Fundamental limits of scintillator performance

In this paper we consider the basic physical processes involved in the scintillation process and discuss the limitations imposed on two important performance parameters, namely efficiency (light output) and speed. Light output is determined by the product of efficiencies of energy conversion, energy transfer and luminescence processes. We propose a procedure by which these partial efficiencies can be obtained for any scintillator and use it to evaluate some known materials. Limits of speed are set by the value of the Einstein coefficient A for the luminescent emission and by transfer rates. The singular significance of the transfer step is illustrated by some Ce-based scintillators. A figure of merit and an 'efficiency-speed' diagram are introduced in order to compare different scintillators. (orig.)