The Emission Mechanisms of the Excited F-Centers in Alkali Halides

Abstract

The decay time and quantum yield of the F-luminescence were measured as a function of temperature for KCl, RbCl, KBr, NaCl, NaF and RbF. In KCl, RbCl and KBr, it was found that the quantum yields are nearly unity below about 80 K and the decay times decrease with temperature rising from 20 K. But, in NaCl, NaF and RbF, the quantum yields as well as the decay times, were found to decrease with temperature increasing from 15 K. The temperature variation of the decay times at low temperatures was analysed by the following model: the luminescence takes place exclusively from the lowest mixed 2s'-state which consists of the hydrogenic 2s-like and 2p-like states mixed through \({\varGamma_{4}}^{-}\)-optical phonons, and the 2p-component in the 2s'-state increases with rising temperature. In NaCl, NaF and RbF, the temperature dependence of the quantum yields at low temperatures could be analysed with the model that the non-radiative transition takes place from the lowest relaxed state to the ground state.