Optical band gap of K2ZnCl4 single crystals doped with Mn2 in the ferroelectric phase

Absorption edge in the mean crystallographic directions of K2ZnCl4 single crystal doped with Mn2+ was studied at different temperature. The data on absorption coefficient versus photon energy were analysed and could be interpreted in terms of spin-orbit interaction and crystal field splitting. Analysis of absorption spectra indicates that for c- and a-axes, the direct and indirect band gaps were shifted towards the longer wavelength (red shift) with increasing temperature. This behaviour could be interpreted in terms of electron lattice interaction. On the other hand the band gap in b-axis increasing as the temperature increases. This behaviour may be attributed to the weak interatomic interaction. The temperature coefficient of energy gap (δEg/δT) was about 1.3 × 10-3 in both a- and c-axes, while it was in the range of 7.6 × 10-3 eV/K to 2.5 × 10-3 eV/K in the b-axis. A weak impurity absorption band was observed only in b-direction which might be attributed to preference of Mn+2 to align in this direction.

Keywords:

• crystals
• optical
• ferroelectric