Research in the field of luminescent materials is reviewed from the vi
ewpoint of possible applications. In some fields the best possible mat
erials have been found; in others they have not. However, even in the
former fields, problems remain. Our approach is based on a considerati
on of fundamental aspects. It deals with the following topics: problem
s in the currently used lamp phosphors, electron transfer quenching, X
-ray phosphors, and scintillators.