that provides a method to establish the vacuum referred electron binding energies (VRBE) in the lanthanide levels. Figure 1 shows that the divalent and trivalent lanthanide ground state level energies change in a characteristic zigzag pattern. With those type of schemes we can predict how deep electrons or holes can be trapped by a lanthanide, and we use them to design or engineer persistent and storage phosphors. The same diagrams are used for understand the preferred valence (2+ or 3+)  of the lanthanides in compounds.

Combined with spectroscopic data, the chemical shift model model provides the VRBE at the top of the valence band and the bottom of the conduction band in a routine fashion. Today this is the only method that can routinely establish such binding energies at an accuracy level of a few 0.1 eV. This is demonstrated in Figure 2 for the very important class of garnet structure type phosphors applied in modern day light emitting diodes (LEDs).