General factors governing the efficiency of luminescence devices

Factors which determine the luminescence efficiency of activated wide band gap materials are discussed in general terms. These materials find usage in a large variety of luminescent devices. The factors affecting the efficiency can be classified into two broad categories. The first has been thoroughly studied and entails interactions which lead to nonradiative dissipation of optical energy at the specific active site. The second set concerns interactions leading to the delocalization and the transport of optical energy away from the originally excited state. Recent spectroscopic results from these studies have allowed the absolute placement of the ground state of the active centers with respect to the intrinsic bands of the host crystal and have allowed us to elucidate the systematics of such placement. These results are relevant to materials which evince the property of persistent phosphorescence and which are of our current interest. Developments in these materials, as well as a number of new applications, will be touched upon.