Temperature Dependence of Auger-Free Luminescence in Alkali and Alkaline-Earth Halides

Auger-free luminescence (AFL) resulting from a radiative transition between the outermost-core bands and the valence bands in BaF 2 , RbF, CsF, CsCl and CsBr has been studied in a wide range of temperatures from 10 to 300 K. The AFL spectra are separated from those originating from the valence-band excitation with use of time-resolved luminescence spectroscopy. It is found that the decay profile of AFL in each crystal is essentially the same throughout the spectrum. The remarkable thermal broadening of the linewidth is verified for all systems. This strongly suggests that the core hole generated on a positive ion induces considerable displacement of the surrounding ions within its lifetime. Based on the present results, the spectral shape of AFL is discussed in terms of a cluster model and a two-band model, requiring further development of the investigations in theory and experiment.