Hot Luminescence and Fast Relaxation of Optical Centers in Solids

Abstract

Optical centers in solids have been in the past and are still nowadays at the center of attention by the solid state community for their basic properties and note worthy applications mainly in optoelectronics. Indeed after excitation they usually display a complex optical cycle, whose end product can be an efficient emission. However several processes like hot luminescence, crossover, nonradiative relaxation, energy transfer, etc. may occur during the cycle, and decrease the emission quantum yield, sometimes down to a complete quenching. On this regard one fundamental question is whether all these processes, with the exception of the hot luminescence, occur before or after the configurational relaxation of the excited state. This question has been studied extensively in color centers in alkali halides, mainly in the F center, which is a model case for most of the optical centers in other materials. The results obtained up to now show in the majority of the cases that the processes mentioned above occur after the electronic excitation reaches the relaxed excited state. However there are a few experimental evidences with doubtful interpretation, which require further investigations by using appropriate techniques, for instance ultrafast spectroscopy.