Fluorescence intensity fluctuations of single atoms, molecules and nanoparticles

In many experiments on single molecules or nanocrystals it has been observed that the stream of emitted photons is interrupted by dark intervals. This phenomenon is a true single-particle effect because in an ensemble the various members emit independently and uncorrelated which generally leads to some constant average intensity of the fluorescence. Several instances are presented where single emitters pass through cycles of full, intermediate or no emission. While the phenomenon appears to be quite universal, the physical mechanisms causing the intensity fluctuations are very diverse and widespread. They include quantum jumps between states of different multiplicity, spectral shifts due to fluctuating environments and trapping of charge carriers. (C) 1998 Elsevier Science B.V. All rights reserved.