ABSTRACT
This chapter provides how relative and absolute locations of lanthanide energy levels affect phosphor performance. It presents the energy levels of the free (or gaseous) lanthanide ions, the influence of the host compound on the location of the 5d levels relative to the 4f levels. However, a trivalent lanthanide ion may accept an electron to form a divalent lanthanide ion. Dipole-allowed transition from a localized ground state to a localized excited state involving one and the same lanthanide ion. The chapter talks about knowledge and experimental techniques on the prediction and determination of absolute location of lanthanide ion energy levels in phosphors. Aspects like lattice relaxation, charge-compensating defects, intrinsic defects, the nature of the bottom of the conduction band, dynamic properties involved in charge localization and delocalization processes, and theoretical modeling all need to be considered to improve our knowledge further. It will be the next step on the route for the tailoring of phosphor properties.
