Temperature dependence of the optical band gap of nearly perfect K2ZnCl4 single crystals in the ferroelectric phase

The absorption edge in the main crystallographic directions of K2ZnCl4 single crystal was studied at different temperatures in the ferroelectric phase. The absorption coefficient was computed and the analysis of the data revealed the existence of two optical transition mechanisms. The data on the arrowed indirect transition was analysed and interpreted in terms of the two valence bands originated by spin-orbit interaction and crystal-field splitting. The momenta E-p was calculated as the energy difference between E-g1, the first valence and conduction band, and E-g2, for the second valence band at different temperatures. The anomalous behaviour of temperature dependence of the band gap E-g in b-axis is attributed to the relatively weak electrostatic interactions between the cations and the stacks. (C) 1999 Elsevier Science B.V. All rights reserved.