Abstract

Detailed information about optical absorption is very important in understanding the optical processes such as luminescence, excitation, reflectance and absorption itself. However, the information for alkali halides is poor compared with the detailed information about other processes which have been reported recently.^1,2) For alkali halides the measurement of optical absorption in crystal is impossible on account of the very high absorption coefficient and as a consequence one has to use other (substitutional) methods. The spectrum of thin film, however, is very broad and shifts to low energy, and the imaginary part of the dielectric constant derived from reflectance spectrum also deviates from the real spectrum of absorption because of the difficulty in measuring the reflectance over the whole spectral region. Besides, in general the imaginary part often does not show structures which are observed but weakly in absorption and excitation spectra. Therefore, we have to find new method to know real information about absorption.

© 1984 Optical Society of America