Anomalous pressure dependence of absorption edges of ZnFeSe semimagnetic semiconductors

Optical absorption edges of mixed Zn 1-x Fe x Se have been measured under hydrostatic pressure for x=0.01, 0.04 and 0.05. The authors found that absorption of ZnFeSe crystals can be considered as a sum of two components: the fundamental absorption edge, and absorption related to presence of iron. This second component weakly depends on pressure and temperature. They suggest that this extra absorption can be assigned to the charge transfer Fe 2+ to Fe 1+ or Fe 2+ to Fe 3+ .