Optical Properties of Alkali-Halide Crystals

Reflectivity data from single crystals of alkali halides have been obtained in the ultraviolet region of the spectrum where excitonic and low interband transitions occur. Following recent calculations for the band structure of KC1 and KI and basing our analysis on the experimental data, it has been possible to predict the properties of the band structure in other alkali halides and describe satisfactorily the low-lying transitions. Furthermore, a close relationship between the conduction band and the energy of the $L$ bands of the $F$ center has been established.