Optical Constants and Exciton States in KCl Single Crystals. I. The Low Temperature Properties

Abstract

Optical measurements were carried out on the reflectivity and absorption tails of KCl single crystals over the region 6.0 to 12 ev in the temperature range 10 to 573°K. With use of these data, Kramers and Kronig analysis was made on reflectivity spectra for three different temperatures 10, 78 and 295°K. The analysed spectra of important optical constants are presented in this article, and their properties are discussed in order to clarify the excitonic picture in a single crystalline lattice. The result is analysed along the theories of Toyozawa and Elliot. It was found that the first exciton line shape and the plateau in the higher energy side of the step are explained by them. The two overlapping components of the first band can be well separated at low temperatures in the case of single crystals, and this permits us to determine an oscillator strength for each component as 0.27 and 0.375 for \(\left(\frac{3}{2},\frac{1}{2}\right)\)- and \(\left(\frac{1}{2},\frac{1}{2}\right)\)-transition, respectively. Attempts were made to express the spectrum by an analytic expression in the first exciton band region.