Dispersion of piezo-optic constants of some alkali halides in the ultraviolet region. II. Deformation potential constants of the valence band

Abstract

Expressions are developed for the deformation-induced changes in polarizability in terms of fundamental frequency shifts and oscillator strength changes using the Lorentz model. The peaks in the absorption spectrum of the alkali halides are identified with exciton transitions associated with the conduction and valence band levels following recent band structure calculations. The large dispersion of piezo-optic coefficients near the absorption edge in KBr and KI is ascribed to the first low lying exciton peak, which is associated with the transition Fs--F + at K=0 in the Brillouin zone. The piezo-optic data are used to evaluate the deformation potential constants of the valence band at K = 0 for KBr and KI.

Piezo-optic birefringence in mixed crystals of KCl-KBr

“…If the resultant polarizabilities for light polarized in directions parallel and perpendicular to the direction of stress are not equal, piezo-birefringence results. Rahman and Iyengar [25] considering only the first exciton peak were able to explain the sign of piezo-birefringence in KBr and K I single crystals. The absorption studies in mixed crystals of KC1-KBr by Mahr [26] indicate the presence of both31 and % peaks, the heights and positions depending on the relative concentration of the ions in the mixture.…”